Two circuits feeding one load

[James McCusker]

Does the NEC permit feeding a single load from two half-sized circuits?
Ex.: A 40 A range fed by two #10 AWG circuits each protected by a 30 A breaker.
Note that this is not the same as parallel circuits where the cables are joined together at each end and protected by one breaker.

 

[iwire]

Sure if that is what the instructions call for.

 

[gndrod]

Does the NEC permit feeding a single load from two half-sized circuits?
Ex.: A 40 A range fed by two #10 AWG circuits each protected by a 30 A breaker.
Note that this is not the same as parallel circuits where the cables are joined together at each end and protected by one breaker.

Hi James,
Does the question really pertain to two 30A SP breakers feeding from the same panel? Check 210.7(B) common trip. rbj

 

[charlie b]

I agree that it is allowed. But that particular example would only supply 30 amps to a range capable of 40 amps. That reduces its possible heat output to 56% of its rating. The owner might not happy about that, but it meets code.

 

[roger]

This is what I picture as two 1/2 sized circuits feeding one load and I like it. :wink:

Roger

 

[RUWired]

Some of the instant hot water tankless unit have multiple circuits going to them.Not sure if this is what you have.

 

[iwire]

I was think of the water heaters around here that used to be on off peak metering.

They would have two separate 20 or 30 amp feeds each supplying one element.

 

[RUWired]

This is what I picture as two 1/2 sized circuits feeding one load and I like it. :wink:

Roger

Roger, that looks like a 40 amp load on a 20 amp circuit regardless of the pole position.

 

[480sparky]

Roger, that looks like a 40 amp load on a 20 amp circuit regardless of the pole position.

I agree.. it's only a matter of time before one of those 20s opens.

 

[480sparky]

Roger, that looks like a 40 amp load on a 20 amp circuit regardless of the pole position.

It won't work that way anyway.... they're on the same phase, so there's no voltage.

 

[roger]

Roger, that looks like a 40 amp load on a 20 amp circuit regardless of the pole position.

No, it is a 40 amp load supplied by two 20 amp circuits.

It won't work that way anyway.... they're on the same phase, so there's no voltage.

Wrong, it will work and supply 40 amps to the load.

The grounded conductor is not shown in the illustration

Roger

 

[480sparky]

Wrong, it will work and supply 40 amps to the load.

The grounded conductor is not shown in the illustration

Roger

But if the breakers are on the same phase, there will be no voltage between them.

 

[roger]

I agree.. it's only a matter of time before one of those 20s opens.

Why do you think that if the impedance is the same on both sides of the load?

Note; the illustration states the load is in the center of the circuit

Roger

 

[roger]

But if the breakers are on the same phase, there will be no voltage between them.

That doesn't matter, there will be voltage at the load.

If there were voltage between them the load would be seeing 240 volts instead of 120.

Roger

 

[480sparky]

That doesn't matter, there will be voltage at the load.

If there were voltage between them the load would be seeing 240 volts instead of 120.

Roger

I guess I'm going by the drawing too literally... the breakers are on the same phase.

 

[RUWired]

That doesn't matter, there will be voltage at the load.

If there were voltage between them the load would be seeing 240 volts instead of 120.

Roger

Roger, you can't have current flow with the load on the same phase unless you have a neutral somewhere in the middle of that load.

 

[roger]

I guess I'm going by the drawing too literally... the breakers are on the same phase.

And that's what we want, think of the current division theory behind parallel conductors.

Both OCPD's will be supplying the load with the same leg or phase and the current will be double what one would provide.

The key to this scenario is that both sides are ballanced.

Roger

 

[480sparky]

And that's what we want, think of the current division theory behind parallel conductors.

Both OCPD's will be supplying the load with the same leg or phase and the current will be double what one would provide.

The key to this scenario is that both sides are ballanced.

Roger

Is this a more accurate drawing?

 

[roger]

Roger, you can't have current flow with the load on the same phase unless you have a neutral somewhere in the middle of that load.

Rick, look at post # 11, this is simply a one line diagram and the grounded conductor is not shown.

Roger

 

[RUWired]

Rick, look at post # 11, this is simply a one line diagram and the grounded conductor is not shown.

Roger

OOP there it is, then i agree!