Wiring 4 wire US 120V/208V-240V ceramic cooktop to 230V EU outlet.

[sofarry1]

TL;DR Summary

How to wire a 120V/208V-240V US cooktop to 230V EU outlet? Thanks for your valuable feedback.

 

[Baluncore]

Welcome to PF.

Unfortunately, your schematic is unreadable. That may be a website conversion problem. Check your original.

The international standard is 230 volts for single phase.
A cook-top wired for 240 volt, should run on the EU 230 volts without a problem.

Connect the ground and neutral, then tie L1 and L2 together to active.

 

[sofarry1]

My question is about the neutral (white) wire. Do I wire it together with L1 (red) or L2 (black) wire to the EU phase?

 

[Baluncore]

My question is about the neutral (white) wire. Do I wire it together with L1 (red) or L2 (black) wire to the EU phase?

I would need to read the unreadable schematic, to determine the way it should be wired in the 240 volt mode. Is there some text on the schematic that identifies the 240 volt mode.

 

[sofarry1]

 

[sofarry1]

Is it still unreadable?

 

[Nugatory]

My question is about the neutral (white) wire. Do I wire it together with L1 (red) or L2 (black) wire to the EU phase?

Neither, and what you want can’t be done.
In North American household wiring there are three voltages available: +120, -120, and 0/neutral. This is done by center-tapping a nearby 240V output transformer and running three wires to the house. The 120 volt outlets are wired to one of the two hot legs and neutral; 240V outlets are wired to the two hot legs which are 180 degrees out of phase so 240V apart.
Four-wire appliances have components that operate on 240V and others that require 120V; the outlet is wired to all three available voltages. Either hot leg will be at 120V relative to neutral and 240V relative to other. (The fourth wire is of course the safety ground, which should never carry current).

You only have two conductors 240V apart so no way of also providing 120 to your appliance. You will not be able to use it.

You will occasionally encounter this problem in the US when an outlet was originally planned for a pure 240V appliance - only +110 and -110 brought to a 240-only outlet from the panelboard, so need to pull a new three-conductor cable before a suitable outlet for the new appliance can be installed.

 

[sofarry1]

View attachment 324691

Neither, and what you want can’t be done.
In North American household wiring there are three voltages available: +120, -120, and 0/neutral. This is done by center-tapping a nearby 240V output transformer and running three wires to the house. The 120 volt outlets are wired to one of the two hot legs and neutral; 240V outlets are wired to the two hot legs which are 180 degrees out of phase so 240V apart.
Four-wire appliances have components that operate on 240V and others that require 120V; the outlet is wired to all three available voltages. Either hot leg will be at 120V relative to neutral and 240V relative to other. (The fourth wire is of course the safety ground, which should never carry current).

You only have two conductors 240V apart so no way of also providing 120 to your appliance. You will not be able to use it.

You will occasionally encounter this problem in the US when an outlet was originally planned for a pure 240V appliance - only +110 and -110 brought to a 240-only outlet from the panelboard, so need to pull a new three-conductor cable before a suitable outlet for the new appliance can be installed.

I have an oven by the same manufacturer Thermador. Connected the neutral white wire to a step down transformer and it works just fine. The cooktop however has no motors whatsoever. There’s a signal transformer that operates at 120V/240V to 12V.

 

[DaveE]

Connect the ground and neutral

No. Violates every safety standard I ever read. Ground wires should never carry current in normal operation.

 

[Baluncore]

No. Violates every safety standard I ever read.

Connect the ground, and connect the neutral.

 

[Nugatory]

No. Violates every safety standard I ever read. Ground wires should never carry current in normal operation.

Weirdly - and to my shock - this used to be allowed in the US code when it was desired to upgrade a three-wire (two hot phases and neutral) outlet for a four-wire (two hot phases, neutral, and safety ground) appliance. This always struck me as totally insane, it is thankfully no longer allowed by the US code, and it only worked because the two hot legs are both 120V from ground.

Would it work in OP's situation? I doubt it, because if I understand european 250V household wiring properly (if not someone who does will speak up) one conductor is grounded and the other is at 250V from ground.

 

[Baluncore]

It may be that the "120V/208V-240V US cooktop" needs different resistive elements installed for the different voltage regions.

 

[Nugatory]

It may be that the "120V/208V-240V US cooktop" needs different resistive elements installed for the different voltage regions.

That is certainly possible, but if so I would expect it to come with specific instructions about how to adapt it for European operation, and it would be unusual to have designed it for four-wire operation in the first place.

 

[Averagesupernova]

No. Violates every safety standard I ever read. Ground wires should never carry current in normal operation.

It's done all the time. Purchase a range in the USA to be used in the USA and a choice is usually given to purchaser of a 3-prong cord or a 4-prong cord. If the kitchen the range is to be installed in has an existing 3 wire outlet then the 3-prong cord is used. There is a jumper that is supplied with the range to connect the chassis with the neutral in such case. Otherwise the ground wire is attached to the frame and the two hots and neutral are hooked to the terminal block.
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In the case of the cooktop in question in this thread I am not willing to say if it can be made to work. I suspect not.

 

[DaveE]

It's done all the time. Purchase a range in the USA to be used in the USA and a choice is usually given to purchaser of a 3-prong cord or a 4-prong cord. If the kitchen the range is to be installed in has an existing 3 wire outlet then the 3-prong cord is used. There is a jumper that is supplied with the range to connect the chassis with the neutral in such case. Otherwise the ground wire is attached to the frame and the two hots and neutral are hooked to the terminal block.
-
In the case of the cooktop in question in this thread I am not willing to say if it can be made to work. I suspect not.

Appliances like that must have reinforced (double) insulation for any accessible conductive parts, so a safety ground isn't needed. In that case if the neutral conductor on the supply side breaks and HV is applied to the appliance side of the neutral circuit, it isn't a hazard. So, yes, there are several permutations you may see in appliance design but they must meet these (among other) requirements.

1) Basic insulation between any conductors in the supply and the ground conductors. So, no current can flow on the ground conductors in normal operation, or in single fault conditions (like an open neutral conductor).

2) Human accessible parts* must either be grounded and have basic insulation between HV and neutral, or have reinforced or redundant insulation from the supply conductors.

The "ground" you describe is likely only used for EMC or other internal purposes. It's not the safety ground we were referring to. Internally, it must be insulated the same way as the neutral conductor, since they may be connected. Likewise, it must be insulated from the true neutral conductors, so that current can't flow through the supply ground if it is wired that way. If it might be connected to ground, or it might be connected to neutral, it must meet all of the requirements for both.

*Including things like necklaces' hanging through slots, or 3 year olds poking knives inside.

PS: This is all based on US and EU standards. I have no idea what they do in Kazakhstan. Also only applies to current requirements. They did lots of scary non-optimal stuff in the past.

 

[Dullard]

What 'is done' and what 'should be' can vary a lot. I had a friend call me with an odd problem: If someone bathed while the oven (broil) or stove top was in use, they got shocked when they touched the tub/shower faucet. It (very specifically) didn't happen when the oven was in 'Bake.' I was intrigued enough to take a look.

After some poking around:
There was no neutral (or ground) in the box which powered the oven. Whoever installed the oven tied the neutral and ground to a convenient copper water pipe (in the wall). The only intentional L-N current in the entire stove was for the indicator lamps (Bake, Broil...). Whenever one of the indicators 'lit,' the plumbing went to an appreciable fraction of 120 VAC. The 'Bake' lamp filament was open - no current - no shock. He was 1 insulation failure away from killing someone. I ran a temporary external neutral and told him to get it wired properly - not sure he ever really understood the risk (or fixed it). Sometimes you just gotta let Darwin work.

 

[DaveE]

What 'is done' and what 'should be' can vary a lot. I had a friend call me with an odd problem: If someone bathed while the oven (broil) or stove top was in use, they got shocked when they touched the tub/shower faucet. It (very specifically) didn't happen when the oven was in 'Bake.' I was intrigued enough to take a look.

After some poking around:
There was no neutral (or ground) in the box which powered the oven. Whoever installed the oven tied the neutral and ground to a convenient copper water pipe (in the wall). The only intentional L-N current in the entire stove was for the indicator lamps (Bake, Broil...). Whenever one of the indicators 'lit,' the plumbing went to an appreciable fraction of 120 VAC. The 'Bake' lamp filament was open - no current - no shock. He was 1 insulation failure away from killing someone. I ran a temporary external neutral and told him to get it wired properly - not sure he ever really understood the risk (or fixed it). Sometimes you just gotta let Darwin work.

It's the Dunning-Kruger problem of DIY. That's why I am pretty reluctant to tell people how to wire stuff like this. I don't know what they know. They don't know when they're doing something scary.

Hire an electrician, unless you know way more than you need to, you've read every piece of documentation you can, and the task is really, really simple.

 

[Averagesupernova]

@DaveE what I described is accurate with any range that can be bought from any big box store in the USA with no 'double insulated' anything. The chassis the you touch while your hands are wet or whatever is directly connected to the current carrying neutral in the cases of kitchens wired prior to what I'm guessing is the mid eighties. There are mistakes made upon installation that can cause the neutral and ground be tied together or reversed in the case of a 4-wire cord. Or in the case of a 3-wire cord the chassis is left floating. Sorry the world isn't how you think it should be.

 

[Dale]

Paused for review

 

[Nugatory]

what I described is accurate with any range that can be bought from any big box store in the USA

You are right - section 250-140 of the NEC allows this exception to the general principle that neutral and ground should be separate, but only for dryers and ranges when connecting to three-wire outlets installed before 1996 (120/240 outlets installed after 1996 would be four-wire so the problem doesn’t arise). This exception isn’t because such setups are preferable - they aren’t - but because it’s impractical to require homeowners to redo the in-wall wiring when they replace an appliance.

 

[Nugatory]

We are closing this thread because the answer to the question in the original post is that there is no safe way of doing what they want, and further discussion will run afoul of the forum rule prohibiting dangerous activities.

Further discussion of American 240/120 wiring should be in a new thread - it’s interesting and important but not directly relevant to the original post.

As with all thread closings, if there is more to say on the subject you can PM me or any other mentor to ask that the thread be reopened.