I&T of Garage Connection

[slippyr4]

Hi all,

I've now more or less completed my garage rewire.

I've got SWA from non-rcd side of CU, which runs to the garage and terminates in a metal garage CU. garage CU has rcd and two mcbs, a socket radial and lighting circuits.

What i'm not clear on is where to do the I&T from, particularly IR and R1+R2 type tests, and how these get filled out on the installation forms.

My best thought was to regard the garage as a separate installation, and as such test and report based on readings taken at the garage CU. Additionally i'd do continuity and IR tests from the main cu, with the supply cable disconnected at the garage CU. Does this sound about right?

any pointers appreciated

slip

 

[Taylortwocities]

Its a sub main from teh main c.u. The supply protective device will be the one in the CU
The supply type will be (depends on how you've run the cable) but if its phase, neutral & earth from the main CU then it will be TN-S.

If you've an earth rod at the garage end its TT.

New EIC cert for the new CU and all the circuits etc in the garage.

 

[securespark]

Not if it's TT at the house.....

If it's TT at the house, with no RCD, that metal CU in the garage is out straight away.

Need to confirm supply type at the house.

 

[slippyr4]

house is TN-S, thus the garage also is TN-S.

So, should I be recording R1+R2's from the garage CU or the house CU?

 

[securespark]

Both, if you've changed one and installed the other.

 

[Taylortwocities]

house is TN-S, thus the garage also is TN-S.

In that case yes, but think about it, if the main supply were TNC-S and you run a length of Twin & earth as a submain to your garage then the supply characteristic of the sub main will be TN-S. It doesnt magically assume the characteristic of the main supply.

 

[Spark123]

In that case yes, but think about it, if the main supply were TNC-S and you run a length of Twin & earth as a submain to your garage then the supply characteristic of the sub main will be TN-S. It doesnt magically assume the characteristic of the main supply.

I don't follow what you are saying, if TN-CS is the characteristic of supply the submain has to comply with the earthing requirements for a TN-CS supply unless it is converted to TT. I don't think it becomes TN-S as the characteristics of a TN-S supply is it has to have a separate earth and neutral all the way from the DNO transformer.

 

[Taylortwocities]

Umm. (quite some time ago) when doing just this scenario as a practical in 2360 we were told that the supply type would be noted on the cert as TN-S (unless it was spiked and then it would be TT).
The Ze at origin for the sub-main being the impedance on its arrival at the garage cu. The Ze having different impedance due to extra influences (earth bonds etc) in the house. Were we advised wrong?

TTC

 

[Adam_151]

Agree with spark123, it might not be immediatly apparent that its TN-C-S it still is TNC-S in my eyes, a bit like the story of the blindfolded people touching up the elephant....

Anyway I reckon you should be including two schedules of results with your EIC (describe the extent of the work *clearly* on the EIC, btw), one for the main board that only has the submain test results on it, and one for your new board that has the full tests for all circuits from the submain board

 

[Spark123]

Ze is the external loop impedance to the installation, the efli at the submain will be Zs.

 

[Adam_151]

Ze is the external loop impedance to the installation, the efli at the submain will be Zs.

But on the Ze box on the top of the shedule of results for the submain board, I'd put the Z's at that board, but I'd make it very clear what I'd done (probably put the Ze and the R1+R2 of the submain in brackets too)

Similar thing with the PFC

The values at the orgin will be on the shedule for the main board and on the first page of the cert, so its not like those values are being got rid of from the cert.

Just seems logical to me, it might be the case that I'd be wrong by doing the above, but that is what I'd do unless I heard better