# Metering the workshop electrical supply query



## Tallis (28 Sep 2021)

I have a house which is tenanted. At the rear of the garden some 25m away I have a shed, which is fenced off from the garden/house and access is via a rear alleyway - this gives me sole use of that shed (lawnmower, maintenance tools etc). 

I have a heavy gauge extension lead which when I want to cut the grass I simply plug in to an external socket at the house - that also allows me on occasion to use the shed as a small workshop for the odd power tool. The tenants are happy with this arrangement, but it is of course less than ideal. 

If I have a proper installation (certified installer etc etc) - I would look to install a dedicated way in the main house supply consumer unit to serve the shed. As the meter/consumer unit is at the front of the house, I'd have the supply cable routed up into the ceiling void and run it out through to the back of the house, conduit/armoured cable down the house, buried under the patio, buried under the garden down to the shed at the bottom of the garden.... and then potentially an additional set of RCDs in the shed itself - sockets/lights rings, job done. 

However - I would like to be able to formalise an arrangement with the tenants with regard electrical usage. At present, we just agree that what little electrical use in the shed is associated with my maintenance of the property. But if I have a more established office/workshop in there, I want that formalised.

*Question 1: *Is there a product on the market which allows me to install an additional electricity meter to monitor the electricity used in the shed? That way I can reimburse the cost of any electricity used, based on a per unit cost at their supplier's tariff. If so, what would I be asking an electrician to install - this will help as I call around to explain what I am after for quote purposes. I guess something like this that is installed in in the consumer unit (although rated appropriately)? A9MEM2110 - modular single phase power meter iEM2110 - 230V - 63A with pulse - MID | Schneider Electric UK 

*Question 2: *I want to afford maximum protection to the main house supply - i don't want to go tripping a fuse in the shed, which then trips the main house supply.... as that will be really annoying for me and the tenants. What is the best way to provide the maximum protection from that happening do you think? 

Thanks for any ideas,

Tim


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## robgul (28 Sep 2021)

Q1 - You can buy a simple electric meter (like the old-style, pre-Smart ones) from electrical wholesalers - just wire it in and you get readings. 
I installed one to monitor the usage on a holiday cottage that I had that was part of my house - they also get used in HMOs

Q2 - Dunno!


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## HamsterJam (28 Sep 2021)

1. As Rob says, you can buy proper meters although if you aren't too worried about absolute accuracy, a cheaper option might be something like an Owl.
2. It‘s called graded protection….
As you move from the load towards the source each fuse, trip, circuit breaker, etc should get bigger and/or have a longer reaction time (and the wires sized to correspond of course). This means that wherever the fault is, only the protection device serving that section of the circuit should trip and not the ones further upstream.
A competent electrician should build this in to their circuit design.


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## nickds1 (28 Sep 2021)

The normal way to do this is a separate circuit from the the utility feed. Use a couple of Henley blocks to split the meter to house CU tails and install a new spur with isolator, probably fused at 40 or 60A. That then goes to the shed meter and then there's a long cable to the shed which has to be very carefully sized which will depend on current, length and physical environment (buried, in a conduit etc). It could be 2 or 3 core depending on earthing arrangements (see below).

In your shed you'll have a metal CU with an RCD/isolator sized to match the main fuse back at the spur. The whole shed is then on an RCD and you have no interference with the house electrics.

Earthing is an important consideration and this is up to the electrician to decide. Safety is everything.


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## woodieallen (28 Sep 2021)

Or if none of that 'floats your boat', go the simpler option of saying £x per month to them. Easier and simpler IMO.


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## Sandyn (29 Sep 2021)

If you used an isolating transformer for power to the shed, you could have your own protection in the shed and not trip the house. Depends how much power you will need


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## clogs (29 Sep 2021)

woodiealen has the best idea.......it does depend on the tennant tho.....
just knock it off the rent and u wont feel it........


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## pils (29 Sep 2021)

is your shed/electricity usage in the contract? Specifically, if you're going " established office/workshop/formalised".


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## Chisteve (5 Oct 2021)

I have a similar situation 

I’m the landlord and have a double garage to the rear of my rented house about 25 m away, i recently had a long term tenants who left the property 

I got the electrics checked and subsequently up graded with new fuse box in house to current standards, also upgraded wire from house to garage to 6mm armoured cable with fuse box in garage and separate trip in house this is enough to run my workshop and I‘ve been assured to run a number of machines at once also got the electrics certified 

I got a new tenant through a friend, part of the tenancy agreement is he pays for electric I use he’s happy with that as the previous tenants were 

I only use this garage about 10 hours average a week for hobby woodworking and restoring tools etc 

Thats my way, it’s stated before they move in as above if there existing tenants knock monies of the rent to save mucking about with meters etc 

As the letting agent said well back in July electricity is cheap 

Hope that’s of help


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