Electrical Mystery of the Day

[Dan Mages]

I rent a house I own in Illinois. As much as i want to sell the place, nothing is selling right now.

My tenant called and told me that the lights in the master bedroom, bathroom, and basement were not working. I figured it was a simple issue like a circuit breaker, so I called my father to see if he can swing by and check out the situation. And it devolved from there.

Some how, part of the house lost ground and other parts of the house lost common. the house is built with rigid metal conduit, which acts as the ground. My neighbor (who is good at this stuff, and is OCD for puzzles) came over as well to advise after my father was stumped. The spent a several hours pulling outlets, lights, and switches looking for loose wires. They tested the circuit panel as well and found no problems there either.

At some point, the issue magically resolved itself. They have no idea what caused it or what fixed it. Any geniuses here have any clues? I heard there were some powerful storms in the area.

Dan

[Dan Hintz]

The conduit itself should not be used as the ground conductor... it should be connected to ground at each location, but the conductor itself should be a separate wire. If it is truly being used as the grounding (and more importantly the neutral) wire, a poor connection of the conduit anywhere along the line will cause a loss of power. Corrosion building up, conduit clamps/screws not tight, etc., will all add to the problem. I would also think that if the conduit is being used for the neutral and/or ground wire, code would not allow you to rent that place... but I'm not an NEC code junky, I just learn what I need to make my own construction compliant.

[Cliff Rohrabacher]

If you lost ground and then magically regained it's mote than likely that there is hot arc somewhere making that ground.,
This happened to me. Wild voltages all over the building some rooms had super dim lights other super bright. Neutral was hot, hot was hot and I had a fire. Sophisticated electronics shut down or burnt out

The ground from the utility company had failed and the power suddenly was acting crazy there was a fire at the outside cable junction where I had put a ground to stop lightening strikes from entering the building VIA cable.

Find that bad ground and solve it.

[Mitchell Andrus]

+1. I've seen the conduit used as ground in comm'l buildings. Flunks the laugh test every time and gives electricians the shivers. One told me he doesn't touch conduit anymore until after he's put a meter on it and determined that it's safe.

Yes, it should be grounded but it's not to be used as the ground or neutral.
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[AL Ursich]

Next time it happens look at things like deep well pumps, freezers, washers and stuff like that.... Turn them off at the panel one at a time and see if it goes away.

I once found a kitchen at a bar that had the new outlets with hot ground and neutral. Where they tied into the old system was a chunk of the old metal covered wire. The inner conductors were too dark to tell white and black and they got it wrong.... Hot to white..... The cat walking along the counter top and stepping on the stainless sink would screem.... when it's tail touched the toster.... Lucky no one was killed.... It was a Beer for Wiring job for the guy who did it.... I found the hot conductor with a neon bulb screwdriver.

AL

[Dan Hintz]

Hmmm, a new idea... no need for a neon tester, just bring a cat. Maybe not as cheap, but it'll let you know where the problem is in a jiffy...

[Mike Circo]

Despite previous comments, in Illinois (at least the Chicago area and suburbs) ridgid conduit is indeed used as the ground, only two wires are ever pulled.

However, the conduit itself must be grounded to earth somewhere in the loop. Either with an earth spike outside, using the water main, or with a spike through the foundation wall near the main circuit box.

Perhaps with all the rain, heat and weather issues, your "earth" connection is flakey.

[Dan Hintz]

Mike,

That just sounds like such a bad idea... a loss of connection from the conduit to ground and a short from line to conduit means someone is going to get a new hairdo, Einstein style.

[Mike Circo]

Mike,

That just sounds like such a bad idea... a loss of connection from the conduit to ground and a short from line to conduit means someone is going to get a new hairdo, Einstein style.

Hey, I don't design them, I just report.

Why is the conduit-ground setup any different from a three wire run in your scenearo? (just asking, not arguing).
Loss of connection on the ground wire would have the same effect. Plus in most circumstances, the conduit is grounded somewhere as it touches concrete the main box, etc. giving more reliability (I'd think)

A short, is a short, is a short. It's bad no matter where it happens, and bad no matter what the design.

Again.... not arguing or defending one setup over another. Just stating facts of the IL building code. Tens of thousands of homes built this way over the last 50 years here, and we haven't lost more to electrical problems than any other design.

[Dan Hintz]

Why is the conduit-ground setup any different from a three wire run in your scenearo? (just asking, not arguing).
Loss of connection on the ground wire would have the same effect. Plus in most circumstances, the conduit is grounded somewhere as it touches concrete the main box, etc. giving more reliability (I'd think)

In my mind, there's a difference... conduit, due to it's "strength" and ability to take a beating, is often left exposed in places where anyone can touch it (such as running it along a concrete wall). A typical 2+1 wire would still have the ground wire covered with the outer sheathing, and it should never be left exposed where someone could damage the sheathing and then touch the bare wires inside.

Also, concrete is not a proper conductor, so conduit attached to a concrete wall would be nowhere near ground potential.

[Mitchell Andrus]

Why is the conduit-ground setup any different from a three wire run in your scenario? (just asking, not arguing).

In a short scenario, you want the electricity to take the path of least resistance back to ground. To 120 volts, a shiny copper wire looks better than a rusty conduit and better than you do, so you want a table saw with crappy wiring to have a copper conductor rather than your skin to use on it's return path - hopefully popping the breaker when it gets there. Without a solid short to ground, the breaker may not offer much protection.

While conduit may make you safe(r) than no ground at all, corrosion or a loose fit at any connection leaves your finger the next best route, especially if your finger is wet and you're holding an open umbrella under a tree in the thunderstorm while standing in a puddle and flying a kite with a key on the string.
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[Dan Mages]

Thanks for the input.

Regarding rigid metal conduit. It is the code standard in the Chicago area and other parts of the midwest. It may not be perfect, but it works well on thousands upon thousands of homes across the state. Keep in mind that my house was built in 1962 when two prong outlets were still the standard. I changed out quite a few after I moved in.

An old timer once gave me another reason why it is still in use... unions. It is more complicated and requires more knowledge to run then romex. This keeps the weekend warrior in check and the union members and shops in business... Its just a conspiracy theory I heard.

[ray hampton]

In a short scenario, you want the electricity to take the path of least resistance back to ground. To 120 volts, a shiny copper wire looks better than a rusty conduit and better than you do, so you want a table saw with crappy wiring to have a copper conductor rather than your skin to use on it's return path - hopefully popping the breaker when it gets there. Without a solid short to ground, the breaker may not offer much protection.

While conduit may make you safe(r) than no ground at all, corrosion or a loose fit at any connection leaves your finger the next best route, especially if your finger is wet and you're holding an open umbrella under a tree in the thunderstorm while standing in a puddle and flying a kite with a key on the string.
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very true and IF YOUR washer machine or dryer are a earth shakers then the conduit could separate at the joint----wire connections are usually made with wire nuts and they can get corrosion or dirty enough to break the circuit path ---tarnish -covered copper wire are not very good conductor

[Cliff Rohrabacher]

Hmmm, a new idea... no need for a neon tester, just bring a cat. Maybe not as cheap, but it'll let you know where the problem is in a jiffy...

It would be a mistake to take this lightly.
The problem can not fix itself, it can only be masked.
You can burn the building down by inattention to a ground fault.

First thing to do is go look at the wires coming into the building. If the metal cable (the ground) is broken anywhere along the power line from the pole going into the building then, your ground is gone. Then, if that's OK and there are no broken cables along the poles on your street, go test the ground circuit. Take a multimeter and look for hot, look for continuity. Don't trust the ground inside the building to be a ground at all. Expect it to be hot, hot enough to blow a a couple hundred amps through your heart and smoke you off in less time than it'll take to realize you are dying.

In fact throw the main breaker first.

[Mitchell Andrus]

very true and IF YOUR washer machine or dryer are a earth shakers then the conduit could separate at the joint----wire connections are usually made with wire nuts and they can get corrosion or dirty enough to break the circuit path ---tarnish -covered copper wire are not very good conductor

Yes, but wire nuts are not designed to be left out in the open, conduit is and if your argument is that copper ground wire might tarnish, so would the black and white rendering the circuit useless and ripe for repair anyway. In most places I've seen conduit, it's used as a basement clothes hanger, cord drape and fork lift backstop. Broken, split, rusted and mangled conduit can still be part of a safe system only if there is a green coated copper wire along side the black and white.

PVC conduit meets code because three wires are pulled.
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