New site...

[NozSpark]

I've been doing some work on a residential site (posh twin unit mobile homes) and have been asked to go to another site..

Now this site is 3ph TT with BS88 fuses supplying 2 sub DB's which then supply the units/lodges via BS88 fuses again.. now all cabling in underground SWA and each unit/lodge has 100mA RCD protection (not TD) in the meter cabinet and 30mA in the CU..

Now as the sub mains are not RCD protected and this is a TT installation I would say that RCD protection is required or the supply needs to be changed to TNS??

Just after some confirmation that I'm correct:Blushing

From a personal POV I'd say that a RCD incommer is a no go as 1 unit could trip out the whole site.

 

[M107]

100mA td on the submains or incommer & bin the 100mA at the unit's/lodges.

If you did rcd the TP TT incomer, im sure (haven't got book to hand to check) the neutral must dissconnect also.

 

[NozSpark]

Going to have a better look tomorrow... I'm sure that there's a suppliers earth terminal, but it's not being used.. If it's TNS I'm going to recommend swaping it over and full test of the site...

don't really want to export a TNC-S earth so don't really know what I'll do if that is the case, would prob have to leave as TT and have 3ph 100mA TD RCD's at the main board as you say!

Will get some photies tomorrow.... if I remember

 

[M107]

Will get some photies tomorrow.... if I remember

Yes I keep forgetting to take pictures.

Been on a school job today 60 double sso in one class for pc's. They wanted me to just extend existing RF that already serves this class plus corridoor & IT office, but I've gone for new circuit just for the pc's......works out a socket roughly every 9 inches.

Back there in the morning to complete 2nd fixing, then it's onto the next job across in another class.

 

[M107]

Right time for bed, now I've done me quote's.

Night mate

 

[NozSpark]

Cheers mate..

I off as well!

 

[sparkytim]

I look after a couple of these type of sites (Electrically) and one is TNS for the SWA BS 88 fused distribution circuits up to each Unit Meter box then TT with 30 m A RCD

The other site is TNCS up to each Meter position and as long as you segregate the Earthing and insulate well at the Unit then you are NOT exporting the PME earth to anything accessible.

 

[Andy™]

I'm sure that there's a suppliers earth terminal, but it's not being used..

r

make sure that the other end of the terminal is actually connected. came accross a TNS type service head used on a TT a few times before, so it wasnt connected

 

[wozz]

is the first enclosure of the installation metal?