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Discuss Garage enclosure in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Mewff91

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Hi all,

Rewired my dads garage today for my part p assessment, i bought an enclosure and a 16amp and 6 amp mcbs for the circuits within the garage. The enclosure only had the din rail in. No earth or neutral bars. The garage is fed from a 32amp mcb from the cu in the house by 2.5 mm cable which is rcd protected. The problem i have is that i have no incommer. Ive seen the garage boards you can get with a main rcd as the incommer but my dad wants the rcd in the house so he knows it has triped if it does!

Seems silly but i feel that a 100a incomer would be too high rating wouldnt it?

Ive got an earthing block which i will fit into the cu for the cpcs of the circuits and i will do the same for the neutrals.
 
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Strima

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Arms
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No neutral or earth bars? What make is the enclosure?

As for the 2.5 protected by a 32A??? What type of cable is it?
 
You've been given a 2 module enclosure and not a garage board, this is no good to you, also your 2.5mm cable is under sized, even if swa max is 31 amp is xple (I think)
 
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robsparky1975

  • Thread Starter Thread Starter
  • #4
I would change the breaker for a lower rating,is it swa feeding the garage? ask yourself would you want your assesment job to be one where you have had to put something together? you can buy a 2 way garage board with a main switch and 2 cbs for about £30.
 
Also def have swa unprotected in house cu as assessor will have you do rcd test in garage, wouldn't be good if you kept tripping house rcd during tests, also no discrimination
 

Des 56

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Arms
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As rob as stated,cobbling a board together for an assessment would be not the wisest move
An assessment candidates "show jobs" are mostly done to his best installation skill,an assessor would be unimpressed by a less than top notch effort
Don't undermine your assessment this way
 
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Mewff91

  • Thread Starter Thread Starter
  • #8
Thanks for the feedback guys!
Cable is 2.5 twin earth, and runs through the ceiling joists in the house straight into the garage.

I will also be doing a cu change in the house so will downsive there.

Think ill just get a garage enclosure like you said with the rcd in the garage!

Thanks for the help guys!
 

telectrix

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yep, protect that 2.5mm at 20A, if part of it's buried in a wall < 50mm without earthed metallic conduit protection, then RCBO it. then no need for RCD in garage. don't forget if there are extraneous metal parts in the garage, these will have to be bonded back to the MET. in 10mm if it's a TNC-S installation.
 
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Mewff91

  • Thread Starter Thread Starter
  • #10
Thanks tel! No extraneous metal parts within the garage.
With an rcbo in the house though if have to remove the rcd from the garage board, if i get one because of discrimination?
Just use a main switch then yes?
Sorry guys just want it to be top notch for the assessment
 
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sedgy34

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  • #11
yep, protect that 2.5mm at 20A, if part of it's buried in a wall < 50mm without earthed metallic conduit protection, then RCBO it. then no need for RCD in garage. don't forget if there are extraneous metal parts in the garage, these will have to be bonded back to the MET. in 10mm if it's a TNC-S installation.
Tel there's no pme export here or have I missed something
 

telectrix

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Thanks tel! No extraneous metal parts within the garage.
With an rcbo in the house though if have to remove the rcd from the garage board, if i get one because of discrimination?
Just use a main switch then yes?
Sorry guys just want it to be top notch for the assessment
. yes, you don't want RCDs in series because of discrimination. just use a D/P main switch in the garage. anything from 40A to 100A ( it's just a switch, the current rating is the max. it will stand).

@ sedgy, i assumed it was a TN system, probably PME, OP has not said as yet. but as no ecp's then it 's irrelevant anyway.
 

telectrix

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1 other thing. the cpc in that 2.5mm is only 1.5mm, so measure the PEFC and apply the adiabatic. you still might have to add an additional cpc.
 
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Mewff91

  • Thread Starter Thread Starter
  • #14
Cheers tel!
Sorry thought i put it in its tncs guys.
 
Due to the twin and earth only having 1.5mm cpc wouldn't it be easier for him to rid the garage and tt it, rcd as main switch obviously?
 
Yeah was thinking the distribution circuit would be best unprotected but it's twin and earth, not always possible, still tt sounds good though?
 

Strima

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Search for a thread on here about exporting PME, very handy to know.
 
Reason for me suggesting tt wasn't really to do with exposed conductive parts etc, more to do with a earth cable needing to be run aside the supply twin and earth, if bigger cpc neededm thought it'd look untidy, think op said it'd be clipped to fench. Now what about damage from uv rays? Sometimes you can ind a reg that'd stop you doing anything.
 
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Octopus

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  • #21
The 2.5mm going to the garage - is it off a FCU off the ring? Does it go all the way back to the cu?

Deffo can't use the enclosure you have.
 

Strima

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Arms
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I would look at changing the supply cable for the garage, do some cable calculations to see what you need in there taking into account diversity etc. When you do the EIC for it attach a copy of your calcs so when the assessor comes round you can show him what you have done and why etc, even reference BS71671, OSG etc. This will show him/her you have used the books and designed you installation to the regulations, may sound a little excessive but if you prepare well for this you should have no problems getting a tick in the box.
 
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Guest55

  • Thread Starter Thread Starter
  • #24
Due to the twin and earth only having 1.5mm cpc wouldn't it be easier for him to rid the garage and tt it, rcd as main switch obviously?
No.
even with only a 1.5 earth , he will still get a much lower Zs from t&e connected to a TN supply than from an earth rod.
And with no extraneous pipework to bond , pointless.
 
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Mewff91

  • Thread Starter Thread Starter
  • #25
Hi guys thanks for all the replies!
The garage supply is a seperate circuit with its own mcb. Currently at 32amps, I will be downgrading this to a 20amp when I change the main cu.
I realise that a lot of you have picked up about the earth only being 1.5mm.

There isn't a massive amount of load in the garage it's only supply a pendant lamp and a tumble dryer.

Also this Is off topic now but do the dno charge for fitting an isolator at the main supply? As its only the fuse and want to get it upgraded!

Thanks in advance
 
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sedgy34

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  • #26
You will have to speak to them they may know what type of fuse is there or you could do it yourself if the seals swim off for the day
 

Jimmy Boy

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Arms
Is it only me who is worried here?
I do tend to speed read sometimes and I do sometimes miss things, but for a kick off the 2.5 was initially protected by 32A breaker, which suggests that the original install was perhaps not designed to meet the regs, other than the OP telling us the cable is run through joists to the house I have seen little by way of design and calculation, VD, mechanical protection,UV protection ( How is this 2.5 cable protected generally ), all of these ring alarm bells, but I wish him luck, but feel he is a little under prepared TBH.

J
 
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Mewff91

  • Thread Starter Thread Starter
  • #31
I'm just coming to this installation, the board in the garage needed changing so I have done that, the cable supplying this board is from the main cu in the house.
In terms of mechanical protection, I assume you mean protection from nails screws etc. I'm only going to be able to check this if I pull down all the plasterboard ceiling.
Where the cable enters the garage from the house it runs in conduit into the new board in the garage.
The cable does not run outside its all run inside the house in ceiling void. Cable is rcd protected at the main cu in the house.
 

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