Designing/specing my circuits...

[Crofter]

So the time has come to chase the local sparkies and get cracking with wiring out the little house.

Hoping to get a few suggestions on what to spec so that I am reasonably well prepared and can shop around for appropriate kit. Always like going into things with eyes open

 

The house is 43m2 total net floor area, divided into a living/kitchen space, a bedroom, a small vestibule/hallway, and a shower room.

There is a 25mm service void throughout, which is not insulated.

DHW will be by UVC with E7. Direct electric space heating.

 

My thinking so far on the circuits I will need:

- 32A ring main covering the living room and bedroom

- 5A lighting ring covering all rooms

- 16A supply to the sewage treatment system (supplier recommended this due to the starting current on the pump)

- 40A (?) for the hob and oven

- 32A for other kitchen appliances and sockets (dishwasher, fridge, cooker hood)

- 16A (?) for the UVC immersion

- 5A (?) for MVHR (it draws something like 60w max so I imagine I want the smallest possible- or can I just spur it off something else?)

- heating I'm not sure about, see questions below

 

Questions:

- there is a washing machine in the hall, should that go on the main ring or on the kitchen circuit?

- with the UVC on E7, does it need two separate supplies for two elements- or does it not work like that? Come to think of it, does an E7 setup need a second CU? That's certainly how it works on my 'Total Control' system in the current house.

- I'm yet to make a final decision on heating, but it will be three separate zones. The baseline plan is a panel heater in the bedroom, another in the kitchen, and a towel rail in the shower room. However I am costing up electric UFH mats instead. Either way, looking at a total load of maybe 3 to 4 kw. And of course I'd be looking to use E7 here as well.

 

Thanks, and sorry for the noob questions!

[ProDave]

Lighting will be 6A (they stopped doing 5A mcb's a long time ago) and will be a radial circuit not a ring.

 

32A usually for hob an oven but check the manufacturers ratings, you might be having a 5 ring induction hob for all we know.

 

The E7 usually has it's own smaller CU, but it can be done with one CU and two main switches but the  CU has to be designed for that and is less common.

 

If the tank has two immersion heaters use the top one for a timed boost from the normal circuits and the bottom one connected to the off peak circuits. If it only has one, use a Horstman (or similar) boost controller.

 

Total control is an old tariff that's no longer available, it will be plain old E7 or E10 for the new house. Seriously look at E10.The off peak times work well for a morning warm up at cheap rate, and late afternoon worm up. It's really only the evening period when you are stuck with the peak rate.

 

Have you found a local electrician yet?

[Crofter]

Still need to pin one down. Have a few leads to go on.

 

I'm assuming there's no physical difference between E7 and E10?

 

Still not really sure how the two rates work when you want to have the choice of how to power something. E.g. if you have a panel heater and you want to be able to power it off cheap rate, but still be able to use it during peak times. How does that all work?

[A_L]

Quote

27 minutes ago, Crofter said:

Still not really sure how the two rates work when you want to have the choice of how to power something. E.g. if you have a panel heater and you want to be able to power it off cheap rate, but still be able to use it during peak times. How does that all work?

 

The whole house is cheap-rate at the appropriate times so all you need is a timer, possibly integrated on the appliance, one period for the off-peak and a manual override/boost for the on-peak use (or additional timed periods if use is regular).

[Crofter]

7 hours ago, A_L said:

The whole house is cheap-rate at the appropriate times so all you need is a timer, possibly integrated on the appliance, one period for the off-peak and a manual override/boost for the on-peak use (or additional timed periods if use is regular).

 

Thanks. My current house has a weird and obsolete tarrif called Total Control, where I have two CUs and all heating appliances are wired to both. Glad the E7/E10 systems are a bit simpler.

[ProDave]

1 hour ago, Crofter said:

 

Thanks. My current house has a weird and obsolete tarrif called Total Control, where I have two CUs and all heating appliances are wired to both. Glad the E7/E10 systems are a bit simpler.

The total control is a good system if you have it.  It has three separate CU's (usually two of them in one box) a normal "house" cu that gets cheap or peak rate according to time. An off peak CU that just gets energised at the off peak times for storage heaters, and the "total control" CU that gets metered at the cheap rate and is powered 24/7 This is only for heating appliances like panel heaters, water heaters, showers etc.

 

If you have this tariff it's worth leeping it for the availability of the 24/7 cheap rate, but do check the standing charges and rates to make sure it remains competetive.

 

E7 and E10 are identical apart from the settings int the DNO's time clock.

[Crofter]

OK thanks everyone I have a bit of a clearer idea of what to do now.

So only one CU needed for an E7 or E10 tarriff.

 

Circuits are now looking like:

- 32A ring main covering the living room and bedroom

- 6A lighting ring covering all rooms

- 16A supply to the sewage treatment system

- 32A for the hob and oven

- 32A for other kitchen appliances and sockets (dishwasher, fridge, cooker hood)

- 16A for the UVC immersion

- ? for MVHR- or power off another circuit

- ? for heating, need to know total load but assume one circuit will be fine

 

The uncertainty over the heating is largely because I have yet to decide on UFH vs panel heaters. I might also consider a plinth fan heater in the kitchen, as I'd like a way to rapidly get the house up to temperature following a period of non occupancy. At 100w/m2 I would be looking at about 3kw total for UFH, but for panel and plinth heaters it might be more than this.

 

Does the MVHR need a circuit? Seems like overkill for something with less power than a single GLS bulb!

Does the size of the kitchen appliances circuit look right, or is it a bit big?

 

Cheers