Voltage readings at detached garage

[starsandstripes]

The lights and garage door opener are functioning OK in a customer's detached garage. The outlets in the garage are not GFCI protected. Voltage readings at outlets are: line to neutral 115 volts, line to ground 26 volts, ground to neutral 26 volts. Readings taken with a Fluke T5. The garage is fed underground from a 100 amp panel in the house. I know I am not getting a good ground and I am inclined to tell the customer the cable to the garage is failing and should be replaced. I think if I tried to install a GFCI it would probably trip.I would appreciate other opinions on this.

 

[ActionDave]

What are the readings at the disconnect on the garage? What are the readings at the house or wherever the garage is fed from? Is it a three or four wire feed?

 

[growler]

I think if I tried to install a GFCI it would probably trip.I would appreciate other opinions on this.

I can't think of any reason a GFCI protected receptacle would trip but you would still have a bad ground.

I often find splices in cable where they are not supposed to be on problems like this. You know, cable burried about 3 inches and cut and spliced.

I would start at the panel and see what you have there. Then first junction box in the garage.

 

[starsandstripes]

This is an old installation, no disconnect at the garage, just one three wire circuit. Readings at the house are good. I' ve seen before where the ground shorted to neutral will trip a GFCI. I guess there is one way to find out.

 

[Smart $]

... I' ve seen before where the ground shorted to neutral will trip a GFCI. ...

And that was more likely than not on the load side of the GFCI, not on the line side.

 

[meternerd]

Any place else you can find a "solid ground" to read to? Neutral should read close to zero to a good ground. If you have to, run a temporary piece of wire from the garage to the house panel ground and measure again to it. Sounds like a high resistance ground wire. For garage to be safe, you should try to find the problem and fix it. A GFI is not equivalent to a EGC.

 

[wptski]

The Fluke T5 Series has an input impedance of 1M ohm which will show ghost voltage.

 

[petersonra]

The lights and garage door opener are functioning OK in a customer's detached garage. The outlets in the garage are not GFCI protected. Voltage readings at outlets are: line to neutral 115 volts, line to ground 26 volts, ground to neutral 26 volts. Readings taken with a Fluke T5. The garage is fed underground from a 100 amp panel in the house. I know I am not getting a good ground and I am inclined to tell the customer the cable to the garage is failing and should be replaced. I think if I tried to install a GFCI it would probably trip.I would appreciate other opinions on this.

You may just not have any connection from N to whatever "ground" you are referencing it to out in the garage.

Since you indicated there are only 3 wires going out the the garage I suspect no N-G bond in the garage.

Check the resistance from N-G out in the garage.

 

[big john]

The Fluke T5 Series has an input impedance of 1M ohm which will show ghost voltage.

Agreed, but no induced voltage will exist between points bonded together, so I'm hard pressed to explain the 26V difference between N-G unless there was a very significant voltage drop present in the neutral.

That he doesn't read correct L-G voltage either really suggests he's got an open ground.

 

[rlundsrud]

You may just not have any connection from N to whatever "ground" you are referencing it to out in the garage.

Since you indicated there are only 3 wires going out the the garage I suspect no N-G bond in the garage.

Check the resistance from N-G out in the garage.

Why would you have a N-G bond at the garage, it isn't an SDS. if you bonded the N-G, at the garage you would have objectionable currents.

 

[K8MHZ]

The Fluke T5 Series has an input impedance of 1M ohm which will show ghost voltage.

Agreed, but ghost voltage won't explain only getting 26 volts from line to ground.

 

[K8MHZ]

Why would you have a N-G bond at the garage, it isn't an SDS. if you bonded the N-G, at the garage you would have objectionable currents.

If only fed by 3 wires, are you saying the required grounding in the garage is not to be connected to the neutral and thus, rely on the earth as a fault path back to the source (neutral)?

 

[kwired]

Better understanding of what is run between buildings is needed. Is it a three conductor cable? Is individual conductors in raceway? Direct bury conductors? Don't let three conductors entering the garage fool you - maybe you have an ungrounded, a grounded, and a grounding electrode conductor. Make sure all three do go back to where the feed originates before you decide one of them has failed. If one is simply going to a ground rod - you may expect readings similar to what you had.

 

[cuba_pete]

nope

nope

If only fed by 3 wires, are you saying the required grounding in the garage is not to be connected to the neutral and thus, rely on the earth as a fault path back to the source (neutral)?

Neither situation is safe nor meets minimum of the code. I surely would not bond the neutral to ground downstream of the main bond to fix another problem.

By connecting the "grounding in the garage" to the neutral is making it grounded, and it's not grounding anymore.

 

[paul]

Sounds to me like they did not run and EGC are using ground rods only as their ground and forgot to bond to the grounded conductor.

 

[paul]

Neither situation is safe nor meets minimum of the code. I surely would not bond the neutral to ground downstream of the main bond to fix another problem.

By connecting the "grounding in the garage" to the neutral is making it grounded, and it's not grounding anymore.

Bonding the neutral downstream was code legal for years. As long as there are no bonded metal gas or water pipes in the detached garage, there are no safety problems. I would have no issues bonding the grounded conductor to the ground rod at the detached garage.

 

[K8MHZ]

Better understanding of what is run between buildings is needed. Is it a three conductor cable? Is individual conductors in raceway? Direct bury conductors? Don't let three conductors entering the garage fool you - maybe you have an ungrounded, a grounded, and a grounding electrode conductor. Make sure all three do go back to where the feed originates before you decide one of them has failed. If one is simply going to a ground rod - you may expect readings similar to what you had.

In his first post the OP says he is dealing with cable feeding a 100 amp panel in a detached garage. In another post he says it's three wires. If the three are as you say, then there should only be 120 in the garage, no 240, and we don't know that for sure.

 

[Netpog]

Marky, he says it's a three-wire cable to the garage, from a 100 amp panel in the *house*.

If it's an open ground, then wouldn't a wiggy show zero volts, where the high impedance meter shows 26v?

 

[K8MHZ]

Marky, he says it's a three-wire cable to the garage, from a 100 amp panel in the *house*.

If it's an open ground, then wouldn't a wiggy show zero volts, where the high impedance meter shows 26v?

Sorry, I stand corrected.

You are probably also correct about the 'wiggy' (solenoid tester) , which is why I always use them when a DVOM shows voltage I can't readily explain.

 

[FREEBALL]

The garage if separate was once allowed to be fed only by 3 wire. At the garage you bonded the grounding electrode system there to the neutral. The ground does not clear a fault only the neutral (grounded conductor) can, That is why its bonded to the ground.