Advice req'd to power log cabin

[Norv]

As I've said before I'm helping a mate build his log cabin so he can live in it. The electrician has just got to come back for 2nd fix. The power for the cabin is going to be taken from a board about 50m away in an old workshop - Here is a picture of it. Its got a 100A main fuse.

How would you do it ?
Could we take the tails out the meter into a Henly block & then back into that inline 100A switch to feed the original CU & then the new set of tails into one of these ? Does there need to be some RCD protection to protect the SWA cable running undeground to the cabin ?

 

[Steve]

Due to the nature of SWA, RCD protection is not nessecary for the cable.

 

[ColJack]

meter - isolator - henley block - old board / new board..

don't mess at the meter as this entails you cutting the main fuse seals..


might just be easier to get the DNO in to put a new supply to the cabin if it's a permanent thing..

 

[Norv]

Contacted the DNO & they have said about 10 weeks before they can start the job & then they wanted the trench dug in a specific place which would have been almost impossible because it was right through the middle of a 3ft thick concrete slab.

I've already checked about cutting the fuse seals & they just said call us when the jobs done to get them re-sealed. To be honest I couldnt believe how easy the conversation went...

Just wanted to know if what I have proposed would be ok.

 

[JohnD]

ColJack is right.

You have that (suppliers) main switch. Put your Henley block downstream of that. Otherwise, there would be no main switch for the entire installation.

You have no need to pull the fuse since you can cut power with that 100A DP switch.

I see it is a MEM one and you will find you can open a sliding hatch on the load side of the enclosure to connect your new 25mm tails to the Henley, without having to expose the (live) supply side terminals.

Why do you want to use that old-fashioned Wylex?

 

[securespark]

Od fashioned? Who're you calling old fashioned?

 

[Norv]

Cheers for the advice. The electrician doing the work is a friend of the family & he's giving me a chance to get some experience.

JohnD - I looked on the TLC site & found that Wylex unit, anyone got any other suggestions, must admit it does look a bit big....

 

[JohnD]

I would have gone for a 4-module 2-way MEM enclosure, with 2 ways taken up by a 100A DP switch; one with (say) a 63A MCB or whatever suits your cable to the outbuilding; and one spare which you might later use e.g. for garden lighting.

It doesn't have to be MEM, other makes are equivalent (but none better ). I would get the same brand as your other CUs. You can get a metal one if it is lilely to get knocked or you are using SWA, or an insulated plastic one. I would say less than half the size of the one you show. Crabtree are good but have a very unusual way of fitting switches and MCBs. MK are nothing special but better than the cheap brands. Some brands do not have a wide range of MCBs, RCDs or RCBOs that you may later want

If you are using SWA, the better brands tend to be roomier inside.

there are a lot of these small units sold as "Garage CUs" but they usually include an RCD; which it will be more convenient for you to have in the outbuilding itself; this is OK if you are using SWA. You can get metal, insulated,or water resistant enclosures.

The Wylex Switchfuse you show has a large replaceable cartridge fuse. Surely the shed won't really have a 100A supply?

MCBs are much easier to reset in the very rare occurence of them tripping; and of course there is no cost, like a spare fuse.

 

[Norv]

I reckon I'll probably use a 16mm cable which is rated at 78 amps (in the TLC book). A 63A MCB will do the job but say I wanted to protect the cable at 70A or I wanted to use a bigger cable. What would you do then?Looking about I cant see any suppliers selling bigger MCB's than 63A.

 

[plugwash]

use a switchfuse

 

[nozspark]

I fitted a much smaller switch fuse than that the other week. It was 80A and was just a little taller than the fuse and about 3 x the width. It took 25m tails with ease, but unfortunately it would be no good for terminating armour.

I'm afraid I can't remember the brand though....anyone??

 

[JohnD]

this is the MEM 80A one. they do a 100A one which is rather bigger

 

[nozspark]

Yep, that's the baby.
When I first saw it I thought that someone was having a joke, but it turned out to be ok.

 

[RF Lighting]

Have you got one for sale John?

 

[JohnD]

Some DNOs fit it, I have an idea in the midlands.