A really stupid question from a dummy!

Thread Starter

speter42

Joined Jun 19, 2014
2
I have, (had), a working 100A underground wire to my garage. All of a sudden, I have 30volts comming from a 120v source... WTF!
All seems to be tight and secure.
PS...(have had a lot of rain lately)
 

wayneh

Joined Sep 9, 2010
16,114
And the question? I think you already know the answer.

How was that wire protected?

BTW, this is potentially a VERY dangerous situation. Turn off that circuit at the breaker box (it IS on a breaker, right?) before getting anywhere near it.
 

matty204359

Joined Apr 6, 2011
105
I have had similar strange voltage readings coming from an improperly grounded GFCI. But I doubt this is the case since its a 100A service to an external structure. but if you do have a GFCI you might wanna check it out.
 

MaxHeadRoom

Joined Jul 18, 2013
19,189
Is this a 240v/120v supply or just 120?
When you say 120v, is this from each 120v conductor to neutral?
What do you measure to ground conductor from each 120v line?
Is this a remote building or attached to the house?
Max.
 

#12

Joined Nov 30, 2010
18,160
All seems to be tight and secure.
C'mon. Be reasonable. You know that can't be the truth.
There must be a defect someplace, and your job, should you decide to accept it, is to find the fault.

Good education and a good meter will find the problem. Lack of understanding and a good meter will get you killed.

At this point in the conversation, I am worried that you're just smart enough to be dangerous.

You're talking to people that do this for a living. We can figure it out, but asking you to stand on wet ground and look for a fault in a 100 amp power line is a scary proposition.
 

Lestraveled

Joined May 19, 2014
1,946
Ditto what #12 said.

When you open the cover of a 120/220V breaker box you are entering into a dangerous area. If you do not have the skills and understanding to SAFELY work in the box, then don't do it. Let someone else do it or seek assistance from someone who is experienced.

Take a moment and think about it. Electrical shocks are extremely painful, even when they are fatal.

Mark
 

Thread Starter

speter42

Joined Jun 19, 2014
2
Is this a 240v/120v supply or just 120? Two 120V lines + the neutral

When you say 120v, is this from each 120v conductor to neutral? YES

What do you measure to ground conductor from each 120v line? About 30 volts
Is this a remote building or attached to the house? Remote

Max.
From the source, there's a 100A breaker going to the garage. Each 120v leg
measures 121 volts from the source.
At the receiving end, (garage), each leg measures about 30 volts...(somewhere between the source and the garage I lose 90 volts from each leg)...Yesterday all worked well, as it has for the last 15 years.
 

inwo

Joined Nov 7, 2013
2,419
See if you still have 240 leg to leg.

If you have open neutral keep the main breaker off to prevent frying things.
 

MaxHeadRoom

Joined Jul 18, 2013
19,189
If you measure 120v from line to neutral, but line to ground is 30v, then this indicates an open or ungrounded situation?
If you measure 30v to both neutral and ground then they both have a problem.
You need to do a test of both neutral and ground continuity with power off.
Preferably with a megger, both high voltage insulation and continuity version.
Max.
 
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