desperately looking for an answer to this one. if anyone has any ideas I would appreciate it.
monthly electric bill averages about $300 a month, went over to look at this to determine the power grabbing appliance and found....................nothing! home owner wants to know if power can leak to ground. he has a 50+ year old house with MANY additional panels and circuits added. (some professionally and many done by previous home owners.) when isolating the sub panels, only the 2-pole 15A seems to be the culprit. The only thing on this circuit is the original fuse panel (4 15a circuits, 2 lighting and 2 receptacles) and some lighting and receptacles in the basement. With ALL the fuses unplugged and ONLY the 2-pole breaker turned on the meter spins like a top. With ALL the fuses plugged back in there is no noticeable difference. Any suggestions?

With a clamp on meter at the service what is the amperage draw per leg?

Assuming there is a main, what is the draw with the main breaker off?

I assume you did the above when isolating the subpanel anyway. What about further isolating the things to individual circuits in the subpanel? What about turning off the breakers in the sub and monitoring the current in the feeder to the subpanel?

I would suspect a high resistant ground fault drawing about 15-20 amps somewhere.

Semano:
IF the billing is excessive, you should contact the utility/POCO to have the meter checked by them. Here in NJ, they have to do it, per the BPU rules.

I see from your profile, you did not state any reference to the electrical trade.

Are you saying that the 'wheel' within the electric meter (utility/poco owned) is "spinning"??

The procedure I would use is a clamp amprobe, and isolate the circuits, based on the meter reading. Then determine what is on the circuit. As sabrown said, with the 'main' off....you should have no load...zero amps on the hot legs.

I also would like to say that IF you have no electrical trade experience, you should not attempt to solve this, but hire a licensed professional.

If you do the math you find out a few amps 24/7 add up real fast. A 6a load @ 240v can be half of your $300 bill
As for the sub;
Are you saying the feeder on and all the branch circuit fuses out the thing is still drawing current? Look for a tap.

Look for thing like stuck attic fan, stuck sump pump, buried line to light post or out building leaking to ground, heater the owner never new he had.
You need to trace that circuit and see where all the cables go.

That would produce more heat than a space heater. In fact, I would expect it to cause a fire.

A space heater, left on 24/7, would run about $160/year in CA. Honestly, $300/month sounds part for an electric bill. I suspect there's no short to ground or wasteful compressor or anything like that, and it's just that he's using $300 worth of electricity a month.

Also check for Refrigerator or Freezer stuck in the defrost mode.

Heat tape energized, Christmas lights left on 24/7, basement lights left on 24/7, dehumidifier stuck on,etc.

Does he have a new laser printer or copier that the owner didn't realize draw lots of current.

Larry

What are the electric rates in CA??? A typical space heater uses 1.5kw. In 24 hours it has used 36kw/h. In 356 days it has used 13,140kw/h. At 10 cents per kwh that's $1314 per year.

The only way to solve this is to do some sleuthing:

1)Clamp hot and then neutral from each circuit with a high quality sensitive ammeter and see if amps drawn = amps returned. Difference = leakage to ground, no difference = powered appliance consumption or faulty appliance.

2)Clamp hot from each circuit and one by one turn on/plug in the appliances/lights on that circuit. Check amp draw and voltage vs boilerplate or wattage and compare, small differences can add up.

"he has a 50+ year old house with MANY additional panels and circuits added" Does that necessarily mean more oportunity for ground leakage or just more legitimate consumption.

"monthly electric bill averages about $300 a month" assuming $150 of that $300 bill is excessive and cost of power is $0.12/kWh at 115V then you are looking for a total power consumption of 1.736 kW or 15 Amps, should be easy to find that.

I wonder also how long this has gone on. Only this month, or since he's occupied the house.

I would say, follow up with tracing out those circuits and find out where they actually run and exactly what is connected to each of them.

I have seen mysterious problems similar to this in the past come to a logical conclusion.
In one case, it was a building with a commercial retail shop on the first floor and a small residential apartment on the second floor. The long-term apartment tenant complained to the owner that for some reason, her electric bill this season was suddenly consistently high at close to $300.00 a month during the summer when she was hardly ever even home and was not using any air conditioning.
It didn't take very long to find the problem. Turns out that someone else from the same company I worked for at the time, had installed a new circuit for a dehumidifier in the basement of the commercial area about 6-months before and had mistakenly tied it into the tenant panel, which was located in the basement right next to the panel for the retail space. [Existing installation]
The funny thing is that the electrician that actually did the install was sent back to troubleshoot the problem a couple of weeks before and after some in-depth diagnostics, his answer was that the electricity "must be bleeding to ground somewhere".
Not to say this doesn't occur, but it seems like for many years, I've heard this excuse used all too often when someone can't locate the actual problem.

Go back to basics, check loading on all individual circuits and add the Ampère values up.
These should match the loading on the phase(s) and neutral.

Turn main isolator switch off, after the meter. The meter should stop. ( chances of a mechanical meter being faulty are remote, although electronic meters I wouldn't trust for erratic readings ).

Then one by one unplug or switch off the appliances. It can be a mammoth task, but if you want to check where the power goes, just do it properly.

Bear in mind that a lot of appliances are still on standby when so called turned off, best is to pull the plug from the socket.
Now these days there are a lot off plug in wallwart and SMPS supplies drawing a couple of watts each 24/7, this adds to a reasonable base load.

And sometimes people complain but they forget how long appliances or lights are left on for sometimes.

Just to add and remove uncertainty of earth leakages.

Isolate and test supply downstream of meter, unplug all appliances, ensure that all lighting ccts are off, dimmers switches off.

Insulation test (Megger) the installation as a whole or circuit by circuit at the time. readings should be in the Mega ohm range for the wiring concerned.

Any lowish readings less than 1 Mega ohm on a circuit should be further tracked down to the cause.

Also label all sockets afterwards with a dymo machine and charge customer as an extra service if they want it.

Just my $0.02 worth on this topic.