2 1pole C/Bs or 1 2pole C/B

[jimgineer]

So,
This is internal to a piece of parelleling switchgear, if that makes any difference.

My gut tells me that this is not a big deal, but I wanted to run this by some other people first.

We have need for 2 loads in a generator enclosure - they are both 120V. One draws 7A, one 17A. We are thinking a 480 - 240/120 XFMR, 10kVA we'll say, and I'm wondering if there's any issues with running out of a 2 pole breaker vs running out of 2 1pole breakers.

Either way, we're going to be running both ends of the transformer windings through protection, and two nuetrals back to the center tap on the transformer. I can't forsee any issues with this... And I would imagine a single 2 pole breaker would be slightly cheaper and easier to mount.

Thanks

 

[DanDel]

Two separate circuits require two separate overcurrent protection devices.

 

[jimgineer]

Not to be a stickler but where code-wise does this come from?

 

[controlsdude]

If you going to protect a device as the transformer on two legs then both breakers have to be mechanically interlock to trip together. That way if one leg trips then the other leg will trip also causing you less damage to equipment. Is this common sense?

Now what NEC code to quote?

 

[jghrist]

There may not be a code requirement for separate breakers on separate circuits, but if you use a 2-pole MCCB and have an overload or short-circuit on one circuit, or if you want to disconnect one circuit for maintenance, you will lose power to both circuits.

This may not make any practical difference in your case, but really, how much will you save using a 2-pole MCCB instead of two 1-pole MCCBs? Actually, according to my out-of-date Grainger catalog, a 1-pole 30A MCCB costs $6.60 and a 2-pole 30A MCCB costs $19.97, so it will cost more to use the 2-pole.

 

[BJC]

The NEC doesn't cover things like generator enclosures. Nema standards do.It covers the connection of generators. If it's going to be connected to a house or other building you can probably get away with it. It's not a thing anyone with experience would look for ( who would expect to see it?) If your making one to sell or rent you might need a UL label.
There is also common sense, two loads, to circuits, two breakers. I can't explain that to you.
If it;s some kind of homemade project, who cares.

 

[dpc]

I'm not sure if this is an NEC violation or not. But for any maintenance on one circuit (and not the other), both circuit must be de-energized. From experience, I can tell you that there will be in increased chance of these circuits being worked hot to avoid taking an outage on both circuits. This may not be the direction you want to go, especially since the cost of doing it correctly is virtually insignificant.

Dave

 

[jimgineer]

Thanks guys I figured this wasn't of huge importance but wanted you opinions