Diagnose An Open Ground

Doing some renovations at a local hotel. Updating bathrooms with new countertops, sinks, tile, the works. In the process are creating a larger countertop in the open sink area (toilet and shower different room) so that it will include a breakfast bar of sorts. Microwave/coffee maker on top and Mini-fridge under the counter. Required me the cut in two new electrical boxes for outlets. I ran the lines when the wall was open and tapped into a previously abandoned junction box. Was the old wall A/C line that is tied into the room circuit. They abandoned it because the breaker was constantly tripping in rooms when the A/C was on and someone used a hair dryer. So they ran dedicated lines just for the A/C years ago and capped off these boxes.

Have done 18 of these rooms over the past few years and never had a problem. This last room suddenly shows an open ground. I twisted the grounds together in the junction box and have a single line that runs through one outlet, continues on to end at the 2nd. Both sets of outlets are showing open ground. Short of ripping everything out, how best do I determine if it is the buildings line that has a break, or something with my install of the outlets themselves. Can't imagine that I forgot to hook up the ground on the first outlet as I specifically remember twisting them together and cutting one leg to pigtail to the outlet.

With an analog multi-meter, how best to test the lines? Obviously black and white work fine, but don't want to short out my meter by taking either to ground.

 

Since an open ground will not read voltage I would suggest testing from hot to ground down the line. When you read 0 you have found the open.

 

What type of wire is there originally..... NM, metal clad ?

 

Can't see much of the cable itself to get a reading of the markings, but it was an older white clad 12/2 with a thinner than usual ground wire. I hooked up to it with yellow clad 12/2 romex with ground.

 

That would have been probably cloth covered NM cable.
The ground was one or two sizes under the main conductors.

 

No cloth covered, white vinyl covered (or whatever the normal coating is). Block wall, furring strips, paneling and drywall over the top. I removed the drywall, opened the paneling enough to run wires, notch out furring strips (and cover with nail plates) and set up the new boxes which I had to excavate into the block wall to fit the remodel boxes. None of the wires were cloth covered. I only can see in each room less than an inch of the wire covering as those wires came into the box from above. All my work was from the bottom of the box down and eventually over under the counter height.

 

I would start at the source and be sure you have a ground there,test HOT to GR. and work the circuit from there until you find the open.
Geo

 

I have had a rather large chunk taken out of my linesman pliers from shorting hot to ground by accident in the past. Please tell me specifically what I should set the multi-meter to, and how I should test the lines. If I test hot to ground what reading should I get? And would this reading indicate that the ground is bad at the source or further down at my hook ups. Thanks for all advice guys.

 

You would set the meter to AC voltage above the level that you expect to read. 120 volts would be a normal reading.

Meters do not short like a pair of pliers.

 

Thanks, pc, that is what I needed to hear. Will test in the morning and see what happens.

 

If you get a reading of 120 Hot to Ground at the source then move on to the next outlet until you get 0 volts Hot to Ground and the problem will be there or between there and the last outlet you texted .
Geo

 

At the incoming source wires in the original junction box - white to black 120v - black to ground 25v - white to ground 25v

Does that make any sense?

 

Digital or analog meter?
.

 

It was with an analog meter.

 

Your going to need to go back to the panel or farther back on that circuit, check in the panel and make sure the grounds are all clean and tight.
Geo

 

Well, I'm not qualified to be messing around with a panel. I will let the owners know of the predicament. They had some vandalism a year and a half ago where someone cut the lock and disconnected the sump in the underground utility room. The room filled with water and soaked all the panels. They dried them out and tested everything. It is a waterfront hotel and the sump is the only thing that keeps the cellar from flooding. They think it was a then recently released employee, but can't prove it. They also cut all the phone lines, opened a fire hose and flooded a dozen rooms and tried to break into the laundry. New security has been installed, but this may be a lingering memento of the day a couple of years ago. Small penance compared to some of the people that go postal and leave a trail of hurt in their wake......

 

Keep us posted on the out come, that being the case I'll bet there are a lot of corroded terminals etc.
Geo

 

I would use a line tester-a lot of meters don't load enough to be good troubleshooters.