superconducting T&E discovered

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As the least incompetent person willing to travel, I have been called to look at an eccentric uncle's smallholding on a remote UK island. The main dwlghouse supply is recent and well installed 3 phase supply, efficently and safely covering the whole house, which has radio teleswitch type night storage heating system. It looks, and is, good.
However
the property has 4 external buildings in a "village street" arrangement. cowshed & workshop in-line abutt onto the gable of the dwelling house. across the "street" is a vehicle garage abutting onto a small farm workers cottage.

these external buildings have become modernised over the years to include such modern accoutrements as electric lighting, power tools including a welder, over-basin water heaters, electric showers, computers, wall heaters,fan heaters, yea verily even radyoe and televysionnes.

ALL of these external buildings have been supplied, since roughly 1980, by a 12m length of 1.5 sq.mm T&E which runs from a spare way in one of the CU's of the main dwelling house, under the floor, out under the village street and into a small CU in the garage. from there, electrical installation has been "organic". So to speak.

I can't quite understand it myself. I guess that wire was run at first for lighting and the whole thing has grown from there. but that wire must have been carrying up to 10kW at times.

anyway this has all come to light because last summer the Old Goat ripped up the village street to resurface it and ripped up the cable under it, thereby depriving all outbuildings of electric.

he has since been using a series of connector blocks to keep the supply up, but these conblocks dont have the superconducting properties the cable must have had as they keep cooking up.

It has fallen to me to organise a replacement supply. I would rather employ an electrician but there are none willing to take on the job due to its remote nature. also, there are many many many features of the site are Unsafe according to regs but practically sound for anyone with a remote islands background. seems unfair to get a professional spark to fix up one part when the rest is such a regulatory nightmare.
The spark who wired the house so well has since tragically died in a gardening accident.

My Questions

I've added up the present loads and thought a bit about diversity and the future and reckoned that I need to carry a max load of 15kW from the dwelling house to the outbuildings.
So I'm thinking around a 25 metre run of 16 sq mm SWA.
could someone verify that's an ok estimate?

I fear that taking 15kW from a "spare way" at the far end of a 12-gang CU is asking a bit much of the CU, not to say impossible to do with SWA.
what would be the best method of terminating the thick SWA at either end? could anyone recomend any actual products/glands?

As a novice with SWA, Im aware its difficult stuff to work with and I'd be really grateful for any advice on working with it - tools, fittings, tricks.

all comments gratefully received, those of a technical and helpful nature particularly so.

by the way, the supply is, definitely, PME.

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Seriously, you'll have to make the supply TT, I guess, as the outbuildings etc will have water supply pipes?


15 k's is around 63A.

You sure that's enough, what with the welders, heaters and showers, cookers etc...?

I take it there's only bottled gas on site?

If you think 63A is sufficient, you'd have to take a submain from another phase, but you'll have to assess load to try and balance it as evenly as possible.

A lot to think about!
 
16mm sounds about right . 10mm would be ok if it was just a single run from main source to load but with submains you need to keep overall volt drop down so 16mm is probablly a better choice..

Do you have any information on the supply arrangements in the house? You say there is a three phase supply, how is this supply split out into single phase? is there a three phase board anywhere? how are the loads balanced across the phases?

Your post is somewhat confusing and incomplete. What is after the garage? does the supply cross back over the road into the other outbuildings? does it cross the road a second time to get back to the first two buidlings? can you provide a map of where stuff is and what the run lengths are?

We can probablly work out what sizes and connection methods would be appropriate but we need ALL the information.

As for the physical side of things. Afaict larger SWA is going to be more of a pain to manhandle than small stuff but the principles of glanding it should be the same.
 
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where's that video of a bit of 1.5mm T&E overloading on an arc welder?
 
if you took the three phase over to the outbuilding on a 5core swa, could you use a smaller cable?

also im a little confused as to what the 1.5 T&E was fused at? it must of been on at least a 32mcb breaker.. wouldnt an electrician notice the cable was wrong?

edit: and also would you wire up a new CU without knowing what each curcuit does?
 
PVC cable in a water filled underground duct ?.

What current rating would this have, certainly not a de-rating factor.

Provided the water is replaced as it evaporates this could be a way to use less copper.

(( This humourous, water cooling cables is not a DIY project, ))
 
Hopefully you only want to do the job once.

I would suggest 25mm SWA from each outbuilding back to the main incomer area. Switchfuse for each SWA.

You state 3-phase supply, a lot will depend on how this is wired up electrically and physically, but if you have 3ph after the meter how are the phases split to the existing house?

Something like a ryefiled board or busbar chamber to split the 3ph into the various switchfuses or CUs.

And if the SWA is buried deep enough the 'road' can be resurfaced again without digging up the cable.
 
here be a sketch of the layout, I appreciate that the textual description leaves something to be desired.




green boxes represent CU's final circuits not shown for clarity.
NB the final circuits everywhere seem to be pretty safe and well installed, apart from a few obvious old rotters, but easily remedied. Its just the supplied to each CU that need replaced.

the supply to the workshop/cowshed does indeed recross the road, at tractor cab height, supported by rope. this has been replaced following vehicle access at least once to my knowledge. this overhead supply is a relatively new arrangement (1997 I think), and I am beginning to think it was because the workshop was originally supplied by a 5A lights circuit direct from the house. I guess the welder may have been the end of that supply. Necessity is the mother of invention!


dimensions to follow shortly.
noted re splitting phases to the buildings.
one of the phases is dedicated to the night storage heaters. the other 2 phases share the general loading of the house. if I recall right, the outbuildings are on the far end MCB of the night storage heater CU... which I suppose might be because this CU is mostly unused in the day time, whereas the workshop is mostly unused in the night time.

it's a nightmare and no mistake. But, on the other hand, it's been working fine for 30 years.

REsPONSES to COMMENTS
the 1.5mm T&E was/is protected by a 32A MCB. I suspect that the "electrician" who wired it knew exactly what it was for and just didnt want to think about it. It was probably protected with a bit of fencing wire before he replaced the supply.

I hadnt even considered taking 3 phase to the outbuildings. seems like a good idea. but thinking about it, the phase that does the night storage heaters is the underused phase most of the time. seems like a good idea to use that for workshop/domestic load, so that it has even load.?

outbuildings all have water supply indeed, but they are all jolly old Alkathene. running water there is a relatively modern concept (1973) that said, there are copper parts so equipotential bonding will be required.

Gas is, of course, bottled.

the phases are individually metered I think, I will take photographs on the next visit.

thanks all for comments thus far.
 
Very odd that someone went to the hassle of an overhead wire for the building next to the house !!!

You say they tried to connect it to the house before, but used the light circuit ?
 
3-4 foot thick stone walls. drylining with a very small gap between the studwork and stone in places. was probably easier to go overhead from the garage, because there is no lining in the garage, all the services are exposed, you can get through the wall easier.

The outbuildings original wiring was all for electric light probably, when the lister lighting generators were popular in the 1970s. (there is an old lister startomatic at the farm, sadly defunct). lighting was a big thing for farming then, as it freed up your other arm after dark.
as power tools started to become affordable, of course you would wire up a socket off your lights. that seems to work, so lets have a few more sockets.... then you get mains electric installed, and you soon forget that your wiring was meant to be just for lighting. I suppose.
 
securespark, why do you recommend changing the existing TN-C-S supply to TT ?

what's wrong with extending the earth conductor from the existing distribution board?
 

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