What Size Earth? (and a couple of other questions)

[neilma]

Hi all,

The board are coming to move my meter next week and I want to make sure I have all the cabling done before they arrive. Currently I'm on an overhead feed and the earth is via a spike in the ground and then what looks like a 6mm cable to the existing meter.

The meter will be moved outside on the wall above where the spike currently is. Do I need to upgrade the earth cable/spike to a larger size and should it be protected in any way up into the meter cabinet (its not at the moment)?

Can I also get your opinions on the following....

1. From the new meter (Currently it has a 100A fuse on the head), I'll connect the tails to a MEM 80A switch fuse ( via 25mm tails).
2. From the switchfuse to the (new) MK consumer unit, i'd like to run 16mm T&E (approx 6 meters) - Will this be ok? (FWL did say to use SWA 25mm but I'm struggling to get that fed through, plus I think I read soimewhere that the Sentry CU's only take 16mm tails?).
3. If I can use the 16mm T&E, will the earth in it be sufficient in size or should I run a seperate 10mm/16mm for it?)

Thanks in advance
Neil

 

[securespark]

The 5500s 100A disconnectors has a cable capacity of 50mm2.

I would endeavour to use 25mm2 SWA, and I personally would not limit current to 80A. If you have an electric cooker and HP shower.......

BUT, if they are moving the meter altogether, why don't you get them to put it exactly where you want it, so that you don't have to mess about with 80A switchfuses and SWA in the 1st place?

Eb's usually limit the DI tails from meter to board to 2 meters in length, so if your new intake position were close to where your board position is, then there should be no probs.

You need 25mm2 tails for L & N, and a 16mm2 earth.

I would also check that the rod is A1, and the connection between 16mm2 cable and rod is protected - there are chambers/enclosures to do this job.

As your supply is TT (overhead), you need to think about RCD protection too.

 

[neilma]

Thanks for the reply. The EB are moving the meter to where I want it and it will end up being over 3 meters to the CU so I was told I need a switchfuse between the meter and the consumer unit. I wanted to get the cabling in before they arrived. My concern is the cable run from the switchfuse to the CU. Is there anything to say I cant run 16mm T&E from the switchfuse to the CU?

Also, shall I uprate the current earth cable from the spike to the meter to 16mm (from its current 6mm)? And if I do use 16mm T&E from the switchfuse to the CU, can I use the Earth within or do I need to run a larger one?

Thanks

 

[securespark]

neil

Why don't you have the two (board & meter) adjacent and get rid of one headache??

 

[neilma]

As the meter and the board are currently positioned half way up the staircase (dont ask!! ) I want to move the meter outside leaving me with the cu inside but shifted over a few feet. This means it wont affect the width of the (narrow) staircase like it does currently.....

So, will 16 mm T&E be ok? Will the board complain about this or does their responsibility end at the switchfuse (as far as their involvement when moving the meter?) - And is it safe (assuming I dont go over 69A - Which I dont currently).

Cheers all

Neil

 

[securespark]

Neil.

I know this is not what your ears are waiting for, but I would bite the bullet and move the whole shooting match to a better position.

 

[neilma]

Yeah, I appreciate what you are saying, but there really is no other way

Thing is, I've got the switchfuse, I have the new CU, I've put the new meter cabinet on the wall. Everything is prepped, I just need to run a cable now to join the lot up.

Either way, though - can I get confirmation that a 16mm Earth is required from the spike to the meter cabinet (protected by somesort)? That'll be one part of teh puzzle sorted

Would appreciate any thoughts to finally put this 16mm T&E debate to bed

Thanks again for your help

Neil

 

[dingbat]

Don't use 16mm Twin & Earth. If you must use 16sqmm and not the, now standard, 25sqmm, at least use proper sheathed single tails. That is cables that have a colour coded insulation as well as their grey outer sheath. Just ask for a pair of 16sqmm meter tails at your wholesaler - he'll know what you mean.

As for the earth, the size depends on a number of factors but for an unprotected, unburied earth cable the regs say you can get away with 4sqmm for an earth fault loop impedance not less than 1 ohm, but why not play safe and go for 16sqmm as well, and use 10sqmm for your equipotential bonding conductor, then everybody is happy!

Hope that helps

 

[neilma]

Great! Thanks very much

 

[securespark]

Dug this out from a previous discussion about running a sub-main to a CU:

QUOTE:


The SWA is not a problem, the Isolator you install in the meter cabinet is connected to the meter by tails, and is therefore the first part of the Customer Installation, this is perfectly safe, within the regs and supply act, and totally acceptable. I would use 3 core as stated, but still use the proper glanding procedure. This would give a really nice earth connection then.

UNQUOTE.


How about a compromise and use 16mm2 SWA?? It exceeds 80A and is a little more workable than 25.

 

[neilma]

Thats a Great idea. Does that have a core for an earth within or will I need to supply another one (and what size would you recommend?)

Thanks VERY much for you help

 

[securespark]

As FW said in that quote above, use 3 core and use yellow as earth (labelled up with G/Y) but also terminate the SWA correctly and use the armour as a cpc too. I guess your Cu is metalclad? This way, you can terminate the SWA into the CU and earth continuity will not be a problem

Also, SWA is much neater than sep. tails.

 

[neilma]

Cool - I will do that then. As for the CU, no, its plastic so I wont be able to terminate the SWA directly to it (as is the swtch fuse). Is there anything you can buy that goes in the meter cabinet that the swa connects to (other than the earth bar or do you just use a gland and use the earth tag on that to connect to the earth bar)?

Same for the CU - For this I was going to break into the armour before the SWA reached the CU , put a glang on it and then run the 3 cores plus an earth lead that is attached to the gland into the CU for termination. Would that be ok?

Thx again
Neil

 

[Big_Spark]

Neil, if you use 3 core, with the yellow core being used as the Earth, then terminating the SWA into a plastic enclosure is not an issue.

For added protection, you could still run a 6mm tag from the gland at each end to the Earth bars of the Consumer unit and the switch fuse. This is desirable, but not required with a third core acting as yout Earth.

 

[neilma]

Great !

Thanks all - As always a great help at putting minds at rest