Question for electrical engineers?

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#2137421 30-Nov-2018 18:52

It looks like there is a circuit breaker 'CB1' on the input. Can you verify the rating of this, and if you can change it (e.g. by replacing with a lower current breaker)?

If you do go for a new plug, you can get a standard plug in 15A; none of this industrial stuff which often doesn't fit sockets. E.g. a PDL Cat 901/15.

Connecting an appliance to an insufficiently large plug is unsafe. Unlike the US where a socket will be protected by a breaker no larger than the rating of the socket (except 15A sockets may be on a 20A breaker), in NZ the circuit protection is *not* sized to protect the socket, appliance, or flex. In some circumstances, a 10 or 15A socket can be on as large as a 25 or 32A MCB. We consider overcurrent protection the responsibility of the appliance.

gregmcc

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#2137425 30-Nov-2018 19:05

Spec sheet clearly show max current for 240V input is 27A, if you were to put a 15A plug on it, it would not be electrically safe.

DarthKermit

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#2137493 30-Nov-2018 19:40

White and black for phase and neutral. Don't the Yanks use some weird system for their wiring colour codes?

SomeoneSomewhere

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#2137507 30-Nov-2018 20:31

Other way round: White neutral, black phase.

Aredwood

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#2137508 30-Nov-2018 20:31

DarthKermit:
White and black for phase and neutral. Don't the Yanks use some weird system for their wiring colour codes?

They use black for phase and white for neutral.

A bit of a worry that even respected US welder manufacturers are putting smaller plugs on their equipment than what the welder uses. I bought a Chinese welder that had a 15A plug, despite the rating plate saying that it draws 27A at 0.75 Power Factor. I just thought "typical Chinese" and got a sparkie mate to wire it into the 32A stove circuit. (stove was previously swapped to gas, so no other load on that circuit).

Apologies to the Chinese for stereotyping their welders.

Ropata

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#2137509 30-Nov-2018 20:34

BOC do it too. In fact, Ive never seen a 20 amp plug on a single phase welder. It seems to go from 15 to 3 phase 415v 4 pin.

mclean

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#2138386 3-Dec-2018 10:24

gregmcc: Spec sheet clearly show max current for 240V input is 27A, if you were to put a 15A plug on it, it would not be electrically safe.

In fairness to the manufacturer, they do say it has to be supplied by a dedicated circuit with appropriately sized overcurrent protection (and installed by a qualified electrician.) In the US a 15A plug/socket can be on a 20A dedicated circuit. In NZ it probably means 15A protection. Why would that be unsafe? Of course the flex and equipment wiring are good for 35A but I'm not aware of any rule against that.

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Sidestep

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#2138601 3-Dec-2018 14:47

I have a similar multiprocess welder (mine's a Firepower MST220i - which is basically an ESAB)
Over here - in Canada - they're particularly useful as a portable welder becaise they'll run off whatever power supply's available - 120 or 240V.

However on 120V 15A you can't do much useful with it. To stick decent metal together you need to remove the 120V adaptor and use the 'big plug'
The one in your picture's a NEMA 6-50, which is the standard 'welding' plug out of all the NEMA options. It's for 240V and 50A supply.

They're a solid lump of metal usually attached to your welder by an 8 AWG cable, and, not needing to supply 120V just have 3 pins - a ground and the two 240 V - without a pin for the white neutral wire. In comparison a NZ 15A plug's a puny little thing.

In NZ your 32A stove circuit should work.

Aredwood

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#2138950 4-Dec-2018 00:06

mclean:
gregmcc: Spec sheet clearly show max current for 240V input is 27A, if you were to put a 15A plug on it, it would not be electrically safe.

In fairness to the manufacturer, they do say it has to be supplied by a dedicated circuit with appropriately sized overcurrent protection (and installed by a qualified electrician.) In the US a 15A plug/socket can be on a 20A dedicated circuit. In NZ it probably means 15A protection. Why would that be unsafe? Of course the flex and equipment wiring are good for 35A but I'm not aware of any rule against that.

Just because you have a 15A power socket, doesn't mean that it will definitely have a 15A circuit breaker as well. As said previously, the circuit breaker might be a much larger rating. Which is perfectly fine assuming that the cable is ok at the larger rating. But trying to pull 27A through a plug that is rated for max 15A - Definitely unsafe.

Unless you have existing 15A power sockets. You are going to need a new socket installed no matter what. So you might as well get a 32A socket installed instead. Labour cost would be practically the same. So pretty much just the price difference between 15A and 32A rated gear. Not much extra cost to do it properly.

As well as being safer, a 32A socket on a correctly rated circuit will mean less voltage drop. Which in turn means that you will get max performance from your welder.

mclean

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#2139008 4-Dec-2018 09:33

Aredwood: Just because you have a 15A power socket, doesn't mean that it will definitely have a 15A circuit breaker as well. As said previously, the circuit breaker might be a much larger rating. Which is perfectly fine assuming that the cable is ok at the larger rating. But trying to pull 27A through a plug that is rated for max 15A - Definitely unsafe.

Unless you have existing 15A power sockets. You are going to need a new socket installed no matter what. So you might as well get a 32A socket installed instead. Labour cost would be practically the same. So pretty much just the price difference between 15A and 32A rated gear. Not much extra cost to do it properly.

As well as being safer, a 32A socket on a correctly rated circuit will mean less voltage drop. Which in turn means that you will get max performance from your welder.

Yes, agree. All I was asking is why would it be unsafe on a circuit with 15A overcurrent protection.

SomeoneSomewhere

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#2139381 4-Dec-2018 19:04

Because 15A sockets are not uncommon, and could be reasonably found on circuits rated up to 25A and potentially more. We have no mandatory relationship between the current rating of a socket and the current rating of the supplying circuit. Someone could easily move or sell the welder and take it elsewhere with different protection.

OP can likely, depending on loading, put a 15A socket on an existing 16-20A power circuit* and make no other changes. Running a new circuit is significantly more work.

* Or get an electrician to do so, depending on qualifications etc.

Tracer

343 posts

Ultimate Geek

#2139384 4-Dec-2018 19:27

What's the duty cycle of the welder when running flat tack on 230 V? It will be <50%, hence the plug is smaller than the max current draw.

Ropata

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#2139389 4-Dec-2018 19:55

Tracer:

What's the duty cycle of the welder when running flat tack on 230 V? It will be <50%, hence the plug is smaller than the max current draw.

Yeah It's a very low duty cycle which I think is why these machines don't come with 32 amp plugs.

Tracer

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#2139400 4-Dec-2018 20:19

Yep, looked at the data sheet, it's 20%.

gregmcc

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#2139402 4-Dec-2018 20:20

Tracer:

What's the duty cycle of the welder when running flat tack on 230 V? It will be <50%, hence the plug is smaller than the max current draw.

To meet the "Electrically Safe" or "Electrically Unsafe" definition as per the Electricity Safety Regulation (Regulation 5)

Putting a 15A plug on a device which lists the maximum current of 27A would pose a risk of wiring catching fire, significant damage etc.. This would clearly fall in to the category of Electrically Unsafe.

As far as using duty cycle of 50%, unless there is some built in device to limit the duty cycle it would be assumed that the duty cycle is 100%

Ensuring that the circuit is protected by a suitably rated circuit breaker would not solve the problem either, as a 15A circuit breaker does not trip at 15A, there is a trip curve, the higher the current the quicker it will trip, you may find running 27A it may take somewhere in the vicinity of 500seconds, that is around 8min 20 seconds. For this 8mins and 20 seconds 27amps is coursing thru your standard 2.5mm power circuit cable, 2.5mm is simply not rated to pass 27A so it turns in to a big heater, plastic starts melting, the wood in your walls that the cable travels through starts to get hot, you have all the makings for a house fire.

Even if you don't reach the point of starting a fire the wiring in this circuit has now become damaged and unsafe.

It has been brought to the attention (in the past couple of years) of the testing and tagging companies that visit businesses to do the electrical testing and tagging that Welders are a problem, they should check the nameplate specifications and if the plug rating is less than the maximum current draw on the nameplate then it's a fail.

My advice:-

Don't listen to anyone here who is not an electrician.

(Yes I am an electrician)

Do not put a 15A plug on your 27A welder, it is electrically unsafe, regardless of you having a modern fuse board with circuit breakers fitted

Typically the only circuit in a house capable of supplying 27A safely would be your oven.

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