Single pole 208V from a delta high leg?

[Nathan Daniels]

So my question is two-fold: 1a) Can I use the high leg of a delta 240V panel with a neutral to power a 208V single phase load without damaging it, and 1b) may I, i.e. does code permit it?

The load is a food warmer, so a simple resistive element. I’m assuming this is not permitted, since I’ve never seen it done, but I’m not sure where to look in the NEC.

That said, I also know a resistive load doesn’t see the difference between 208V between two lines and 208V between a line and a neutral.

 

[Nathan Daniels]

….this particular panel is a Square D and the breakers are 120/240 rated.

 

[don_resqcapt19]

….this particular panel is a Square D and the breakers are 120/240 rated.

You need a straight rated breaker if any pole of the breaker connects to the high leg.

 

[Nathan Daniels]

Thanks! Doesn’t get more concise than that!

 

[Jraef]

You need a straight rated breaker if any pole of the breaker connects to the high leg.

But to flesh that issue out, if this is a Square D QO based panel, ALL of the 1 (and 2) pole QO breakers are "slash rated", meaning you CANNOT use them for 1 pole 208V. So your ONLY option (in QO type) is to buy a 3 pole breaker and only use 1 pole of it, which wastes 2 other pole spaces in your panel. Can the device run on 240V instead of 208? If so, you only use 2 pole spaces for that.

Option 2 involves having to use a Square D 480/277V "NF" style panelboard, where the 1 pole breakers are rated for 277V. But if you don't already have that panelboard, this doesn't make sense.

 

[Nathan Daniels]

Can the device run on 240V instead of 208? If so, you only use 2 pole spaces for that.

The device initially used 240V elements, but lead time for these is obscene due to very low demand (the overwhelming majority of professional restaurants use 120v or 208v elements, according to the supplier). At the customer’s request, The end solution will have to be to use 120V elements, thereby doubling the current and increasing the rate of future failure, unfortunately.

 

[Jraef]

Yeah, sucky lead times are making people look into oddball options that would otherwise not make much sense. In this case though, the limitations will get in your way.

 

[jim dungar]

But to flesh that issue out, if this is a Square D QO based panel, ALL of the 1 (and 2) pole QO breakers are "slash rated", meaning you CANNOT use them for 1 pole 208V. So your ONLY option (in QO type) is to buy a 3 pole breaker and only use 1 pole of it, which wastes 2 other pole spaces in your panel. Can the device run on 240V instead of 208? If so, you only use 2 pole spaces for that.

There is a version of 2-pole QO breakers rated for straight 240V. These are almost always special order so you rarely see them outside of catalogs.

 

[electrofelon]

There is a version of 2-pole QO breakers rated for straight 240V. These are almost always special order so you rarely see them outside of catalogs.

They have an "H" suffix, i.e QO220H

 

[jim dungar]

They have an "H" suffix, i.e QO220H

Which is not to be confused with the QOxxxxVH and QHxxxxx which are both higher AIC breakers.

 

[electrofelon]

Which is not to be confused with the QOxxxxVH and QHxxxxx which are both higher AIC breakers.

I wish manufacturers could use simpler part numbers and not make it so confusing. For Siemens, they do a good job with their standard plug on and bolt on breakers, that is q/b120, q/b120H, q/b120HH. Then just when you think perhaps Siemens has it together, you look at their QR frame breaker and the H is all over the damn place. A three pole 200A in 10k, 25k, 65k, and 100k: QR23B200, QRH23B200, HQR23B200, HQR23B200H

 

[zbang]

@Nathan Daniels -
this seems to come up almost monthly, and for many reasons is just a Bad Idea(tm). A quick search of the forums should turn up those threads.