Shared Neutral Current Additive 120/208?

D

donniet1977

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I'm remodeling my kitchen and am bringing it up to code. My service is 120/208. I wired up my first multiwire circuit. I decided to read neutral current flow with a clamp on ammeter to make sure everything was cool. I had a 1 amp load and a 2 amp load on the two hots. I expected to see something less than 2 amps on the neutral but was surprised to see the full 3 amps. The hots are fed from opposite busses. Can anyone help me figure this one out?


Thanks,

Don
 
Lectrician said:
Then your clamp meter is wrong.

What loads are these?
Click to expand...

Refrigerator at 1 amp and 3/8" drill motor at 2 amps. I was using a cheap off brand clamp on ammeter but it doesn't seem that would be the culprit here. I might have to increase load and test again.
 
You could run into odd readings at low loads, and also with inductive/capacitive loads too. Many cheapy clamp meters are no good at low currents. There are also harmonic currents to consider.
 
Lectrician said:
You could run into odd readings at low loads, and also with inductive/capacitive loads too. Many cheapy clamp meters are no good at low currents. There are also harmonic currents to consider.
Click to expand...


After more thorough testing I am even more troubled.

Quick recap: My service 120/208, hot to hot is 208.

With an 8.5 amp toaster oven on one circuit and 11 amps on the other circuit which feeds the fridge (about 1 amp) and space heater (temp) my neutral current reads 19.2 amps. I'm using an Amprobe ACD-15 Pro clamp on ammeter. This condo has been wired with mostly MWBCs ever since it was built from what I can tell. Have the neutrals been overloaded the whole time?! I'd really like to get on the feed to my panel which is just a subpanel but I just don't have the room.



Thanks,

Don
 
I'm both embarrassed and happy to say that after further troubleshooting I discovered that the outlet we wired temp for testing was miswired and being fed by the wrong circuit. This led to all loads being on the same leg. I was a little lazy in my initial troubleshooting and made too many assumptions. One assumption was that there was a problem in the first place.

I think the initial problem I saw with the 3 amp neutral was simply due to low inductive loading along with meter creep.

Final Reads Ignoring Fridge (<1 amp) which is always on:

CKT 1 on 2 off - In=9.1A
CKT 1 off 2 on - In=11.9A
Both CKTs on - In=12.0A

Thanks for the replies.
 
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