I recently had an electrician add two new 20-amp circuits, EMT, and outlets to the interior of my attached garage. The new work initially runs a very short distance from the breaker panel to a junction box. Out of curiosity I opened the junction box (w/power off) and I discovered that the two new circuits share a single neutral wire upon entering the junction box then branch out to create two separate branches of outlets. The single neutral is pigtailed to two neutral wires within the junction box that travel with each respective branch of outlets. Is this okay (e.g., safe, within code, etc.)? I have typically only seen individual hot and neutral wires for each circuit and I am concerned about this install and potential safety issues. Any help would be appreciated and thank you for your comments and any guidance!
I have attached a simple diagram of what was installed.
Other details include:
– He added two single-pole breakers (they are stacked but no handle between them).
– Panel is on exterior wall of garage and he ran three 12g THHN wires within wall (one hot from new circuit #1, one hot from new circuit #2, and one neutral) to a 4″ metal junction box on interior garage wall directly behind breaker panel.
– Distance from exterior panel to interior junction box is less than 6″. I live in Southern CA and most panels are outside and house built 2000.
– All work is within EMT since garage walls are finished.
– After the junction box, each hot wire runs on a separate branch with its own neutral and ground wire within EMT to a GFCI outlet. From there, additional outlets branch out from each GFCI for a total of three outlets on one circuit and two outlets on the second.
– Within junction box, the single neutral from panel is pigtailed to two new neutral wires -each running along the two new branches (first connecting to the GFCIs) then to each new outlet.
– Aside from the initial junction box, each hot and neutral wire is attached to each outlet without using pigtails.
There's nothing wrong with this as long as the two breakers are on opposite legs of the system. If you're concerned put a volt meter between the hots of the two circuts. If it reads 240 you're ok; the circuts are on opposite legs and the neutral loads will cancel each other out. If it reads 120 the circuits are on the same leg and the neutral loads will add together and possibly overload the neutral.
Thanks for your time and comments MIke! As suggested, I checked with a voltage meter and it was 240. In addition, the placement of the two breakers (stacked) would also indicate they are on opposite legs.
I am wondering if either a handle tie or 2-pole breaker should have been installed and if they should have given me a heads up. The electrician never told me about the single neutral and there are no markings in panel or on their work to warn others. Ugh.
I am going to call in another electrician to check out the work. What bugs me, aside from spending money on questionable work, is that I originally asked for two separate 20amp circuits (and ability to extend branch in future if needed) and for whatever reason he installed a single neutral. The new junction box is literally attached to back of panel and he would have only needed another couple of feet of wire. Any recommendation for a great electrician in San Diego? Thanks again! RB
What part of San Diego? If you're in no rush I can check it for you. [email protected]
If you ever install a GFI breaker it will trip both breakers if one circuit faults. It won't work at all if you ever install a combo AFGF breaker.
That’s what they call a multi-wire branch circuit aka shared neutral.
If I remember correctly, both breakers have to be tied together so if one circuit of the multiwire branch circuit has a fault, both circuits will open simultaneously.
I also believe that the neutral wire has to be continuous by pigtailing at devices instead of landing 2 individual neutral wires on a device and using that device as the splice point to the next device.
See attached picture, even though it is very low tech...
Thanks for the comment and your time! See my response to Mike above. Thanks for your service too! Also, a Navy Vet (FMF HM).
You’re welcome and thanks for your service as well.
You can normally buy a handle tie and put it on yourself if you wanted to.
Good luck and let us know what the new electrician has to say. Since it’s already in conduit, you could always just have them pull in a separate neutral too if it is bothering you.
A single neutral from the main panel is a superior way to do the job! I will try to explain. With separate neutrails from the main panel, each circuit has a two way path. Current flows equally in the Hot and Neutral wire in opposite directions. That gives you a voltage drop that is equal on both wires. In your situation, when both circuits have a load, the neutral conductor has a lower voltage drop. That is due to two hot wires sharing some of the current. Whatever they share does not go thru the neutral conductor. Therefor the total voltage drop is lower and more efficient.
I will attempt to explain! If you take two equal 120V loads and connect them in series. Say two 100 watt bulbs, you can put them across a 240V source and they will both work at 120V. In this case you have no current in the neutral wire because it doesn't exist! Think about it. Then if I add a neutral wire it has no current flow.
Now let's add a 60 Watt bulb in parallel with one of the 100 Watt bulbs, the neutral conductor will carry only the unbalanced current. The 60 Watt load.
I hope this explanation will help you understand more about electricity in general!
Marvin F. Malm PE (retired)
I called and spoke to the owner and expressed my concerns with the original work. He was courteous, concerned, and responsive. He immediately came out and replaced the two 1-pole breakers with a 2-pole breaker.
Thanks for the help, guidance, and expertise!
Absolutely unnecessary! Now if one circuit is overloaded it will shut off both circuits. Then you don't know which circuit popped the breaker. I think he did that just to satisfy your concern. But it was still the wrong thing to do!
Marvin F. Malm PE (ret)
I respectfully disagree.
National Electrical Code states that the panel board where the multiwire branch circuit originates, all ungrounded conductors must be provided a means to disconnect them simultaneously [210.4(B)].
Hence, the 2 pole breaker.
I agree that the Code says that. However, I believe that is for a 240 V Branch circuit. In this case it is two 120 V circuits. Perhaps we are getting into a GRAY AREA. I see no safety reason to connect the breakers mechanically. Two 120 V circuits going to two separate outlets are not usually connected to mechanically trip together!
This may be a case for debate by a higher authority!
Thank you for an interesting conversation!
Marvin F. Malm
A good reason to gang 120v circuits with a shared neutral, is to signal to some future electrician or home owner, who needs to rearrange things inside the panel, that the breakers need to remain on opposite legs.
You have a point but a tag on the Neutral would serve that purpose. It just rubs me wrong to trip a breaker that is not involved in an overload. Example: A freezer is on one circuit and the other is for tools. If you overload the tool circuit it will power off your freezer. If the homeowner is not aware of the non-standard arrangement, they may lose all the frozen food!
Thank you for the interesting dialog!
Marvin F. Malm PE (ret)