consumer unit upgrade

[brightlight]

I am pricing up a garage installation and the house cu has a split load with one rcd side and the other been a main. Would this need to be upgraded to duel rcd under 17 th regulations if i was only intending to come off spare way on rcd side to metal clad db using 4mm 3core swa? thank you for your help.

 

[roukel01]

no, cables concealed in a wall requiring rcd protection is a new 17th edition requirement, this does not mean that installations designed and constructed to 16th edition and beyond are unsafe... only your work must comply to new 17th regs, not the rest of the installation.

 

[Yooj]

As roukel01 said, it's fine...but make sure you take the distribution circuit from the RCD side, remember to price an upgrade to main-bonding (if required). Bear in mind that if you are coming off of the RCD side, then there is no neeed to have a separate RCD/RCBO in the garage CCU, as you are already covered by the main CCU RCD, and you would have issues with discrimination if you were to add an RCD device in the garage CCU...Therefore, by not adding an RCD, it means the cost of the job is less.

Alternatively, add an RCBO in the non-protected side for the garage circuit, and then the rest is the same as above.

Yooj

 

[brightlight]

Cheers for your help. just a reply about not fitting to rcd side at house cu . would it be still possable to use rcd side at house but not connect at cu but use earth spike with 10mm earth to earth bar and then install rcd to protect garage?

 

[Mr Mark Sparks]

Cheers for your help. just a reply about not fitting to rcd side at house cu . would it be still possable to use rcd side at house but not connect at cu but use earth spike with 10mm earth to earth bar and then install rcd to protect garage?

the rcd in the house will still trip because of the l-n inballance

 

[Yooj]

I am not exactly sure what you are saying...but for an RCD to operate, it is not reliant upon a CPC, therefore, if I am understanding you correctly, you will still have issues with discrimination as the house RCD could still operate due to an earth fault, even if the garage is TT'd, assuming you come off the RCD side of the main CCU.

Edit: Ha, Ha, Mr Mark Sparks beat me to it.

Yooj

 

[Mr Mark Sparks]

sorry yooj

 

[Yooj]

It is prefereable to connect to the RCD side of the main CCU as I am assuming that you are going to be running the distribution circuit within the fabric of tyhe building, and that you are not going to encase it in steel conduit/trunking...therefore to comply with 17th, the distribution circuit will need to be RCD protected anyway. This makes the garage CCU cheaper anyway as you do not need an RCD...unless you have already purchased it.

Yooj

 

[brightlight]

does it have to be steel conduit can i not use plastic as i have some 20mm plastic conduit spare

 

[Mr Mark Sparks]

you said you were using swa so no need for conduit

 

[brightlight]

i am its just becouse yooj mentioned steel conduit . and i was wantinh to use plastic conduit in the garage to be able to run my cables!!!

 

[Yooj]

Hi Brightlight...Just re-read your post...no need for steel conduit/trunking if you are using swa (good spot Mr Mark Sparks ) as this provides the necessary mechanical protection when running the cable in a concealed fashion, i.e. through the wall.

Your plastic conduit will be fine in the garage.

Given the swa...you can run the distribution circuit from either side of the main CCU, and the only thing to consider, which we mentioned before is discrimination of RCD devices if you ran off of the RCD side of the main CCU and you also had an RCD in the garage CCU.

Yooj

 

[TPES]

If your using SWA to supply the garage CU then you can feed off the Main switch side of the board, Then use an RCD as the incomer on the garage CU. The SWA does not need RCD protection.

 

[Had8Lives]

Think the original question may have been misunderstood. If you running SWA from the Main consumer unit you don't need to RCD protect it at the house end as the cable has an earth metallic sheath. You can supply the SWA from an unprotected way in the Main Consumer unit and then have an RCD in the garage. As for the earth spike it depends on the type of earthing on the main consumer unit. If it's TNCS you're not allowed to export the earth, so you will need a spike (TT system) at the garage end and earth the sheath of the SWA at the house end but not the Garage end. That way if the cable is damaged the breaker will trip in the main consumer unit.

 

[Guest123]

If it's TNCS you're not allowed to export the earth

Hi.

A PME system can be exported provided that the either of the following 2 conditions are met

1. There are no extraneous conductive parts within the outbuilding i.e steel frame, water service, gas service etc.

2. If there are conductive parts, then the equipotential zone needs to be extended to the outbuilding via main equipotential bonding conductors sized accordingly i.e a minimum of 10mm2 for each service back to the MET within the house, unless the sub-main is greater than 10mm2 itself.


Personally if there are conductive parts within the outbuilding then I always TT regardless of sub-main size.

I know not really relevant on a small sub-main but you can do it.

Hope this helps.