3 Phase Load & 1 Phase load on same branch ckt.

[steve66]

I have a 3 phase 480 volt branch circuit specified to run a 3KW duct heater. (20 amp circuit)

Can the same branch circuit also feed a 277 V, single phase duct heater??

The branch ckt. would be fed from a 3 pole breaker, so all the conductors would be disconnected at the same time. And a neutral would be ran with the branch ckt.

Steve

 

[480sparky]

My first question is, "Why?".

 

[steve66]

To save having to run another branch circuit for a load that draws very little current (i.e. change order). Even with both heaters, there is less than 4 amps.

Steve

 

[480sparky]

Shooting from the hip, I'd say there's no NEC violation, but there very well could be one that's not coming to mind right now.

Just a poor design, IMPO. If running a seperate circuit means a change order, you mean it was designed this way?

 

[steve66]

Both units were scheduled for 480V, 3 phase. But when they were recieved, one was 277V.

I'm not sure why you think its a poor design. I don't see any big difference between this and placing two receptacles on the same circuit.

Steve

 

[480sparky]

If one unit came in as 277 instead of 480, then you should have a 480 circuit planned for it. So instead of pulling 3 wires, you only need two.

It's a poor design in that you cannot turn just one of the heaters off. We're talking 480, so it's a commercial or industrial job you're working on. Plans & specs are pretty much the norm. And they are expecting you to follow them.

Do you routinely put 120v receps on the same breakers as 240v receps?

 

[steve66]

Do you routinely put 120v receps on the same breakers as 240v receps?

No, but with heaters, I know exactly what the load will be. And I'd be crazy to run a homerun for every receptacle.

Each heater can still be turned off with the disconnect at the heater.

I'm doing the design, not the actual installation. The electricians are the ones that want to run a new branch circuit for the 277V heater.

If it needs a separate circuit, no big deal. But I still don't see any reason not to combine the heaters on the same circuit.

Steve

 

[480sparky]

I guess the reason it 'rubs me the wrong way' is the same for a lot of others.... I've just never seen it done.

Unless there's a Code restriction against it, I don't see why you can't do it.

 

[cowboyjwc]

I guess the reason it 'rubs me the wrong way' is the same for a lot of others.... I've just never seen it done.

Unless there's a Code restriction against it, I don't see why you can't do it.

I agree. The only other problem I might see is the unbalanced load on one of the legs giving you the potential for the neutral to carry a greater load. I know it's not a lot, but......