Garage CU

[Robo]

Recently did a house rewire and am about to start the garage next to it. I have a 10mm armour feed from a 40a RCBO in the house. The garage is a double with a room upstairs and has an outbuilding attached. So im gonna have 2 rings, 2 lights, elec door, compressor. Am i ok to get a dual RCD board for the garage.??I dont see why this would b a problem but a small gagare cu simply wont do the job.Cheers

 

[sparks1234]

You are already covered RCD wise by the RCBO in the house

 

[electricAl]

No distrimination beween devices...

Is the garage seperate, or attached. Earthing arrangement details?

How`s the Part P registration going BTW ?

 

[The Truth]

yes use your twin RCD board in the garage if the armoured cable goes all the way back to your main distribution board then simply swap the 40amp RCBO for an MCB. then you have local RCD protection where it should be...in the garage.

if its a PVC T/E cable concealed from the DB to the SWA connection then your stuffed as you need the 30mA protection on the T/E cable. in this case just use a normal main switch board in the garage and live with the inconvenience of the RCBO tripping in the house if a problem arrises.

could talk all day about earth rods, garages earthing arrangements yawn but just get it checked out by a real sparky before you get in too deep.

obviously part p blah blah blah

 

[Robo]

Thanks for the advise so far. The house is tnc-s. And the garage is 10m away from the house. I havent put the 10mm cable in yet, was gonna mount to ip rated adaptable box at house end and keep inner sheaf on cable and put it straight into into the back of the board. then run cable under ground through garage wall and make other end off into DB. I thoguth 40amp RCBO would protect cable incase it ever got damaged. And im unsure of the board to use. Iv asked a few blokes i work with and some say RCBO is fine for cable and Then get a DB with mainswitch only and house rcbo will protect circuits. And others have said RCBO to protect cable. Then use split board in garage so i have local protection and can split circuits.

Iv had my spark mate come and test house and am notifying building control as i really can not warrant the 500 pound part p expense.

Any more help on the right board and protection of cable (RCBO/MCB> would be much appreciated. I have a split board at the min but can change it. Customer got me and insulated board. I think i should change this to a metal back at least so its better to gland cable in.??

Really good site. Cheers robo

 

[Ridgey88]

Hi Robo,

What you can do, as there are as many different ways to do it as you like, none of them are the wrong way just different, is to;

fit a 40a rcbo selective (time delay) in the house, run the swa out to the garage cu, and then have a split load board or rcbos or just a 30ma rcd as the main switch, however you like.

personally i would run it of a 40a rcbo and then have 6module cu in the garage, with main switch and 4 circuits, mcbs.

as for whether to fit a metal clad cu or plastic all depends on the risk of mechanical damage?? if you have a plastic cu then just place it out of reach, i.e above 2.5 meters and that would be fine.

are you extending the house earth or making it a TT

regards

ridgey

 

[Robo]

Thanks for help ridgey. Time delay rcbo? Never herd of them. Its a c type and not a b. You said that u would have a 6way borad with main sw and 4 mcbs. What about local protection, or is it ok to just have rcbo in house. The house is tncs and was just gonna extend this. 10mm cable and earth armouring. At present i have a twin hager rcd board with 2x63a rcds. i asked for metal back as its easier to put conduits into. Got home and the divs had given me a fully insulated board so may have to make do.

 

[Ridgey88]

Hi robo, no problem.

Yes I would just have a small 6 module board with mcbs, and an rcbo back in the house. This is acceptable, NICEIC guy said so himself.

Yes time delayed or selective rcbo this would provide discrimination for a CU in the garage with additional rcds.

Extending the house earth with 10mm is fine, if you earth the armouring then there is no need to provide rcd protection for the submain unless fed part in t&e

cheers

Ridgey

 

[Robo]

Thanks once again. Iv not come across these RCBO (time delay/selective devices). I guess these are different to a normal rcbo?? Sorry to b a pain in the ---. Reason i ask is theres already a normal c type rcbo fitted. Sounds hefty, i have a 40a mcb which i could swap if the present rcbo is no good.

I can not seem to find the notes i have on discrimination. Could any1 explain this so i can get a better grasp of it.

Robo

 

[Mac]

Thanks once again. Iv not come across these RCBO (time delay/selective devices). I guess these are different to a normal rcbo?? Sorry to b a pain in the ---. Reason i ask is theres already a normal c type rcbo fitted. Sounds hefty, i have a 40a mcb which i could swap if the present rcbo is no good.

I can not seem to find the notes i have on discrimination. Could any1 explain this so i can get a better grasp of it.

Robo

http://www.dormansmithswitchgear.co...info/technical_Data/Discrimination_Values.pdf

 

[Ridgey88]

Generally! No one fits type B rcbo's as the wholesalers dont stock them. so type C is the norm!

As for time delay/selective they will trip on a earth fault between 130 and 500 miliseconds (i think) or between 50% + the rated tripping time and 100% + the rated tripping time. so for example, if you had a selective type C rcbo at the house CU and had two standard 30ma rcds or type C rcbo's in the garage CU, then if an earth fault was to occur then the garage protecive devices would trip before the house would because of the time delay.

Hope that explains it.

Ridgey

 

[Robo]

I think i follow what your talking about mate. A standard 30mA rcd should trip in under 200 ms and your saying that a selective or time delay would trip between 130 and 500ms. This meaning the garage rcd is more likely to trip first than the House RCBO. This is therefor giving discriminitation between the two devices.

I assume u just ask foir a time delay rcbo when going to whole saler?? i dont seem to have much look with whole salers. always bloody give the wrong items. i Think u said the swa didnt even need this rcbo so i may swap it for 40a Mcb?

Thanks for your help ridgey

 

[The Truth]

Robo,

your nearly there! but...

'time delayed' RCBO's don't exist..... time delayed RCD's do

if you really really want rcd protection on that swa cable ( which is a little overkill ) then you need a
100mA / 63amp time delayed RCD mounted in a separate enclosure adjacent to the main consumer unit. Simply feed this RCD from a 40amp mcb in the consumer unit. At the garage end your 30mA RCD board will do the rest.

to keep things simple... you dont need an RCD to protect that SWA cable so just use a bog standard 40amp MCB in the consumer unit to feed the SWA. At the garage end you have your 30mA RCD board to do the rest.

I would only really use the time delayed option mentioned above if your earthing system was a TT earthrod system where you need rcd's for everything.

 

[Robo]

Thanks THE TRUTH

Yup thats plain and simple.Well atleast i know understand discrimination and these time delayed RCDs.

Will swap the rcbo for an mcb and keep the split board in the garage. Just incase one rcd goes faulty they dont loose all lights etc.

Cheers Robo

 

[The Truth]

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