New installation to outbuilding

[DRDAVIDBANNER]

I'm new to the forum to Hi!

I'm putting an installation into a Log cabin in my parents garden, I've installed the cabling installed a separate 2 way RCD protected CU in the cabin. The cable is earthed at the main CU in the house and protected on the main CU by another RCD. However I want to achieve discrimination between the 2. I see a couple of options I'd like to know if anyone is sure on the regs for this as I can't seem to find it in BS7671:2008

1) Install a time delayed RCD in the CU in the house.

2) - (This is the option I am, unsure about). - As the building is a fair distance from the main property, I'd like to earth it separately (TT system), if I do this, do I keep the cable earthed at the main CU? If I keep it earthed at the main CU does it make the entire installation a TT system since the new earth rod will essentially be connected to the main earthling terminal.
- Also if I do connect it at both ends will I still get discrimination

I hope this is clear,

thanks in advance - Pete

 

[Engineer54]

First off, ...what earthing system do you have at the house??
What sort of distance are we talking about here to the Log Cabin??
What type of cable have you installed to the Log Cabin, and how have you installed it??

No need to have an RCD device on a sub-main supply cable, If you want to provide it with RCD protection then you will need to install an S Type RCD device ...quite expensive. You only need to TT this out building if it is a really good distance from the house, and you have a PME earthing system at the house, and the outbuilding has extraneous metal work or say a water supply fed in copper or steel pipe. ...In other words, Don't Do It unless you absolutly have too!! lol!!

 

[DRDAVIDBANNER]

Hi, thanks for the reply.

The house is TN-C-S, PME. The distance is approx 35m , I've installled 4mm armoured twin and earth, partically bured (under a patio) and then fixed to a wall with cleats for the majority of its lengh, then buried at a depth of 600mm for 3m before it enters the cabin.

So am I right in saying I DO NOT need to RCD the cable in the house? Just connect it to a 20amp MCB?

Thanks

 

[Engineer54]

The cable you have installed, is NOT suitable for direct burial i'm afraid. You should have used SWA cable for this installation. The distance isn't excessive, and if no water or other service at the cabin, no need for a 10mm bonding conductor . I strongly suggest you change this cable if you want this installation to last as it's also not the best cable for exposed external wiring either.... If using SWA as your sub-main cable then no need for it to be RCD protected. I wouldn't say the same for T&E cable though!! lol!!!

 

[DRDAVIDBANNER]

Sorry, I have been unclear here, the cable is steel wire armoured. Thanks for the info, I'll just run it off the a 20amp MCB and RCD it in the cabin.

thanks again

 

[Engineer54]

Sorry, I have been unclear here, the cable is steel wire armoured. Thanks for the info, I'll just run it off the a 20amp MCB and RCD it in the cabin.

thanks again

My mistake...lol!! I hope you have terminated both ends of that SWA cable with the appropriate sized glands and supplementary earth leads??

You still have one rather large problem ...This is notifiable work, and as such needs notifying to the LABC and needs testing by a scheme provider registered electrician. It would have been cheaper in the long run to have employed such an electrician in the first place to install this installation. Your going to be surprised just how much the LABC will want from you now!!!

 

[DRDAVIDBANNER]

The SWA terminates inside the buildings at both ends, at the CU in the cabin in fact. The end in at the main property is earthed, the cabin isn't yet, it's not fully complete yet, nothing is energized yet. I can get the work signed off by a Part P that I know, however the fact that its is notifiable is recent news to me. Can I notify after the fact?

thanks

 

[Engineer54]

Best wait for a scheme provider electrician here to answer that question.. As far as i know you need to notify ''prior'' to any work being started. But i'm a long way off from UK where there is nothing like the regulatory paraphernalia you have in UK these days!!...lol!!

 

[Engineer54]

Just a quick couple of questions... Is your house CU plastic or metal?? ....If plastic, how have you earthed the SWA armouring, as your cables armouring ''NEEDS'' to be earthed ??

 

[DRDAVIDBANNER]

Its plastic, I have some SWA earthing "nuts" I think they are referred to. Basically a metal end that enables you to attach supplementary earthing bonds to it.

Just been looking at my local authories building controls, to do the work I "should" have notified them, then got the work signed off by a part p electrician. I'm going to have to get my friend to sign it off, then notify them - as though he has done the work. He'll need to fill in an Installation Certificate and a notice of inspection by the looks of things.

I feel a bit foolish I must admit, I am planning on going for part p myself early in the new year and would have liked to have used the job in my assessment - looks like that is out of the window!

I thought your location was a wind up I must admit!

 

[Engineer54]

No, ...It's Not a Wind Up!! lol!!

You must have a very good friend there then, ...as most electricians would refuse point blank to sign off another's work, as they will then become entirely responsible for the whole installation if, ...god forbid anything goes wrong and harms someone!!!

 

[ackbarthestar]

Three options as far as Part P goes
1/ Notify the LABC now before you do any more work...... usually 48 hours before you start work.
2/ Get a Part P electrician to complete the work and let him/her notify for you
3/Register with an authorizing body and use the job as part of your initial assessment... and then notify the LABC yourself.

As E54 states 2-core 4mm2 SWA glanded and bonded/connected to MET can either be
1/ Glanded off at the Shed CCU Earthing terminal and used as the sub-main cpc
2/ Glanded off into a plastic enclosure at the shed and not connected to the shed ccu then put in an earth electrode (lol :rofl: ) as your new earth for the outbuilding.

As long as the SWA is earthed at the MET there is no need to provide RCD protection for a TN system, but you will need to provide an RCD at the shed CCU.

 

[DRDAVIDBANNER]

That sounds promising, the ideal outcome here would be to complete the work to the correct standard and then use it in my initial assessment and as you say then notify the LABC myself.

Wouldn't an autherising body require that the work be signed off by a qualified electrician first though? Or require me to have notified the LABC first?

thanks

 

[ackbarthestar]

That sounds promising, the ideal outcome here would be to complete the work to the correct standard and then use it in my initial assessment and as you say then notify the LABC myself.

Wouldn't an autherising body require that the work be signed off by a qualified electrician first though? Or require me to have notified the LABC first?

thanks

If this is the way you want to go then phone up one of the authorizing bodies and say you want to register with them for part P. fill out their forms, pay the money and wait for them to contact you with an assessment date.

 

[sharpener]

Depends a bit on how helpful your LABC are. Mine were happy to inspect after I had changed the CU urgently when we moved in (lots of probs on old installation), and then re-inspect after I had done a complete re-wire and tested/self-certified, all on the one notification and payment. Same again for loft conversion electrics later. Am not on any competent persons scheme (but am a Chartered Electrical Engineer).

You might have more trouble if you have started the work already!