Axiom Home Page Forums General Discussion Technical Questions Need some input

Back on 5/9 I came home to find that half of my electrical service to the house was down. It is a 100-amp service. I traced the problem back to the taps from the electric company. Turns out that one leg of the service had failed, so I called PECO (Philadelphia Electric Company), they sent a service tech to the house and he confirmed that the issue was in the underground feed and that one leg had failed. The tech pulled the meter and installed jumpers to restore service to the balance of the house until they could make a permanent repair.

It was that evening that I noticed a buzz coming from the sub and the axioms, at first it was intermittent but soon after it became continuous. My feeling was that the ground was floating and that was the problem. A couple of days ago a crew came to locate the open and dig up the sidewalk. I mentioned this issue to them and they told me that the neutral could be floating as well. It was not until today that the service was repaired.

Unfortunately the buzz is still there, I have checked all of the receptacles for ground and all is fine, I reversed polarity, still didn't work. I have checked all the interconnects and have tried the process of elimination but to no avail.

The panel is grounded to an old led water service, which may be the problem. I'm going to install an 8' ground rod to see if that clears the issue.
Any thoughts or input would be a great help.

Thanks,
CAV 104 (Jim)

Grab a voltmeter (set to AC auto range or a manual range of at least 125V) and check voltage between ground and neutral - not sure what an acceptable level is numerically, but if you have more than a volt or two, I'd suspect that - there's always some distributed capacitance between the two, but shouldn't be over a volt or two.

Another - but strange, thing to consider, and this is a long shot - those three light polarity testers available from Home Depot (two greens - you're clean!) can be misled. If you swap neutral and hot and someone at some point has wired a phantom ground (tied it to the neutral line), the tester will show the polarity is correct even though the ground is actually hot. Again, not likely in your situation but people have been killed incorrectly renovating K&T (knob & tube) runs.

Bren R.

While you have the voltmeter out, select the resistance function, and measure the resistance across the gound and neutral, and again across the ground and hot side.

Gnd to neutral - you should read the resistance of the ground and neutral wires back to where they tie together at the building load center. (If the outlet is 20 feet from the panel, you will be reading the resistance of 40 feet of wire plus the connection between them) A couple of ohms is what you want to see, maybe 0-5 ohms. Anything much higher than that, and you have bad connection between the neutral and ground somewhere. Most likely, at the panel or the load center if it is in a separate location. The voltage drop across this resistance is what Bren was telling you to measure. In the computer business, we raised a flag after it got higher than 1.5 vac. You would normally expect to see 100-500 millivolts. Seems to me that the 300mV range is about right.

Gnd to hot - You should get a very high, or infinite resistance.

When measuring the voltage, the sum of the 2 volatges that you read between ground and hot, and ground and neutral should add up to exactly what you read between the neutral and hot.

You're power is definately still hosed (technically speaking, of course.)

Thank you gentlemen for the advice. I'll get back to you soon.
Thanks again,
CAV104 (Jim)

Bren,

My basement is typical old city construction, rock walls with mortar and dirt. I checked for voltage between neutral and ground (inserted probe directly into dirt between rocks) and picked up 1.5 volts.

Spoke to some neighbors who have the same underground feed, one of them complained that his electrician got a little shock when he removed the cover from the box that houses the taps. He has issues with his service as well and has contacted PECO. The underground service is circa 1950 and is led sheathed, it may have seen it's best days. I'm starting to suspect that the cable is breaking down and starting to leak.

Any ideas on how to eliminate the 1.5 volts between neutral and ground or am I screwed until the service is replaced.

Thanks,

Jim

At this point, I'm going to say don't try it yourself. Don't need anyone shocked or killed.

Our house was built in the mid 60s, just checked 4 different circuits some at the tail, some at the head, some with loads, one without and all register in the millivolts range.

Bren R.

I'll second Bren again. Don't try to fix it.

1.5 vac is a little high. There's probably a transformer breaking down in your area.

Bren,
Thanks for the info. I'll contact PECO and have them resolve the problem.

Thanks guys,

Jim

Problem fixed. Wanted to let you guys know that the electric company ripped up my sidewalk and replaced the underground service. No more Hummmmmmmmmmmm. BTW they did pour a new sidewalk when they finished.
Again, thanks guys for the input.

Jim