Nec 240.15 overcurrent devices

[jaggedben]

I believe per 240.15 B3 yes you could use 3 single pole breakers with a handle tie. Note there could not be any line to neutral loads.

B1 lets you do it for line to neutral loads.

 

[electrofelon]

B1 lets you do it for line to neutral loads.

So if I have one machine, say a flux capacitor press, than takes three phases and a neutral, is that a multiwire circuit?

 

[jaggedben]

So if I have one machine, say a flux capacitor press, than takes three phases and a neutral, is that a multiwire circuit?

Yes, per the definition. And it meets the exception in 210.4(C)(1).

(I don't believe flux capacitor presses typically operate at less than 1000VAC or 1500VDC, but ymmv.)

 

[electrofelon]

Yes, per the definition. And it meets the exception in 210.4(C)(1).

(I don't believe flux capacitor presses typically operate at less than 1000VAC or 1500VDC, but ymmv.)

Yeah I agree it meets the definition, but you think that's the intention? Just because a single piece of equipment takes a neutral conductor shouldn't make the circuit a multi wire branch circuit. Seems to me there should be something in there about separate loads.

 

[jaggedben]

Yeah I agree it meets the definition, but you think that's the intention? Just because a single piece of equipment takes a neutral conductor shouldn't make the circuit a multi wire branch circuit. Seems to me there should be something in there about separate loads.

I don't know why it matters, seems off topic. 240.15 doesn't ultimately care whether there's one or many. It's ultimately concerned with whether individual breakers are rated for the application. Basically you can use individual handle-tied breakers where they are confident they can handle faults.

 

[electrofelon]

I don't know why it matters, seems off topic. 240.15 doesn't ultimately care whether there's one or many. It's ultimately concerned with whether individual breakers are rated for the application. Basically you can use individual handle-tied breakers where they are confident they can handle faults.

So when do I need a common trip on a 120/208 system?

 

[jaggedben]

So when do I need a common trip on a 120/208 system?

I think never? Nor for 120/240 single phase. Just handle ties.

 

[wwhitney]

So when do I need a common trip on a 120/208 system?

For a 2-wire L-N or L-L circuit, or 3-wire L-L-L circuit, never. For a 3-wire L-L-N or 4-wire L-L-L-N circuit, if the circuit supplies both L-L (or L-L-L) loads and L-N loads, you need common trip; if it supplies L-N only, it does not.

Cheers, Wayne