240V wild leg panelboard

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olc

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How do you load 120V loads to a panelboard that is connected to 120/240 wild leg?
Skip all the spaces connected to the middle leg?
Use a separate 1 ph panelboard for 120V loads?

(thinking out loud)
If the only 3 phase load is a rooftop (HVAC) unit does it make sense to have a 1 phase panelboard (with a main circuit breaker) plus a separate 3 phase main disconnect for the RTU?
 
Seen it done both ways. Every installation has it's pros and cons.

If you have limited number of circuits seems common to just use the three phase panel.

If you have a lot of 120 volt circuits - separate single phase panel becomes favorable.
 
I recently had a similar situation at a renovated tire center. Before I even started work I opened the existing MB panel and found that it was completely loaded with breakers, several of which were tandem breakers and where a majority of the phase 2 (high leg) slots were there were breakers installed with no wiring to them. Not knowing what I was going to run into I ended up installing a 3-phase, 42 circuit panel on the opposite wall thereby giving me more 120V spaces if I needed them. As luck would have it I found that some of the existing, 20A, 240V circuits for the car lifts originated on adjoining tandem breakers that were plugged into the 120V slots. It took me a while to correct but I'm also glad I installed the 42 circuit ML panel on the opposite wall. I ended up using about 10 spaces, including two 30A, 240V circuits for lifts on the side car bay.
 
I did one project where they specified a special order panel for this application. There were spaces for 4 three phase breakers, but the remaining spaces only had connections for A or C phases.
 
jumper said:
GE by chance? Had one of those at the college in VA. Never have found another.
Click to expand...

They were pretty common, from most manufacturers, before 1985ish after that their use definitely fell off. I wonder if UL Listing requirement changed?
 
I went looking for one of the "special" panelbds before I started the thread.
My application will almost fill a 42 space pandlbd with mostly 120V circuits.
There will only be one (maybe two) 3 phase loads. And maybe one 240V-1Ph load.

This is a complete renovation including moving the service.
The existing panelboard has a lot of blank spaces on the second leg.

240V-3 phase is common around here so you have to watch for it. It helped that the panelboard had "wild leg" written in magic marker right across the top. I have run into a panelboard labeled 208V-3ph that was actually 240V - 3 phase.
 
goldstar said:
I ended up using about 10 spaces, including two 30A, 240V circuits for lifts on the side car bay.
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And those two pole breakers if using the wild leg can not be the common slash rated, they must be full voltage 240 rated, a slash rated breaker is 120 volts to ground, so won't clear a ground fault on the 208 wild leg
 
olc said:
I went looking for one of the "special" panelbds before I started the thread.
My application will almost fill a 42 space pandlbd with mostly 120V circuits.
There will only be one (maybe two) 3 phase loads. And maybe one 240V-1Ph load.

This is a complete renovation including moving the service.
The existing panelboard has a lot of blank spaces on the second leg.

240V-3 phase is common around here so you have to watch for it. It helped that the panelboard had "wild leg" written in magic marker right across the top. I have run into a panelboard labeled 208V-3ph that was actually 240V - 3 phase.
Click to expand...

Call Eaton, Sq D, etc. They may still be available, IDK.

Jim D just said maybe lost listing, who knows what happened.
 
olc said:
My application will almost fill a 42 space pandlbd with mostly 120V circuits.
There will only be one (maybe two) 3 phase loads. And maybe one 240V-1Ph load.

This is a complete renovation including moving the service.
The existing panelboard has a lot of blank spaces on the second leg.
Click to expand...

With all this info, I would definitely choose the 2-panel option. A 12-space for the 3ph and 240 1p loads (room for a new 3ph or one or two new L-L loads), and whatever suits the 1ph load quantity with a few spare spaces.
 
tom baker said:
And those two pole breakers if using the wild leg can not be the common slash rated, they must be full voltage 240 rated, a slash rated breaker is 120 volts to ground, so won't clear a ground fault on the 208 wild leg
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I wouldn't say "won't clear the fault". Just hasn't been designed, tested, and listed for that application. Could catastrophically fail in the right circumstances where the straight 240 volt version shouldn't.
 
tom baker said:
And those two pole breakers if using the wild leg can not be the common slash rated, they must be full voltage 240 rated, a slash rated breaker is 120 volts to ground, so won't clear a ground fault on the 208 wild leg
Click to expand...

What about the B phase (wild leg) on a 3 pole breaker then?
 
kwired said:
Three pole breakers are usually straight 240 volt rated (no slash rating) so not a problem.
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I agree the breaker used must have a minimum voltage rating for the voltage of the panel it is used in. In this case the panel is fed 120/240V 3PH 4 wire delta. Minimum voltage rating for a 2 pole and 3 pole breaker is 240V.

I guess I have never ran across a miniature 2 pole breaker with less than a 240V rating.

Example, 2p SDQO
http://static.schneider-electric.us...rs/QO-QOB Circuit Breakers/0730CT9801R108.pdf

Jim
 
Jamesco said:
I agree the breaker used must have a minimum voltage rating for the voltage of the panel it is used in. In this case the panel is fed 120/240V 3PH 4 wire delta. Minimum voltage rating for a 2 pole and 3 pole breaker is 240V.

I guess I have never ran across a miniature 2 pole breaker with less than a 240V rating.

Example, 2p SDQO
http://static.schneider-electric.us...rs/QO-QOB Circuit Breakers/0730CT9801R108.pdf

Jim
Click to expand...
You better look again. It is difficult to find a 2 pole miniature that is not rated 120/240. QO versions that are straight 240 volt have suffix "H" in the catalog number
 
Jamesco said:
I guess I have never ran across a miniature 2 pole breaker with less than a 240V rating.
Click to expand...

The vast majority of small (e.g. residential style) molded case breakers 2 pole breakers are rated as 120/240V. This means they are suitable for a L-G voltage or 120V and a L-L voltage of 240V.

In a wild leg source the maximum system voltage L-G is 208V therefore you cannot use a 'slash rated' breaker, like a QO230, instead you need a straight 240V one like a QO230H
 
jim dungar said:
The vast majority of small (e.g. residential style) molded case breakers 2 pole breakers are rated as 120/240V. This means they are suitable for a L-G voltage or 120V and a L-L voltage of 240V.

In a wild leg source the maximum system voltage L-G is 208V therefore you cannot use a 'slash rated' breaker, like a QO230, instead you need a straight 240V one like a QO230H
Click to expand...

Thanks dungar for the clarification.

2014 NEC 240.85 Applications.


240-85 Applications was first added to the 1996 NEC.

I wonder how many 120/240V 3PH 4W Delta fed panels are still out there with 2P 120/240 rated breakers installed on the "B" phase wild leg?

I wonder how many of the 2P 120/240V breakers were still being installed on the wild leg after the 1996 NEC was adopted by AHJs.

Jim
 
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