SWA, T&E or tails??

[HappyHippyDad]

Evening all..

I am currently doing my first full rewire. The customer is having the wall knocked down with the meter/cutout and CU on it. the plan was to move the CU under the stairs and get DNO to move the supply to the same place. They have said they cannot move the cutout to where the CU will be. The approx length from cutout to CU will now be around 8m so I need to add a fused switch. My questions are about which type of cable to use:

1. I could use 2 core 25mm SWA (seperate 16mm earth) but I am unsure of how easy this is to bend through the route? It will be going straight up from the meter box and then 90degress into the house wall entering directly under the first floor floorboards. What is the best way to get it through the wall without putting too much strain on it (with regards bending angle)?

2. BS7671 states 25mm to be used, however I am fusing down to 80A, could I not use 16mm SWA as CCC is 87A?

3. Could I use tails as at no point will the tails be buried in the wall. They will be going directly under the floor boards from outside the house (suitable protected outside) and then down from the ceiling directly behind the new CU (there will be a cavity behind new CU as I will bring out from the wall). Do they need to be protected if they are not getting buried in the wall?

4. Which is easier to move around/use T&E (16mm or 25mm), SWA (16mm or 25mm) or tails?

5. Which is the best fused switch to use? KMF, wylex metal? Can I gland SWA into a KMF or does it need an adaptable box?

Cheers chaps:biggrin:

 

[Simonslimline]

T&E only goes up to 16mm with a 6mm cpc.

 

[Octopus]

I would go down the SWA route then you don't have to worry about RCD protection... where ever you run them.

 

[Deleted member 26818]

I wish I could find in BS7671 exactly where it states 25mm needs to be used?
I seem to remember that some DNOs would move a cut out a short distance if the consumer was disabled?

 

[NDG Elecs]

I would preferably use 16mm 2 core SWA, fused down as you say. Never been keen on tails over such lengths running through a buildings fabric. You will be able to find out bending radii of the SWA online. The bigger casing on the Wylex switch fuses makes it a lot easier to terminate into. These ones:

Might be a bit of a swine to pull the SWA through though.

 

[Octopus]

I wish I could find in BS7671 exactly where it states 25mm needs to be used?

Its the pretty pictures in the OSG that most people refer to..... but I would say good practice.

 

[Andy78]

Evening all..

I am currently doing my first full rewire. The customer is having the wall knocked down with the meter/cutout and CU on it. the plan was to move the CU under the stairs and get DNO to move the supply to the same place. They have said they cannot move the cutout to where the CU will be. The approx length from cutout to CU will now be around 8m so I need to add a fused switch. My questions are about which type of cable to use:

1. I could use 2 core 25mm SWA (seperate 16mm earth) but I am unsure of how easy this is to bend through the route? It will be going straight up from the meter box and then 90degress into the house wall entering directly under the first floor floorboards. What is the best way to get it through the wall without putting too much strain on it (with regards bending angle)?
You would need to chase the brick out a bit to follow the bend then seal afterwards. Bending a cable that size isn't too much trouble with a couple of weetabix for brekky. I would be taking it down and under the ground floor as first choice though.

2. BS7671 states 25mm to be used does it ?, however I am fusing down to 80A, could I not use 16mm SWA as CCC is 87A? which table are you using for this data ?

3. Could I use tails as at no point will the tails be buried in the wall. They will be going directly under the floor boards from outside the house (suitable protected outside) and then down from the ceiling directly behind the new CU (there will be a cavity behind new CU as I will bring out from the wall). Do they need to be protected if they are not getting buried in the wall? Use SWA

4. Which is easier to move around/use T&E (16mm or 25mm), SWA (16mm or 25mm) or tails?

5. Which is the best fused switch to use? KMF, wylex metal? Can I gland SWA into a KMF or does it need an adaptable box? KMF will not accept a gland so you will need an extra box. Metal clad unit is less fiddly.

Cheers chaps:biggrin:

Remarks in red

 

[Plonker 3]

To make bending the SWA easier, simply drill the hole through the wall on a angle.

 

[amlu]

https://www.tlc-direct.co.uk/Products/CGFS100.html
fitted a couple recently, solid metal box with 32 and 25mm holes on top and bottom. value for money.

 

[HappyHippyDad]

I wish I could find in BS7671 exactly where it states 25mm needs to be used?
I seem to remember that some DNOs would move a cut out a short distance if the consumer was disabled?

ok, ok smarty pants! That OSG does have a lot to answer for!

To make bending the SWA easier, simply drill the hole through the wall on a angle.

Simple!! Cheers Dillb.

 

[Risteard]

Which is the best fused switch to use?

I presume you mean a switch fuse rather than fused switch.

 

[bigspark17]

3- if at no point do the tails go buried in wall tails all the way! Still need a metal switch fuse being greater than 3M from meter! Is under stairs best design place for cu? What height will it be?

 

[ipf]

Oh the woes of today......... what's wrong with a bit of 2H10 and a big mallet :wink5:

 

[uksparks]

Personally I would rather move the board so it's closer to the cutout so that i didn't have to fuse it down, I would rather have the capacity in the supply should I want to add juicy appliances.

 

[richy3333]

3- if at no point do the tails go buried in wall tails all the way! Still need a metal switch fuse being greater than 3M from meter! Is under stairs best design place for cu? What height will it be?

Have to agree. I'd never put a CU under the stairs. It's just isn't a good design.

 

[richy3333]

Evening all..

I am currently doing my first full rewire. The customer is having the wall knocked down with the meter/cutout and CU on it. the plan was to move the CU under the stairs and get DNO to move the supply to the same place. They have said they cannot move the cutout to where the CU will be. The approx length from cutout to CU will now be around 8m so I need to add a fused switch. My questions are about which type of cable to use:

1. I could use 2 core 25mm SWA (seperate 16mm earth) but I am unsure of how easy this is to bend through the route? It will be going straight up from the meter box and then 90degress into the house wall entering directly under the first floor floorboards. What is the best way to get it through the wall without putting too much strain on it (with regards bending angle)?

2. BS7671 states 25mm to be used, however I am fusing down to 80A, could I not use 16mm SWA as CCC is 87A?

3. Could I use tails as at no point will the tails be buried in the wall. They will be going directly under the floor boards from outside the house (suitable protected outside) and then down from the ceiling directly behind the new CU (there will be a cavity behind new CU as I will bring out from the wall). Do they need to be protected if they are not getting buried in the wall?

4. Which is easier to move around/use T&E (16mm or 25mm), SWA (16mm or 25mm) or tails?

5. Which is the best fused switch to use? KMF, wylex metal? Can I gland SWA into a KMF or does it need an adaptable box?

Cheers chaps:biggrin:

HHD have the DNO explained why they won't move the supply? I've had similar things done. They normally take their cable back to the outside so the joint is 'accessible', joint a new section that is then long enough to reach the new point required. Recently had this done on a 3 phase supply into a house, the new run was about 5 meters.

 

[bigspark17]

Personally I would rather move the board so it's closer to the cutout so that i didn't have to fuse it down, I would rather have the capacity in the supply should I want to add juicy appliances.

Dont see how its relevant as op has stated db is gunna be 8M away so irrelevant! If you use a cable capable of taking the dno full service fuse isolate it at that rating

 

[HappyHippyDad]

HHD have the DNO explained why they won't move the supply? I've had similar things done. They normally take their cable back to the outside so the joint is 'accessible', joint a new section that is then long enough to reach the new point required. Recently had this done on a 3 phase supply into a house, the new run was about 5 meters.

I dont think its set in stone that the supply will be moved to the outside, but I think its highly likely as that will be a much cheaper option for the customer. He may have to pay me more to extend the tails/SWA but I expect western power would have charged a great deal more than myself! The DNO options are to move it outside (outside wall is approx 30cm away from present supply) or to move it approx 6-7m (I think 8m was an exaggeration!) to the middle of the house.

 

[HappyHippyDad]

With regards point 3, which is easier to manipulate.. SWA or tails? I'm assuming tails bend a little more than the equivalent sized SWA?

 

[bigspark17]

Tails far easier and far easier to terminate! Have you not done much with tails or swa? This is pretty everday stuff for a spark id of thought.

 

[Lucien Nunes]

a bit of 2H10

*No protection required
*Chase with a finger chisel
*Includes 24mm² CPC
*45mm bending radius
*Stays where you put it unlike those huge black plastic snakes that leap up and bite you

Or 2H16 up to 100A

 

[jackhammerJIM]

As Dillb said drill down at an angle to get you under the floor . On this job i stitch drilled out a 3rd of a brick on a downward angle . If the existing gas meter had been in a recessed box i would have followed suit .

 

[7029 dave]

*No protection required
*Chase with a finger chisel
*Includes 24mm² CPC
*45mm bending radius
*Stays where you put it unlike those huge black plastic snakes that leap up and bite you

Or 2H16 up to 100A

2H16 is the biggest ive done, 19L1.5 in multi.

 

[bigspark17]

View attachment 30528View attachment 30529


As Dillb said drill down at an angle to get you under the floor . On this job i stitch drilled out a 3rd of a brick on a downward angle . If the existing gas meter had been in a recessed box i would have followed suit .

Waw have you really installed another meter box next to dno box! If you have that is shocking imo. Put ur switch fuse in the dno box, if its on. The owners property its theirs not dno so you may add your sw fuse in there! Flobbogasted at that pic!!

 

[Simonslimline]

Waw have you really installed another meter box next to dno box! If you have that is shocking imo. Put ur switch fuse in the dno box, if its on. The owners property its theirs not dno so you may add your sw fuse in there! Flobbogasted at that pic!!

Looks like a gas box not electric.

There is a G written on it.

 

[bigspark17]

So its comon practice to mount isolator armoured and ipbox in a gas meter chamber??

 

[Simonslimline]

So its comon practice to mount isolator armoured and ipbox in a gas meter chamber??

I think you have misunderstood what Jackhammer wrote to be honest.

 

[uksparks]

Dont see how its relevant as op has stated db is gunna be 8M away so irrelevant! If you use a cable capable of taking the dno full service fuse isolate it at that rating

It would be poor design to have no discrimination between the DNO fuse and the one you put in. It would be best to leave s gap of one fuse size so take it to 63A. Are you suggesting that it's ok to have two 100A fuses in line? Yes it might well protect the cable but it's not a great idea.

its not irrelevant.

 

[bigspark17]

It would be poor design to have no discrimination between the DNO fuse and the one you put in. It would be best to leave s gap of one fuse size so take it to 63A. Are you suggesting that it's ok to have two 100A fuses in line? Yes it might well protect the cable but it's not a great idea.

its not irrelevant.

Excuse me? So your suggesting using dno full capacity in one post then slating use of it in another.? Why is it bad practice fusing your submain at same as dno cutout on a capable ccc cable,? Can u explain?

 

[davesparks]

So its comon practice to mount isolator armoured and ipbox in a gas meter chamber??

No, the gas meter is in the gas box, the switchfuse is in the electric box waiting for a supply to be installed

 

[Plonker 3]

Excuse me? So your suggesting using dno full capacity in one post then slating use of it in another.? Why is it bad practice fusing your submain at same as dno cutout on a capable ccc cable,? Can u explain?

You never heard of discrimination?

 

[Leesparkykent]

You never heard of discrimination?

How would you go about achieving full discrimination between the DNO fuse and the one in the switch fuse then on a domestic setup such as the OP's? IMO it will be nigh on impossible.

 

[Plonker 3]

How would you go about achieving full discrimination between the DNO fuse and the one in the switch fuse then on a domestic setup such as the OP's? IMO it will be nigh on impossible.

Maybe so, but at least design it to allow for it.

 

[Leesparkykent]

The total let through energy of the downstream fuse will have to be less than the pre-arcing energy of the upstream fuse to achieve full discrimination.

 

[Midwest]

Interesting discussion on discrimination, a question I've asked myself before, and received conflicting replies.

The meter box belongs to the owner of the property, but the DNO has certain requirements; BS 8567 (gas is BS 8499).

I asked my DNO (SSE) before on what they would expect to see in such a situation, as here. I asked DNO what would they say about extended tails, 'We would expect a switch fuse, as it is a submain'. Could I put equipment in said box, answer 'No not really, what are you thinking of? Switch fuse? 'Ahhh, okay'.

Considering size of fuse in switch fuse (i.e. DNO 100a, switch fuse 80a), I asked Elecsa tech support for advice;

'Without referring to the time current characteristics of each device for the exact information we believe that the fault protection characteristics of each device will be similar but not the same.

They do provide fault and overload protection for the whole installation. Therefore there will certainly some discrimination with overload protection.

The final decision regarding the discrimination of the two devices would be down to the designer of the installation'.

 

[telectrix]

might be an idea to use a MCCB instead of a sw.fuse. cost permitting. this should ensure the MCCB tripping before the \DNO fuse. discuss?

 

[bigspark17]

might be an idea to use a MCCB instead of a sw.fuse. cost permitting. this should ensure the MCCB tripping before the \DNO fuse. discuss?

Mccb would clearly take out the supply before dno fuse. Domestically 80A is usially suffiecent but with some customers adding multiple electric showers and u/floor leccy heating they are demanding alot more. Had a call out last winter where customers off supply, dno fuse on the pole had gone 60A on pole, 80A in dno head 80A switch fuse! They replaced it with 80.

 

[jackhammerJIM]

Waw have you really installed another meter box next to dno box! If you have that is shocking imo. Put ur switch fuse in the dno box, if its on. The owners property its theirs not dno so you may add your sw fuse in there! Flobbogasted at that pic!!

Box on the right houses the gas meter you wally !

 

[davesparks]

Just to stir the pot a little bit,

Why does the submain fuse need to discriminate with the service fuse?
Why shouldn't you have 2x 100A fuses in series?

 

[Plonker 3]

Just bad design really. Why bother fitting smaller BS1362 fuse in spurs or plug tops?

 

[Midwest]

But in the case of fault protection, could you be certain that an 80 would go before a 100, and in terms of supply, restricting owner to 80amps?

 

[Plonker 3]

But in the case of fault protection, could you be certain that an 80 would go before a 100, and in terms of supply, restricting owner to 80amps?

Seriously?

come on now, how often have you seen over 80 amps being pulled on a supply for a long enough for it to blow the fuse under normal load conditions?

 

[Midwest]

Seriously?

come on now, how often have you seen over 80 amps being pulled on a supply for a long enough for it to blow the fuse under normal load conditions?

As I said, posted the same question a while back, and this was one of the replies. I'm willing to be convinced either way.

 

[grumpyjohn01]

https://www.tlc-direct.co.uk/Products/CGFS100.html
fitted a couple recently, solid metal box with 32 and 25mm holes on top and bottom. value for money.

I've used a few of these to supply submains etc & I agree top value and a decent quality unit,but I've been thinking...what about amendment 3? they don't comply eh?

 

[Midwest]

Do at the mo though. Bit small for 25mm tails IMO.

 

[grumpyjohn01]

I have a feeling I might be designing quite a few shed / workshop supplies before 1/1/16 ! (to be installed at a later date of course!) 25's fit OK I reckon from below behind DIN and hockeystick in and don't say bending radius....show me a domestic where the bending radius isnt compromised somewhere..

 

[Midwest]

Prefer the slightly bigger Wylex one myself. They are apparently coming up with a A3 design soon, expect it will be the old one with a metal lid over fuse & switch. Car manufacturers wouldn't sell many cars, if their new models were designed like that!

 

[grumpyjohn01]

Car manufacturers wouldn't sell many cars, if their new models were designed like that!

I have one word for you..Volkswagen..lol

 

[amlu]

I've used a few of these to supply submains etc & I agree top value and a decent quality unit,but I've been thinking...what about amendment 3? they don't comply eh?

One I bought and fitted around a month ago had a hinged steel flap over the fuse, not plastic like they show on the photo.

 

[Midwest]

I have one word for you..Volkswagen..lol

They don't make switch fuses.