Wild leg - Single Phase

[Sparky32297]

Walked into this one. 1200 amp 3 phase 120/240 volt delta service with high leg. The customer has a large 240 volt heating load single phase all around the plant. He has installed 6 single phase panels some with the wild leg and some without the wild leg, probably in an effort to balance the load on the service. All the panels have a neutral installed. Since I have never run across this before I have two questions. Is this code legal? has anyone seen this before or am I living a sheltered life ?

 

[renosteinke]

Welcome to the 'fine print' of the NEC

Using the 'wild leg' for the 240v circuits is never a code problem. If the panels have ONLY 240v circuits in them, you don't have any code problems. It's the presence of the the neutral, which suggests that there are 120v loads, that creates a code problem.

Look at the tiny print onside the door of the main panel, on one of those upside-down stickers. It will list the power distribution systems for which the panel is listed. Where it mentions 240/120 Delta, it will say something like 'multipole only.' In other words, you're not supposed to have 120v circuits originate from that panel.

Yes, I recognize that there are millions of panels out there where they simply skipped every third space. There are also a multitude of 'split buss' panels out there tht were developed to specifically adress this issue.

So- what are you supposed to do? As best as I can figure it, you are supposed to take the two "normal" legs, and use them to feed a separate panel, from which all of your 120v. loads will originate. Otherwise, you're using the main panel in a way not consistant with it's labelling - an Article 110 violation.

The second half of this answer is a bit more subtle. Can you see the transformers that supply the place? Are there two transformers (one larger, one smaller) on the pole? Or, are therer three, with one much larger than the others? The point I'm getting at is that you probably want to talk to the PoCo about getting "real" three phase power if you either have serious three-pahse loads, or a lot of 120v loads. You want to consider changing your place over to a 208/120v "Wye" system.

The change in voltage from 240v to 208v IS a problem if you are using it to create heat. It should not be an issue for motors and the like.

 

[busman]

The change in voltage from 240v to 208v IS a problem if you are using it to create heat. It should not be an issue for motors and the like.

Are you sure you don't have that statement backwards?

Mark

 

[texie]

A 1200 amp 120/240 delta...don't think I've ever seen one that big. Typically if you have this much load the POCO would just give you a 208/120 wye service. You mention it would seem they were trying to balance the load. You might want to check the POCO setup, as they usually don't size them for balanced 3 phase loading. A hot and high leg with neutral to a single phase panel is sure odd, but I'm not sure specifically how that violates code. One would think it would/should. In any event you would need 240 rated breakers (not 120/240) to connect line to line load using the high leg. Might it be in the cards to convert this to a 208/120 wye system? I would think the POCO would go along with it with that much load.

 

[texie]

Are you sure you don't have that statement backwards?

Mark

No. He is indicating that the 240 volt heaters are going to loose about 25% of capacity at 208 volt. But we don't know how they are sized or what they do so we can't say if that's an issue. If they are , say, used on an injection molding machine might be a big deal. If they are just for space heat and are already oversized, it may not be a big deal.

 

[renosteinke]

Texie, you are correct; I was referring to the dramatic loss of heat that heating eelements will make when the voltage is reduced.

I came across this issue in restaurants, where the dishwasher has a 'booster heater' that brings the house hot water up to the temperatures required for sanitizing. The equipment almost always was ordered with the wrong heating elements in it.

By contrast, most motors have nameplate ratings that make it acceptable to feed them from either source.

 

[Strathead]

By contrast, most motors have nameplate ratings that make it acceptable to feed them from either source.

But overload heaters and/or dial settings need to be adjusted for motors. Just a reminder. Not a problem like the loss of heating capacity, but a requirement none the less.