New outbuilding question.

[OutOfTheGame]

First post and I'm looking for some advice if someone would be so kind.....I am a qualified electrician but it's been a long time (17 years) I've been in management so be kind

I'm looking for some advice I have an outbuilding that I wish to run a cable to. The cable I ran is a new 16mm2 2 core steel wire armour buried in soil it currently runs to the edge of the main building, it's 25m long.

The problem I have is getting a cable to the edge of the main building internally approx 10m from the (TN-S) supplied main board.

I can think of three choices (without major disruption)

1) there is an existing 20mm plastic conduit plastered into the wall, one thought was using a 16mm2 3 Core SWA and strip it back to the singles and use that existing drop which would only be the last two meters of the run. I haven't got any to check but I don't think the inner round sheathing would fit down a 20mm conduit?

2) Drop that last 2m down the cavity (yes I know....)

3) Down the outside of the building (asthetically would not look good)

No option is ideal but without major upheaval I can't think of another way. Any suggestions would be greatly appreciated.

Obviously cavity isn't ideal due to unsupported cable and potential thermal derating due to insulation but it's NOT polystyrene. It would be going down so no potential to transfer damp.

The conduit method is obviously reducing the mechanical protection of the cable and possibly reducing its thermal dissipation properties.

Second question is when I do get a cable in place what options do I have for joining in an enclosure attached the outside of the building? The outbuilding has an EV charger attached and living annex accommodation so would likely need the installation to hold maximum 64A I have never seen terminals rated for such a load.

I have looked everywhere and cannot find a reference method for singles in plastic conduit to calculate the cable. I know under normal circumstances that SWA would support a higher current but I intended to derate accordingly.

My ability to sign off the work has long expired so I'm just doing the donkey work and a colleague will inspect and test the installation.

 

[James]

3 x 16mm cable wont go down a 20mm conduit so that route is out of the question.
swa down a cavity is not an issue in my book.
outside the building is not likely to be an issue but as you say, it may spoilt the appearance.

 

[OutOfTheGame]

3 x 16mm cable wont go down a 20mm conduit so that route is out of the question.
swa down a cavity is not an issue in my book.
outside the building is not likely to be an issue but as you say, it may spoilt the appearance.

Hi, I tried with 3 cores of 16mm2 cables from an offcut of the 2 core I have and they do go down with room to spare.

 

[OutOfTheGame]

Trial with some offcuts

 

[James]

16mm singles are between 8 and 12mm diameter depending on the type.
just seen your picture, the armoured cable cores seem to fit ok. (smaller insulation layer than 6491 singles)
are you intending to conduit all the way to the board?
p.s. it may be tight running even the separate singles from the swa down the conduit if there are any bends.

 

[OutOfTheGame]

16mm singles are between 8 and 12mm diameter depending on the type.
just seen your picture, the armoured cable cores seem to fit ok. (smaller insulation layer than 6491 singles)
are you intending to conduit all the way to the board?
p.s. it may be tight running even the separate singles from the swa down the conduit if there are any bends.

The board end will remain SWA it's easy to get too it's the opposite end where it drops down the inside of the outside wall for around 2m. It comes out into a wiska box that used to supply my shed it's no longer needed hence the secondary joint question.

 

[mainline]

Second question is when I do get a cable in place what options do I have for joining in an enclosure attached the outside of the building? The outbuilding has an EV charger attached and living annex accommodation so would likely need the installation to hold maximum 64A I have never seen terminals rated for such a load.

A suitable enclosure with Henley blocks.

 

[James]

Rotary isolator?

 

[OutOfTheGame]

Rotary isolator?

Possibly although it will be under floor boards so not "inspectable" but good idea as can get 100a rated fairly easily. Could do a resin joint it I guess as they don't require inspection, but it would be indoors

 

[mainline]

Possibly although it will be under floor boards so not "inspectable" but good idea as can get 100a rated fairly easily. Could do a resin joint it I guess as they don't require inspection, but it would be indoors

OutOfTheGame said:
Second question is when I do get a cable in place what options do I have for joining in an enclosure attached the outside of the building?

So is the joint in or outside.

 

[OutOfTheGame]

OutOfTheGame said:
Second question is when I do get a cable in place what options do I have for joining in an enclosure attached the outside of the building?

So is the joint in or outside.

It could be either to be honest, easiest to do inside but if I choose inside I would have to put under floorboards so not easy to inspect, I could join it in an ip rated box on the outer wall and fill with raytech gel but then there is the question of what terminals to use inside?

 

[loz2754]

DIN rail enclosure would also work.

 

[James]

It could be either to be honest, easiest to do inside but if I choose inside I would have to put under floorboards so not easy to inspect, I could join it in an ip rated box on the outer wall and fill with raytech gel but then there is the question of what terminals to use inside?

Rotary isolator on the outside wall will serve as an ip rated junction box and a place to terminate the swa into.

 

[mainline]

It could be either to be honest, easiest to do inside but if I choose inside I would have to put under floorboards so not easy to inspect, I could join it in an ip rated box on the outer wall and fill with raytech gel but then there is the question of what terminals to use inside?

Torpedo joint inside, once done it's done.

 

[OutOfTheGame]

Thanks for all the ideas.

what is the concensus on best way to run the cable?

Method 1, 2 or 3?

 

[davesparks]

Stripping it down and squeezing it into a buried 20mm conduit sounds like a bad idea to me, you'll end up needing to RCD protect the distribution circuit.
How would you be intending to gland the SWA at the point it joins to the PVC conduit?

As for the joint i'd use through crimps or din rail terminals if it has to be in an enclosure on the wall or probably a torpedo joint if it's hidden away.

As far as terminals for a load like that go through crimps are obviously available for all sizes of cable. Regular DIN rail terminals are available up to 95mm and DIN mounted bolted terminals go up to very high current.

 

[OutOfTheGame]

Stripping it down and squeezing it into a buried 20mm conduit sounds like a bad idea to me, you'll end up needing to RCD protect the distribution circuit.
How would you be intending to gland the SWA at the point it joins to the PVC conduit?

As for the joint i'd use through crimps or din rail terminals if it has to be in an enclosure on the wall or probably a torpedo joint if it's hidden away.

As far as terminals for a load like that go through crimps are obviously available for all sizes of cable. Regular DIN rail terminals are available up to 95mm and DIN mounted bolted terminals go up to very high current.

Hi, thanks for replying.

The existing conduit is a dissused one that basically comes down the inside of an internal wall and pops out in a wiska box mounted on the outside of the building, I would terminate it in there.
That drop is about 2M, the sections before and after that drop would remain in SWA the idea was to use 3 core SWA internally so that I could earth the armour of the existing external 2 core SWA.

To get rid of the outer sheath I was going to use an adaptable box with a SWA gland one side and a stuffing gland holding the inner circular section in the other side, before finally going to the individual cores for that drop.

The cable will indeed be RCD protected by a 100ma RCD protecting the cable itself and then 30ma RCDs in the outbuilding.
The intention was either to terminate in there or second choice would be a normal torpedo joint and going down the cavity therefore remaining 100% SWA.

 

[nicebutdim]

I don't see three 16mm cores going through this 20mm conduit. Yes it has been proven they'll fit into a straight length and you can ensure they go in nicely, but that conduit goes through a wall and that means one of two things: 1. it has been bent and those bends will flatten it slightly. 2. Slip bends are fitted and they'll bust off.

By all means give it a go if you think it's worth trying, but don't pin your hopes on it.

 

[brianmoooore]

The cable will indeed be RCD protected by a 100ma RCD protecting the cable itself and then 30ma RCDs in the outbuilding.

It's only in limited circumstances that you will get discrimination between the two RCDs, and if any part of your supply cable, where it is not SWA, is buried within 50mm of the surface of a wall, the first RCD is required to be 30mA, not 100mA

 

[OutOfTheGame]

I don't see three 16mm cores going through this 20mm conduit. Yes it has been proven they'll fit into a straight length and you can ensure they go in nicely, but that conduit goes through a wall and that means one of two things: 1. it has been bent and those bends will flatten it slightly. 2. Slip bends are fitted and they'll bust off.

By all means give it a go if you think it's worth trying, but don't pin your hopes on it.

That may well make the decision for me but I put the conduit there is straight down the wall with one 90° bend about one foot from the end. I guess once the boards are up and it won't go I could just go cavity route?

I was just trying to discuss to see if there were any better ideas out there among all you experienced people as well confirm the options I had come up with were making the best of a bad job.

If I do manage to get the cores down does anyone know how much it at all ill need to derate the cable? Would I just consider the whole cable to be reference method A or B? It's in a standard cavity brick wall with dry-lined dot n dab over the top.

 

[davesparks]

To get rid of the outer sheath I was going to use an adaptable box with a SWA gland one side and a stuffing gland holding the inner circular section in the other side, before finally going to the individual cores for that drop.

Once the outer sheath is removed from the SWA it needs to be enclosed in conduit, the bedding layer is not compliant as an outer sheath and cannot be left unenclosed.

The cable will indeed be RCD protected by a 100ma RCD protecting the cable itself and then 30ma RCDs in the outbuilding.

That does not comply for protecting a cable buried in the wall, with the armour removed, and conductors protected by PVC conduit, it will have to be protected by 30mA RCD.

The intention was either to terminate in there or second choice would be a normal torpedo joint and going down the cavity therefore remaining 100% SWA.

 

[nicebutdim]

I can't help wondering about earthing arrangements and how important aesthetics really are when attempting to make the best of a less than ideal situation.