troubleshoot power outages

[lisco]

Situation: Customer has older home with aluminum and some replaced copper wire. No problems in 30 years. Calls us and said that he came home from work and his power was out in one part of his house. No breakers were tripped. He went to his window a/c unit and turned it on. The rest of his house turned on. Another day he was sitting in his living room. He had an oscillating fan on. He said it began to slow down, then stopped. The other things in that part of the house turned off at the same time (i.e, tv, cable, refrigerator) He went to his window unit, turned it on, everything else turned back on. I had one of my employees check every outlet, attic connections and voltages at both load centers. He found one mis-wired receptacle. Thought possibly that was the problem. All checked out good at that point.

Originally, thought it was an open neutral; however, all outlets, etc had good voltages.

Any ideas as to what else can be checked?

Did anyone see Gremlins?

 

[peter d]

Open phase or open neutral for sure. And quite possibly it was a problem on the utility side that got repaired.

 

[480sparky]

Did you check for any loose connections?

 

[mdshunk]

I have seen utility taps become marginal (hot's, not neutral in your case), and sorta "weld" themselves back for a spell under heavy load, then open at some point later on. It may be of some benefit to do a quick and dirty FOP test from the breaker's terminal of the effected circuit(s) to the furthermost typically effected receptacle to see how many millivolts you measure to see if you might have missed a marginal connection inside the house someplace.

 

[peter d]

It may be of some benefit to do a quick and dirty FOP test from the breaker's terminal of the effected circuit(s) to the furthermost typically effected receptacle to see how many millivolts you measure to see if you might have missed a marginal connection inside the house someplace.

How do you do a FOP test?

 

[mdshunk]

How do you do a FOP test?

Pretty simple, in reality. When measuring a contactor's health, for instance, when the circuit is powered and the contactor is pulled in, measure millivolts from the line terminal to the load terminal. Ideally, you'd measure from the copper conductor before the line terminal to the copper of the conductor where it comes out of the load terminal, if there's any exposed. A perfect connection will read -zero-. The millivolts will go up in relation to how bad the contacts are. Same deal with fuseholders, etc. Not nearly as accurate for a test like I described above, due to the long wire necessary to perform that test, but will still give you relative numbers to compare.

 

[peter d]

So that means you need a pretty fancy, very accurate DMM then, right?

 

[mdshunk]

So that means you need a pretty fancy, very accurate DMM then, right?

Ideally, but meters marketed to HVAC guys measure millivolts very accurately, due to the fact that millivolts need accurately measured to troubleshoot flame sensing controls on heating equipment. Not an expensive piece. For troubleshooting, all you're looking for is relative numbers anyhow.

 

[76nemo]

Here's another scenario where loop impedance testing like what the Ideal 61-165 can do. No, that's not FOP, but it can work. Go ahead Marc, shoot the 61-165 down:roll:

 

[electricalperson]

Here's another scenario where loop impedance testing like what the Ideal 61-165 can do. No, that's not FOP, but it can work. Go ahead Marc, shoot the 61-165 down:roll:

i love that tool

 

[LarryFine]

Did anyone see Gremlins?

Not since AMC stopped making them.

You have an open line conductor in or ahead of the panel, and the window AC is a 240v unit.

 

[quogueelectric]

You have an alluminum wire burning itself to oblivion cooking nice and HOT probably melting the box around the receptacle as we speak.
First and foremost do you really think it is safe to run an airconditioner on a circuit that is known to be aluminum and have problems??
REFEED THE AC!!!!
You do eventually have to find the molten mess that might not even be in a box it may be an open splice in the attic that is igniting some insulation tinder paper .
The circuits usually fail closest to the panel where the heaviest current is and it may not be a bad idea to put this temorarily or permanently on an arcfault breaker to protect the living inhabitants of the dwelling from fire.

 

[peter d]

You have an alluminum wire burning itself to oblivion cooking nice and HOT probably melting the box around the receptacle as we speak.
First and foremost do you really think it is safe to run an airconditioner on a circuit that is known to be aluminum and have problems??
REFEED THE AC!!!!
You do eventually have to find the molten mess that might not even be in a box it may be an open splice in the attic that is igniting some insulation tinder paper .
The circuits usually fail closest to the panel where the heaviest current is and it may not be a bad idea to put this temorarily or permanently on an arcfault breaker to protect the living inhabitants of the dwelling from fire.

That's quite a leap in logic, don't you think? There is a great chance that this problem is in the outside distribution and has absolutely nothing to do with AL wire.

 

[JohnJ0906]

Situation: Customer has older home with aluminum and some replaced copper wire. No problems in 30 years. Calls us and said that he came home from work and his power was out in one part of his house. No breakers were tripped. He went to his window a/c unit and turned it on. The rest of his house turned on. Another day he was sitting in his living room. He had an oscillating fan on. He said it began to slow down, then stopped. The other things in that part of the house turned off at the same time (i.e, tv, cable, refrigerator) He went to his window unit, turned it on, everything else turned back on. I had one of my employees check every outlet, attic connections and voltages at both load centers. He found one mis-wired receptacle. Thought possibly that was the problem. All checked out good at that point.

Originally, thought it was an open neutral; however, all outlets, etc had good voltages.

Any ideas as to what else can be checked?

Did anyone see Gremlins?

Sounds like an open line. It is being backfed through the A/C unit.
I've seen this a few times, although I usually see the backfeed through an electric water heater.

 

[gar]

080627-0644 EST

lisco:

Get a long extension cord. Connect the EGC of the cord to the grounding electrode. If copper or iron water pipe enters the house connecting to it should be good. Now you have a reference point from which to make voltage measurements.

When the malfunction occurs measure the voltage from your earth reference point to neutral and each hot wire as they come from the meter on the wire itself. If these voltages are correct the problem is within the home. Obviously for this first test you do not need the long extension cord. If you suspect a bad connection to earth, then put a screwdriver in the ground outside and use it for your reference.

If within the home, then probe various circuits for incorrect voltage. Start with the output side of the breakers.

If there is a high resistance in the neutral path from the pole to the main panel, then with varying loads in the building there will be varying voltages between earth and the two hot leads. When one hot goes up in voltage the other will go down. Depending upon where bad connections are it may be more sensitive to look between neutral and the hot wires. For quickly changing conditions you would like two meters for this monitoring.

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