Ze on campsite

[tombennetts]

Hi all.
Currently working on a campsite installing new hook up points. Just had a new 3 phase supply installed. Each phase feeds a separate consumer unit which in turn feeds 4double hook up points each. The supply is tncs up to the hook ups (protecting the swa) and tt at the hook ups. The ze at the hook ups varies from 240 ohms to 790 on one earth rod. Anyone got any good ideas on lowering the ze, as at the moment the rcd's aren't operating due to the high earth path I'm assuming!
Thanks
Tom

 

[topquark]

Connecting TNCS to a caravan is not allowed, it has to be TT'ed

It can still be TNS.

 

[nickblake]

I was going to say some thing but i cant remember what it was lol oh age eh ...... lol ..... as they guys have said cant use TNCS on a caravan park

 

[tombennetts]

not sure if that reply posted then. What i mean is that the pme from the supply is used to protect the armoured cables, but it does not enter the hook up points as pme is not allowed to supply the caravans. Sorry if i didnt explain very well. Is this not the standard way of going about this then?
Thanks for all the fast replies

 

[Guest123]

i have tested the rcd's. a few were tripping at 1 x but none seem to want to at 5 x

Makes sense because at 5x the fault current would be 150mA, using the above sum 50/0.150 = 333ohms

 

[tombennetts]

so the tncs cannot be used to protect the armoured then?! its easy to disconnect them from the supply and swap it to the tt at the hook ups, i thought that it could be used however though as its not supplying anything portable.

 

[Big n Daft]

We're assuming it's for caravan hookups so 721.411.4 applies (see the note prohibiting TNCS (PME)).

As it says on the tin.........Big n Daft.
Never done a tin can alley in my life.
Sits in corner, pointy hat with 'D' on his head

 

[topquark]

As it says on the tin.........Big n Daft.
Never done a tin can alley in my life.
Sits in corner, pointy hat with 'D' on his head

You ain't daft mate, as you've done your time under the 15th you've got a whole lot of experience to share !!!

 

[nickblake]

You ain't daft mate, as you've done your time under the 15th you've got a whole lot of experience to share !!!

totally agree were all still learning

 

[NMc]

Read the regs TNCS is not premitted

 

[tombennetts]

can anyone clarify whether its ok to keep the pme protecting the rcd's or if i need to swap it over to the tt side?
would it be acceptable to link all the armoureds on each particular run inside the single phase board, then all the hook ups could benefit from each others earth rod, as well as sticking one by the single phase.

 

[topquark]

Just so we're all on the same page, can you just clarify where the RCD's are

 

[tombennetts]

sorry, they are actually rcbo's on the hook ups. one for each outlet. There is a 100mA rcd protecting the individual armoureds from the supply.
I would have a quick flick through the regs book but its not one of the books i keep on my bedside table. Thinking maybe i should now!

 

[nickblake]

Thats fine its the PEN conductor of the hook up point that needs to be connected to an earth electrode , reg 708.553.1.14 the RCD's are required to disconnect both live and neutral reg 708.553.1.13 , as for the armoureds if its terminated into a metal clad board with the proper glands then the armour will be connected together assuming the cable runs go back to the same CDU

 

[topquark]

^^^^^ what quick draw McGraw said

 

[nickblake]

sorry, they are actually rcbo's on the hook ups. one for each outlet. There is a 100mA rcd protecting the individual armoureds from the supply.
I would have a quick flick through the regs book but its not one of the books i keep on my bedside table. Thinking maybe i should now!

may be a good idea its section 708 page 190