Shed CU install for registration assessment, catenary wire question

[ZEDEZ]

I've got my registration assessment with Elecsa coming up soon so I don't want to be making any mistakes that'll be pulled up.

Decided to go with a CU install at my my house in the shed, as it's something I've been meaning to do anyway, and it gives me time to make sure everything is 100% spot on.

You know how it is - you have everything planned out and it's only as you've got a specific part of the job to do the next day you really start thinking about it. Anyway, my original plan was to run the SWA feed along the alley wall, and then underground to get across the front of the garden gate (from which it would have a clear run in soil to the shed). I inspected the run properly a few days ago, and it's going to be quite a bit more involved to do that than I originally thought - I've got the foundations of the house to deal with as well as a concrete path I'd have to cut into yada yada - anyway - so I decided I'd instead run the SWA up the wall on a catenary wire to the shed.

The shed is roughly 2.7m away from this corner wall, and the highest point on the shed I can hang the catenary would be 2.5m. It's 2.5mm SWA, and this whole area is a private alley behind the house, so no traffic or anything like that.

I've never had any dealings with installing catenary before or the regs surrounding it, so I was wondering if someone could point me in the right direction.

EDIT:

Just looking through some books now. It's looking to me that unless it's 3m or over, it's a no go. Hoping someone will tell me otherwise!

 

[Andy78]

There are no heights under general rules that I am aware of for cables installed on a wire. Just the usual rules on adequate support for the cable.

I would have probably channelled the concrete personally though.

 

[Octopus]

I think the 3m is a "guide" as the vast majority of sheds are not that tall.

So start the catenary at a height of over 3m and slope it down to the highest point possible on the shed. When installing catenary wires, using tensioners are a must

 

[davesparks]

When you say a private alley do you mean it is owned by you or it is a communal alley for multiple properties?
If you don't own the land then you would need the owners permission to run this cable across it whether is is overhead or underground.

 

[Pete999]

I've got my registration assessment with Elecsa coming up soon so I don't want to be making any mistakes that'll be pulled up.

Decided to go with a CU install at my my house in the shed, as it's something I've been meaning to do anyway, and it gives me time to make sure everything is 100% spot on.

You know how it is - you have everything planned out and it's only as you've got a specific part of the job to do the next day you really start thinking about it. Anyway, my original plan was to run the SWA feed along the alley wall, and then underground to get across the front of the garden gate (from which it would have a clear run in soil to the shed). I inspected the run properly a few days ago, and it's going to be quite a bit more involved to do that than I originally thought - I've got the foundations of the house to deal with as well as a concrete path I'd have to cut into yada yada - anyway - so I decided I'd instead run the SWA up the wall on a catenary wire to the shed.

The shed is roughly 2.7m away from this corner wall, and the highest point on the shed I can hang the catenary would be 2.5m. It's 2.5mm SWA, and this whole area is a private alley behind the house, so no traffic or anything like that.

I've never had any dealings with installing catenary before or the regs surrounding it, so I was wondering if someone could point me in the right direction.

EDIT:

Just looking through some books now. It's looking to me that unless it's 3m or over, it's a no go. Hoping someone will tell me otherwise!

What wire are you using as a catenary wire? and how are you going to join the wire to the house and shed? personally I would have chased the concrete

 

[ZEDEZ]

Good idea, I hadn't thought about sloping it like that.

Regarding the tensioners, I hadn't bought any yet. I've got the wire, the clamps, and heavy duty hooks to suspend from. I was going to fix the wire on the house wall, get the wire to the right length just shy a few MM, and then fix it to the shed (so the 4 screws on the shed hook end would essentially bring it up to tension).

 

[Octopus]

Good idea, I hadn't thought about sloping it like that.

Regarding the tensioners, I hadn't bought any yet. I've got the wire, the clamps, and heavy duty hooks to suspend from. I was going to fix the wire on the house wall, get the wire to the right length just shy a few MM, and then fix it to the shed (so the 4 screws on the shed hook end would essentially bring it up to tension).

For your assessment?

https://www.tlc-direct.co.uk/Products/FXSTRAIN.html

Go on, spend the £2.25 + VAT and do it properly.

 

[Martin Kerr]

You can buy a catenary wire kit from most wholesalers , 3mm wire rope complete with fixings ,adjustable tensioner etc

 

[Andy78]

2.5mm seems a wee bit on the small side for feeding a CU.

 

[ZEDEZ]

Hi Pete. I bought some 3mm galvanized "wire rope" from Homebase (says on the back maximum load of 155kg), and a couple of heavy duty hook on square plates. I realise now that there are proper catenary kits you can get that come with all the necessary

I'm thinking I might just chase the concrete now. I've got a 230mm grinder that hasn't yet seen much use. I'm just worried I won't be able to get down to the required depth. I will be re-filling the chase with concrete though.

 

[Octopus]

Hi Pete. I bought some 3mm galvanized "wire rope" from Homebase (says on the back maximum load of 155kg), and a couple of heavy duty hook on square plates. I realise now that there are proper catenary kits you can get that come with all the necessary

I'm thinking I might just chase the concrete now. I've got a 230mm grinder that hasn't yet seen much use. I'm just worried I won't be able to get down to the required depth. I will be re-filling the chase with concrete though.

There is no stated "required depth" for SWA in any material (a glaring omission of BS 7671 IMHO) - so use your judgement, and remember you are planning to cover it with concrete!

 

[ZEDEZ]

The SWA (XLPE) is being fed from a 20a MCB, and the Shed CU will only have a 16a & 6a RCD protected MCB's feeding a couple of sockets and 2 lights.

In my circle we'd refer to a setup like this as "maggot", but given what it'll be used for, it'll do

Edit: I'm aware this probably won't provide for discrimination in the even of a a L-N fault, but given the distance from house CU and Shed, it's not really an issue.

 

[ZEDEZ]

There is no stated "required depth" for SWA in any material (a glaring omission of BS 7671 IMHO) - so use your judgement, and remember you are planning to cover it with concrete!

Amazing, thanks for this nugget!

 

[Octopus]

Amazing, thanks for this nugget!

This is one thing the IET need to get sorted out, even if only a list of recommendations.....

 

[Andy78]

Amazing, thanks for this nugget!

Have a look at 522.8.10.
Where the ground is likely to be disturbed it must be at a sufficient depth. In flower beds and lawns etc this would apply.
An accepted burial depth for marked cables is 600mm.

 

[davesparks]

I think the 3m is a "guide" as the vast majority of sheds are not that tall.

So start the catenary at a height of over 3m and slope it down to the highest point possible on the shed. When installing catenary wires, using tensioners are a must

I've not installed many catenaries, but I never used tensioners on the few I have done. I'm not sure I'd say they are a must really.
You've got to get a sensible amount of the slack out of the wire before attaching the tensioner anyway as they don't have that much travel in them, and by that point you might as well just fit it with the right amount of sag from the outset.

 

[HandySparks]

I'm thinking I might just chase the concrete now. I've got a 230mm grinder that hasn't yet seen much use. I'm just worried I won't be able to get down to the required depth. I will be re-filling the chase with concrete though.

If it's just a short run under a concrete path, I'd drop in a piece of plastic conduit, waste pipe or similar. Concrete over, then push the swa through later. Gives you options for changes or additions and ensures that there's no damage to the cable sheath while concreting.

 

[ZEDEZ]

For your assessment?

https://www.tlc-direct.co.uk/Products/FXSTRAIN.html

Go on, spend the £2.25 + VAT and do it properly.

Thanks Murdoch.