Power Circuits in Service Cupboard.

[Triassic]

I’m trying to list my various socket, outlet and lighting requirements for my new build.

 

The one area I’m unsure if is my services room. I’ve got an ASHP, Sunamp unit(s), MVHR system, UFH manifold. What circuits do I need and what size, also socket outlets. Plus is there anything else I might want to include in the wiring scheme?

[ProDave]

ASHP, MVHR and Sun Amp definitely on their own circuits.

 

My UFH manifolds are run from the "heating controls" circuit. 6A

 

Sockets in the plant room are one ring final feeding utility, garage and plant room.

[Jeremy Harris]

As @ProDave said.  I have three radials for these, a 20 A one that supplies power to the Sunamp, a 16 A one that supplies power to the ASHP and a 6A one that supplies power to the MVHR. 

 

The Sunamp needs two supplies split off from this radial; one always on supply that is low current (it's fused at 3 A inside the control unit) and a supply for the 2.8 kW/3 kW rated heater (which is the same as an immersion heater, so typically around 12 to 14 A).  I have a 20 DP isolator in the feed to the Sunamp, which then supplies power to the PV diverter (with an over-ride switch and timer) and also supplies power to an FCU with a 5 A fuse that supplies the always on power to the Sunamp.  The 5 A fuse in the FCU is only there to protect the low power cable supplying the Sunamp control box, and the 20 A DP isolator allows all the power to the Sunamp to be isolated easily.

 

Because my ASHP only draws a maximum of 2.32 kW (around 10 A maximum) and as the UFH pump and control circuitry only draw a tiny amount of current (less than 1 A) I run both from the same radial, with a similar arrangement to the Sunamp.  I have a 20 A DP isolator that allows power to the whole heating/cooling system to be switched off locally, the ASHP is fed directly from that, the receivers for the thermostats are fed from an FCU with a 3 A fuse and the control box, which also supplies the UFH pump and valves, is supplied by another FCU with a 3 A fuse.  Again the 3 A fuses are only there to protect the cables supplying the equipment.

[epsilonGreedy]

An electric patio heater as seen in french cafe outdoor terraces is on my list of special extras.

 

Someone else on this forum mentioned an electric car charging point in the garage. Who knows how many amps a future battery technology will be capable of absorbing.

[Jeremy Harris]

Single phase AC  home car charge points are limited to 7 kW by design, but you can go up to 21 kW with a 3 phase AC charge point.  Higher power DC charge points require DNO approval, as well as a 3 phase supply, I believe. 

 

The limitation is primarily the local distribution network, which will be sized to provide an average of around 2 to 3 kVA per phase per dwelling at the substation.  Provided that a car charge point isn't charging 24/7 then diversity should take care of the potential overload on the local distribution network, although the DNOs are concerned and are looking at how they may fund local network infrastructure improvements, to allow a higher average power per dwelling, if electric cars that require a high power domestic charge point become widespread.

 

As someone who's owned a PHEV for nearly 5 years, I'm not convinced there is any requirement for a high power domestic charge point, at least nothing higher than the 21 kW that's available from a  3 phase domestic supply.  Most people will have their car sat still for hours, either at home or at work, accepting that some people drive all day as a part of their job.  A typical EV uses around 200 to 300 Wh/mile, and round-trip charge efficiency is pretty good, probably around 85 to 90%.  With a car sat parked for, say, 10 hours overnight, a 7 kW single phase AC charge point would be able to deliver around 70 kWh, which would equate to around 60 kWh or more of usable energy, or something like 200 to 300 miles of range for the following day. 

 

That's almost certainly more than enough for most people who commute by car every day, and if they also have the opportunity to top-up charge at work then their daily range could easily be a lot greater.  I've found that I only really need around 20 miles of electric range for well over 90% of my normal driving.  I typically drive around 32 miles a day on weekdays (16 miles each way) and can charge at both ends of the journey.  At weekends I do a regular shopping trip of around 12 miles in total, and don't need to charge other than at home.  It's the small number of longer trips away that need more range, but there are now a lot of places to charge, so, for example, we can go away on holiday and almost always charge wherever we are staying (I've yet to find any hotel or self-catering place where I've not been able to charge).

[ProDave]

I got called to our old house, still a B&B. They had a foreign guest in an EV and wanted to plug in his charger.  It claimed to be rated at 7KW but had a moulded on Schuko plug on it. But given a Schuko plug is rated at 16A, I am intrigued to know how it can deliver 7WK

 

I cobbled together an adaptor and it charged his car overnight from a 13A plug without melting the plug or blowing it's fuse.

[Jeremy Harris]

Just now, ProDave said:

I got called to our old house, still a B&B. They had a foreign guest in an EV and wanted to plug in his charger.  It claimed to be rated at 7KW put had a moulded on Schuko plug on it. But given a Schuko plug is rated at 16A, I am intrigued to know how it can deliver 7WK

 

I cobbled together an adaptor and it charged his car overnight from a 13A plug without melting the plug or blowing it's fuse.

 

 

That's the "carry with the car" charger, commonly called the "granny lead".  The UK ones are only rated at 10 A, as they run on a 13 A plug, which won't really supply 13 A for long periods of time (I believe the 16 A Schuko is the same, in not being rated for 16 A continuous use).  I doubt that the charger he had was rated at more than 3 kW, as that seems to be about the maximum for all the European single phase granny leads I've heard of, even the Tesla one that is supplied in Europe (with a 16 A Schuko) is only rated at 13 A, 3 kW. 

 

The granny lead that came with my car is rated at 2.3 kW at 230 VAC, but that's more than enough to fully charge my PHEV in a  few hours. 

[Jeremy Harris]

7 minutes ago, epsilonGreedy said:

 

Would some outdoor garden/boarder illumination lights (presumably 12v LED) warrant their own circuit hanging off a dedicated RCD?

 

I'd go for an all-RCBO CU and run the outside circuit on a dedicated circuit.  I can't get my head around the logic in having a standard 17th Ed CU, with just two RCDs.  The additional cost of an all RCBO CU over a standard 17th Ed one is pretty small when compared with the whole cost of the electrical installation.  I fitted a 12 way CU for our 2 bedroom house, plus another 4 way all RCBO CU for the external services (garage, treatment plant, car charge point and water pump and treatment system).  In the overall scheme of things it may have cost me around £100 more than a standard 17th Ed CU for the whole lot, but it's a great deal more convenient to have every circuit on a dedicated RCBO.

[oranjeboom]

Not meaning to hijack this thread, but I',m looking to future proof as much as I can here and currently busy in the 'plant room' which would  potentially also be the route for a future cable to outside charging point for a PHEV/EV. It's a cavity filled bungalow wall which will have EWI going on next year at some point, so I was thinking of just chasing a route up the exterior wall, up into the eaves/soffit and fixing some conduit into the channel. This will then be covered by the EWI and hopefully then just means pushing in the required cabling at some point in the future for my Tesla which by then will be half the price that they are now....

 

If I go with the above, what size conduit should i fit? I was thinking worst case with cabling 6-10mm

[Jeremy Harris]

Cable size depends on the length more than anything else, as with a single phase domestic supply you're not going to have a charge point that's larger than 7 kW.  The maximum current would be around 30 A, which is OK on 4mm² up to a distance of around 35 metres.  I'd be inclined to run SWA in the wall, rather than fit conduit, as if there are any bends it will be a pig to pull a thick cable through once the conduit is behind EWI,  You can always just leave excess SWA coiled up, with the outside end sealed up, until such time as you're ready to fit a charge point. 

 

A 7 kW charge point will usually have a 40 A  double pole  protected circuit, so worth looking at whether there's space in your consumer unit for a DP RCBO or whether you'll need an additional small consumer unit to supply the charge point.

 

The Tesla home fast charger needs a 3 phase supply, so would require a new supply to the premises.  A 7 kW single phase AC charge point will take around 9 hours to charge a base Model 3 from fully discharged.

[Triassic]

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Edited October 3, 2018 by Triassic

[Triassic]

1 hour ago, oranjeboom said:

hopefully then just means pushing in the required cabling at some point in the future for my Tesla which by then will be half the price that they are now....

1

I was also thinking about buying a Tesla at the end of the build using the money Id saved. Looks like I might be just about able to buy a second-hand electric bike !!

[Temp]

On ‎29‎/‎09‎/‎2018 at 15:45, Triassic said:

I’m trying to list my various socket, outlet and lighting requirements for my new build.

 

The one area I’m unsure if is my services room. I’ve got an ASHP, Sunamp unit(s), MVHR system, UFH manifold. What circuits do I need and what size, also socket outlets. Plus is there anything else I might want to include in the wiring scheme?

 

I'm not 100% up on the latest rules but I would go for a CU that has separate RCBO in each power slot/circuit. Indoor lighting circuits can share an RCD if you want to save money.

 

External circuits such as feeds to a freestanding garage/shed typically use an MCB and SWA cable to the garage/shed. In there they fit a "garage CU" with RCD. To some extents it depends if it's an integral or separate garage and how the earthing is done.

 

Think about how you group rooms together on one circuit. The most likely rooms to cause trips are the Kitchen (eg Toaster) and Utility room (washing machine/dryer) and outside circuits (lighting, power to shed etc). I would arrange these to be on separate circuits to your TV/PVR or computers. This way if the toaster or heating element in the oven or dishwasher fails it doesn't trip out your PC or TV/Recorder. Outside lighting can also be prone to failure/water ingress problems.

 

So I would have circuits and radials something like..

 

Sockets (Kitchen & Utility) 

Sockets (Living room, home office, dining room) 

Sockets (Bedrooms) 

Sockets (Bedrooms if needed) 

Lighting (Up)

Lighting (Down) 

Outside lights (eg lights on PIR sensors)

ASHP, UFH, Stats

SUNAMP

MVHR

Interlinked Smoke Alarms

Electric shower?

Outside socket/car charger?

Garage/shed ?

 

MVHR don't draw much power so it's possible to have a separate circuit or run it from a FSU/Spur off one of the Socket rings.

 

 

Edited October 3, 2018 by Temp

[oranjeboom]

6 hours ago, JSHarris said:

Cable size depends on the length more than anything else, as with a single phase domestic supply you're not going to have a charge point that's larger than 7 kW.  The maximum current would be around 30 A, which is OK on 4mm² up to a distance of around 35 metres.  I'd be inclined to run SWA in the wall, rather than fit conduit, as if there are any bends it will be a pig to pull a thick cable through once the conduit is behind EWI,  You can always just leave excess SWA coiled up, with the outside end sealed up, until such time as you're ready to fit a charge point. 

 

It's only going to be around 10m in length and not too many changes in direction, but a pre-fiitted SWA would probably be easier than forcing a cable down a bit of conduit.

 

https://www.tlc-direct.co.uk/Products/SW4slash2.html ? 49 A 4mm....

 

6 hours ago, JSHarris said:

 

The Tesla home fast charger needs a 3 phase supply, so would require a new supply to the premises.  A 7 kW single phase AC charge point will take around 9 hours to charge a base Model 3 from fully discharged.

 

Oh well, no Tesla for me then, maybe just a Renault Zoe. I do have a substation on the corner of my plot however - ideal for charging whatever I need, theoretically.

 

 

Thanks @Temp for the suggestions. I've left most of the radial circuits for the electrician so hoping he's thought about stuff like that. Although I've already had to replace the hob cabling to 6mm.

[Jeremy Harris]

22 minutes ago, oranjeboom said:

 

It's only going to be around 10m in length and not too many changes in direction, but a pre-fiitted SWA would probably be easier than forcing a cable down a bit of conduit.

 

https://www.tlc-direct.co.uk/Products/SW4slash2.html ? 49 A 4mm....

 

 

 

The current rating depends on how the cable's installed, and yours will end up being under EWI, so needs to be de-rated. 

 

TLC have a cable size/voltage drop calculator here: https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html that's a good general guide, but there needs to be a de-rating factor applied if the cable is installed in a way other than clipped direct or buried.

[oranjeboom]

Thanks Jeremy. I'll run this all by my electrician to be sure also.

[DaveRodda]

hello... I have a 20 DP isolator in the feed to the Sunamp, which then supplies power to the PV diverter with an over-ride switch and timer and also supplies power to an FCU with a 5 A fuse that supplies the always on power to the Sunamp. 

 

pcb assembly process

Edited November 28, 2018 by DaveRodda