sub-DB reading higher than feeder DB

How is consumption measured ? (proper KVA or just amps ?) could be waveforms/phase thing if the meters are not the same type.

Any generation equipment connected (solar panels that sort of thing)

How far out is it - could it be within metering accuracy ?

just ideas.

Mike.

Are we talking here of instantaneous load readings ? if so the load may have changed perhaps substantially, between taking readings  in the different locations.

Also double check that the same units were used for all readings, Amps ?  KW ? KVA ? All three phases measured, or just one ?

Or are we talking of true consumption in KWH over a reasonable interval such that slightly different times of taking the readings are of little consequence.

If true consumption IN THE SAME UNITS is being measured, then the reported results are most unlikely. If however Kva hours are measured at the distant building, and Kw hours are measured at the main building, then a higher reading at the distant building is possible if the power factor is bad enough.

If none of the above, then one of the meters must be either faulty or being read incorrectly, or is wrongly connected.

Common errors include a blown fuse in the “voltage” circuit of one or two phases, or wrong ratio current transformers fitted, or one current transformer the wrong way round.

Electricity meters are generally reliable, errors in connections or in the programming of modern digital meters are more likely. As are reading errors is a menu has to be navigated.

The “total units” reading is generally what is required. Accidentally reading only “night time units” on the main meter, but “total units” on the distant one could give the results reported.

Thanks very much.

Hi Mike and Broadgage,  do you know which distribution board consumption is likely to be accurate?

Nick1967: 
 

Hi Mike and Broadgage,  do you know which distribution board consumption is likely to be accurate?

Not really without more details, and preferably photographs. Are we talking about loading at any one time, correctly measured in kilowatts, or we talking about total energy consumed over some time, correctly measured in kilowatt hours, sometimes known as “units” for billing.

If the main meter is installed by the electricity company and is read for billing purposes, than that is more likely to be accurate than a fleabay special installed by persons unknown.

If single phase, then SOME of my earlier remarks are no longer relevant. 

Whilst not answering your question, in cases where there is concern over sub metering, I advise the occupier to switch off their main switch to see if any other users (including communal lighting etc) suddenly loose power! Obviously be mindful of your freezers, fish tanks and anyone on life support!

This applies to cases where usage is higher than expected, not your strange situation. I can only suggest that as has been mentioned, the quality of the sub meter.

I've got one to resolve for a client (although to me the answer is obvious) in as much as he supplies converted “cookers traditionally found in farmhouses” to electric. Needless to say a purchaser has complained about the £200 a month increase in their electricity bill…..

I'm not sure what the purchaser expected his bill to be……..

Regards

BOD

The absolute classic I found was an installation where the peak and off peak meter tails had been commoned in a Henly block to supply a single set of tail which fed another Henly block where they were split again to supply their respective consumer units. The electric Aga was running up a huge bill as it was never charging on the “off peak” tariff as it charged after each use. A bit of rewiring dramatically reduced the bill.

It is quite amazing what  installation designs some people come up with, there’s a job I have not got around to going and looking at yet, an electrician doing other work was asked to check out a garage and garden office installation because of RCD tripping issues in the garage, but he said he can’t sort it out because he “cannot find out where they are supplied from”, I guessing it’s from the meter via the main switch and consumer unit, but there’s quite possibly a surprise in store.

Picking up on the comments by @mapj1 if there’s PV on the roof it is possible the upfront meter could run backwards, so the landlord could be on a winner with whoever pays the bill based on the second meter paying more than the bill for the first meter.