Caravan hook-up point

[rosewood]

Evening all,

Some of you may remember a previous post i put up not long ago about sizing of supply cable to a caravan park.
It was the cheaper option to have the DNO ramp up the voltage and blast it down to the caravan field 400m down.

So now i have a 'sub main housing' in the caravan field with a 3phase TNC-S supply. Obviously i have to drop the earth and put a stake down at the 'sub-main housing'.

My question is do i need to put a stake down at every hook up pole or can i connect them all back to the one main stake?

Maybe a stupid question but im unsure on it so worth asking!

Many thanks in advance

 

[yellowvanman]

Nothing in the regs to say you have to have a rod for each outlet.

 

[telectrix]

i would earth the armour of your SWA from the sub-main to the TNC-S ( just at one end), then TT rod each hook-up.

 

[rosewood]

i would earth the armour of your SWA from the sub-main to the TNC-S ( just at one end), then TT rod each hook-up.

it would be a lot more expensive doing it that way tho surely? if i can use the one rod for all of it then i would be cheaper to do that

 

[sedgy34]

Evening all,

Some of you may remember a previous post i put up not long ago about sizing of supply cable to a caravan park.
It was the cheaper option to have the DNO ramp up the voltage and blast it down to the caravan field 400m down.

So now i have a 'sub main housing' in the caravan field with a 3phase TNC-S supply. Obviously i have to drop the earth and put a stake down at the 'sub-main housing'.

My question is do i need to put a stake down at every hook up pole or can i connect them all back to the one main stake?

Maybe a stupid question but im unsure on it so worth asking!

Many thanks in advance

MO each caravan supply would have a rod

 

[telectrix]

it would be a lot more expensive doing it that way tho surely? if i can use the one rod for all of it then i would be cheaper to do that

it would be cheaper, but should that 1 rod's connection corrode, break, be removed by a numpty, all pitches lose their earth. also you have a much longer earth path for each pitch. you can have 2 hook-ups at each point sharing a rod between 2 (or it may even be 4, not got regs. to hand)

 

[spark 68]

Here are a couple of pages from GN7 (amd1), it was quicker to scan this than to try and explain.

This may help.

 

[rosewood]

Thanks just what i was looking for!

 

[Adam W]

Guidance note 7 seems to say you can do either.
I would go with one at each pillar, for the reasons Tel suggested, especially if it's a site where caravans are moved around regularly.

 

[Engineer54]

Why on earth (excuse the pun) would any electrician want to rely on a single earth electrode to protect a complete caravan site?? Drive a decent depth rod at each take-off pillar and connect these rods together using the armour of the SWA cable your using for your site distribution!!

Your dealing with public safety here, not trying to save the site owner a few bob. The RCDs in these pillars are by no-means a fool proof protection!! Doing these sort of installations on the cheap is not an option, they will come back and bite you, ...and hard!!

Do the job properly, and cover your own arse in the process!! lol!!

 

[Knobhead]

To follow on from E54’s post.
An earth rod at each off take gives one of the best scenarios for a good earth nest. Each rod is supporting the others giving a wide spread.
As has been said it’s safety not the site owners profit at risk.

 

[High Tower]

Also numerous rods in parallel will significantly reduce the over all zs for each pitch!

 

[Knobhead]

Sorry I didn't make it clear that the rods would / should be linked.

 

[spark 68]

Agreed, one rod at each pitch would give a far lower overall Zs, and redundency incase of losing the earthing at one or more point.

GN7 (ref post #7) suggests the preferred way is to have a single TT earthing point at the pitch DB, but notice the 100mA (or greater) RCD protecting the distribution board supplying the cables to the pitches to give discrimination against the individual 30mA RCD's at each pitch, this also negates the argument of the R2 being slightly higher on the cable runs, as this will be relatively negligble on the TT system protected by the RCD at the pitches source DB.

I suppose you could have the best of both by including the 100mA RCD (or greater) in the topology suggested by Tony and E54 (in the TNC-S system), as this would then give some backup RCD protection in the event of a single RCD failure at the pitch.

GN7 suggests you could do it either way though, and still comply, Tony and E54's method is the best and safest solution without a doubt, but it is the most expensive.

There is nothing in the regs stopping you doing it the other way.

I will get my tin hat on now lol.

 

[Engineer54]

Agreed, one rod at each pitch would give a far lower overall Zs, and redundancy in case of losing the earthing at one or more point.

GN7 (ref post #7) suggests the preferred way is to have a single TT earthing point at the pitch DB, but notice the 100mA (or greater) RCD protecting the distribution board supplying the cables to the pitches to give discrimination against the individual 30mA RCDs at each pitch, this also negates the argument of the R2 being slightly higher on the cable runs, as this will be relatively negligible on the TT system protected by the RCD at the pitches source DB.

I suppose you could have the best of both by including the 100mA RCD (or greater) in the topology suggested by Tony and E54 (in the TNC-S system), as this would then give some backup RCD protection in the event of a single RCD failure at the pitch.

GN7 suggests you could do it either way though, and still comply, Tony and E54's method is the best and safest solution without a doubt, but it is the most expensive.

There is nothing in the regs stopping you doing it the other way.

I will get my tin hat on now lol.

I will say it again, The Reg's relating to TT systems seriously do need amending, this is just another example that substantiates that need!! lol!!

 

[spark 68]

I will say it again, The Reg's relating to TT systems seriously do need amending,

The pages posted are taken from the new GN7 amd1 lol!

 

[wildgoose]

I've done one or two of these in the past.

Strongly advise to TT every post outlet. It's the safest way of doing things and a benefit is that the multiple rods bring down the overall ZE when they're all in circiut - you won't of course see this value on the test cert because each post outlet should be tested in isolation.

 

[Engineer54]

The pages posted are taken from the new GN7 amd1 lol!

And Based on What?? lol!!

 

[Engineer54]

I've done one or two of these in the past.

Strongly advise to TT every post outlet. It's the safest way of doing things and a benefit is that the multiple rods bring down the overall ZE when they're all in circuit - you won't of course see this value on the test cert because each post outlet should be tested in isolation.

Not sure i understand your reasoning here?? If all the rods are solidly linked via the SWA cable(s) as they should be. Why would you test each post in isolation?? (eg ...using the value of the single rod, with the linking to the rest of the system disconnected) Pretty pointless linking the multiple rods, if your going to disconnect them for testing. The whole idea, is to bring the Ra level way down, to make the campsite earthing at each post as good as it can be. Done properly you'll be at, or very close to TN values with the RCD's virtually providing additional protection...

So Yes, each rod should be individually tested when installed, and also possibly during each annual out of season testing. But ''Never'' when your testing the overall installation, at post locations!!

 

[boberty]

just had a look in regs and it says you cant earth the outlets to a pme system, they have to be connected to a rod 708.553.1.14/ 708.411.4

 

[Engineer54]

just had a look in regs and it says you cant earth the outlets to a pme system, they have to be connected to a rod 708.553.1.14/ 708.411.4

Errrr, That's why were talking about TT systems here. Where did anyone mention distributing PME in this thread???