10mm T&E for Consumer unit supply

[Sav]

Morning everyone,

Hope your all well.

Just a a quick question. We have been asked to quote for a HMO conversion, in a domestic property. So basically, the developer buys these houses and makes rooms out if them.
Leach room is basic, small ensuite shower ( not electric ), lights and a few sockets. There is a communal kitchen and each room is supplied by its own consumer unit.
There are 2 circuits, lights and sockets.
What I'm asking is, the consumer units are fed via 10mm T&E that go down to 60A isolators, which in turn go into a big Henley block.
There are about 5 rooms, so five isolators.
I would have thought that the consumer units for each room , from the isolators had have 16mm earth ?
Obviously things like communal smokes and fire alarm system etc are fed from landlord board.
The supply is a TN-S single phase

regards,
sav

 

[Plonker 3]

Why a 16mm Earth?

What bonding is being done in each room?

 

[Octopus]

So are you putting RCD's by the house incoming supply to protect the 10mm T&E - that's not an ideal position - you need to be thinking of SWA IMHO

 

[Knobhead]

Isolators or switch fuses at the intake? How is the 10mm to be run? To many questions yet.

 

[Sav]

Ok. The set up his current electrician has is as follows

single phase TNS 100A BS1361. Tails into single meter.
From there into Henley blocks using 25mm tails.
From Henley blocks, 25mm tails into Mk60A isolator.
From isolator 10mm T&E ( presume buried in wall & under floor etc into consumer unit.
Consumer unit has 30ma RCD main switch and 2 circuits. Lights and sockets.
I also would have though swa from isolator into consumer unit.
But I would use 16mm ??
bonding as far as I could see is main gas and water in 10mm. I couldn't see an earth from the metal isolators to the MET though. Also couldn't see any supplementary bonding in the rooms. That's why the alarm bells rang in the head.
But I don't think 10mm T&E is the way to go ?
Sav

 

[GLENNSPARK]

Morning everyone,

Hope your all well.

Just a a quick question. We have been asked to quote for a HMO conversion, in a domestic property. So basically, the developer buys these houses and makes rooms out if them.
Leach room is basic, small ensuite shower ( not electric ), lights and a few sockets. There is a communal kitchen and each room is supplied by its own consumer unit.
There are 2 circuits, lights and sockets.
What I'm asking is, the consumer units are fed via 10mm T&E that go down to 60A isolators, which in turn go into a big Henley block.
There are about 5 rooms, so five isolators.
I would have thought that the consumer units for each room , from the isolators had have 16mm earth ?
Obviously things like communal smokes and fire alarm system etc are fed from landlord board.
The supply is a TN-S single phase

regards,
sav

cant see myself renting off this fella though....

 

[GLENNSPARK]

this keeps cropping up does this.

inappropriate cable type for the proposed feeders

as Murdoch has quite rightly pointed out the way forward here is SWAs with bottom end additional protection for finals...

 

[D Skelton]

63A cut out for a DB supply with only a socket and light circuit?? What's the max demand of each unit, 20A? I'd be looking at maybe a 20A MCB in a DB at the origin then on to a local two way RCD DB fed via SWA sized accordingly with a 16A for the sockets and a 3A for the lights. Will each unit be seperately metered and if so, will that be a suppliers meter or a private landlords meter?

As others have said there is far too much we don't know to provide accurate advice so I'm only speculating, one thing is for sure though and that is this installation needs some proper thought out design. Slinging in 63A switch fuses and T+E submains just doesn't cut it I'm afraid.

 

[Guest55]

16mm for 1 sockets & 1 lights circuit ?

do me a favour , the existing 10mm is already hideously over rated as it is for what will unlikely be more than 20A per unit after diversity

4 or 6mm t&e subs in pvc trunking to each bedsit is the sort of cost savy design you should be considering.

 

[guest119]

So is the 10mm tne then fused at 100a or am I reading this wrongly?

Boydy

 

[Jimmyb]

63A cut out for a DB supply with only a socket and light circuit?? What's the max demand of each unit, 20A? I'd be looking at maybe a 20A MCB in a DB at the origin then on to a local two way RCD DB fed via SWA sized accordingly with a 16A for the sockets and a 3A for the lights. Will each unit be seperately metered and if so, will that be a suppliers meter or a private landlords meter?

As others have said there is far too much we don't know to provide accurate advice so I'm only speculating, one thing is for sure though and that is this installation needs some proper thought out design. Slinging in 63A switch fuses and T+E submains just doesn't cut it I'm afraid.

a 20mcb at the start wilpl trip at same time as 16 if a fault occurs

 

[londonlec]

Ive done these a few times.

Large DB beside meter etc. 6mm cable to small RCD CU in each room. Either T+E (run surface) or SWA, as others have said.


Edit: 20/32A breaker feeding each room.

 

[D Skelton]

a 20mcb at the start wilpl trip at same time as 16 if a fault occurs

Depends on the fault, if it's a direct short then so will a 32, a 40 or a 50. A gamble as to which one will go first. The only way to prevent this would be to use an HRC fuse, overkill for such an installation IMHO.

 

[Zebra Stripe]

Some partial discrimination between the upstream ocpd and the final circuits imo would be a good thing here, especially if the incomers are some distance from the flats.
And in this instance an HRC fuse (Switch fuse) to MCB in CU, would be better than MCB to MCB.

Infact, if your not worried about OCPD discimination and the posibility of the upstream device (MCB) operating under fault conditions on a flats final circuit, why worry about a front end RCD being installed?

 

[D Skelton]

The OP could go for 45A HRC fuses then, I still think it's overkill though, especially cost wise. How many short circuit faults are we anticipating will occur?

Front end RCDs are bad for a whole host of reasons as they trip under many different conditions.