Caravan hookup on tnc-s

[cadspark]

I was on small touring caravan site yesterday looking at a caravan electrics for a client.

I've not done any caravan site work but the onwner asked me to look at a few things whilst I was there.

The site has only one hookup point with four commando blue sockets on 16a RCBO's in a hookup box mounted on a wooden post. This has been fed with 6mm 3 core swa from bs3036 rewirable which is on a tnc-s earthing arrangement. There is no earth rod at all.

Obviously I realise under the regs exporting tnc-s to a caravan hookup point is an absolute no no. I intend to disconnect the 3rd core used currently for the earth and probably run it in parallel with the live and sleeve it in brown. The armour I will leave connected at the supply end and disconnect from the hookup end as this is an extraneous conductive part.

I will put an earth rod in at the hookup and run it into the hookup supply unit. Would it be acceptable to run the earth rod into an adaptable box mounted low down on the post or does it have to be an earth pit box?
Your thoughts on any of the above would be appreciated.

 

[malcolmsanford]

Is there a reason you don't want to use a pit box? I always question why does someone want to do away with something that is designed for the specific task, and adapt something that isn't.

Obviously from your post you seem to know what your doing so there must be a reason you want to use your method. As long as your can protect you connection as to the Regs section 526 and you label it to Reg 514.13.1 then I see no problems with that.

 

[telectrix]

asd above, but why do you want to parallel up the 3rd core with the live. serves no useful purpose, as the neutral will still be 1 core. unless you want to put sockets on separate fuses.

 

[cadspark]

The post is surrounded by grass so I just thought it would look nicer not having an inspection pit dug into it. The only reason for running the third core in parallel is so I have somewhere to terminate it at both ends rather than cut it.

 

[telectrix]

so you should leave it earthed at 1 end ( the TT end ) . terminate the other end into a blind connector.no reason why not have 2 separate lives, each feeding 2 sockets.

 

[MarkieSparkie]

cadspark, a plastic inspection pit box (SERPT205, £25.85+VAT) will give better protection, whilst being easy to fit. If you don't want to use this then an earth rod box (MECB75G, £5.49+VAT) is the next best alternative. The part numbers and prices quoted are from the current Senate Electrical catalogue.

 

[Chr!s]

I was on small touring caravan site yesterday looking at a caravan electrics for a client.

I've not done any caravan site work but the onwner asked me to look at a few things whilst I was there.

The site has only one hookup point with four commando blue sockets on 16a RCBO's in a hookup box mounted on a wooden post. This has been fed with 6mm 3 core swa from bs3036 rewirable which is on a tnc-s earthing arrangement. There is no earth rod at all.

I would place an electrode iat the origin of the distribution circuit along with an additional electrode at the hook up.

Obviously I realise under the regs exporting tnc-s to a caravan hookup point is an absolute no no. I intend to disconnect the 3rd core used currently for the earth and probably run it in parallel with the live and sleeve it in brown. The armour I will leave connected at the supply end and disconnect from the hookup end as this is an extraneous conductive part.

This would contravene Reg 524. I would leave as an earth and connect it to an electrode at the supply end.If volt drop is an issue you could use it as a neutral.

The armor is an exposed conductive part, connect it at the supply end and also to the additional electrode at the hook up.

I will put an earth rod in at the hookup and run it into the hookup supply unit. Would it be acceptable to run the earth rod into an adaptable box mounted low down on the post or does it have to be an earth pit box?
Your thoughts on any of the above would be appreciated.

Regards

Chris

 

[Deleted member 9648]

Chris.....If you connect the armour to both supply earth AND the electrode you will introduce the TNCS......bit pointless really.

 

[Chr!s]

Chris.....If you connect the armour to both supply earth AND the electrode you will introduce the TNCS......bit pointless really.

Maybe my post was not too clear, i said supply end, not the tnc-s supply, the distribution cable will be connected to two electrodes:

Divorced entirely at the origin of the distribution circuit.

1, at the supply end of the Distribution
2, at the hook up

This way no potential is taken out to the hook up.

Chris

 

[cadspark]

Thanks for your responses. I will go for the earth rod box. I'll earth the armour from the TT end only.

 

[Deleted member 26818]

You should earth the armour at the TN-C-S end, as this is the end where the protective device for the cable is situated.

 

[Jimmyb]

can you use a rod and connect it striaght to the sockets, for some reason ive always thought it needed to be though a protective device.

Also wouldnt using the the extra cable as a live reduce voltdrop ? maybe not needed but....

 

[javelinpc]

Hi
Earth rod box/cover and "safety electrical connection" label acceptable.
Armour MUST be earthed at supply end - any fault will introduce TNC-s fault to neutral and therefore not acceptable to TT installations
ONLY phase and neutral to be transferred to TT system and separate earth rod AND RCD ESSENTIAL to be at the hookup end.
TEST before commissioning for use and values for RCD trip times must now comply with 17th ed:2008 values.

David