Batman:

 

how many A is a normal house mains electrical supply rated to? sorry dumb Q

 

63A on single phase normally

(Apologies, I seem to have violated some syntax rule in this post -- my hyperlink goes on and on...)

SomeoneSomewhere:

 

One other consideration that I haven't seen mentioned is the risk of a broken mains neutral causing earth rise - this gets worse the more earthed equipment is outside the building, and a metal-bodied car in a carport is nearly the textbook example of this, just behind the garden tap.

 

The charger may disconnect the supply to the car if this occurs (due to voltage out of limits), which would reduce the load on the building and thus the volt drop down the neutral, but the voltage between the building earthing system (including the car chassis, as switching earth is generally forbidden) and true earth would still be excessive and potentially fatal if there were other high-power loads in the property. I'm surprised the decision wasn't made on Day 0 that the charging equipment would be completely isolated, line neutral and earth, from the chassis of the car.

 

This appears to be behind yet another set of new UK rules, which look decidedly simple and cheap compared to ours.

 

I'm still trying to get my head around the MEN earthing system, but my impression is that -- in the unlikely but still possible case that my residential breaker board loses its connection to true earth, then my electrical safety depends on my neighbours' earth rods -- their (rather roundabout) connection to the neutral in my residential outlets, and their (rather distant) earth-connection to the earth on which I'm standing (when touching my car while it's charging), makes for a scary scenario.   And as you point out -- which I hadn't before considered -- I'm at risk if someone is currently charging their EV in a nearby garage, or is using a cord-connected power-tool outside while standing near my property.

Kind of the reverse. If you lose your connection to the supply neutral, your safety depends on *your* earth rod (which is invariably kinda bad). More load on your property makes things worse. Everything connected to your house's earthing system, be it metal water pipes and external taps, your car, or anything else, is now live relative to ground. Generally, inside a house this is not a *huge* issue because everything is either floating or equally live, but outside it is a major hazard. This is why we bond conductive services; so that your stove does not become live while your taps are earthed; if things really do go wrong, it is better for both to be live. The risk is at the boundary between 'inside' and 'outside'. This is also why they tell you, when leaving a derailed train or a car that's hit lines, to jump out and never touch the vehicle and ground at the same time.

If your lights suddenly start getting brighter and dimmer when you turn things off and on, and especially if they get brighter than normal, call the power company or lines company ASAP.

I'm pretty sure the risks from such faults (floating-neutral, floating-earth) would be adequately mitigated by a (spendy) RCD-B (https://www.evnex.com/articles/ev-charging-and-type-b-rcds) or by a recently-developed (and significantly less expensive) widget from Bender (https://fournais-bender.dk/wp-content/uploads/RCMB121_D00267_00_D_XXEN.pdf) which has a DC breaker as well as an RCD-A. 

As you have pointed out: IET certified the use of a (suitably sized) DC breaker plus an RCD-A as an alternative to the RCD-B quite recently.   Quoting from your linked reference: "One solution to the issues with separate TT earthing systems for EV charging equipment is the use of open PEN detection devices. These devices are relatively new and at present, there are no product-specific standards. The 4th edition provides the guidance that installers need to select and install these new protective devices, in Section 5.3.5." 

We're in bleeding-edge territory here!   But... I really want one of these RCMBs in the outlet I'm using to charge my EVs.   Are they available here?   Can I find an electrician who will install and certify?

Unfortunately not. RCDs and that RCMB (essentially just the sensor from an RCD) do not detect current flowing in the earth (by design) and even if they detected a fault, opening phase and neutral doesn't help because the chassis of the car is still connected to building earth. You need to cut power to the whole installation as the whole installation is a hazard. Cutting earth *may* work but is generally illegal as contacts are an extra point of failure, and regulators really don't want a situation where the phase and neutral are connected but earth is not - and a contact getting stuck is more likely than your main neutral failing. I suppose a safety-rated contactor closing the earth first, verifying continuity, and then closing the live conductors should be adequately safe - but that's not allowed for in our rules and would be a violation of one of the most set-in-stone no-exceptions rules out there - under no exceptions, for no reason, can a switch be put in an earthing conductor.

Undervoltage/overvoltage relays could detect a fault (effectively this is the single-phase-only PEN loss detection device they refer to), but you still need a contactor or remote-trip breaker to turn the power off to the whole building. Cutting power to the car charger only works if the car charger is the only significant load on that supply; the person putting the kettle on and cooking tea will fry whoever is poking around figuring out why the car won't charge.

Mode 3 chargers are basically just a contactor, some switchgear, some controls, and a box. There's pretty much the same in a mode 2 IC-CPD. Mode 4 is where the power electronics start getting involved. That said, slower charging is almost invariably going to be more efficient and better for your battery. The same goes for phone and laptop charging, too.

SomeoneSomewhere:

 

If you lose your connection to the supply neutral, your safety depends on *your* earth rod (which is invariably kinda bad). More load on your property makes things worse. Everything connected to your house's earthing system, be it metal water pipes and external taps, your car, or anything else, is now live relative to ground. Generally, inside a house this is not a *huge* issue because everything is either floating or equally live, but outside it is a major hazard. This is why we bond conductive services; so that your stove does not become live while your taps are earthed; if things really do go wrong, it is better for both to be live. The risk is at the boundary between 'inside' and 'outside'. This is also why they tell you, when leaving a derailed train or a car that's hit lines, to jump out and never touch the vehicle and ground at the same time.

Thanks, this makes sense to me!  Here's what I understand from what you wrote above: If my main switchboard ever loses its connection to supply neutral, there may be fatal consequences.... so you'll want the probability of occurrence to be very small (even when multiplied by the number of residential connections in the whole of NZ).    Well... I can certainly imagine this fault happening as a result of a storm.   My residence is connected via overhead dropline from a power-distribution line which runs through trees on the road-reserve at the edge of my property.  Until the tree branches near the powerline were (finally!) trimmed a couple of years ago, my neighbourhood's distribution-breaker would trip (with a loud bang!) a few times a year.   I'd guess this to be a 3-pole breaker with a fault-tolerant design, and I'm happy to trust that the power-restoration crew are always testing the earth and neutral supply to the breaker before they close it again.   The lines crew *might* conceivably visually-inspect all of the droplines in my neighbourhood, but I can't see how they could possibly assure the neutral-integrity all dropline-connections to main switchboards... leaving open the possibility that the gust of wind (on a rainy night) which caused the distribution-breaker to trip had severed someone's neutral connection but left their phased and ground still connected?   Hmmm...  if a tree branch falls on the overhead drop line, is there anything in the NZ electrical code which assures that the neutral connection is only severed if phased and ground are also severed, when a dropline is yanked from its roofline connector on a residence?   I can vaguely imagine physical means for this assurance, e.g. a longer tension-releasing loop on the neutral than on phased and ground... and I would expect this to be very well-explored territory for NZ electrical safety, so -- despite the terrible consequences of such a fault occurring on my residential property I'm not going to lose any sleep over it!   

Even so... I really do hope the portion of the final NZ PAS 6011 that is written to be understandable by the general public (and which I hope will be required to be distributed to the client by any installer of an EVSE) will contain your advice:

If your lights suddenly start getting brighter and dimmer when you turn things off and on, and especially if they get brighter than normal, call the power company or lines company ASAP. 

Nicely phrased!   I hope you'll submit ;-)

SomeoneSomewhere:

 

Unfortunately not. RCDs and that RCMB (essentially just the sensor from an RCD) do not detect current flowing in the earth (by design) and even if they detected a fault, opening phase and neutral doesn't help because the chassis of the car is still connected to building earth. You need to cut power to the whole installation as the whole installation is a hazard. Cutting earth *may* work but is generally illegal as contacts are an extra point of failure, and regulators really don't want a situation where the phase and neutral are connected but earth is not - and a contact getting stuck is more likely than your main neutral failing. I suppose a safety-rated contactor closing the earth first, verifying continuity, and then closing the live conductors should be adequately safe - but that's not allowed for in our rules and would be a violation of one of the most set-in-stone no-exceptions rules out there - under no exceptions, for no reason, can a switch be put in an earthing conductor.

 

Do you happen to know if there is provision in the NZ electrical code for the residential supply of 100 VAC or 200 VAC single-phase power? 

This question is relevant to this thread because this residential supply would allow us to do level-1 "trickle" charging or level-2 "slow" charging on used EVs from Japan, using their OEM equipment.

If we were trickle-charging or slow-charging most of our nation's EV fleet, most of the time, then I think that'd be a good thing from a greenhouse-gas reduction standpoint, from an electrical safety-standpoint (because the currents are lower), and also from a grid-stability standpoint (because the power-surges are much smaller).   

In the particular case (mine) of a residence with a 6-panel PV array, a 24 kWh Leaf can be trickle-charged (8 A, 115 VAC) during mid-day hours in the summer, and slow-charged (8 A, 230 VAC) up to 60% every night; taking it up to 100% on an overnight slow-charge if I'm planning on driving more than 50 km the following day.   Works for me anyway... but only because I happened to have a spare 2 kVA step-down transformer I could use to power the trickle-charger.  (This is a utility-grade autotransformer from the US, stoutly encased in steelplate; but regrettably it doesn't isolate.   So: I reckon my current trickle-charging setup, even though it has its own RCD, has roughly the same electrocution risk as any of the other AC-powered equipment I use outside my house, plus an additional risk from its inductive spike which I perhaps incorrectly have judged to be insufficient to dissuade me from using it ;-)

Looking for the bright side on the e-waste from biffing all those lev-1 and lev-2 charging cables from all of those Japanese used-EVs (mostly Leafs I think) we'll be importing over the next few years under current policy and regulatory settings.... I'm vaguely thinking it'd be possible -- but probably not cost-effective -- to build up a mode-3 EVSE that'd trickle charge safely when connected to a bog-standard 10 A 230 VAC outlet.     What do you think?

Step 1: secure an offshore container-load of OEM Japanese Leaf charging cables -- these are I suspect e-waste in Japan, because there's *no* legitimate market for them anywhere in the world AFAIK.   Japanese AC power is 100 VAC 50/60 Hz single-phase on a level-1 charging cable, and a level-2 charging Japanese cable has a NEMA 6-20 plug for its 200 VAC 50/60 Hz split-phase supply.   I happen to have one unit of supply currently, which I'd be happy to donate to any geek who has a credible plan for design & manufacture & NZ sale of lev-1 and lev-2 installed-EVSE in NZ.   My unit is a (scary!) 15 A 200 VAC Nissan Leaf charging cable that someone (not me ;-) had "cleverly" fitted with a 16 A blue (caravan-style) plug.   Well it's clearly unsafe for continuous use, given that a 20% derating would allow a 16 A plug to power at most a 12.8 A charger, and given that it was designed for use only on Japanese-style 200 VAC (despite its unconvincingly-pasted-on label declaring "230VAC 15A 50Hz").   Well ... I have taken the not-insignificant personal risk of lev-2 charging my Leaf for an hour at 15 A (nominal) 230 VAC using this charging cable, and nothing overheated or even got perceptibly warm, not even the caravan plug/socket... so I reckon it'd be a good starting point for anyone who wants to take up this design/prototype/manufacture/sell "business opportunity" despite its current import-approval and regulatory-approval "risks".

Step 2. Design a cost-effective unit that'll meet all relevant specs in NZ -- including the RCD-B which would be the budget-breaker I suspect... 

<value-disclosure>I think the WorkSafe requirement for a continuous monitoring of earth-faults -- if it can be fulfilled only by a spendy RCD-B -- will either be widely ignored or it will slightly improve personal safety at a significant environmental and economic cost, for all future mode-3 EVSE installations in NZ, and for all future mode-2 charging in NZ.   Transforming all OEM-supplied (and most currently-supplied) mode-2 charging cables in NZ into e-waste is a terrible outcome from an economic and environmental perspective IMHO!   So I'm really hoping that someone will do the hard-yards of figuring out how to use a wide variety of mode-2 charging cables safely here.   An insistence on an expensive safety measure is IMHO an appropriate regulatory stance only if the IC-CPDs really are likely to kill more people by electrocution and residential fire than are currently dying from the excess leukemia caused (at least arguably!) by breathing BTEX-polluted air that results from the production and consumption of automotive petrol here in godzone. </value-disclosure>

Generally speaking it's pretty rare. Fatigue failure caused by movement in the wind over years seems to be more common than a tree taking out one line and not the other, especially as I think newer drops are done with multicore cable rather than two separate lines. This also usually gives plenty of warning as the strands break one-by-one, meaning the lights start flashing quite badly when you're down to 1-2 strands.

One of the recommendations of the Perth case was to set up over- and under-voltage alarms on smart meters and make sure they actually got investigated, as people are loath to call their power company in a fault...

 

Do you happen to know if there is provision in the NZ electrical code for the residential supply of 100 VAC or 115 VAC single-phase power? 

This question is relevant to this thread because this residential supply would allow us to do level-1 "trickle" charging or level-2 "slow" charging on used EVs from Japan, using their OEM equipment.

 

 

 

If we were trickle-charging or slow-charging most of our nation's EV fleet, most of the time, then I think that'd be a good thing from a greenhouse-gas reduction standpoint, from an electrical safety-standpoint (because the currents are lower), and also from a grid-stability standpoint (because the power-surges are much smaller).   

In the particular case (mine) of a residence with a 6-panel PV array, a 24 kWh Leaf can be trickle-charged (8 A, 115 VAC) during mid-day hours in the summer, and slow-charged (8 A, 230 VAC) up to 60% every night; taking it up to 100% on an overnight slow-charge if I'm planning on driving more than 50 km the following day.   Works for me anyway... but only because I happened to have a spare 2 kVA step-down transformer I could use to power the trickle-charger.  (This is a utility-grade autotransformer from the US, stoutly encased in steelplate; but regrettably it doesn't isolate.   So: I reckon my current trickle-charging setup, even though it has its own RCD, has roughly the same electrocution risk as any of the other AC-powered equipment I use outside my house, plus an additional risk from its inductive spike which I perhaps incorrectly have judged to be insufficient to dissuade me from using it ;-)

Looking for the bright side on the e-waste from biffing all those lev-1 and lev-2 charging cables from all of those Japanese used-EVs (mostly Leafs I think) we'll be importing over the next few years under current policy and regulatory settings.... I'm vaguely thinking it'd be possible -- but probably not cost-effective -- to build up a mode-3 EVSE that'd trickle charge safely when connected to a bog-standard 10 A 230 VAC outlet.     What do you think?

A transformer is simply another item to fail and another set of losses, plus you typically lose another 1-2 percentage points of efficiency when running multi-voltage SMPSs at low rather than high voltage.

I'm pretty sure autotransformers are noncompliant here for safety reasons, as many faults result in line voltage on the output.

Apparently some EVSE with adjustable charge current can be adjusted down to 6A or lower. 6A 230V is equivalent to 12A 120V, which I believe is the maximum allowed on a standard US socket. A delay for charging is probably better than intentionally charging slowly from a grid point of view; increased time-of-use metering is adding financial incentive to this.

<value-disclosure>I think the WorkSafe requirement for a continuous monitoring of earth-faults -- if it can be fulfilled only by a spendy RCD-B -- will either be widely ignored or it will slightly improve personal safety at a significant environmental and economic cost, for all future mode-3 EVSE installations in NZ, and for all future mode-2 charging in NZ.   Transforming all OEM-supplied (and most currently-supplied) mode-2 charging cables in NZ into e-waste is a terrible outcome from an economic and environmental perspective IMHO!   So I'm really hoping that someone will do the hard-yards of figuring out how to use a wide variety of mode-2 charging cables safely here.   An insistence on an expensive safety measure is IMHO an appropriate regulatory stance only if the IC-CPDs really are likely to kill more people by electrocution and residential fire than are currently dying from the excess leukemia caused (at least arguably!) by breathing BTEX-polluted air that results from the production and consumption of automotive petrol here in godzone. </value-disclosure>

As I've said several times, an RCD, type B or not, does nothing to detect earth loss. Earth loss protection is already mandatory in IC-CPDs and has been for years, and is cheap. This is different to PEN/main neutral loss.

One person dying or being disabled for life from sustained electric shock is going to do a hell of a lot to damage reputation and uptake on cars. The results are really not pretty. Go look at the WA case I linked earlier.

Compared to the car itself the IC-CPD is free and contains practically no resources. Ignoring safety and trying to retrofit equipment to save a few bucks and a few kilos of copper cable that will be scrapped anyway is not good.

NEMA plugs/sockets are illegal here because they're a serious shock hazard; they're far worse than NZ plugs before we added the insulated pins.

SomeoneSomewhere:

 

As I've said several times, an RCD, type B or not, does nothing to detect earth loss. Earth loss protection is already mandatory in IC-CPDs and has been for years, and is cheap. This is different to PEN/main neutral loss.

 

Hmm... you seem to know the answer to the question that caused me to start this discussion -- what exactly is meant by the phrase "earth loss protection" in the context of the NZ PAS for EV charging in NZ?  

I'm thinking it can't possibly mean "(true) earth loss protection", as that can't possibly be detected (AFAIK) by an IC-CPD.   However an IC-CPD could certainly failsafe whenever there's a loss in continuity of PEN between it and the vehicle, and the RCD(s) on the circuit could certainly failsafe whenever the current on their neutral supply wire doesn't match the current on their phase supply wire.   But... how could there be any continuous monitoring of the voltage potential between (true) earth in the vicinity of the EV being charged, and the PEN on the charge-cable?

The UK has a somewhat-similar earthing system to NZ, and its regulators don't seem to accept the proposition that current standards on mode-3 EVSEs are sufficient to protect against PEN faults.   

"... each year there are around 400 reported incidents of broken Protective Earth and Neutral (PEN) conductors on TN-C-S (PME) earthed electrical installations, with around 10% of these causing an electric shock. When the PEN conductor is broken the neutral voltage can rise with respect to true earth and the normal protective earth forms the return path for any current that could flow.... The new rules mean that in nearly all circumstances the installer will need to install a dedicated earth rod for the charge point and connect the charge point as a TT earthed installation.... Myenergi have developed a solution that does provide full protection against a potentially dangerous electric shock when the PEN conductor is broken. The patent-pending protection device, which is built into the new Zappi EV charger, isolates the output if the voltage is outside of the statutory limits. Further protection is provided by tripping the output from the charge point if there is any indication of a fault current – extending the concept of RCD protection to this new application."  (https://myenergi.com/pen-protection/)

I'm left with the impression that the NZ PAS is either regulating to require all new installations to be on the bleeding-edge of currently-available charging equipment (such as Myenergi's Zappi, or the Mennekes-branded IC-CPD with its thermal-sensors in its caravan-style 16A plug), or they're being unhelpfully vague about just what sort of "earth loss protection" is required.   Which is it, I wonder?   Well it's just a consultation -- I'm not qualified to deliver the answers but I reckon I can ask some possibly-important questions!   

I do hope others are reading and responding, so that we can end up with an NZ PAS which has at least one section which delivers useful advice to the NZ consumer, with the remaining sections being impenetrably arcane to the general public, but are delivering safety and reliability improvements by giving instruction and guidance to the practicing electrician and to anyone who is importing marketing or selling EVSEs in NZ.

 

Hmm... you seem to know the answer to the question that caused me to start this discussion -- what exactly is meant by the phrase "earth loss protection" in the context of the NZ PAS for EV charging in NZ?  

 

 

 

I'm thinking it can't possibly mean "(true) earth loss protection", as that can't possibly be detected (AFAIK) by an IC-CPD.   However an IC-CPD could certainly failsafe whenever there's a loss in continuity of PEN between it and the vehicle, and the RCD(s) on the circuit could certainly failsafe whenever the current on their neutral supply wire doesn't match the current on their phase supply wire.   But... how could there be any continuous monitoring of the voltage potential between (true) earth in the vicinity of the EV being charged, and the PEN on the charge-cable?

A 'PEN' (Protective Earth and Neutral) conductor is the main neutral between your main switchboard and the lines network, where the conductor is doing double-duty as both earth and neutral.

The earth continuity testing required is just the protective earthing (PE) conductor within the installation, between the MEN switchboard and the load. The Wikipedia article on earthing systems has some more diagrams and explanations.

The UK has a mix of TN-C-S (PME, comparable to MEN), TN-S (mostly old buried paper-insulated lead sheathed cable), and TT (no connection between supply neutral and installation earth; RCD becomes safety critical and the sole protection against shock).

MEN is the sole system accepted for use in NZ and changing this would require legislation and significant retraining and awareness campaigns across electrical workers. Small IT installations are also allowed but are uncommon - supply by isolating transformer or isolated inverter/genset.

We also allow extension of the MEN system to outbuildings under some circumstances (L & PEN only, not separate PE/N) and for MIMS/pyro cable but this is disallowed for use with EVs.

It is impossible to detect 'true earth' loss as it's impossible to get a true earth. Any such testing requires various assumptions, but generally the concern is PEN breakage over anything else.

Mennekes-branded IC-CPD with its thermal-sensors in its caravan-style 16A plug

 

...

 

The patent-pending protection device, which is built into the new Zappi EV charger, isolates the output if the voltage is outside of the statutory limits.

That has nothing to do with earth loss; we require either plugs to be derated to 80% or temperature monitoring to be provided to guard against plugs melting. I think this is fairly standard internationally and was in the first versions of the EV rules, and honestly space heaters and other long-term high loads should probably have the same requirement sooner or later.

The myenergi system is just an over/undervoltage relay. They've been around for decades. The issue is that you're going to have a lot of false positives if you want to set it close enough to be useful, especially being located at the end of a subcircuit. Look out for your car stopping charging because your aircon/water pump/other motor load cycled on during evening peak...

The comments from myenergi are very much marketing copy and not the views of regulators I suspect.

OK thanks for your detailed response.   

I'm hoping that the NZ PAS includes an understandable definition such as yours: "The earth continuity testing required is just the protective earthing (PE) conductor within the installation, between the MEN switchboard and the load."

But... sorry to keep harping on this, as it seems you understand and I'm completely failing to understand your explanations.   Is is even feasible to continuously monitor the connection between these points.   

I'm thinking that the most that can be continuously monitored (in the context of any EVSE in NZ, unless it is out-of-regulatory-compliance-because-wired on a TT circuit) is the connection between the PE input to an RCD-A, to the PE output on the charging plug, through a resistor on the vehicle being charged, and back to the neutral pin on an RCD-A.   And -- that'd be safe enough to satisfy me even for a high-amperage (6 kW) AC charging circuit, as long as I remember to (at least occasionally) assure its connectivity to my residential earth-ground electrode.   

And I'm even more confused by the current (lack of, AFAIK) a clear definition of earth-continuity monitoring for an IC-CPD that's compliant with the current-draft NZ PAS.   Any "earth continuity" monitoring on an IC-CPD will, I believe, be monitoring the continuity of the circuit between its PE output, through the PE on the charging cable to the vehicle, through the charging plug-and-socket on the vehicle, through a resistor in the vehicle, and back again to the IC-CPD through the neutral pin on the charging plug-and-socket on the vehicle.   This is indeed an important safety device... and I do understand that it's feasible to implement... but I'm left to wonder how whether any or all of the IC-CPDs in my possession actually assure this?   

I'm *guessing* that every IC-CPD currently in NZ was designed so that it should cease to charge whenever its CP-PE circuit is disconnected, even though (according to Wikipedia, which is IMHO not a reliable source of information about standards!) the J17772 standard allows a charging current of 16 A  (!) in this mode: "The live wires of public charging stations are always dead if the CP-PE (Protective Earth) circuit is open, although the standard allows a charging current as in Mode 1 (maximum 16 A)."   Gadzooks.    It's really hard to believe that this was ever allowed in the J17772 standard, but then again it's merely an assertion in a Wikipedia article... and my main concerns are (still, after all this to-and-fro):

* it can not be possible for anyone to determine compliance with a safety regulation that requires "earth continuity" unless there's an understandable specification of the circuit whose continuity is being monitored

* if any NZ regulatory agency advises (or requires!) consumers to purchase electronic goods which include a rarely-found/bleeding-edge safety feature, then I suspect this regulatory advice will be be widely ignored (or any enforcements heavily resented) -- unless this advice includes an understandable and compelling case for consumers to pay extra to gain this safety feature.   

 

I'm hoping that the NZ PAS includes an understandable definition such as yours: "The earth continuity testing required is just the protective earthing (PE) conductor within the installation, between the MEN switchboard and the load."

 

 

 

But... sorry to keep harping on this, as it seems you understand and I'm completely failing to understand your explanations.   Is is even feasible to continuously monitor the connection between these points.  

Yes, trivial, and has been required since the first set of EV rules years ago I believe.

 

I'm thinking that the most that can be continuously monitored (in the context of any EVSE in NZ, unless it is out-of-regulatory-compliance-because-wired on a TT circuit) is the connection between the PE input to an RCD-A, to the PE output on the charging plug, through a resistor on the vehicle being charged, and back to the neutral pin on an RCD-A.   And -- that'd be safe enough to satisfy me even for a high-amperage (6 kW) AC charging circuit, as long as I remember to (at least occasionally) assure its connectivity to my residential earth-ground electrode.   

 

 

 

And I'm even more confused by the current (lack of, AFAIK) a clear definition of earth-continuity monitoring for an IC-CPD that's compliant with the current-draft NZ PAS.   Any "earth continuity" monitoring on an IC-CPD will, I believe, be monitoring the continuity of the circuit between its PE output, through the PE on the charging cable to the vehicle, through the charging plug-and-socket on the vehicle, through a resistor in the vehicle, and back again to the IC-CPD through the neutral pin on the charging plug-and-socket on the vehicle.   This is indeed an important safety device... and I do understand that it's feasible to implement... but I'm left to wonder how whether any or all of the IC-CPDs in my possession actually assure this?   

 

RCDs have nothing to do with it. RCDs never have an earth connection.

See the above diagrams in the Wikipedia article. Earth and neutral are linked in your main switchboard. All the EVSE has to do is check that it has continuity between neutral and earth, while testing with a sufficiently low current to not trip an RCD, and it then knows it has continuity back to the installation main earthing busbar.

Earth electrodes are of very limited utility in the faults we're talking about; all that matters is that there are enough of them in your general area - you, your neighbours,  and the lines company provisions a bunch of very deeply driven ones. That's what Multiple Earthed Neutral refers to.

SomeoneSomewhere:

 

Earth and neutral are linked in your main switchboard. All the EVSE has to do is check that it has continuity between neutral and earth, while testing with a sufficiently low current to not trip an RCD, and it then knows it has continuity back to the installation main earthing busbar.

 

OK thanks I *finally* understand!  The RCD-A is a crucial component of the earth-continuity monitoring, for without it the IC-CPD could only be monitoring the continuity of the downstream connection of PE to neutral.   As you say, if the upstream connection of PE to neutral (at the main earthing busbar) had high impedance, the RCD-A would trip.

SomeoneSomewhere

  

 

Earth electrodes are of very limited utility in the faults we're talking about; all that matters is that there are enough of them in your general area - you, your neighbours,  and the lines company provisions a bunch of very deeply driven ones. That's what Multiple Earthed Neutral refers to.

 

Oh dear, I'm afraid I don't follow your reasoning here -- but maybe the problem is that we're talking about different faults?   Or maybe I'm just being overcautious... I'm sure there were generous safety margins when the earth electrodes were installed in the vicinity of my residence, but these margins would be dependent on assumptions about fault currents which *may* not be valid when both I and my neighbour are fast-AC charging our EVs, the galv earth-electrodes on our residences have become somewhat corroded since they were installed in a damp clay soil decades ago, and ... well there are many other factors I'm sure e.g. conductivity of soils... 

NZECP 35:1993:

 

4.1 PERMISSIBLE TOUCH VOLTAGES

Where works are installed in a special location or a frequented location as defined in this Code, the touch voltages shall be within the limits set in clauses 4.1.1 and 4.1.2.

 

4.1.1 Special locations.

 

(a) Works installed in special locations and operating at voltages not exceeding 66 kV shall comply with the requirements of curve A1 of figure 3, page 12 of this Code.

 

...

 

4.1.2 Frequented locations.

 

(a) Works installed in frequented locations and operating at voltages not exceeding 66 kV shall comply with the requirements of curve B1 of figure 3, page 12 of this Code.

 

Am I correct to interpret this as requiring the touch-voltage of my car while it is charging should not exceed 400 V, unless I were charging my EV in a special location (as defined in this guideline): "within a school’s grounds or within a children’s playground, or within a public swimming pool area, or at a popularly used beach or water recreation area, or in a public thoroughfare within 100 metres of any of the above-named locations."

Oh dear... anyone living near a school -- and the school itself -- will have to comply with the requirements of curve A1, i.e. with a touch voltage not exceeding 70 V.   Hmm... that sounds to me a lot like that UK regulation on protection against PEN-faults, wouldn't you agree?   

And I further *suspect* that unless there's a clever circuit that is estimating the voltage of (true) earth by time-averaging a multiple-phased AC power supply (as is vaguely disclosed in the salespitch for the Myenergi Zappi I had quoted earlier), then you really cannot protect against PEN faults unless you have another earth electrode, near the EV being charged, that is providing a an earth-reference voltage that's not being dragged around by whatever ground-fault currents are flowing in the neighbourhood.   

Then again... for all I know, the safety margins for the placement of earth electrodes in NZ MEN residential supplies are sufficient to reduce the risk of a PEN-fault in NZ significantly below the risk in the UK.  But if not, i.e. if the safety margins and compliance-levels are roughly the same in NZ and the UK, then: 400 PEN faults/year in the UK * 10% shocks/PEN fault * 5 million people in NZ / 67 million people in the UK = 3 shocks per year in NZ as a result of PEN faults.   That's not very many.   Even if it increases a hundredfold as a result of massive uptake of EVs, this won't be a major cause of death; but if it were possible to inexpensively mitigate this risk then that's definitely worth considering... but...

I'm guessing the PEN-fault risk can not be affordably mitigated for residential-sized EVSEs in NZ (given that putting an EVSE on a TT subcircuit would be spendy, as well as introducing massive new risks from e.g. lightning strike in the vicnity) until ... perhaps... it becomes possible to purchase some inexpensive battery-powered protective-widget that sits on the top of its own groundstake, that has a wired (and fused-for-safety at micro-amps) connection to supply neutral, and that has a wireless (e.g. wifi or bluetooth) connection to the EVSE whose PEN-fault safety it is monitoring.   Now *that* sounds doable to me, and at a very-rough estimate I'd expect to be able to manufacture distribute sell and install in quantity for NZD 1000.   Well of course there'd be significant design risk as I have amply demonstrated in this thread that I lack basic competency in power-systems-engineering!   Well... this speculation about how a *possibly* feasible device might address a *possible* regulatory response to NZECP 35:1993 is far beyond the scope of this thread on NZ PAS, so ... I'd suggest that any further discussion of this wild idea be done on a separate thread, or (given that IP would be developed) it'd be best done in confidence.

cthombor:

 

SomeoneSomewhere:

 

Earth and neutral are linked in your main switchboard. All the EVSE has to do is check that it has continuity between neutral and earth, while testing with a sufficiently low current to not trip an RCD, and it then knows it has continuity back to the installation main earthing busbar.

 

 

OK thanks I *finally* understand!  The RCD-A is a crucial component of the earth-continuity monitoring, for without it the IC-CPD could only be monitoring the continuity of the downstream connection of PE to neutral.   As you say, if the upstream connection of PE to neutral (at the main earthing busbar) had high impedance, the RCD-A would trip.

 

Please re-read it. Everything you just wrote is wrong.

PE and neutral must never be connected downstream; they are connected in one location only: the MEN link in your MSB.

RCD is unrelated to this. The only reason I mentioned it (I shouldn't have) is that it's easy to accidentally trip the RCD when testing the upstream earth-neutral link so your test circuit needs to be appropriately designed.

RCDs only trip on current imbalance. Nothing else at all. They have no connection to earth and do not care about earth, for about the fifth time.

cthombor:

 

SomeoneSomewhere:

 

> Earth electrodes are of very limited utility in the faults we're talking about; all that matters is that there are enough of them in your general area - you, your neighbours,  and the lines company provisions a bunch of very deeply driven ones. That's what Multiple Earthed Neutral refers to.

 

Oh dear, I'm afraid I don't follow your reasoning here -- but maybe the problem is that we're talking about different faults?   Or maybe I'm just being overcautious... I'm sure there were generous safety margins when the earth electrodes were installed in the vicinity of my residence, but these margins would be dependent on assumptions about fault currents which *may* not be valid when both I and my neighbour are fast-AC charging our EVs, the galv earth-electrodes on our residences have become somewhat corroded since they were installed in a damp clay soil decades ago, and ... well there are many other factors I'm sure e.g. conductivity of soils... 

 

NZECP 35:1993:

 

 

4.1 PERMISSIBLE TOUCH VOLTAGES

Where works are installed in a special location or a frequented location as defined in this Code, the touch voltages shall be within the limits set in clauses 4.1.1 and 4.1.2.

 

4.1.1 Special locations.

 

(a) Works installed in special locations and operating at voltages not exceeding 66 kV shall comply with the requirements of curve A1 of figure 3, page 12 of this Code.

 

...

 

4.1.2 Frequented locations.

 

(a) Works installed in frequented locations and operating at voltages not exceeding 66 kV shall comply with the requirements of curve B1 of figure 3, page 12 of this Code.

 

 

Am I correct to interpret this as requiring the touch-voltage of my car while it is charging should not exceed 400 V, unless I were charging my EV in a special location (as defined in this guideline): "within a school’s grounds or within a children’s playground, or within a public swimming pool area, or at a popularly used beach or water recreation area, or in a public thoroughfare within 100 metres of any of the above-named locations."

 

Oh dear... anyone living near a school -- and the school itself -- will have to comply with the requirements of curve A1, i.e. with a touch voltage not exceeding 70 V.   Hmm... that sounds to me a lot like that UK regulation on protection against PEN-faults, wouldn't you agree?   

 

And I further *suspect* that unless there's a clever circuit that is estimating the voltage of (true) earth by time-averaging a multiple-phased AC power supply (as is vaguely disclosed in the salespitch for the Myenergi Zappi I had quoted earlier), then you really cannot protect against PEN faults unless you have another earth electrode, near the EV being charged, that is providing a an earth-reference voltage that's not being dragged around by whatever ground-fault currents are flowing in the neighbourhood.   

Then again... for all I know, the safety margins for the placement of earth electrodes in NZ MEN residential supplies are sufficient to reduce the risk of a PEN-fault in NZ significantly below the risk in the UK.  But if not, i.e. if the safety margins and compliance-levels are roughly the same in NZ and the UK, then: 400 PEN faults/year in the UK * 10% shocks/PEN fault * 5 million people in NZ / 67 million people in the UK = 3 shocks per year in NZ as a result of PEN faults.   That's not very many.   Even if it increases a hundredfold as a result of massive uptake of EVs, this won't be a major cause of death; but if it were possible to inexpensively mitigate this risk then that's definitely worth considering... but...

 

I'm guessing the PEN-fault risk can not be affordably mitigated for residential-sized EVSEs in NZ (given that putting an EVSE on a TT subcircuit would be spendy, as well as introducing massive new risks from e.g. lightning strike in the vicnity) until ... perhaps... it becomes possible to purchase some inexpensive battery-powered protective-widget that sits on the top of its own groundstake, that has a wired (and fused-for-safety at micro-amps) connection to supply neutral, and that has a wireless (e.g. wifi or bluetooth) connection to the EVSE whose PEN-fault safety it is monitoring.   Now *that* sounds doable to me, and at a very-rough estimate I'd expect to be able to manufacture distribute sell and install in quantity for NZD 1000.   Well of course there'd be significant design risk as I have amply demonstrated in this thread that I lack basic competency in power-systems-engineering!   Well... this speculation about how a *possibly* feasible device might address a *possible* regulatory response to NZECP 35:1993 is far beyond the scope of this thread on NZ PAS, so ... I'd suggest that any further discussion of this wild idea be done on a separate thread, or (given that IP would be developed) it'd be best done in confidence.

 

"Works" basically refers to powerplants, transmission lines, substations, distribution lines etc. Your house, and any other installation, is expressly not works and the rules for works do not apply, except for portions of the installation operating at high voltage (e.g. the feed into a transformer in the bottom of a shopping mall). Those sections are about making sure you can't get a serious shock by touching a transformer on the roadside.

As I've already said in this thread, the solution to handle PEN faults exists: set up the over/undervoltage monitoring in smart meters and roll a truck when repeatedly triggered. Given this was one of the recommendations that came out of the Perth report, I expect several lines companies are looking at this now.

Your solution would be horific from a FMEA perspective and people would immediately figure out that all they need to do is stick a jumper from the independent earth to the installation earth to completely defeat it.