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

 

[Sintra]

Sounds like you need to install multiple electrodes or else find better ground for the existing ones.

 

[topquark]

More rods, either extra or stack them up to go deeper (I'm assuming they're new).

 

[Guest123]

Additional rods/tapes/mats etc

Even at 790 ohms (which is bad) a 30mA RCD should still operate before the touch voltage threshold is exceeded. Have you tested the RCD's at all???

 

[KFH]

With a 30mA RCD it should be operating with an earth electrode resistance of up to 1667Ω. Ze = 50/.030. 50 is the max touch voltage. While it would be a good idea to get the Ze close to or less than 100Ω (OSG says over 200Ω may not be stable) is this the fault or is something else wrong?

 

[truckster]

Probably too late now but what we used to do was to strip back about 5m of 25mm green/yellow and bury it in the trenches with the swa, used to get really low Zs that way.

 

[nickblake]

What i would do is install a rod at each hook up , or as sintra has stated use multiple Rods ,realistically and has been mentioned the readings should be less that 200 ohms for stability ,see if there are any damper area's some where that doesnt catch the sun to much happer a rod in and do an earth rod test to see what the conductivity is

 

[NMc]

Use a quility earth rod which you can screw another one on so that you drive it deeper. Should lower the resistance

 

[tombennetts]

i have tested the rcd's. a few were tripping at 1 x but none seem to want to at 5 x
. came across this at a house and bashed another electrode in which did sort it. the ground is very dry and very rocky so worried it may take lots of electrodes at the higher ze hook ups.
got alot pf sorting out to do on some old hook ups that are run on 2.5mm flex on a run of 50 metres underground using the pme that was supplied on the old board!

 

[Big n Daft]

The supply is tncs up to the hook ups (protecting the swa) and tt at the hook ups.
WHY
Am I missing summat or is my head not working properly???

 

[topquark]

The supply is tncs up to the hook ups (protecting the swa) and tt at the hook ups.
WHY
Am I missing summat or is my head not working properly???

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

 

[Sintra]

The supply is tncs up to the hook ups (protecting the swa) and tt at the hook ups.
WHY
Am I missing summat or is my head not working properly???

Because it's a caravan park.

 

[tombennetts]

i mean that the pme supply protects the armoured but is not taken into the hook ups, as pme is not permitted to supply caravans. Sorry may not have explained it very well there, or is that not the way you would have done it?!

 

[KFH]

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

 

[topquark]

i mean that the pme supply protects the armoured but is not taken into the hook ups, as pme is not permitted to supply caravans. Sorry may not have explained it very well there, or is that not the way you would have done it?!

It's fine mate, just preferable to get the Ra on the rods down.

 

[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.