Power to Garage and two Sheds Using Old Consumer Unit


Postby dents12 » Mon Jan 02, 2017 3:08 pm

Good afternoon.
I will be getting some quotes for some electrical work soon and your advice and views on the best installation would be appreciated.

I have an old (must be 30 yrs old ) consumer unit in the house with 6 fuses and also switch box 100amp ,,this is for the cooker and hob,which comes from a henly block . There is also an switch box that feeds the garage .maybe there called isolaters.
The garage has also old 3 fuses in the cu and says not to exceed 60 amps with just socket for main and lights

Now that’s my current set up . so I need new consumer units

I want more sockets in my garage 5 probably and 2 light circuits . lights for in and the other for driveway and some garden lighting.(not low voltage)

Now I also need power eventually to get two large sheds I plan on having which will need sockets and also lights .
My question is how is this best accomplished do you think ? to give me an insight before I get the quotes.

as i thought it would be easist for cables to go to sheds from the garage
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Postby ericmark » Mon Jan 02, 2017 11:56 pm

You state "Not low voltage" do you realise that low voltage AC is 50 ~ 1000 volts and below 50 volts is called extra low voltage, and 63 - 0 - 63 or 55 - 0 - 55 is called reduced low voltage?

So if you have terms correct I am thinking your going to use 12 volt lighting? Daft as it seems Part P still applies to extra low voltage.

So let us look at the main problem. Today we need metal consumer units and RCD protection, so if the main consumer unit is changed in the house then the supplies from out buildings can either have RCBO's in the house, or fit RCD's in each outbuilding. The RCBO option is likely the cheaper, as you can take say a 20A supply to each outbuilding and use a switched FCU for the light switch so the out building does not require a consumer unit.

However having the supply to out building not protected with a RCD in the house but having a RCD in the out building may be better than having to go inside the house to reset. However one would hope you don't need to reset very often.

The RCBO in house does mean the cable to outbuilding is protected so that is the way I would go. The make of consumer unit is limited if you want RCBO's which have double pole switching. You can get RCBO's with double pole switching which are still only one module wide, the neutral current is not monitored by the device but it still switches it with the line, this means a fault in the out building will not affect anything in the house.

Since it is normal to use 2.5mm cable for sockets if using a radial then 25A is limit and if using a ring final then 32A is the limit. If you daisy chain the outbuildings then either all need to be rings or all radials not all consumer units have the option of 25A RCBO or MCB so likely jumps 20A to 32A.

So step one is work out load, you have lets say 4 stages.
13A max you can use fuse connection units (FCU) for supply, not need for any fuse in out building thinner cable and you could even use a RCD FCU and power out buildings before you change house consumer unit.
20A you will need something to reduce max amps for lights, a switched FCU will do, you can have sockets on a radial.
32A now sockets need to be on a ring final.
Over 32A need consumer units in out building.

Remember house supply is 60, 80 or 100 amp, so having a large supply to garage could mean you blow the main fuse, if some one uses the shower in the house.

My garage is integral my shed is fed from a 13A supply, I am unlikely to ever exceed 13A.

Cable size depends on distance as well as current, fridge or freezer needs a supply which does not have a large volt drop, although less than 100W run they use maybe 2000W on start, unless inverter type, volt drop can cause overload to fail. So do say if freezer is to be used.

I would likely daisy chain out buildings as unlikely to use all at the same time. But one has to work out volt drop and routes.
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Postby collectors » Tue Jan 03, 2017 7:51 am

A little bit over kill, but if you have the room i would put two split load boards in with the amount of outside stuff you are fitting. If not a split load board with 2 rcds would be fine.
I am not sure if the rules have changed,? but i was hearing that only metal board will be the only ones you can use in the future.
But at the moment there is a great deal on here for split load boards at £30 each.

[url]http://www.seldirect.co.uk/bg-cudp16610-10-way-dual-63a-rcd-17th-edition-consumer-unit-10-mcb-s-100a-m-s.html#.WGtWdFwzzEY
[/url]
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Postby ericmark » Tue Jan 03, 2017 10:31 am

421.1.201 Within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS EN 61439-3 and shall:

(i) have their enclosure manufactured from non-combustible material, or

(ii) be enclosed in a cabinet or enclosure constructed of non-combustible material and complying with Regulation 132.12.

NOTE 1: Ferrous metal, e.g. steel, is deemed to be an example of a non-combustible material.

NOTE 2: The implementation date for this regulation is the 1st January 2016, but does not preclude compliance with the regulation prior to that date.

The consumer unit can still be made of plastic but enclosed in a metal box.
[img]http://electrical.theiet.org/wiring-matters/55/-images/consumer-units-fig1.jpg[/img]

Because the consumer unit is in the main more expensive now, using a high integrity consumer unit allows a three way split, two ways have RCD's the third way uses RCBO's which is a RCD and MCB combined. [img]https://www.electricalcounter.co.uk/custom/upload/images/products/2/270x270/SCREWFIX_CUDP16616.jpg[/img] I hope the pictures work, it's a pain not being able to see the post when you post, one can't correct errors.

If the picture has worked you will see a link on the neutral bar which means you can have three neutral bars, two for the RCD's and one for the RCBO's feeding items like out buildings from a RCBO means if there is a fault only the out building is effected, same applies to sensitive supplies like freezer having a dedicated RCBO for freezer means you will not lose it should something go faulty on the general ring final.

On the pre-view seems pictures don't work, but link is shown.
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Postby dents12 » Tue Jan 03, 2017 10:29 pm

[quote="collectors"]A little bit over kill, but if you have the room i would put two split load boards in with the amount of outside stuff you are fitting. /quote]

So i could have one for my house and the other one in my Detached garage .that could feed the sheds i plan to have built later ??

That would be ideal if i could use the existing cable that supply's the small cu in the garage at the moment .as i would not have to dig up my patio .Even if the cable needed replacing ,its only one route for me to dig up.

Im sure the electrician will know that the box will have to be metal (if he doesnt i will tell him :-) and the extra cost for for 2 large units does not concern me as it would be more practical than digging my patio up in multiple routes. .
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Postby ericmark » Wed Jan 04, 2017 3:06 pm

If fed from a MCB or RCBO in house consumer unit as long as they are selected to match the existing cable, then yes you can do it that way.

If fed from a Henley block before the consumer unit then the cable must match the supply fuse so likely 16mm or 25mm so bit on the expensive side.
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Postby dents12 » Thu Jan 05, 2017 7:05 pm

ericmark wrote:If fed from a MCB or RCBO in house consumer unit as long as they are selected to match the existing cable, then yes you can do it that way.

If fed from a Henley block before the consumer unit then the cable must match the supply fuse so likely 16mm or 25mm so bit on the expensive side.


Its an old cartride fusebox in the house at the moment ,im pretty sure the garage must be fed from one of the fuses as i cant see any off the henley block to the garage ..

So when he fits the new consumer box in the house all he has to do is connect the garage Cu to same size mcb as the old house Cu i presume?
and that will power the,, say 10 way dual rcd in the garage .

If thats the case i just need him to fit two new 10 way cunsumer units .

Am i correct?
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Postby ericmark » Thu Jan 05, 2017 10:22 pm

It would seem the likely answer is yes. What you have to consider is a house with no RCD protection over the years may have developed many faults in both fixed wiring and appliances. Personally I feel two RCD's are not enough, I would also use some RCBO's.
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