10mm T&E for Consumer unit supply

[GLENNSPARK]

cost is important but compliance always comes first...as does good design/practice...

 

[guest119]

There may be access issues also re tripped devices, ones which require landlord only access.

Boydy

 

[D Skelton]

I couldnt agree more, cost is important and would be the difference winning or loosing the job, but to be honest I've got no idea what HMOs are...her majestics office? Her majesties orders??? Himmlers marching orders??
I suppose HRC fuse carriers in a metal clad main board would be cheaper than a number of switched fuses.

House of Multiple Occupancy.

You're right, I'd love to know where to find somewhere to purchase new wylex rewireable fuse boxes though!

 

[Zebra Stripe]

Just re-use an old one and repair any damage to the original enclosure. Im sure most are still good for another 20 or so years service.



Only kidding!!

 

[Guest55]

i like how everyone automatically throws in the demand for swa just because the word "submain" is used.

really ? for internal wiring in a domestic dwelling ??
and of course we're all going to chase in this oversized cable with additional labour costs of --- pounds...........

this job is so simple its beyond back of smoke packet design.........

dno cut out >>>> tails to 6 way 100A CU >>>>> 5 ways for bedsits , 1 for landlord >>>>>>>> 40A mcb >>>>> 6mm T&E >>>>>> 4 way CU in bedsits >>>>>> 20A skts + 6A lts.

and as the upstream device is double the rating of the highest downstream , you've even got decent chance of discrimination.

 

[D Skelton]

Just re-use an old one and repair any damage to the original enclosure. Im sure most are still good for another 20 or so years service.

I don't tend to keep old gear that I rip out, let alone sell it lol.

I stand by what I say. MCB's up front. Without that you're looking at 5 x switchfuses, 5 x 45A HRCs, 6mm SWA cable and a lot of bother.

The fact remains, the installation of MCBs up front is perfectly compliant and gives more than adequate discrimination for overload purposes. In the unlikely even of a short circuit on a brand new installation, then the main DB would just have to remain accessible wouldn't it.

Spec switchfuses, lose the work, it's really that simple.

 

[Zebra Stripe]

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

Well, you have to go by what was asked surely, in this case he was saying presume burried in a wall

 

[Zebra Stripe]

I don't tend to keep old gear that I rip out, let alone sell it lol.

I stand by what I say. MCB's up front. Without that you're looking at 5 x switchfuses, 5 x 45A HRCs, 6mm SWA cable and a lot of bother.

The fact remains, the installation of MCBs up front is perfectly compliant and gives more than adequate discrimination for overload purposes. In the unlikely even of a short circuit on a brand new installation, then the main DB would just have to remain accessible wouldn't it.

Spec switchfuses, lose the work, it's really that simple.

Hey I like the selective quote...makes me look a bit rogue'ish...so tell me why suddenly on the attact? its all opinion if compliant to BS7671 or some other suitable Regulation

 

[D Skelton]

Hey I like the selective quote...makes me look a bit rogue'ish...so tell me why suddenly on the attact? its all opinion if compliant to BS7671 or some other suitable Regulation

It was meant in jest my friend

I know it is all opinion, that's why I value discussions such as these

 

[Zebra Stripe]

Oops:lipsrsealed2:

Hey thats why Im banned from texting especially when trying to get into some women's ........

So just out of interest, and I am by no means fluent in this aspect, but, Im led to believe that discrimination or even partial discrimination is not possible between MCB and MCB.

 

[sparksburnout]

Can I just ask, why are some guys speccing SWA when it is within the confines of a domestic dwelling??? Are we anticipating the occupants to be trying to dig the place up?

 

[D Skelton]

Re: 10mm T&E for Consumer unit supply

Oops:lipsrsealed2:

Hey thats why Im banned from texting especially when trying to get into some women's ........

So just out of interest, and I am by no means fluent in this aspect, but, Im led to believe that discrimination or even partial discrimination is not possible between MCB and MCB.

It depends entirely on the prospective fault current. Discrimination for the purpose of overload protection is entirely affordable though.

- - - Updated - - -

Can I just ask, why are some guys speccing SWA when it is within the confines of a domestic dwelling??? Are we anticipating the occupants to be trying to dig the place up?

Because that's what the OP said the customer asked for.

Are you happy to bury a non-RCD protected T+E submain in the wall then?

 

[sparksburnout]

Re: 10mm T&E for Consumer unit supply

It depends entirely on the prospective fault current. Discrimination for the purpose of overload protection is entirely affordable though.

- - - Updated - - -



Because that's what the OP said the customer asked for.

Are you happy to bury a non-RCD protected T+E submain in the wall then?

No of course not, there would be an RCD protecting each one, as someone has already suggested. No one is going to price for SWA and expect to get the job???

 

[Zebra Stripe]

Yes overload I understand, but with short circuit its more complicated. I thought cascading/discrimination was usually in the ratio 2:1 with fuses or perhaps a mixture of fuses and MCBs. Although I've read that you need the downstream device to have a total I2t less than the pre arcing I2t of the upstream device, I've yet to get round to fully grasping this aspect and to be honest have never been in a situation where I've need the knowledge. Perhaps I need to read up on this and maybe start a new thread.:smile5:

 

[D Skelton]

Re: 10mm T&E for Consumer unit supply

No of course not, there would be an RCD protecting each one, as someone has already suggested. No one is going to price for SWA and expect to get the job???

An RCD up front and then another in the board?!

Dunno where you get your SWA from but I get it cheaper that T+E.

 

[Zebra Stripe]

Re: 10mm T&E for Consumer unit supply

No of course not, there would be an RCD protecting each one, as someone has already suggested. No one is going to price for SWA and expect to get the job???

Can you explain what you actually mean? So are you saying put a front end 30mA RCD on each supply to each flat with T&E submain burried?

 

[nickblake]

Loads of switch fuses and henly block dont like the sound of that,, one main switch to isolate the Complete supply then one decent TP CU with single phase conversion kit , with a circuit supplying each Flat, if its a new install the i would use a 3 core swa and use 16mm reason for this is if they decide to up grade the flats in the future then the supplies are there , always plan for the future

 

[D Skelton]

Yes overload I understand, but with short circuit its more complicated. I thought cascading/discrimination was usually in the ratio 2:1 with fuses or perhaps a mixture of fuses and MCBs. Although I've read that you need the downstream device to have a total I2t less than the pre arcing I2t of the upstream device, I've yet to get round to fully grasping this aspect and to be honest have never been in a situation where I've need the knowledge. Perhaps I need to read up on this and maybe start a new thread.:smile5:

That only applies to fuses. What you don't want to have is a situation where a circuit tripping a downstream device causes the upstream fuse to have to 'prepare to trip' to use a phrase. Pre arcing is a state where the fuse is subjected to the fault current but has not yet tripped. The more this happens the more damaged the fuse becomes.

Say for example you have a DB where the highest rated MCB is 50A and you plan to supply this via a sub main. If for example you choose a 63A fuse and it has a prearcing current of 45A (it won't have, this is purely an example) then this is bad design. You would need to uprate the supply fuse or, if possible, downgrade the downstream device.

A very simplistic explanation I know.

 

[D Skelton]

Loads of switch fuses and henly block dont like the sound of that,, one main switch to isolate the Complete supply then one decent TP CU with single phase conversion kit , with a circuit supplying each Flat, if its a new install the i would use a 3 core swa and use 16mm reason for this is if they decide to up grade the flats in the future then the supplies are there , always plan for the future

And you've just priced yourself out of the work!

 

[Guest55]

jesus , dunno wtf's going on in this thread anymore so im out.