I ran into this with UK supplied gen-sets.
In the UK, the center point of the wye is the neutral. no question.
Even when a 220 Volt transformer is used for 220 Volt single phase loads, one end of the winding is grounded and by convention is called the neutral.
If 110 Volts is needed it may be derived from a center tap on the 220 Volt transformer (if there is one present).
So we can have a single phase circuit (or one phase of a three phase installation) where one end of a 220 Volt winding is grounded and by convention called the neutral. 110 Volts may then be supplied from a center tap on a 220 Volt transformer.
We will have 110 Volts to ground/neutral and 220 Volts to ground/neutral.
The AHJ may not accept this arrangement.
And I agree with David. You may use a center tap to derive 110 Volts but you can not call it a neutral.
The transformer may need to be overload protected on the primary side.
With the single phase gen-sets a two pole breaker was used to protect both 220 Volt lines.
These sets were reconnected to North American standards before use.
Bill
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"Why not the best?"
Jimmy Carter
You may only get 110 Volts if there is a 110 volt tap on the transformer.
If you use three single phase 220 Volt transformers AND one or more have a center tap at 110 Volts you may supply 110 Volts, subject to local codes.
If you are using a three phase transformer you may not have 110 Volt taps.
Perhaps someone from the UK may add something.
Bill
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"Why not the best?"
Jimmy Carter
I've never seen a standard LV distribution transformer with anything other than a neutral point and the three phase connections brought out. It appears that you will need another transformer designed to take 380V or 220V on the primary and provide 110V on the secondary.
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If we learn from our mistakes I'm getting a great education!
Not especially Bill. Our distribution systems in the UK and Europe are pretty much standardised as 400V/230V with solidly earthed neutral. We don't see the oddities such as 'corner grounded' or phases with a centre-tap that you guys in North America have. I guess the generator you saw was a 9-lead or 12-lead machine being used in an unconventional manner.
The UK does tend to use 110V centre-tapped transformers (55V-0-55V) as a reduced risk source of power for the construction industry. Most professional portable tools are designed to run on this supply.
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If we learn from our mistakes I'm getting a great education!
Actually it was four lead single phase machines. The sets were spec'ed for 120/240 Volts. They were supplied with one end of the 240 Volt winding grounded instead of the center tap grounded as per North American standards.
The explanation was that in the UK, 220/380 Volts in wye configuration is standard with the wye point as the neutral and grounded. When a single phase transformer was used, one end was grounded and by convention called the neutral. The center tap was a 120 Volt tap and not a neutral.
It was a glitch that we straightened out. The suppliers were good people and we had no further issues with a good number of gen-set purchases and installations.
I was aware that 110 Volt tools were in use but I was not aware that the supply was 55V-0-55V.
Thanks again for the information.
Bill
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"Why not the best?"
Jimmy Carter
