Single phase Edison circuit?

Status
Not open for further replies.
S

sfav8r

Senior Member
Location
San Francisco Bay Area
I just went on a repair call on a multi-unit apartment bldg. Each unit had this same configuration. I apologize for the poor picture, but I had to take it with my cell phone. Each unit has a single 120v feed of #10 wire. HOWEVER, each unit also has a multi-wire branch circuit protected by a 30 amp breaker. Where I come from that puts the fully loaded Neutral at about 60 amps. How does stuff like this happen? I'm not sure how well the jumper wire shows in the picture.

There is 220 at the main disco. It would be very easy to pull the other phase into the 30a discos. The problem is the old meters are 120v.
 
Chris6245 said:
Just curious. If the metering is only 120volt where is the 220 volt comming from?
Click to expand...
Good question. Apparently the main disco is ahead of the individual meters.
 
sfav8r said:
Where I come from that puts the fully loaded Neutral at about 60 amps.
Click to expand...

So there is no overcurrent protection for this panels feeder?

Or is there a single pole 60 amp breaker supplying this feeder?
 
Best suggestion in the short term would be to replace that 2-pole breaker with a pair of 15a breakers.
 
LarryFine said:
Best suggestion in the short term would be to replace that 2-pole breaker with a pair of 15a breakers.
Click to expand...

I think before we recommend changing any over current device more must be known.:)

I never think the best option is to change a breaker without knowing the circuit.

Somewhere in the feeder supplying that panel must be a over current protection and it that may well be the proper size for the circuit.
 
Iwire, that was part of his concern. He has 120v coming in and a jumper across the top of the breaker, then on the load side he has a black-red-white feeding everything.
 
Ahhhh...I missed the jumper...now that I read the post again I see what is going on. If it's #10 wire feeding the 2 pole 30 then it's still only a 30amp circuit and IMO can't be considered a MWBC. I agree with Larry on this one, should be 2 SP15's

Each "branch circuit" could draw a continuious load of 24 amps and the 2pole 30 won't trip and the #10 feeding it would have 48 amps on it.
 
Last edited:
Chris6245 is right, that is exactly my concern. To answer a couple of the other questions:

The 30a disco is feed from a gutter which is fed from a 125a main disco. That is the only place that there is 220v. They put 1/2 the units on one phase and 1/2 on the other. Apparently, at some point in the buildings history, someone decided to install a 2nd circuit to each unit and maybe had seen a multi-wire branch circuit and figured that was a good way to go...unfortunately with only one phase, they failed to grasp the concept. I would say that this installation has been like this since about the mid sixties.
 
I forgot to mention, the problem with replacing the 30a breakers with 15a breakers is that it doesn't meet the minimum service requirements. However, I would agree that from a safety perspective it is the thing to do.
 
I had a similar setup at an eight unit building where they just wanted things "patched up". I told them liability wise I would not patch up the antique, deteriorated system. Instead I gave them a bid to replace it all with new services and circuit breakers for all the branch circuits to get rid of all the fuse boxes full of 30 amp Edison fuses.
Two weeks later they called and accepted my offer.
 
Status
Not open for further replies.
Top