CU/ tails chage advise

[c.randall7]

Hi guys got a quick question for all you pro's out there.

I'm doing a board change for an assessment and it seems a bit strange. It's a PME system with 100A main fuse, 25mm from the meter to a 63A type B DP CB then the tails drop down to 10mm T&E for about 5m to the CU. The main earth also drops down from 16mm to 10mm at this point. My first thoughts are that it's boarder line safe and not the way to do things. The max demand is less than the 63A but still not very happy with it.

My question is should i just uprate the tails and main earth (25mm, 16mm) or should i change this 63A CB as well. Bare in mind the 5m run and that it's an assessment job.

I would be greatful of any replys

 

[boballum]

Your meter tails and earth conductor are coorect for your 1st board however im pretty sure that 10mm t&e is not rated at 63a use amtech or the regs to check, ideally a 63a switchfuse using a BS88 fuse would be used to provide adequate discrimination along with 16mm t&e depending on installation method, the current carrying capacity drops rapidly when enclosed in trunking

 

[DurhamSparky]

Upgrade Tails to 25mm and earth to 16mm

as per 17th Regs PME should be NOTHING LESS for a 100amp Fuse! (p.s is it actually 100a or is that what the sticker says??) i would also change the 63a DP Isolator to a 100A DP for the sake of £10

also ensure Main Gas and Water Bonding is Present with this sized at 10mm

 

[c.randall7]

Thanks for reply. I haven't pulled the fuse to have a look, it says soo on the wooded board it's mounted on, but i will have let the fuse 'fall out' if i'm to change the 63A switch so I'll have a look. Gas and water is 10mm but it's all terminated in the CU earth bar so i'll also fit an MET. Do you think the assesser will be happy with the 5m run? or should i fit a 100A fused DP switch?

 

[DurhamSparky]

hi mate!

leave gas and water in the earth bar of CU its fine there!

fit he 100a DP isolator in place of the 63a one!

Contactum Mains Switch (or a similar one from screwfix etc) http://www.screwfix.com/prods/53010...rs/Wylex-100A-DP-Incomer-Main-Switch-Isolator

 

[c.randall7]

the link you sent, is that not just for main switch in CU? If so the new board i'm fitting has all the rcd,s and main switch with it or can i fit that in the meter cuboard out side of the CU were the 63 is?

 

[DurhamSparky]

yes mate! as your Meter Tails are over 3m you need a Switch and the 100a Isolator is the Tricky!! it should be a straight swap for the 63a one! (nothing wrong with leaving the 63a one in mind) just makes its rating higher should the fuse ever be upgraded by the DNO and it can carry a higher rated current!

 

[c.randall7]

Sorry to harp on! should it be fussed say 80a for discrimination or is a stright DP isolator fine (as per regs)

 

[Guest123]

The MCB is there for a reason as tails over 3M require additional overcurrent protection so you cant take it out and fit a double pole isolator, a switchfuse would be acceptable but unless you feel the max demand exceeds 63A I would leave it in.

You will need to upgrade the cpc as at 4mm, it isn't large enough to act as both cpc and main protective bonding conductor. Clipped direct a 10mm T&E will carry 64A so technically is acceptable but I wouldn't be happy leaving it and as you have to upgrade the cpc anyway you might aswell change all of it.

The 25mm tails & 16mm main earth from the meter to the MCB are fine.

 

[c.randall7]

Thanks alot guys you have confirmed what i was thinking just needed to be sure, i'd gutted if failed my assessment over it! thanks again