I just found the source of a -yuge- vampire load. Measuring amps at the 240V mains entrance going between the pole and my house: L1: 4.8A, L2: 18.2A, GND: 12.5A.

I go up into my attic and turn off the local breaker on the air handler. The A/C was already off and has been for a couple months, yet still we are getting bills like it's the middle of summer. Now I measure: L1: 4.8A, L2: 5.8A, GND: 1A.

It seems I've been continuously dissipating 1.5kW into some part of my house for months, and it didn't burn down. How lucky am I? How much does it take to burn down a house? I don't know, but I know that it takes more than 12.4A, for this house at least.

 

Did you try turning off the main breaker and measuring between pole an the house?
But if you are getting billed for it, it must be after the meter!
Was the 12.5a on GND conductor at the actual panel?
Max.

 

Where are you measuring this GND current? Are you referring to Neutral current? the neutral takes care of the unbalanced load. In your last measurement L2=5.8a minus your L1=4.8a equals the unbalanced current of 1a. Your first set of numbers sounds like you have a load imbalance on your panel( more 120v loads on L2 than L1)..
However shutting off the A/C and your measurements there make no sense to me at all, a 13a 120v load from an A/C unit that's not running. The only thing that remotely makes any sense is if some large 12a load shut off just before you made the measurement..

 

Did you try turning off the main breaker and measuring between pole an the house?
But if you are getting billed for it, it must be after the meter!
Was the 12.5a on GND conductor at the actual panel?
Max.

I can't just turn off the main breaker. I have severely unacceptable multiple taps coming out of the top of the main breaker, such that half the loads don't even run through it. I have two branches, the one to the AC and one to a "sub"-panel in my closet, running unfused through my attic. I've known about this since shortly after I bought the house and have been meaning to have it fixed but it won't be cheap and I haven't had the money.

Where are you measuring this GND current? Are you referring to Neutral current? the neutral takes care of the unbalanced load. In your last measurement L2=5.8a minus your L1=4.8a equals the unbalanced current of 1a. Your first set of numbers sounds like you have a load imbalance on your panel( more 120v loads on L2 than L1)..
However shutting off the A/C and your measurements there make no sense to me at all, a 13a 120v load from an A/C unit that's not running. The only thing that remotely makes any sense is if some large 12a load shut off just before you made the measurement..

Neutral, you're right. I only called it ground because I had just come from the main breaker panel where the neutral is grounded a foot away to large ground rod.

No there is no mistake, no coincidence. I had my wife on the phone watching the amp clamp on the breaker panel while I went up and turned off the A/C breaker. Not fully believing that this A/C could really be the problem, I switched it back on again and she reported a return to the previous 18.x amps. I turn it off again, back to 5.x amps.

 

Can you measure the ground current in the three paths marked in brown, blue and yellow on your diagram? That will give you a clue to where to start looking. If the cable to the garage is underground, I would suspect that one first.
Keith

 

Ditto on the underground. I just discovered I had enough current going into ground to blow a 15A breaker. I thought it was my garage door opener but I got to thinking that it seemed like it always blew when it rained or snowed. We have a light pole out front and I think my wife put a shovel into the Romex line going out to it.

 

Can you measure the ground current in the three paths marked in brown, blue and yellow on your diagram? That will give you a clue to where to start looking. If the cable to the garage is underground, I would suspect that one first.
Keith

I think the disappearance of the fault after isolating the A/C points to that being the culprit, however i think your suggestion, among other things, warrants a closer look. After replying to @gerty about neutral vs ground, and circling where I took the measurements in my diagram, I'm realizing that my flaw might be deeper than just terms. I'm not actually sure where I took the "GND" measurement. I suspect that my diagram is correct and I was actually measuring neutral, I need to verify that. However, I'm not sure what it would mean. That A/C is a 240V unit, it has no 120V loads. It has no neutral conductor in the romex going to it; just black L1, white L2, and bare GND. The only thing I can think of that would cause a high load on just one leg when it has power, is an internal short to the metal frame of the A/C. That's really the reason why I've been thinking of it as a "ground current" fault. But if I really was measuring ground, not neutral, and still had current flowing then I might have another problem. And yes, garage power is under ground.

Now as for what inside the A/C could be the issue... something with a fixed resistance and capable of a sustained dissipation of 1.5kw without bursting into flames... I'm suspecting a heater coil fused open, fell from its insulated perch, and came to rest against the inside of the enclosure. But even that explanation seems hard to accept, because I have pulled the wires off the heater coils a few months ago as the contactor was shorted and the heater coils were constantly on.

 

You took the current measurements at the same place I would've. Next thing I would do is meter the 50a breaker going to the garage. If you get any kind of reading, I would then go to the garage panel, remove cover and check to see if it's lower. That would indicate an underground issue..

 

If you're constantly using 1.5 KW with no appliances turned on, the power is being dissipated through a phantom load someplace. If the power is just generating heat and not doing any work (like running a motor), you would be seeing a lot of smoke or steam inside your house or something coming out of the ground outside. Try getting an infrared imaging tester and look for a hot spot.

 

We have a light pole out front and I think my wife put a shovel into the Romex line going out to it.

Is that legal? When I was researching code requirements to run electricity to a pond, conduit or armored cable was required within a couple feet of the surface (IIRC).

 

I grew up near Chicago and never saw a wire in the house that wasn’t in conduit. I was stunned when I move to near Rockford about 90 miles NW of Chicago. All house wiring (except in the basement near the floor) is Romex. Sure is easier but surprising when you’ve never seen it.

I have no idea if underground Romex is (was) code here but it wouldn’t surprise me.

 

I grew up near Chicago and never saw a wire in the house that wasn’t in conduit. I was stunned when I move to near Rockford about 90 miles NW of Chicago. All house wiring (except in the basement near the floor) is Romex. Sure is easier but surprising when you’ve never seen it.

I have no idea if underground Romex is (was) code here but it wouldn’t surprise me.

Is it perchance Type UF?
UF stands for Underground Feeder. It is also sometimes called "direct burial cable". It looks like Romex, but has a tougher jacket that's usually more tightly sealed around the inside conductors. This also makes it harder to strip. It's also typically gray. In most US locales, it is legal to directly bury it without conduit. It still needs to be at least 18" deep and have a marker ribbon above it.
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As for the TS question, I'd be looking at the backup heater coil in the AC unit. 1500 watts is equal to a pretty big space heater, but won't necessarily smoke and burn. Toasters and toaster ovens come with 1000 watt ratings. With that much power being dissipated, the unit may never cool down. It will likely be pretty warm even from the outside of the housing.
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Lastly, if you suspect it's a short to ground, BE CAREFUL, the last thing you want to do is turn it into a short to your body!

 

Strantor is not an amateur. He will find it. The only idea I can add is that my neutral line had an ilegal splice in it and suffered from high ohms. The unbalanced current was going through my copper water pipes to the clamp outside the house!