Best way to feed Garage electrics?

[wacman]

Recently had a 17th ed split load CU fitted in house. Garage has its own circuit fed directly from a 20 amp MCB in the house CU, which is rcd protected.

I have a couple of questions:

1, From the 20A in the house to the garage Fuse box is fed via 4ft of 2.5mm Twin & earth...is this cable size acceptable? Garage will have 2 x 80 watt flourescent lamps, and 1 radial circuit with 3 socket outlets. main loads will be freezer, treadmill and occasional Tumble dryer.

2, As its an old style fuse box in the garage, I plan to get this replaced with a 2 way consumer unit, as the house already has an rcd, would it be a good idea that the garage CU didn't have an rcd? I'm thinking nuisance tripping.

 

[SirKit Breaker]

Recently had a 17th ed split load CU fitted in house. Garage has its own circuit fed directly from a 20 amp MCB in the house CU, which is rcd protected.

I have a couple of questions:

1, From the 20A in the house to the garage Fuse box is fed via 4ft of 2.5mm Twin & earth...is this cable size acceptable? Garage will have 2 x 80 watt flourescent lamps, and 1 radial circuit with 3 socket outlets. main loads will be freezer, treadmill and occasional Tumble dryer.

2, As its an old style fuse box in the garage, I plan to get this replaced with a 2 way consumer unit, as the house already has an rcd, would it be a good idea that the garage CU didn't have an rcd? I'm thinking nuisance tripping.

This reply assumes garage is detattched and not integral.

Take you garage feed at house CU to non RCD side of CU. Use SWA cable from house to garage and terminate into garage CU,( it will not require RCd protection if it is installed correctly) ensuring you also terminate the armouring to earth. The cable size will depend on length of run and loading, without seeing job i wont guess. Then wire up garage CU for whatever your heart desires to have in the garage in twin and earth. By doing this you will stop a fault in the garage knocking off circuits in the house.

Cheers.........Howard

 

[sparkylad]

Hi Sir Kit- are you advising the OP not to have any form of RCD protection to the garage ? or am I reading your reply incorrectly ?

 

[wacman]

should add...garage is attached to house, current house Cu is understairs, this then feeds straight through the cavity into the garage fuse box. This run is no more than 4ft of 2.5mm T & E. Also, both sides of the house CU are RCD protected.

 

[sparkylad]

In that case then, there is no need for an RCD fusebox in the attached garage. The 2.5 supply cable would not usually be the preferred size, however your total loading will i suppose be less than this. The only thing to check would be the manufacturers recommendations for minimum size conductors for the main isolator on the new fusebox [ consumer unit].

 

[SirKit Breaker]

Hi Sir Kit- are you advising the OP not to have any form of RCD protection to the garage ? or am I reading your reply incorrectly ?

No mate, I am trying to say that the SWA to the garage CU doesnt require RCD protection, but as you have rightly picked up on, i didnt say that his circuits in the garage do. but as my he has an integral garage my previuos post is pretty much irrelevant.

Cheers..........Howard

Its been a long day, ive had a few and the barbie is on

 

[jeremy]

I would un RCD the feed into the garage (ensure it's protected through the cavity) but then use a RCD main switch or RCBO,s for each circuit garage side. What sort of rating is a tumble drier, and if thats on and the compressor kicks in on the freezer, will the 20A ( type B I presume) be able to handle the current spike?

 

[davelerave]

ya 20amp is small for this

preferable not to rcd the sub-main

no rcd on the freezer if rules allow

 

[wacman]

Right...think the best course of action will be to re-wire up the lights and sockets to old fuse box in garage (they currently have rubber insulation) then get the electrician back to sort out Garage CU and feed from house while i observe. I should add I'm only half qualified for this so hence getting the electrician back for advice on the trickier bits. I have 2330 L3 and 16th ed. My sparky has said he will work with me on this to give me some experience.

 

[wacman]

to RCD ....or not RCD...that is the question...i'm now totally confused? lots of conflicting answers on here. is there a right or wrong way of doing it? ...as in rcd in house....rcd in garage but not in house? or just different sparkies have different preferences?

 

[davelerave]

it's preferable not to rcd sub-mains

no point having 2 30ma's in series -whichever way you go

 

[jeremy]

If your garage equipment affects a house rcd, then anything that trips in the garage or outside( hedgeclippers etc) will mean resetting alarm clocks , lost computer stuff, ie nuisance tripping. On the other hand if you're away and the house appliances trip the rcd, you're freezer is off till you come back. Unlikely I know but has happened often enough. Garage sockets for portable equipment must be rcd protected unless your garage is upstairs and every cable is surface run. If the socket for freezer is clearly labelled as such then no need for RCD. If costs allow I would put it on its own rcbo. Unfrozen frozen food is really annoying.

 

[wacman]

Great stuff lads! really interesting. I really need to get some practical experience with a sparky, only way to learn IMO, very frustrated at the mo, have paper qualifications but can't do jobs. So from what you're saying would this be acceptable.... un - rcd the feed in the house CU then take the feed to the garage from an MCB in house CU, then Have a 4 way unit in garage with RCD protection for lights and sockets, consider having tumble dryer on its own circuit, and freezer on a seperate circuit with rcbo.

 

[davelerave]

no rcd preferably on freezer-if rules allow

slight risk with the rcbo's that a trip goes un-noticed

 

[jeremy]

Good point about the un-noticeable trip. Even if the casing became live (which would involve the earth disappearring from the circuit/appliance, ) probably no chance of person touching it and ex conductive parts in a garage ( no central heating, metal water pipes etc)

 

[wacman]

good stuff...keep it coming. so no rcd or rcbo on freezer. Next question is the size of cable supplying the garage and size of mcb in house CU. Its about 4ft from house Cu to garage CU. cable goes straight through cavity then up garage wall in pvc trunking to CU. Currently its 2.5mm T & E. This ok?

 

[Adam W]

4mm radial for garage from 30 or 32A MCB using house rcd, or separate RCBO on unprotected side
Lighting on fused spur.

... Or would that be over-simplifying things?

 

[jeremy]

Why not chuck in some 6 or 10mm. Upgradeproof and cost difference shouldn't be much. Don't forget through wall protection!! If Through wall protection is conductive should it be earthed? ideas welcomed.

 

[sparkylad]

wacman. the garage is treated as part of the main property if it is as you say attached. Unless you want to make uneccesary work ,then there is no need to change the supply cable.
On the point of RCD protection
1. If you have cables buried in the plaster less than 50mm deep then you will probably need RCD
2. All 13A. sockets in a domestic property require 30-ma RCD [ unless installed and identified as being for the permanent use of a specific piece of equipment.