I am wiring a panel to help a customer get caught up. they are taking 220vac single phase from a transformer and tying L2 to ground and then using a white wire as neutral to go to a 220vac single phase air conditioner. They are also doing this on a second single phase transformer only using the center tap as 110vac hot. Never seen this before, National electric code states no white or gray neutral on a 220vac single phase circuit. Sounds dangerous to me!

does any one know if this is even legal or code?
because I will not wire it this way!

 

I would argue these are likely both an SDS and thus subject to the rules in 250.30, as opposed to 250.20, which is for services.

I have no problem at all with the first installation. The second one is a little odd but probably ok.

Note that 250.26 (2) might appear to require this but a careful read of this paragraph says that if applies to "ac premises wiring systems". I don't see this as a premises wiring system as defined in article 100.

--
Bob

 

That voltage level isn't "unsafe" per se. In the US we use a lot of 480V symmetrical, in which any one leg is 277V to ground. The feed you describe is equivalent to one leg of a three-phase voltage feed commonly used in other countries, 415Y/240, which is double our common voltage of 208Y/120.

The problem will come if the air conditioner mfgr did things based on the idea that you would power it with two legs at 120V to ground and 240 to each other, such as using lower voltage-rated power wiring (doubt they would do that) or putting in varistors selected for 120V from each leg to ground (I have seen this).

So from a technical perspective the answer is, it depends -- on what the manufacturer assumed, and how he implemented those assumptions. As far as code is concerned, I can't say except to mention that having a hot-neutral circuit at 240V or more isn't prohibited; lighting in a lot of commercial buildings is done with a hot and neutral from that 480Y/277 voltage I mentioned earlier.