Electrical – Identifying an unknown and intermittent source of electric power usage

Turned out to be the High Limit switch. The switch had burnt out, which caused the burner not to fire. Turns out when the limit switch senses the heat box is too hot, it shuts down the gas and forces the blower to continue so it will clear the excess heat. When the switch failed it always told the system that the furnace was over heated, so the burner would not come on and the blower would run constantly to try and clear the excess heat.

To trouble shoot this issue I used an ohm meter to test each sensor, to make sure it was open/closed as it should be. Another way to test would have been to use jumpers to bypass the sensor all together, until the faulty sensor was located.

100 KiloWatt-Hours a day? (a tick over 4 KiloWatts continuous, that's nine 400W sodium lights burning 24x7) with nobody home? Summer and winter? That's murderously wrong and I would not put up with that for one minute let alone one month.

It would help to have a "second opinion" meter up at the meter. It wouldn't work to put the Sense there, as it relies on listening to subtle signals that won't make it 700'. The upshot of the 700' is that voltage drop becomes very, very important. Pay close attention to your instantaneous voltage and current numbers coming off the Sense. Any appreciable voltage drop indicates you're spending a lot of money making 700' of wire warm. 1400' of 4/0 cable is 0.1124 ohms.

It would help to get instantaneous kw (not kwh) readings from the meter. Back in the day you'd look at the spinning disc with a stopwatch, but hopefully your smart meter has a way to read it.

700' is a lot of property to secure

I am puzzled at why the power company gave you power 700' away from the point of use, instead of traversing the 700' at 2400 or 9600 volt distribution voltage. There must be a reason; that reason might have something to do with it. I can't guess the whole story, but large properties often have complicated things going on.

Such a large spread (and cable run) is hard to secure, so illegal tapping is a possibility. (marijuana grow, typically). So it's very important whether there are any other structures near you where that would be possible. Criminals may have tapped anywhere along the 4/0. 100kw/day is 17 amps at 240V, interestingly at the limits of 12AWG wire (the criminals don't care about voltage drop since you're payin'.) Under these conditions (12AWG/17A)voltage drop will be 6 volts per 100 feet, so the thief could be 500 or even 1000 feet away and still get usable power. Modern ballasts and LEDs will run on any voltage 100-277V.

If you find a rogue cable, typically cheap Romex, go no further and call the sheriff or state police. They know what a rogue cable means, and they'll come in sufficient force.

You might also consider any legal use by other facilities on the property, especially ones where electric heat might be in use. (forgotten fallout shelter? Sorry, just watched 10 Cloverfield Lane.) In simplest terms, look at what cables are exiting the meter pan. It should only be the supply and your 4/0. Does your 4/0 make any other stops on the way to your house?

Chase it

Now it's go after it with the measuring devices (assuming you get an ammeter you can use up at the meter pan, e.g. the meter itself).

I would turn off the main at the house and go up and look at the meter. If the meter stopped, it's a transmission (voltage drop) problem which I agree isn't likely if the cable is really 4/0. I suspect you'll still see a ~4KW load... and then, you have to check other loads.

You will want to check current on every conductor, and also on every ground bond, including the one at the transformer.

• If power is leaking from a hot to earth, it'll show up on one ground bond or another, likely all of them. There should never be current on that except during a lightning strike.
• If you see equal current on both hots, that's a 240V tap, probably a bad guy.
• If you see equal current on one hot and neutral, that's a 120V tap, 4kw is a lot for 120V so something funny is going on.
• If you see imbalanced currents on hots and neutral but the lower hot + neutral equals the higher hot, that is a 120/240V tap, criminals wouldn't bother, that's more likely a proper load on your property.

If all else fails, have somebody come out with a FLIR camera at 5am and walk the cable route. 4KW is a lot of heat, like 3 burners on your stove going full tilt. That will show up on a FLIR, and if it's leakage in the cable, there'll be a red spot on the ground above it.

You might have the power company pull the meter to allow you to unhook the 4/0 - and then reconnect the meter, and see what it does. Or perhaps your generator interlock provides a way to do the same thing.

• If you still have 4KW of load, then you need to chase other taps of that meter.
• If disconnecting the 4/0 ends the load, and your house is the only load on the 4/0, then you have a tap of some kind, either one of yours you don't know about, or a crook.

Lastly I need to at least mention the generator and interlock; make sure all that is in good order. Again, a 5am inspection with a FLIR will expose a ~4kw drain.