Supply feed to holiday home

[pc1966]

Just make sure that the devices that this cable is connected to are also rated at 90c then all is well.

In this case you can safely ignore the 90C rating as the size of the cable is down to volt drop.

For example the 95mm XLPE 90C SWA cable is rated at 239A (Table 4E4A, method D) so at 63A your I2R loss is just over 14 times lower, so your table values for 20C ground -> 90C insulation rise scaled to that will be of the order of 5C (i.e. cable runs at 25C is in duct in ground at 20C).

Wrangling and terminating 95mm on the other hand is a serious issue!

 

[sclarkin]

In this case you can safely ignore the 90C rating as the size of the cable is down to volt drop.

For example the 95mm XLPE 90C SWA cable is rated at 239A (Table 4E4A, method D) so at 63A your I2R loss is just over 14 times lower, so your table values for 20C ground -> 90C insulation rise scaled to that will be of the order of 5C (i.e. cable runs at 25C is in duct in ground at 20C).

Wrangling and terminating 95mm on the other hand is a serious issue!

Interesting.
Yeah been a long time since I've worked with 95mm and above. Sure I can dig out my old club hammer to help with termination ?

 

[brianmoooore]

Wrangling and terminating 95mm on the other hand is a serious issue!

I actually have 95mm2 SWA as a submain to my own house. Not chosen because it was required, but because a supplier delivering a reel to a job I was doing damaged the cable, leading to me rejecting it.
Replacement was delivered to site, but the damaged cable not removed, so an undamaged section ended up feeding my house.
It terminates into a surprisingly small galvanized adaptable box with crimped lugs on the conductors. 25mm2 tails are also fitted with crimped lugs, and the pairs of lugs bolted together before the box was resin filled.

 

[pc1966]

Interesting.
Yeah been a long time since I've worked with 95mm and above. Sure I can dig out my old club hammer to help with termination ?

I don't normally work with anything big, so last year when I had a job that might need it I bought just 1m of the planned cable to get a feel for what I might be getting myself it for and to check the glands would fit properly, etc.

Can't imagine what the postman though of it!

 

[pc1966]

It terminates into a surprisingly small galvanized adaptable box with crimped lugs on the conductors. 25mm2 tails are also fitted with crimped lugs, and the pairs of lugs bolted together before the box was resin filled.

Interesting, though in my case the tools I have only crimp up to 50mm so would have to think about borrowing/renting something for above that.

The likes of the Al cable are sectorial, presumably you get special quadrant shaped crimps for them?

If cable cost were the driving factor for the OP I would be looking at the 70mm 4-code aluminium option with some sort of resin filled termination, probably going to 16mm 4-core copper and then finally pairs of the 16mm to terminals indoors so you can IR test each core separately.

Based on the illustration here, for minimum inductance factor I would pair opposite cores, so brown & grey for L and blue & black for N for the cable:

https://www.clevelandcable.com/media/pdfs/BS5467-PVC-aluminium-conductor-mains-cable.pdf

While it might need to be TT if a caravan like metal building, for a house it will probably need to be considered the same for supply Zs being too high so still a delay RCD up front at the outbuilding CU. However, the data for 4-core 70mm copper has the armour down as 131mm CSA so above the 10mm copper equivalent needed for extraneous bond TN-C-S so could supplement any local earth rod OK and keep the Zs down far lower than just a rod or two.

I guess it would meed the end of cable Zs for a 63A fuse on 5s disconnection but not checked that, really would need a check for the actual cable armour R2 and supply Ze.

 

[pc1966]

If cable cost were the driving factor for the OP I would be looking at the 70mm 4-code aluminium option with some sort of resin filled termination, probably going to 16mm 4-core copper and then finally pairs of the 16mm to terminals indoors so you can IR test each core separately.

Really it should be 5-core 16mm, so there is a copper CPC linked to the major cable's armour to keep the overall path above 10mm if TN-C-S is considered (or even just marginal on the supply fuse end-of-cable Zs limit).

 

[sclarkin]

Thanks all for the responses.
It's a shepards hut in one of their fields.
The farm is already a tt supply

 

[Spoon]

I'd like to see the process of laying out 300 meters on 95mm cable. Doesn't look like fun.

 

[pc1966]

I'd like to see the process of laying out 300 meters on 95mm cable. Doesn't look like fun.

Yes, better to fight an arngy python that have been overdosing on ------...

 

[Mike Johnson]

Easy, tie one end to the Combine Harvester, put the reel end on the forks of the Tractor and pull. ?

 

[Spoon]

Easy, tie one end to the Combine Harvester, put the reel end on the forks of the Tractor and pull. ?

Think you might want some rollers over that 300 meters, unless you want your cable to be 400 meters long. ?

 

[timhoward]

Something I’ve long wondered - can this amazing toy also lay cable or would it end up too near the surface?

 

[brianmoooore]

300m of 95mm2 2C SWA should weigh about 1000Kg, so no big problem at all for the type of gear found on a farm. I used a small trailer with the reel threaded onto a length of steel bar tied across the top of the trailer sides.
95mm2 SWA isn't as big as some of you are thinking.

 

[brianmoooore]

Something I’ve long wondered - can this amazing toy also lay cable or would it end up too near the surface?

Never used one, but the required depth for laying pipe is every bit as much as for cable, so the answer is yes. The warning tape would be the problem.
We have a 400m long service pipe to our property, which sprung an expensive leak about three years ago. The pipe is 60 years old, so I was looking at these machines with a view to replacing it, but in the end the leak was easily found, along with the reason for it, so it was just repaired.

 

[brianmoooore]

It looks like the design of the shepherd's hut is the problem, if they think they need a 63A supply. Too many instantaneous water heaters with no allowable diversity I suspect.
I have a as yet unused (and possibly never to be used) site for a shepherd's hut to complement my holiday cottages, but I did some design work on it, and it's possible to be all electric and run on a supply of 6kW.

 

[sclarkin]

It looks like the design of the shepherd's hut is the problem, if they think they need a 63A supply. Too many instantaneous water heaters with no allowable diversity I suspect.
I have a as yet unused (and possibly never to be used) site for a shepherd's hut to complement my holiday cottages, but I did some design work on it, and it's possible to be all electric and run on a supply of 6kW.

Yeah I think 63 is too much but they have spec 9kw shower, heating, range style cooker

 

[brianmoooore]

Loose the instantaneous shower, and fit a 3kW pressurised storage cylinder. Feeds the sink and basin as well, and gives a far better shower than any instantaneous one. Arrange cooker to load shed both the water heater an the room heating when in use. Water heating off for a while won't matter, and if a cooker is pumping 6kW of heat into the hut, they won't mis the heating either.
2kW should be more than enough fixed heating for an insulated hut, but a 2kW portable heater can be provided as well for exceptionally cold weather, and just plug into the socket circuit.

 

[sclarkin]

Loose the instantaneous shower, and fit a 3kW pressurised storage cylinder. Feeds the sink and basin as well, and gives a far better shower than any instantaneous one. Arrange cooker to load shed both the water heater an the room heating when in use. Water heating off for a while won't matter, and if a cooker is pumping 6kW of heat into the hut, they won't mis the heating either.
2kW should be more than enough fixed heating for an insulated hut, but a 2kW portable heater can be provided as well for exceptionally cold weather, and just plug into the socket circuit.

Thanks the customer has obviously outsourced the hut to a specialist company but saying that they are a new start up so will pass on some ideas for her to forward on to them. May even become their recommended installer ?

 

[pc1966]

Good luck for the project, hopefully you get it and can let us know how it all pans out.

One aspect to consider carefully is the supply access, and if this holiday home would ever be used while the main home owners are away. As it is TT, the SWA will need a 100mA or 300mA delay RCD before it (as well as a fused-switch or similar for OCPD, more to protect the home main fuse and assuming it is 100A otherwise no usable selectivity).

To make sure that delay-RCD is very unlikely to trip you should plan on using a CU that has double-pole RCD on all circuits. Even cheap dual-RCD boards do that. But given the overall cost already and the benefits of easier fault isolation, etc, I would suggest an all-RCBO CU, but then look for the RCBO that are neutral-switching so you don't end up with a N-E fault taking out everything. The recent compact RCBO from Fusebox, Wylex, and Crabtree all seems to be DP switching and are reasonably priced.

Don't forget to include SPD. I think some of the CUs come pre-fitted anyway, such as this:

Wylex NM906FLEXS 100a Main switch+Type 2 SPD 9 Way Consumer Unit

Buy Online Wylex NM906FLEXS 100a Main switch+Type 2 SPD 9 Way Consumer Unit from Edwardes Brothers, 24 Hour UK next day delivery

www.edwardes.co.uk

If the main home is feed from overhead lines it might be worth checking it already has SPD, or maybe making the recommendation that they should consider adding some.

 

[JD6400]

Never used one, but the required depth for laying pipe is every bit as much as for cable, so the answer is yes. The warning tape would be the problem.
We have a 400m long service pipe to our property, which sprung an expensive leak about three years ago. The pipe is 60 years old, so I was looking at these machines with a view to replacing it, but in the end the leak was easily found, along with the reason for it, so it was just repaired.

They are quite good , but that particular one would probably only manage a depth of around 400mm and not the required 1000mm
Across productive agriculture land.
But even with a more substantial mole and blade along with a machine somewhere in the region of 10 times the horse power of the one in the picture , unless you can 100% guarantee no stones or sharps in what you are moleing , I would not want to put my name and liability to the job.

As a company we generally install 3 or 4 runs like this a year , the largest we have done from memory was around 780m.
It is all about having correct kit , and at a push can be carried out single handed , but is a obviously a lot quicker and more straight forward with a 2 or 3 people.
What ever you do , always lay and never pull a cable of this length.