Installing a Sub Meter

walec · Jan 16, 2010

Hi all, just been to a job where there is an annex attached to the house. Problem is Granny lives in the annex and has the electric heaters and lights on night and day. The owners want to work out how much electric she is using, the supply currently being on one meter to the house and annex. I believe there are two options
A) Get the DNO to put a new supply and Meter
B) Install a sub meter and a seperate CU for the Annex
I have heard of these sub meters, I believe land lords use them but I have never put one in.
Any advice or alternative suggestions welcome.

pennywise · Jan 16, 2010

60 Amp Single Phase Digital Check Meter

one of these. It would be cheaper you putting in the check meter and a separate CU.

boatnik1 · Jan 16, 2010

Depends on the wether current supply to the annex is running off existing rings or if there is a single supply for the annex. From your post I suspect the former. Ideally isolate the circuits in the annex from the main dwelling and supply them from a seperate CU either in the main dwelling or annex depending on convenience.
Just connect a meter as in pennywise post into the supply from the L&N blocks to the annex CU
Meter connections 1 L in 2 N in 3 N out 4 L out. Obviously the earth also runs to the annex CU.
You could always really P*** off the granny by installing a coin slot or card meter and setting the units rate over the actual cost.

walec · Jan 17, 2010

Thanks Guys,

So just so I am clear, split the tails install the meter, feed to a seperate CU dedicated to the annex and deduct the meter reading from the bill to work out what to charge Granny...or put a coil/slot meter in as boatnic1 says which I find quite amusing but I bet Granny wont!

boatnik1 · Jan 17, 2010

Sounds about right. Either supply to the annex or if the existing annex circuits are from the house CU but not shared with the house circuits then the sub meter and CU could be installed along side the house meter/CU to avoid having to run a seperate supply to the annex.
I mentioned the slot meter a little tongue in cheek but they really can be an asset for older people as they have a very real idea of their electricity use as they use it and are not be surprised at the end of a month/ quarter when they refuse to believe the numbers. Sometimes the reality of energy charges can be quite a shock for elderly people. I have fitted quite a few coin sub meters for this very reason even when a normal credit meter is installed in the property. It can be a nice little earner, a cheap recon slot meter, a couple of tails, and an hour of time gets around £70-£100 and the customer has the money to pay the bill when it comes in (providing they can keep their sticky fingers out of the coin drawer between bills). It's worth asking.