split rcd board

[sblakey1]

just a quick one,

my cu is split with rcd protection which is good,

however i want to un wire a circuit from the RCD protection and place it on the unprotected side as it powers my garage and within my garage i already have a 2 way rcd cu fitted.

is it simply a case of removing the neutral and moving it to other side ??

 

[starspark]

if you take it off the rcd side then the supply cable from the main board to the rcd board outside is not protected what type of cable is used for this run?and how is it protected because it most probably requires rcd protection.

 

[sblakey1]

hi,

its run in 6mm T&E clipped underneath the upper level flooring. its then passes into my garage that is adjoined to the house.

its currently sitting on a 32a mcb that was left from the builders as the garage used to be a sales room so a ring was fitted.

ive now removed the socket that it terminated on and installed a 2way CU with rcd, that is 6a mcb lighting and 20a mcb for a small radial circuit.

 

[ericmark]

hi,

its run in 6mm T&E clipped underneath the upper level flooring. its then passes into my garage that is adjoined to the house.

If that cable is within 50mm of floor base or ceiling the it will need RCD protection.

its currently sitting on a 32a mcb that was left from the builders as the garage used to be a sales room so a ring was fitted.

ive now removed the socket that it terminated on and installed a 2way CU with rcd, that is 6a mcb lighting and 20a mcb for a small radial circuit.

With RCD protection the earth loop impedance can be quite high but if removed from RCD protection then the ELI must be within the permitted parameters for the MCB used. You say 32A but not if B, C, or D type the latter would require an ELI of 0.35 ohm which is same as Ze on most houses so could not be used without RCD protection. What is the Zs at the garage and what size MCB are you using.

I would not be surprised if you don't understand. The meters used to measure Z are expensive and not normally found in DIY hands and I would think it may be cheaper to get an electrician to do work than buy meter. Also you may be better using a RCBO than trying to use MCB.

 

[dmulholland]

Use an rcbo then get rid of the rcd in the garage as not good practice to have two rcbo/rcd inline.

I could tell you where to buy but I dont know how to do a link

 

[AndyPRK]

what expensive kit do you use to measure Z ?

a milli ohm meter ?

 

[sblakey1]

ok the supply cable is on 6mm T&E its fed from my CU (approx 4meters in length) in the house on a type b 32a MCB. this then follows underneath the flooring which at the points i have looked at is at the required depth / height from ceiling, the builders also have went the full hog and installed metal plates to stop screwing in to the joist where they pass through

it terminates in my garage where i have connected it to a 4way db with 63a 30ma isolator/rcd.

circuit 1 = 6a Type B MCB (lighting)
circuit 2 = 20a type B MCB (Radial power Circuit with 4 points)

readings from the garage are

R1&R2 = 0.09 Ohms (lighting) 1.5mm L/N/CPC singles in conduit
R1&R2 = 0.10 Ohms (sockets) 2.5mm L/N/CPC singles in conduit

Ze at garage DB is 0.33

Loop/ Zs = 0.42 ohms (lighting)
Loop/ Zs = 0.39 ohms (sockets)

 

[Spark123]

what expensive kit do you use to measure Z ?

a milli ohm meter ?

An earth fault loop impedance tester usually.

 

[flameport]

a milli ohm meter ?

Don't even think about connecting one of those to the supply.
It will be transformed into a ball of flames.

(Zs/Ze is measured with the power switched on).

 

[sparkyspike]

(Zs/Ze is measured with the power switched on).

Ze is. Zs is calculated by measuring R1+R2 with the power switched off!

Anyway, back to the question, I would keep the circuit breaker on the RCD side, and replace your RCD incomer in the garage with a normal isolator. Unless you're certain that your cables do not require RCD or mechanical protection, in which case you can move the circuit to the unprotected side. I would guess that this isn't the case.

 

[sblakey1]

thanks for the reply..

personally im happy with the supply cable been on the unprotected side as its concealed away and not accessible plus im not intending to drill holes or rip flooring up any time soon (my G/F would kill me been a new house and all)

my only concern is that i didnt want my garage to trip off the supply to my sockets in the house.. i would like them to be individually separated. hence the db unit in the garage. it allows me to keep every thing separate. and allow for local isolation. plus the lighting circuit feeds an outside Floodlight and in the event of failure i wont lose my tv!!

an RCBO would yes be handy but when i already got the parts fitted to the boards already in terms of RCD / MCBS i dont want to have to go down that route of purchasing just for the sake of been easier.

 

[333rocky333]

is it simply a case of removing the neutral and moving it to other side ??

The live and the mcb would need moving also.
Is there a spare way.

 

[sblakey1]

yes got a spare way.

 

[flameport]

Zs is calculated by measuring R1+R2 with the power switched off!

It can be calculated or measured directly.

 

[AndyPRK]

could someone point me in the right direction on how to do this please.
Thanks

Sorry OP.