RCDs on switchboard for a new home

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mattwnz

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#249250 2-May-2019 15:45

In a new home we had specified all electrical circuits were to have RCDs on them. The electrician has installed the distribution board and installed RCDs. However when we quizzed them to make sure the RCDs were on all circuits, they said that all circuits that need to be on RCDs, were on RCDs. However they said hadn't installed RCDs on the following circuits, Hobbs, Oven, Hot water cylinders, Heatpumps etc. This is because they say that those circuits will encounter 'nuisance tripping'.

Does anyone know how common nuisance tripping would be on a new home with all new appliances etc?. I have read that nuisance tripping can occur on old appliances, such as old ovens where cobwebs may have gotten in. I notice in Australia they seem to require all circuits in the switchboard to be on RCD's. However in NZ there doesn't appear to be the same requirement yet? It does seem that Australias regulations on this are a lot stricter than in NZ, as in some states it appears you have to get RCDs installed on an existing home before you are allowed to sell it.

Should we insist they do install them on all circuits as it said in the specs? Or is the risk of nuisance tripping too large?. Does anyone have them installed on all circuits, such as ovens, heatpumps etc? I guess if it does cause problems with nuisance tripping, the RCDs could always be removed.

TechSol

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#2229532 2-May-2019 16:01

I would leave it as it is. Nuisance tripping on a hob and oven is a good possibility, and for similar reasons on a hot water cylinder too (hint: it's the elements)

For HeatPumps, the units are located outside, any moisture is going to drive you to distraction if there is an RCD.

I'd leave it be.

elpenguino

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#2229558 2-May-2019 16:46

You have to know what the point of the RCD is. Not how it works but when it provides protection. You'll notice that basically they're used for circuits which can be used for plug in appliances (and lighting).

This is because of the higher chance of you encountering a plug in appliance which is either faulty or has a damaged flex than encountering , say, a hot water cylinder in which the earth becomes non-functional.

Nuisance tripping aside you don't need em for HWC or ovens.

If you've got a reference to different practices in Oz please cite because there's a reason we call our wiring standards AS/NZS 3xxx.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

andrewNZ

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#2229577 2-May-2019 17:12

I think the electrician has done the right thing.
RCD's won't provide any real benefits in those circuits, and they will cause trouble unless you use 100mA RCD's. 100mA RCD's provide no real protection for people, they're for equipment protection.

If you're looking for better fault protection on the other circuits, you'd be better to look at arc fault detection devices (which are likely to become a requirement soon) but they're pretty expensive.

They detect arcing in the circuit and so should significantly reduce the chance of an electrical fire.

gregmcc

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#2229592 2-May-2019 17:32

From a legal point of view, fixed wired appliances (such as stove hot water, heat pump) do not require RCD protection.

Power sockets and lighting point required RCD protection.

Hot water and stoves are well known to cause nuisance trips of RCD's due the elements, IMO it wouldn't hurt to have the heat pump on a RCD, but as it's a fixed wired appliance it ok to not be on a RCD

mattwnz

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#2229593 2-May-2019 17:33

andrewNZ: I think the electrician has done the right thing.
RCD's won't provide any real benefits in those circuits, and they will cause trouble unless you use 100mA RCD's. 100mA RCD's provide no real protection for people, they're for equipment protection.

If you're looking for better fault protection on the other circuits, you'd be better to look at arc fault detection devices (which are likely to become a requirement soon) but they're pretty expensive.

They detect arcing in the circuit and so should significantly reduce the chance of an electrical fire.

Thanks Andrew. Do those Arc fault ones have to go on each and every circuit. Or can one cover multiple circuits, or even the whole house, like a full house surge protector does.

mattwnz

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#2229600 2-May-2019 17:38

gregmcc:

From a legal point of view, fixed wired appliances (such as stove hot water, heat pump) do not require RCD protection.

Power sockets and lighting point required RCD protection.

Hot water and stoves are well known to cause nuisance trips of RCD's due the elements, IMO it wouldn't hurt to have the heat pump on a RCD, but as it's a fixed wired appliance it ok to not be on a RCD

Thanks Greg. The stove is an induction hob, so would that be prone to the same type of problems as an old style resistive of element?

There is an external switch for the heatpump, and maybe it is also plugged into an external socket, although not sure. So I may ask them to get that onto an RCD.

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gregmcc

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#2229604 2-May-2019 17:44

mattwnz:

andrewNZ: I think the electrician has done the right thing.
RCD's won't provide any real benefits in those circuits, and they will cause trouble unless you use 100mA RCD's. 100mA RCD's provide no real protection for people, they're for equipment protection.

If you're looking for better fault protection on the other circuits, you'd be better to look at arc fault detection devices (which are likely to become a requirement soon) but they're pretty expensive.

They detect arcing in the circuit and so should significantly reduce the chance of an electrical fire.

Thanks Andrew. Do those Arc fault ones have to go on each and every circuit. Or can one cover multiple circuits, or even the whole house, like a full house surge protector does.

Depending on the brand the AFD's may have RCD protection built in as well, currently these are expensive and not so common and as yet there is no legal requirement for them in NZ (although this is subject to change in the near future)

neb

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#2229799 2-May-2019 23:25

andrewNZ: If you're looking for better fault protection on the other circuits, you'd be better to look at arc fault detection devices (which are likely to become a requirement soon) but they're pretty expensive.

They detect arcing in the circuit and so should significantly reduce the chance of an electrical fire.

Aren't AFCI's meant more for 110V countries where arcing is easier to detect because of the higher currents involved? I thought that was the reason why they were pushed less in 220-240V countries.

andrewNZ

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#2230478 3-May-2019 21:04

It is being suggested that arc fault detection may become mandatory in the next few years. I can't see any reason it won't be.