Discuss Garage supply CPC in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

yes i agree re supplying one circuit, but the highest pefc will be at the second db. so if the cpc for the supply cable is sized according to the fault current hear i cant see a problem re the final circuits within the garage .
 
I don't think it ever should, but is sometimes misused. If you needed this situation (to accomodate bonding etc at the supplied location) then you should install an EMT and supply a separate earthing conductor from that EMT back to the MET.

Focus on the beer mate! I cried off going coz it was pi**ing down and it's over a mile.

do you mean install a seperate main bonding conductor ?? re (tncs)
 
do you mean install a seperate main bonding conductor ?? re (tncs)
Only if there is bonding to do (ie extraneous conductive parts in the outbuilding) AND you are exporting the earth.

For this particular case, (attached?) garage, in practice then you'd just bond back to the MET IF you had any bonding to do.

What you have done is fine.
 
yes i agree re supplying one circuit, but the highest pefc will be at the second db. so if the cpc for the supply cable is sized according to the fault current hear i cant see a problem re the final circuits within the garage .
In reply you are cascading mcb's which due to the reduced earth size allowed for standard circuits this then sets up a siuation where it has a knock on effect when the circuit is reduced again, in the scope of things this would give premature limits to circuit sizes especially for circuits with mcb ratings approaching that of the D.B. supply mcb.. e.g. 40amp (b) D.B. supply down to a 32amp ring main supply off sub board, tabled guides for circuit sizes would be contravened in some situations leaving a non compliant zs value hence you should apply table 54.7 unless you can prove through the adiabatic equation that the circuit your installing will comply ..... its usually too late at the end of the job to find your values are higher than expected and because you could say have a zs value of 0.9ohms covering the D.B. it would only give an allowance of 0.25ohms left for a ring main hence its so easy end up with a installation that dosn't comply.
Its was introduced i assume because it was a situation often tripping electricians up when supplying multiple circuits and finding they couldn't comply so it was implemented to ensure you would comply and if you so choose to hve a smaller earth you had to calculate it and prove its compliance.
 
See it all the time Guitarist but as i said it doesn't mean it doesn't comply it means you got to prove it does and i often used to find an earth upgrade to be neccessary esp' on the longer supplies with close fuse ratio's in the cascade.
 
I had exactly the same issues a while ago but I cannot find the thread. Anyway, Lenny helped me out with the "let through figures" in relation to the amount of fault current the protective device in the main DB will actually "let through". If it's a modern MCB (in my case an RCBO) then let through figures that can be used in the adiabatic are lower than the fault current calculated. It meant that the supply to garage CPC could be smaller. The problem was the T&E CPC feeding the adaptable box where it met the SWA. I will see if I can find the figures I refer to.

I believe these figures (I2T) are manufacturer specific and need obtaining from the specific manufacturer of the PD.

EDIT: Found it; http://www.electriciansforums.net/e...ectrical-regulations/48549-cpc-size-help.html
 
Last edited by a moderator:
See it all the time Guitarist but as i said it doesn't mean it doesn't comply it means you got to prove it does and i often used to find an earth upgrade to be neccessary esp' on the longer supplies with close fuse ratio's in the cascade.

Hope there are no plumbers reading this thread. I would hate for their preconception that electricians "just stick wires in" to be spoilt. :rolleyes2:
 

Reply to Garage supply CPC in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock