Why a separate earth for caravans

[timhoward]

What, you don't take your regs into the pub! Shame on you.

Not tonight! I’m in proud dad mode as my teenage daughter has a gig and is doing great!
Anyway, back to the topic in hand….!

 

[pc1966]

So if they have TNS or TT then I can use the installation earth?

Technically yes, but many "TN-S" supplies are actually off segments with a PME conductor, just they look separate at the DNO cut-out.

Personally I would TT it unless the main supply was already TT.

Also for the cable I'm probably gonna use 3 core 10mm SWA. But what if I used 2 core and used the armouring as the main earth? Crazy talk?

The two issues with using the SWA armour are:

• If using a 16A or 32A "commando" socket you will struggle to have any reliable connection to the armour. For hard-wiring to a fixed unit with glands no problem
• The end of cable Zs for disconnection has to be met. For TT supply (RCD before the SWA run) then no problem as RCD will disconnect on any sort of armour impedance, but if TN to the caravan point you ought to check it is met.

See also this article:

Electrical installations in caravan/camping parks, caravans and motor caravans

As the warmer weather approaches and with summer around the corner, thoughts turn to holidays. Chief Engineer Geoff Cronshaw reminds us of the requirements of BS 7671:2008+A3:2015.

bit.ly

 

[Calebp43]

So if they have TNS or TT then I can use the installation earth?
Also for the cable I'm probably gonna use 3 core 10mm SWA. But what if I used 2 core and used the armouring as the main earth? Crazy talk?

Does anyone have a reply to this?
I'm just curious.
Also yes I am confident enough to carry out the work. I just ask a lot of silly questions on this forum that play in my mind because I don't like asking my colleagues silly questions lol

 

[Calebp43]

Technically yes, but many "TN-S" supplies are actually off segments with a PME conductor, just they look separate at the DNO cut-out.

Personally I would TT it unless the main supply was already TT.


The two issues with using the SWA armour are:

• If using a 16A or 32A "commando" socket you will struggle to have any reliable connection to the armour. For hard-wiring to a fixed unit with glands no problem
• The end of cable Zs for disconnection has to be met. For TT supply (RCD before the SWA run) then no problem as RCD will disconnect on any sort of armour impedance, but if TN to the caravan point you ought to check it is met.

See also this article:

Electrical installations in caravan/camping parks, caravans and motor caravans

As the warmer weather approaches and with summer around the corner, thoughts turn to holidays. Chief Engineer Geoff Cronshaw reminds us of the requirements of BS 7671:2008+A3:2015.

bit.ly

Yet again you have came to answer stuff. Thanks pc
(And everyone else. Pc just seems to be a regular question answerer xD)

 

[Calebp43]

Still like to know if this is for a tourer or a static…. But the 10.0mm mentioned on #3 suggests something big.

Sorry it's a static. And about 30m run I'm cable

 

[davesparks]

How’s the wording of the regs on this?

I’m sure it says a rod for a caravan park, not for just a caravan plugged into a house…

ESQCR needs to be considered here which prohibits the TNCS earth being connected to tbe metalwork of any caravan or boat.

 

[davesparks]

So if they have TNS or TT then I can use the installation earth?
Also for the cable I'm probably gonna use 3 core 10mm SWA. But what if I used 2 core and used the armouring as the main earth? Crazy talk?

Without actually being on site an seeing the installation we can only guess at what you can or can't do.

I assume by 'main earth' you mean use it as the CPC? Yes generally it is acceptable to use the armour as the CPC, that is after all how the cable is designed to work. But you need to do the calculation to confirm its suitability, if you are unsure/want us to check your calculation then post the relevant information along with what your results were and we can have a look and help you.

If you do need to set up a seperate TT earthing system then you will need to consider how you are going to isolate the CPC of the SWA from the new TT earth you create.

 

[Calebp43]

One of the lads I work with is saying that the caravan will need a pitch. You know like a box with a caravan hookup point like a commando socket type thing.
I have looked in regs book and page 316 (721.510.3) says "where there is more than one electrically independent installation, each independent installation shall be supplied by a separate connecting device and shall be segregated in accordance with the relevant requirements of BS 7671"
Seeing as this person only has 1 caravan that leads me to believe that they won't need a pitch? I can run the armoured straight into the consumer unit in the caravan.
Have I misenterperated anything there?