120V generator connected to dwelling 120/240v panel

Merry Christmas

ASIsparky

Member
Location
Philadelphia, PA
Occupation
Electrician
Is there an manual transfer switch or something? How are you feeding the panel from the generator?

>Any issue with connecting both panel phases to 120V through a back fed common trip breaker using a pigtail? (no double lug)
>We intend to use the standard panel stickers and notices. I do not see a reason to add any but could be wrong.

What prevents someone from closing this breaker when poco power is on? They would be closing the breaker into a bolted short.
What happens if a breaker trips, someone other then the HO is looking to see what tripped, and turns that breaker on? How many non-electricians are going to bother to read labels on the panel before switching a breaker?
Usually with this type of setup, the main breaker interlock prevents the generator backfeed breaker from turning on unless the service breaker is off.
 

Todd0x1

Senior Member
Location
CA
I wouldn't worry too much about overloading neutrals on MWBCs, the generators that are 120v only and have a L5-30 output 25 amps. Chances of severely overloading a MWBC neutral are slim.

I would approach it this way:
Install interlock to 2P breaker with L14-30 inlet. Supply L14-30 cord. There are L5-30 to L14-30 adapters with both hots on the L14-30 wired to the hot on the L5-30, this is usually called 'both sides hot'. If the homeowner has a 120v generator they can go buy the appropriate adapter to plug it into their house.
 

busman

Senior Member
Location
Northern Virginia
Occupation
Master Electrician / Electrical Engineer
I have done this, but only with a separate manual transfer panel (think Reliance) and did not put any 2-pole or multiwire circuits on the separate panel.
 
Is there an manual transfer switch or something? How are you feeding the panel from the generator?

>Any issue with connecting both panel phases to 120V through a back fed common trip breaker using a pigtail? (no double lug)
>We intend to use the standard panel stickers and notices. I do not see a reason to add any but could be wrong.

What prevents someone from closing this breaker when poco power is on? They would be closing the breaker into a bolted short.
What happens if a breaker trips, someone other then the HO is looking to see what tripped, and turns that breaker on? How many non-electricians are going to bother to read labels on the panel before switching a breaker?
Thank you for your response. As stated in the OP, there is an inter lock in place.
 
I wouldn't worry too much about overloading neutrals on MWBCs, the generators that are 120v only and have a L5-30 output 25 amps. Chances of severely overloading a MWBC neutral are slim.

I would approach it this way:
Install interlock to 2P breaker with L14-30 inlet. Supply L14-30 cord. There are L5-30 to L14-30 adapters with both hots on the L14-30 wired to the hot on the L5-30, this is usually called 'both sides hot'. If the homeowner has a 120v generator they can go buy the appropriate adapter to plug it into their house.
Thank you your help.
 
This is for a portable generator right? If you're worried about the AHJ, just install a standard L14-30 generator inlet as if you are going to be using a 120v/240v (4wire) generator and have the customer purchase an L14-30 to L5-30 adapter for $30 or so. The adapter will be the piece that joins both phases together, and doesn't need to be present for inspection. We all know that a dishwasher and disposal will not overload a 12 AWG wire. As someone mentioned , just combine the MWBC into a single branch circuit with a pigtail if needed.
Thank you for the help!! I did not realize the adapror joined phase A and B. Done and done.
 
I always worry at the guy who comes next who doesn't understand what you did and why. And, there is no way to rely on written instructions being followed hy HO now or in the future. Once in a while I'd leave a note in a box if something non-obvious was there to save a future electrician some troubleshooting/tracing time, but the note you want is different.
I agree. I am like everyone else on this thread. Open box and discard instructions LOL. Then dig out ot trash later. So not a fan of instructions.
 
Thank you everyone. It is so much appreciated.
After some looking and math at my home, I was able to point out that the refer and a microwave will max out the unit. (numbers she could understand)
She is now looking to get a regular 240V 3000W unit. It will cost 1/2 as much as the other unit an put out twice the power.

So on the next one, I will try to reason away from the 120v unit.
If I cannot, I will have them purchase the cord adptor as recommended by ASIsparky and Todd0x1.
 
Last edited:

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
After some looking and math at my home, I was able to point out that the refer and a microwave will max out the unit. (numbers she could understand)
She is now looking to get a regular 240V 3000W unit. It will cost 1/2 as much as the other unit an put out twice the power.

Just be aware that the maximum load on either phase of the 240V 3000W unit is probably limited to 1500W even when the other phase is unloaded, due to the current rating of the generator windings.
 
Top