New outbuilding question.

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.

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.

James said:

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.

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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.

Trial with some offcuts

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.

James said:

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.

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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.

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? 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.

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A suitable enclosure with Henley blocks.

Rotary isolator?

James said:

Rotary isolator?

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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:

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

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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.

mainline said:

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.

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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?

DIN rail enclosure would also work.

OutOfTheGame said:

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?

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

OutOfTheGame said:

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?

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Torpedo joint inside, once done it's done.

Thanks for all the ideas.

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

Method 1, 2 or 3?