Author Topic: 240v electrical questions  (Read 1615 times)

Offline slip knot

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240v electrical questions
« on: December 13, 2015, 08:18:18 PM »
I had a situation with a 240v window unit AC. The breaker keeps tripping off and I spent the better part of this afternoon trying to find the problem. wall plug looked ok. breaker box had no obvious issues either. I started checking voltages and found them ok at each leg but found something a bit unusual to me. With the plug wiring cut loose and the breaker in the off position I get 1.3 v between the white wire and the bare wire. nothing between the black and bare wires. I thought that the breaker maybe leaking thru that small amount so I pulled the wires off the breaker and still get the same readings? This is a dedicated circuit and all it feeds is one plug. The GFCI on the AC trips as soon as power is turned on. The breaker will trip off at varied times, somtimes it may stay on for a few hours sometimes just seconds. it will even trip when nothing is plugged in.

I plan on replacing that run of wiring but I'm a bit concerned about the 1.3v coming from somewhere in that circuit and is that causing the GFCI to trip. all of the connections inside the box are tight, just re-checked them.

I tried checking some of my other 240v circuits and all but one of them read normal but one read 3v between each leg and the nuetral bus with the breaker in the off position. I'm thinking I may have an issue there as well.

Any thoughts?
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Offline Matt_T

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Re: 240v electrical questions
« Reply #1 on: December 14, 2015, 11:52:35 PM »
If you're using a DMM a bit of (ghost) voltage is normal. With both ends disconnected the 0v between black and ground warrants further investigation.

Offline walrus

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Re: 240v electrical questions
« Reply #2 on: December 15, 2015, 07:04:35 AM »
It's a 240 volt load, why is there a gfci? Is there a neutral conductor, so a 4 wire cable, 2 hots, neutral, ground?
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Offline slip knot

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Re: 240v electrical questions
« Reply #3 on: December 15, 2015, 08:28:32 AM »
The GFCI is built into the air conditioner cord. 3 wire conductor. The gfci trips as soon as power is applied.

The 0v reading showed ghost voltage of .05v and it fluctuated some as expected. the white had 1.3v exactly,everytime I tested it.

I'm planning on replacing the wire and the breaker this week but I'm thinking I've got other issues here. possibly a bad PoCo ground/common connection. The lights flicker in the house like a motor load is coming on but nothings running.

Started with nothing and still have most of it left.

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Offline walrus

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Re: 240v electrical questions
« Reply #4 on: December 16, 2015, 05:06:28 PM »
The GFCI is built into the air conditioner cord. 3 wire conductor. The gfci trips as soon as power is applied.

The 0v reading showed ghost voltage of .05v and it fluctuated some as expected. the white had 1.3v exactly,everytime I tested it.

I'm planning on replacing the wire and the breaker this week but I'm thinking I've got other issues here. possibly a bad PoCo ground/common connection. The lights flicker in the house like a motor load is coming on but nothings running.

the gfci is checking from cord end to the unit  not the house wiring. i think you are wasting time changing breaker and wire. The white wire in your house wiring? Is the unit 240 volts or 120 volts?  Digital meters will read 1 volt  anywhere anytime, unless they are touching each other. You don't have an old simpson meter around do you? is the circuit coming from your main panel or a sub panel?
« Last Edit: December 16, 2015, 05:09:37 PM by walrus »
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Offline slip knot

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Re: 240v electrical questions
« Reply #5 on: December 16, 2015, 05:19:50 PM »
The white wire is one leg of the 240v line.  I wouldn't change the wire out except that this circuit tripped with no load on it after I started checking it, so I suspect theres something wrong with it. I'm going to upgrade from 12ga to 10ga while I've got my fat ass under the house.

The original AC unit wouldn't start up for me last week. GFI wouldn't reset. I figured the GFI plu was screwed up so I cut it out and put a regular plug on it. then the breaker tripped out right away. Went down and bought a brand new AC this Saturday and it tripped the GFI when I plugged it in. Basically the same as the first unit.  scratchhead

I'll drag out my old analog meter and see what it reads.
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Offline slip knot

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Re: 240v electrical questions
« Reply #6 on: December 18, 2015, 07:34:50 PM »
Well, I squeezed my fat a$$ under the house today and found this coming out of the back side of a Jbox. Ya'll think this might be my problem?

Went ahead and upsized the wire to 10ga. Got it all pulled in and will land everything tommorow. But I believe I found my problem
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Offline walrus

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Re: 240v electrical questions
« Reply #7 on: December 18, 2015, 08:04:33 PM »
Well, I squeezed my fat a$$ under the house today and found this coming out of the back side of a Jbox. Ya'll think this might be my problem?

Went ahead and upsized the wire to 10ga. Got it all pulled in and will land everything tommorow. But I believe I found my problem
Wow, I guess you did. Didn't expect cord end gfci to pick up a fault  in circuit. Wonder how that happened?
Would have been a good problem to use a megger on.
« Last Edit: December 18, 2015, 08:09:00 PM by walrus »
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Offline brslk

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Re: 240v electrical questions
« Reply #8 on: December 19, 2015, 12:14:52 AM »
Didya find a dead rat near it?
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Re: 240v electrical questions
« Reply #8 on: December 19, 2015, 12:14:52 AM »

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