There's three phases, one feeding the house, one for the garage/studio and one not in use (kept free to elec car one day). 

I know the wiring layout and have drawings, I'd really be happy to pay someone to work this through as I'm not confident in trying to do this myself. Does anyone know someone who can offer this service ? I'm near Princes Risborough in Bucks ... 

There's three phases, one feeding the house, one for the garage/studio and one not in use (kept free to elec car one day). 

I know the wiring layout and have drawings, I'd really be happy to pay someone to work this through as I'm not confident in trying to do this myself. Does anyone know someone who can offer this service ? I'm near Princes Risborough in Bucks ... 

Adam, you are along the right lines already - "divide and conquer". You say that your consumption ceases when you turn off all three RCDs. Where are they please?

If you turn on each one separately, it ought to be reasonably obvious where the leccy is going. An hour's observation should be plenty to register 4 kW of power.

Then, having found the responsible RCD, you turn off all the MCBs and repeat the process with one on at a time. Start with the highest value.

As ever, photos always help us to understand the installation.

OK you have no 3 phase loads, just two groups of singe phase loads.  So if it is one RCD per phase then one of your 3RCDs should be off all the time as it feeds nothing at all. The other two should plunge one building into darkness each.

How awkward it is to turn everything off ? If you can that is fastest.  then have someone standing beside  the meter calling the readings every few minutes as you walk round putting things back on one at a time 5 mins apart?  You need to allows some time, as it is possible it is a very heavy load that is intermittent Even so, ten circuits in an hour is not too foolish.

I presume in the studio and in the main house each has some sort of main fuseboard - is it the sort with real hot-wire fuses you need to pull , or the sort with circuit breakers you can flick ?.

Post images if you like and we can chat you through it.

Again start by turning it  all off, and

First division, is the heavy load coming from the house or the studio.

Then isolate all the loads in the offending building but leave the supply to it on. Again, bring up one circuit at a time, a few mins apart, making notes of meter rate vs time as you go. 

Once you know that it is breaker 6 in board 2 or whatever that is the biggest load, then look at the drawings - what is on that breaker.? Turn it all off at the wall or unplug it, and then swicht the supply to that circuit back on. If the current still rises, there is another load you have missed.

If not go round again plugging stuff back in one at a time and see when the readings start to rise.

Mike.

adam spearing said:

There's three phases, one feeding the house, one for the garage/studio and one not in use (kept free to elec car one day). 

@Chris Pearson