Supply to 10KVA tranny. Considerations?

[DaveS79]

Evening all

Been asked to install a supply to a 10kva Tranny. Will be sitting 2 metres away from the CU in photo which is situated in enclosure. Also from this same CU a seperate circuit will be run to a site canteen 30 metres away to supply 3 sockets. Just thought I would check to see if I am missing any considerations I need to take in to account with this? As can see from photo supply is TNCS. Would others take any issue with this with canteen being so far away and potentially consider installing an earth rod? As this is a construction site I am a little bit more concerned than would be otherwise. Also do my calcs seem correct? I've got 10KVA at 43 amps. So to be sure covered all potentialities would need to install a 50 amp type C MCB and 10mm SWA or is this overkill could potentially 6mm and 40 amps be ok? Would like to try to avoid 10mm if can, as as you can see glanding space within enclosure pretty tight....any advice on how best to gland off the two SWA's required in such a small CU and enclosure would also be appreciated.

Cheers 

 

[ProDave]

Construction site pretty much says don't connect anything to TNCS earth.  Some DNO's even refuse to provide an earth for a site supply.

 

[Fleeting]

TN-C-S isn't totally precluded from construction sites and judging from the meter it has been serving another purpose. The pic isn't clear but is that main rcd switch only rated at 40A and your loading is going to exceed that. It looks like there is a 100A fuse at the service head.

 

[DaveS79]

Construction site pretty much says don't connect anything to TNCS earth.  Some DNO's even refuse to provide an earth for a site supply.

Blimey really. Thanks Dave.

TN-C-S isn't totally precluded from construction sites and judging from the meter it has been serving another purpose. The pic isn't clear but is that main rcd switch only rated at 40A and your loading is going to exceed that.

Thanks Fleeting. I had tried to edit post to include the uprating of RCD main switch that would be required. Will dig a bit deeper into regs regarding tncs on construction sites. In what circumstances would you be particularly happy to stick with it?

Also he was a little unclear on the supply and metering but did seem to suggest that the enclosure has just been installed for this purpose so perhaps they have just used an old meter

 

[Fleeting]

Blimey really. Thanks Dave.

Thanks Fleeting. I had tried to edit post to include the uprating of RCD main switch that would be required. Will dig a bit deeper into regs regarding tncs on construction sites. In what circumstances would you be particularly happy to stick with it?

Also he was a little unclear on the supply and metering but did seem to suggest that the enclosure has just been installed for this purpose so perhaps they have just used an old meter

Regulation 704.411.3.1 refers to PME on a construction site. I agree that the supply company will generally not provide an earth, where ESQCR 2002 Regulation 9(4) forbids a distributor from providing an earth to caravan or boats it only suggests special consideration for a building site however the distributor is not likely to consider it. Would I be happy to utilise PME on a construction site no, the requirements for maintaining the requirements of BS7671 would be too unpredictable. 

I still believe that service was serving another purpose he doesn't say it has just been installed.

 

[Fleeting]

Plus the use of red and black conductors gives it some age.

 

[DaveS79]

Plus the use of red and black conductors gives it some age.

Regulation 704.411.3.1 refers to PME on a construction site. I agree that the supply company will generally not provide an earth, where ESQCR 2002 Regulation 9(4) forbids a distributor from providing an earth to caravan or boats it only suggests special consideration for a building site however the distributor is not likely to consider it. Would I be happy to utilise PME on a construction site no, the requirements for maintaining the requirements of BS7671 would be too unpredictable. 

I still believe that service was serving another purpose he doesn't say it has just been installed.

Thanks Fleeting. Well spotted. I'm not myself comfortable with just using the PME. Unless he can provide more info and a safe plan for earth rods won't be taking him up on it.