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120 volt outlets reading 240

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Thread starter #1
I put a sub panel in my garage last October and it has worked fine until today. All my outlets are now reading 240 when i put it in they read 120. I tried a few things now I can't get my breaker in the house that controls the sub panel to reset.
 
#4
You have obviously a dangerous problem. My advice is very simple: Since you have to ask, ...call an electrician.
 
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kinarfi

Well-Known Member
#5
Your neutral has come loose in you panel or further back and one of your receptacles on the other leg is back feeding 120 on to the neutral. Turn every thing off and unplug everything until you find where you lost your neutral. If you need more help, let me know and I'll draw you a picture of what's going on.
 
Thread starter #6
Could it have came loose in the house panel? Should I replace the circuit braker for the sub panel? I would like the picture if it is not to much trouble.
 
#7
The breaker not being able to be reset is probably a sign of what people have stated above.
Your problem could be anywhere, but if its just in the garage, then its something in the garage sub-panel. Or the connections to the breaker for the sub-panel in the house panel.

Somewhere a wire is loose and is connecting parts that shouldn't be... I would advise you to remove anything that's plugged in.

And maybe keep a fire extinguisher out..
 
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#8
Start at the begining, check the breaker to see if there are any loose wires, then check the back of your sub. If everything seems to be connected, then you'll have to do an ohm meter test on your sub, if the ohm meter reads a low resistance the you have a short circuit and should replace your wires. (just make sure none of the outlets are live, you wouldn't beleive how many people I've seen destroy an ohm meter that way)
 

MikeMl

Well-Known Member
Most Helpful Member
#9
Did your original feed to the garage have two different 120V circuits? If so, they could be fed from two different breakers that are sitting on opposite sides of the main panel, which would put 240V between L1 and L2. If something has come adrift, or some wire is pinched somewhere, that could manifest as 240V in a single duplex outlet.

btw- when I wired my garage, I ran three conductor (Red, Blk, Wht, with bare ground) from the main panel to groups of daisy chained outlets. When installing the outlets, I break out the tab between the two brass screws. One gets the Red wire, the other gets the Blk wire, and the neutral (white screw) gets the white wire. The feed comes from a dual-ganged 240V breaker. This way every outlet in the garage/workshop has 240V in the box, even though the outlets have only 120V between the narrow prong and the wide prong. That provides the equivalent of two 20A circuits into the workshop for higher capacity. If I need 240V to run a welder, etc, I can replace a ganged 120V outlet with a four prong outlet wired for 240V in any box in the garage. When I showed this to the inspector, his eyes glazed over, but he agreed that it passes code...
 

Diver300

Well-Known Member
#10
It could be that the neutral has broken somewhere, and that there is a large, (so low resistance) load between the opposite phase and neutral. That would pull the neutral to nearly 120V in the opposite direction to your 120 V feed. That would be just about 240 V from your live to what neutral is at the moment.

(All the sockets in here are 240 V, 13 A. 3 kW appliances can be plugged in anywhere)
 

kinarfi

Well-Known Member
#11
by chance is the breaker that won't reset a gfi breaker? you can tell because it has a white wire from it to the neutral bar and the black and white wire from the branch circuit
 

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kinarfi

Well-Known Member
#12
definitely possible, if possible, post a photo of your breakers, worth a thousand words.
 
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Thread starter #13
I went out this morning and unhooked the main breaker in the garage the 240v that feeds the panel. Went in to flip the breaker on to check the voltage and it still will not reset so I guess I will start there and replace it.
 
#14
It could be the breaker but it could also be the wire. Unplug the house breaker from the wire and try to reset it. This will tell you if the problem is the breaker or if it is the wire.

By the way, check if there is a brass screw inside the garage panel. If there is one, it must be removed. This screw is connecting the neutral wire, the white one, to the ground. This brass screw must be present but only to the first swicth or panel that enter into the house. Nowhere else. But even if the screw is there, I don't think that it is your present problem.
 
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kinarfi

Well-Known Member
#15
Need more info, What type of wire did you run to the garage, 2 conductor with ground, 3 conductor with ground, Triplex, is it buried, overhead, is the garage attached or separate.
kinarfi
 
Thread starter #16
I replaced the breaker in the house ( it was bad would not reset even after I pulled it out of the panel) that restored power to the garage. Started checking the wiring got 3 out of the 4 circuits fixed. But what ever happened yesterday fried all of my shop lights. So I didn't mess with that one yet but if it gives me any trouble I am just going to rewire it.
 
#17
Well feeding them 240 instead of 120 was definitely what burned them out! :D

I would say youre lucky there wasn't a fire!:eek:

So since replacing the breaker fixed the problem, it was either a faulty breaker, or loose wiring to the breaker.

Glad you got it fixed!
 
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kinarfi

Well-Known Member
#18
That was most likely cause by having a high wattage heater or air compressor on the other leg of power and when you lost your neutral, the voltage became unbalanced and fed the lights with 240. The neutral only carries the unbalanced load, that is if A phase has 10 amps flowing and B phase has 4 amps, the neutral carries the difference of 6 amps. I really hope you found where neutral opened up, in the U.S.A. the neutral is never switched (unless the phase is on the same switch), so you should never have lost your neutral.
 
#19
Your neutral has come loose in you panel or further back and one of your receptacles on the other leg is back feeding 120 on to the neutral. Turn every thing off and unplug everything until you find where you lost your neutral. If you need more help, let me know and I'll draw you a picture of what's going on.
Draw the picture, pleased
 
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