LV Panelboard Voltage Ratings

[PhaseShift]

Are most LV panelboards rated for 120/240V or are there some with a maximum rating of 120/208V? It seems like most 3-phase panelboards I have seen are have a 120/240V rating for the bus which are capable of being fed by a 208V 3-phase supply. I was just curious if there were panels rated at only 120/208V?

 

[Dennis Alwon]

I believe most panels are rated at the higher voltage 240V which means they can be used for 208v also. If they were rated 208 then you could not use them for 3 phase 240V systems. That would be more inventory etc.

 

[Jraef]

Voltage ratings have to do with spacings between live parts, like bus bars and terminals. There are basically only 2 levels of spacings, 600V and 300V. There is no such thing as 480-600V 1 phase service (that you would use this way) so basically all 1 phase service panels and load centers are built to the 300V standard in that aspect.

But when you get into 3 phase panels under 300V, there are differences in the construction between a 208Y120V panel and a 120/240V 3P4W panel. That's because you have to be restricted from plugging in 1 pole breakers to the red (high) leg on the 120/240V 3P4W systems. So it's not really about the voltage, its about the bus arrangements.

 

[LarryFine]

But when you get into 3 phase panels under 300V, there are differences in the construction between a 208Y120V panel and a 120/240V 3P4W panel. That's because you have to be restricted from plugging in 1 pole breakers to the red (high) leg on the 120/240V 3P4W systems.

I've never seen a mechanical means of avoiding the high leg in a panel, only self control.

 

[jim dungar]

I've never seen a mechanical means of avoiding the high leg in a panel, only self control.

There is no NEC or UL requirement to prevent installing incorrect breaker onto the high-leg.

However, most manufacters will factory assemble a custom panel with the B-phase missing from some breaker locations.

 

[Jraef]

...will factory assemble a custom panel with the B-phase missing from some breaker locations.

That's what I meant. The top half of the bus was missing in the B phase. But looking at it in some catalogs I have around here, I guess it's no longer a regular option on panelboards and not available at all on load centers. Used to be, but I haven't used a 120/240V 3P4W system in a lot of years. That explains why I see so many questions from people as to why they are reading high voltage on some of their breakers. I thought you had to out of your way to try to tap off the high leg, I guess it's not so hard to do any more.