Tapping 120V from a 240V circuit

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Jbyars

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I am installing a new industrial style oven that runs on 240Vac - 15A which also has a 120Vac - 1A ventilation fan.
Is it NEC compliant to tap off of the conductors going to the oven for the fan?
We would pull 4 #12 conductors 2 Hot, a Neutral, and a shared ground which will run back to a single phase 120/240Vac panel with a 2-Pole 20A breaker.

I understand that I would be creating an unbalanced system, but aside from that is there any other concerns I should consider?
 
What you have is a MWBC (multi wire branch circuit). No different than a stove or dryer has with the exception of the wire size.
 
I don't see any practical or safety problem but look at 210.4(C). The two-pole common-trip breaker is required via exception 2.
 
jaggedben said:
The two-pole common-trip breaker is required
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Just curious what is the purpose of that safety measure, other than 2 independent poles of a 3 wire sharing a neutral which yes can carry the return of the other pole. I do get it, but it seems like another fool proof issue adopted to eliminate the unaware service people from getting bit.

Good idea I guess but come on ..
 
Another C10 said:
Just curious what is the purpose of that safety measure, other than 2 independent poles of a 3 wire sharing a neutral which yes can carry the return of the other pole. I do get it, but it seems like another fool proof issue adopted to eliminate the unaware service people from getting bit.

Good idea I guess but come on ..
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Whether for a dedicated load or a MWBC, it's a good idea, and usually required.

For manual use, a handle tie will suffice, but a 2p breaker is cheaper than two 1p breakers and a tie.
 
Another C10 said:
Just curious what is the purpose of that safety measure, other than 2 independent poles of a 3 wire sharing a neutral which yes can carry the return of the other pole. I do get it, but it seems like another fool proof issue adopted to eliminate the unaware service people from getting bit.

Good idea I guess but come on ..
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Well for one thing, any time you have a line-to-line load it should have a common trip breaker.
 
LarryFine said:
Whether for a dedicated load or a MWBC, it's a good idea, and usually required.

For manual use, a handle tie will suffice, but a 2p breaker is cheaper than two 1p breakers and a tie.
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Haven't checked recently but at one time I figured it to cost about same either way for 15 and 20 amp QO breakers. Advantage for MWBC's is independent trip, though you still end up shutting second pole off during a reset.
 
jaggedben said:
Well for one thing, any time you have a line-to-line load it should have a common trip breaker.
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Without comment on whether that is the best practice, (2017) 240.15(B)(2) says that's not required when there are just line-to-line loads on a circuit on a 120/240V system.

As to why 210.4(C) Exception 2 requires common trip when an MWBC serves L-L loads and L-N loads (as otherwise it wouldn't be an MWBC), I assume it's so the L-N loads on leg A don't end up in series with the L-L loads and a 120V N-B supply, should only the A side breaker trip.

Cheers, Wayne
 
wwhitney said:
Without comment on whether that is the best practice, (2017) 240.15(B)(2) says that's not required when there are just line-to-line loads on a circuit on a 120/240V system.

As to why 210.4(C) Exception 2 requires common trip when an MWBC serves L-L loads and L-N loads (as otherwise it wouldn't be an MWBC), I assume it's so the L-N loads on leg A don't end up in series with the L-L loads and a 120V N-B supply, should only the A side breaker trip.

Cheers, Wayne
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Yet that happens when a service or feeder fuse blows, or even just an ungrounded conductor fails somehow.

And sometimes confuses the heck out of whoever is trying to troubleshoot it.
 
Jbyars said:
I am installing a new industrial style oven that runs on 240Vac - 15A which also has a 120Vac - 1A ventilation fan.
Is it NEC compliant to tap off of the conductors going to the oven for the fan?
We would pull 4 #12 conductors 2 Hot, a Neutral, and a shared ground which will run back to a single phase 120/240Vac panel with a 2-Pole 20A breaker.

I understand that I would be creating an unbalanced system, but aside from that is there any other concerns I should consider?
Click to expand...
I just did almost the exact thing on a well pump rewire. Submersible pump required a 20A 240V circuit. I pulled a neutral in addition to the two phases, and powered a 120V receptacle for the water softener and water filter from one leg of the same circuit. Receptacles were GFCI-protected since it was in an unfinished basement. Saved space in the panel, and some wire too. As others have said, it has to be a two-pole breaker or two single-pole breakers with a common trip handle tie.



SceneryDriver
 
SceneryDriver said:
As others have said, it has to be a two-pole breaker or two single-pole breakers with a common trip handle tie.
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Since the circuit you described serves both 240V and 120V loads, it has to be a common trip breaker, not two single pole breakers with a handle tie. Handle ties don't make the breakers common trip, just common manual disconnect.

Cheers< Wayne
 
wwhitney said:
Since the circuit you described serves both 240V and 120V loads, it has to be a common trip breaker, not two single pole breakers with a handle tie. Handle ties don't make the breakers common trip, just common manual disconnect.

Cheers< Wayne
Click to expand...
You're right. I should've been more clear; I was thinking of a MWBC using a handle tie. In my case, I used a 2P breaker.


SceneryDriver
 
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