Drain on Electric Power Supply

I have a problem identifying a power drain on my domestic electric supply.
This is bugging me ‘cos I can’t find the source of this small electrical drain of 100 watts.
I have recently acquired a supply monitor which works simply by having a current transformer on the supply live and an electronic device which monitors real time energy usage. I wanted to check very crudely that a new digital electric meter was at least getting the same order of consumption that I measured. Which I might add does with in reasonable limits.

Now for the problem. I detected a drain on my supply of 100 watts with everything I could think of isolated. I searched for the source of this 100 watts so as to identify what was causing it. What I determined was that by Isolating the downstairs sockets at the consumer unit, the drain went immediately to zero, so at least I could determine that all upstairs circuits and all lighting circuit and garage were not the cause of this 100 watt drain.
Easy I hear you say, the cause must be some items on standby such as Computers, Printer, TV’s, DVD recorders, Micro Wave oven, Cooker, maybe fridges or freezers switching on. So I was determined to identify the source of the drain just for my own curiosity, so I systematically went to each and every socket and spur outlets through the downstairs of the house. This entailed switching off ALL of the devices to which I referred earlier. Still I had a 100 watt drain. I then thought I must have been mistaken when I isolated the downstairs sockets at the consumer unit. So I once again Isolated this circuit and immediately the drain went to zero. Re-established the ring main and the drain re-appeared.
Now I am at a loss to determine what is the source of this drain is, as I systematically switched each and every outlet off and still could not eliminate the 100 watt drain.
So there must be another circuit attached to the downstairs socket ring main which is the source of this power drain. Items such as Intruder alarm is supplied from the Upstairs circuits so it is not that.
There is no Earth leakage as I have RCD (Residual Current Detection) devices on the Ring Mains which trip with 20mA earth leakage, so there is no earth leakage.
I have ran out of ideas now.
With the wealth of knowledge and experience out there, has anyone any suggestions as to what this drainage could be. There must be something else supplied from this ring main of which I am unaware.
OK 100 watts is not that much but it amounts to about 2.5kwh per day or 10 kwh per week or 500 kwh per year which amount to about £70 per year. Not a bank breaker but worth identifying I feel.
Has anyone any suggestions?

Hi Hysteresis

Long time no talk. Hope you & yours are well.

If you have access to any equipment, it might be worth doing some insulation resistance tests, L/E and N/E. I would also break down the ground floor (ring final, I assume?) circuit.

I would split the circuit at an outlet you think is roughly midway, then reconnect each side of the ring final one at a time to see where this "drain" appears.

If it is a radial circuit, just split the circuit at an outlet and see if the "drain" disappears.

This way you can pinpoint where the problem is.

Oh, those sparks will do anything for a laugh. Wiring up a 100W light bulb inside the wall is a good one!

Seriously, 100W isn't such a small thing. I'd be concerned about it too.

I presume your device does show wattages of between 0 and 100 when the socket circuit is off and a small load is working?

I had a small untraceable leakage on my ground floor circuit, but no others.

I guessed it might be to do with damp, as it included outdoor lighting, unheated garage, and unheated utility room containing washer and drier.

Sadly I don't remember what it was. I have a monitor but it is inaccurate below about 300W.

I suppose you haven't got a burglar alarm?

Maybe the neighbours have tapped through the party wall and are running their tv off your ring. Wouldn't be the first time.

John D v2.0 said:

Maybe the neighbours have tapped through the party wall and are running their tv off your ring. Wouldn't be the first time.

Click to expand...

I once worked on an old cottage, the CU had been removed and I was stripping out lead/rubber cable. When I got to the kitchen my cutters suddenly developed a hole in the jaws.
It appears the kitchen had originally been part of the neighbouring cottage and nobody thought of altering the wiring.

Hysteresis said:

I have recently acquired a supply monitor which works simply by having a current transformer on the supply live and an electronic device which monitors real time energy usage.

Click to expand...

Those things measure CURRENT not watts. They should be banned as they do not do what they say and not as described.

Current at zero power factor will produce zero watts.

Have you actually checked on your suppliers meter that there is this drain?

Hysteresis said:

I had a 100 watt drain. I then thought I must have been mistaken when I isolated the downstairs sockets at the consumer unit. So I once again Isolated this circuit and immediately the drain went to zero.

Click to expand...

You need to be careful about inductive or capacitive loads. The sort of meter you're using can't tell the difference between a real (resistive) load and an imaginary one.

Does your electricity supplier meter record this 100W load?

What's up in the loft? TV amp, something like that?

Hi Securespark,
As you say long time no talk. Hope and your family are well.
I appreciate your suggestions. The inevitable problem is knowing the physical ring route in order to identify the drain source. It will be a case of trial and error I fear. Wish me luck.

100 watt lamp in the loft. Wired off the ground floor sockets because that was the only circuit live when the wiring in the loft was run.

But is your electricity supply meter registering anything as your monitor may simply be inaccurate and as EFLI says it may be picking up a bit of stray leakage and displaying that as 100 watt.

Hysteresis said:

Wish me luck.

Click to expand...

In spades!

Thanks everyone for your suggestions. I will make a general reply to all helpers.
I have discounted damp/earth leakage as the circuit in question had an RCD protection.
Neighbours tapping into my supply is not an option, it is a detached property and the nearest neighbour is 30 metres away. The builder could have course been very naughty but I don't think this a possibility.
I fully understand that these cheap domestic power indicators measure current with total disregard to Power factor and Voltage, but they normally assume a voltage of 240v ac and a Power Factor of some thing between unity and 0.9. There will be virtually no domestic device that is either Inductive or capacitive with a lower PF.
I also appreciate that these domestic power measuring devices are not that accurate but are indicative of consumption. The point here is that I have a drain of around 100 watts with all of the known outlets from the down stairs ring are switched off and in this state, isolating the ring at the CU eliminates the drain. I do have a TV signal amplifier in the loft and also an intruder alarm in the oft but both of these devises are as far as I can determine are on the Upstairs ring. I think I will have to confirm that they are on the upper ring but I do am sure they will be.
It is difficult to determine that the official meter is measuring a 100 watt drain as the unit only measures to a resolution of 0.1KWh and is a digital meter so no rotating disc to observe. SO with a drain of 100 watts I would have to monitor the Meter for an hour to record 0.1 KWh whereas the unit I have bought measures consumption in instantaneous kw.
I think I have a long identification process infant of me and that is made a little worse with an inpatient other half.
Thanks for all of your advice. I will post a solution when I find it.

Hi Osian DIYer,
No lamp in the loft. The point here is that I measure 100 watt drain which disappears when I isolate the Down Stairs ring, so it is on this circuit. I have discounted earth leakage as this would be detected by the RCD. As explained in an earlier rely, instantaneous consumption on the supply meter is difficult as it only measures in KWh and is a digital Smart meter.