Multiwire Circuit Correct?

N

npavicic

Member
Location
Westland, Michigan
Occupation
Electrical Inspector
A detached garage is wired with two separate 20-amp circuits. Receptacles and lights. Two conductors black & white with equipment ground. The contractor brought out a multiwire circuit. Three conductors black, red & white with equipment ground. The contractor then splices the white conductors from the two separate 20-amp circuits white ground wires in the j-box that come from the home service panel. There is a two-pole switch for the disconnect. Where there is an in and out with the conductors from a receptacle box, he does not pigtail the white grounded conductors. He explains this is not necessary since the connection is made in the J-box
from the home where the multiwire neutral is located. Is this a violation? Additionally, since both garage circuits are separate and only black phase conductors, should
the red phase conductor used on the other circuit be identified as the red phase? I would have expected the garage wiring to use three conductor w/ground throughout the garage. I appreciate any thoughts on this installation.
 
1) MWBC-✓
2) Disconnecting means-✓
3) Two conductor cable does not require the black to be re-identified as a red conductor-✓
4) Not sure what you mean by:
npavicic said:
Where there is an in and out with the conductors from a receptacle box, he does not pigtail the white grounded conductors
Click to expand...
A pigtail would only be required for the shared neutral of the MWBC.
 
npavicic said:
... Where there is an in and out with the conductors from a receptacle box, he does not pigtail the white grounded conductors. ...
Click to expand...
Hmmph. If we look at the letter or 300.13(B) this could be considered a violation since that rule simply applies 'in multi-wire branch circuits' which is what you've got there. However this is pretty overkill if we're talking about a box where only one hot is present and it's downstream of where the neutral is combined, as you would not experience the issue with an energized open neutral in such a location. Plus with a two-pole switch as disconnect makes it much less likely someone would work on the circuit without both hots disconnected.
 
npavicic said:
A detached garage is wired with two separate 20-amp circuits. Receptacles and lights. Two conductors black & white with equipment ground. The contractor brought out a multiwire circuit. Three conductors black, red & white with equipment ground. The contractor then splices the white conductors from the two separate 20-amp circuits white ground wires in the j-box that come from the home service panel. There is a two-pole switch for the disconnect. Where there is an in and out with the conductors from a receptacle box, he does not pigtail the white grounded conductors. He explains this is not necessary since the connection is made in the J-box
from the home where the multiwire neutral is located. Is this a violation? Additionally, since both garage circuits are separate and only black phase conductors, should
the red phase conductor used on the other circuit be identified as the red phase? I would have expected the garage wiring to use three conductor w/ground throughout the garage. I appreciate any thoughts on this installation.
Click to expand...

The grounded conductor is only required to be spliced through at the j box where the multi wire circuit splits . Past that point they are essentially separate 20 amp circuits . that must have a means to simultaneously disconnect both of the ungrounded conductors . So 300.13(b) wouldn’t apply at outlet locations on each 120 circuit so the devices can provide the grounded conductor continuity


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jaggedben said:
Hmmph. If we look at the letter or 300.13(B) this could be considered a violation since that rule simply applies 'in multi-wire branch circuits' which is what you've got there. However this is pretty overkill if we're talking about a box where only one hot is present and it's downstream of where the neutral is combined, as you would not experience the issue with an energized open neutral in such a location. Plus with a two-pole switch as disconnect makes it much less likely someone would work on the circuit without both hots disconnected.
Click to expand...
300.13(b) would only apply if he tried to use a device to provide continuity of the grounded conductor at the shared neutral location , but he doesn’t he said the shared neutral is spliced through at that location. So he can use the devices on the seperate 20 amp circuits for grounded conductor continuity on that circuit passed the point of the splice
 
npavicic said:
I would have expected the garage wiring to use three conductor w/ground throughout the garage. I appreciate any thoughts on this installation.
Click to expand...
Why do you think this needs to be done. Once the 3 wire from the house reaches the garage then you just need 2 wire cable for each circuit.
 
jaggedben said:
Hmmph. If we look at the letter or 300.13(B) this could be considered a violation since that rule simply applies 'in multi-wire branch circuits' which is what you've got there.
Click to expand...
The usual interpretation is that only the portion of the branch circuit in which you do have more than one ungrounded conductor is an MWBC.

Cheers, Wayne
 
2023NEC

Article 100 Definitions

210.4(A) (B) (C) Multiwire Branch Circuits

240.15(B)(1) Multiwire Branch Circuits

300.13 (B) Device Removal (the receptacle) "The white wire should be pigtailed with the other one at the first outlet .....the grounded conductor (neutral) shall not depend on the device connections such as...receptacles.....where the removal of such devices would interrupt the continuity."

Because it will cause a series circuit and the voltage will be additive at each outlet and will eventually equal the source voltage.
This one of the rules of a series circuit.

Thus, causing different voltages at different outlets, resulting in higher/lower voltages. Serious problems.

And, each circuit should be on different phases when you stab it into the bus bars, most likely you will use a two pole CB.

Thanks for reading
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TX+MASTER#4544
 
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