tempory supplys to cabing on construction sites

[jonney88]

hi iv been getting conflicted understanding of bs7671 for the correct way to install site temps on tnc-s systems,, weather to export the earth and do with out the earth rod or to have a tt system with type s rcd,,my understanding is if u were to export or extend the earth you will have to ensure the metal cabins meet the bonding requirments of the existing building therefore of some installations would be unethical on larger supplys

 

[driverman]

I'm under the impression that Buildings sites must not be tn-c-s and a TT sytem must be installed with an up front RCD for all circuits and 30mA RCd for sockets.

 

[Octopus]

You need to talk to the supplier, they are the ones who have the final say and will refuse to connect in specific situations

 

[cobrauk]

We have over the last year had new single phase and 3 phase builders temp supply's installed by the suppliers, and they are installing tn-c-s self connect to the temp supply now, they never use to do this, it was always strictly a TT installation, why they changed I do not know, perhaps they do not care what we do after their meter ?
But the regs clearly state what you should do on a site so follow that unless someone tells you different.

 

[driverman]

We have over the last year had new single phase and 3 phase builders temp supply's installed by the suppliers, and they are installing tn-c-s self connect to the temp supply now, they never use to do this, it was always strictly a TT installation, why they changed I do not know, perhaps they do not care what we do after their meter ?
But the regs clearly state what you should do on a site so follow that unless someone tells you different.

Most DNO's supplies are tn-c-s at point of entry. I think it is down to the electrician if he wishes to use the TN-C-S connection. Even in a normal everyday installation. But as you say.................BS7671 to go by

Re after the meter.............No, they don't care, as long as it does not interfere with there network!

 

[jonney88]

basically wat im asking is, I want to know a is the correct way is to provide a supply to cabins,(used for offices welfare and storage),
so tnc-s ,,,export earth meaning bonding the cabins to wat the rest of the building is, no rcd protection feeding a 3phase db at the cabins then feed trannis and cabins from there,
or tnc-s,,,,rcd type s (swa glanded into plastic eclosure) feeding to section board with earth spike at section board site

 

[vernam616]

Earth rod banged in everytime

this was my main job for 2 years solid, wiring and connecting up construction site cabins etc.., and never connected to the TNCS connection

 

[davesparks]

You do mean a suitable earth electrode/nest designed, installed and tested don't you?

Your post implies that you are suggesting just putting one rod in and nothing else!

 

[jonney88]

yes Im iplying using a single earthrod back feeding the swa on the tt side not the tnc-s

 

[davesparks]

yes Im iplying using a single earthrod back feeding the swa on the tt side not the tnc-s

That's no good is it! You will almost certainly require multiple rods to achieve a good Ra. What value of Ra would you normally work to?

What do you mean back feeding the SWA? The armour should be connected to the earth relevant to its source, not the TT earth you are creating at the end of it. The armour must also be isolated from the TT system you create.

 

[barneybhoy]

If its going to be supplying transportable cabins (portacabins) 717.411.4 says that a pme system is not allowed unless at all times it is under the supervision of a skilled person

 

[firemanowl]

Listened to one of the nic blokes at exeter elex a while ago talking about exporting pme. Some boffin has done a load of tests and concluded that there is no problems doing it. I think there is going to be something in the new regs coming out? But not 100% on that though, they said it was going to make a big difference to caravan sites.
Has anyone else heard anything?

 

[Darkwood]

Listened to one of the nic blokes at exeter elex a while ago talking about exporting pme. Some boffin has done a load of tests and concluded that there is no problems doing it. I think there is going to be something in the new regs coming out? But not 100% on that though, they said it was going to make a big difference to caravan sites.
Has anyone else heard anything?

Are we talking about extending the Equipotental Zone or Exporting PME.... One is a no no in the context of this thread , can you guess which .
I ask because its often confused between the 2 on the forum.

 

[davesparks]

Is it actually possible to export PME? Would that not involve selling it to a buyer in another country?

 

[Knobhead]

Listened to one of the nic blokes at exeter elex a while ago talking about exporting pme. Some boffin has done a load of tests and concluded that there is no problems doing it. I think there is going to be something in the new regs coming out? But not 100% on that though, they said it was going to make a big difference to caravan sites.
Has anyone else heard anything?

The NIC make their own rules up regardless of the IET.

No one in their right mind believes anything they say.