Slightly OT: Street Recabling

[Chris K]

Just had a circular from the local PowerCo saying that over the next three months they will be replacing all the mains distribution on the estate - about 200 properties built in the 1980s. We've had many and frequent cable failures in the road, some quite spectacular, & I guess they have decided enough is enough.

Does anyone know what the actual procedure they follow is? They claim occasional planned supply interruptions and property access restrictions but it is hard to imagine how they achieve this without removing old cable sections first & being off supply for protracted periods.

Chris K

[The Natural Philosopher]

What they will probably do is put generators into blocks of houses whilst they fiddle with sections of cable.

Normally the outages will be whilst sections are taken in and out. Not long term..

Then they will dig up and replace the underground cables.. Messy and days.

[Chris K]

Looks like investing in some surge protection is needed then. Feels like taking out a section and replacing it and all the property feeds ought not to be quick but they may have slick methods. Hope the road is wired as a ring rather than single feed as I'm right at the end...

Chris K

[Dave Plowman (News)]

Strangely, they've just been repairing the cable outside my house. Seems it's original installed well before WW2. According to the foreman.

[Dave Liquorice]

I doubt the cables will be in ducts direct buried armoured and with the price of copper they aren't likely to leave the old ones in the ground...

So I should imagine they will open up a trench along the route of the old cable lay a new one along side, joint in the house connections to the new cable then cut across the feed old to new. They will have a pretty good idea how many house joints they can get done in a day and how long it will take to cut across the feed. They may leave the old cable live to feed onwards to houses not yet on the new cable. Remember these guys are not completely averse to working live either...

[Dave Plowman (News)]

It is round here, with pretty old wiring. When it exploded taking out one phase, they simply fed it from the other end until they got round to fixing it. I never knew they could do that. ;-)

[Dave Liquorice]

The 11kV here can be fed from either end and there are two routes into that either end. Sections between those points can also be isolated. So a fault in a middle section can be isolated then the rest of the line fed from the ends.

This normally works very well until an ice storm brings down a number of lines and snaps the poles at one end. There isn't an isolator between us and that end so we where off for 36 hours whilst they planted new poles etc...

[harryagain]

A lot of the old cable will be abandoned. Where possible they will use moles to go under hard surfaces to save digging up. They will put in the main run first and transfer the individual branches to properties on a piecemeal basis. If the houses are densely packed, there is lots of scope for major f**k ups, (ie damage to other services) including ones you own. You need to keep a very close eye on things, especially when they come onto your property. It's helpful if you know where your buried water, drain . telephone and gas pipes are so they don't get damaged and if they do they fix them properly. Worthwhile taking a day off work to watch things. They often employ some cowboys.

[Andrew Mawson]

When they recabled the 11kv to the transformer on poles in my vegetable garden they did it live - scary I reckon - I took loads of pictures. When my meter cabinet was moved end of last year again it was done live but that was a mere 240v !

AWEM

[Brian Gaff]

Warning this may start a new thread, sorry.. Well seems a pretty new installation to need replacing. Don't recall much being done here in my life time so kind of makes you wonder what they did it with.

Brian

[Brian Gaff]

Yeah I'd imagine the main hazard during this is holes full of blind pedestrians after the yobs remove all the protective covers and bollards!

Brian

[Tim Watts]

On Friday 15 February 2013 17:55 Chris K wrote in uk.d-i-y:

I would imagine that:

1) They will dig a trench along the line of the old cable and all its joints to the houses and lampposts. Trench will be wide to accomodate new cable and new joints next to the old ones. 2) New cable goes in and is powered. This could be all new distribution or jointed in parallel (temporarily) with the old cable. 3) Each load feed will be cut and rejointed to the new cable - live - as is usual with low voltage circuits. 4) The old cable will be removed and possibly the joint to the new cable redone, depending on the logisitics employed. The main cable is (usually) fed from both ends (cul de sacs being a usual exception) so rejointing the main cable will not lead to power loss.

It's not going to be very disruptive in terms of road digging - one trench at a time, but it is going to be a bugger of a lot of work for the jointers. I don't know how long a live cable joint takes these days, but when my dad was supervising these in the 60's it was not a quick procedure. Looking at youtube and some of the new methods where they crimp or bolt clamp the conductors, use a lot of majorly heavy heatshrink and fast set potting compound, I suspect the time has come down a bit.

[Tim Watts]

On Saturday 16 February 2013 00:12 Dave Plowman (News) wrote in uk.d-i-y:

Most street cables are fed from both ends by default for exactly this reason. Usually, where there is a junction (at a road intersection) you'll find a link box with a set of 3 fuses, soemwhere in the 300-500A region.

Cul-de-sacs are the exception, sometimes being one legged - unless the cable has somewhere to go, eg down a footpath at the end and into another road.

[Tim Watts]

On Saturday 16 February 2013 00:11 Dave Liquorice wrote in uk.d-i-y:

Aluminium - have been for decades. But, even so, yes, lot's of £££ worth.

[Tim Watts]

On Saturday 16 February 2013 09:03 Andrew Mawson wrote in uk.d-i-y:

11kV live working must be a new thing - in my dad's day, it would require isolation and locking both dead ends to earth for the duration.

[Dave Liquorice]

When they adjusted the tapping on our transformer due to over voltage on our 240v they did the full SIDE. Switch off, Isolate, Dump, Earth proceedure. Took longer to do all that than shift the tapping...

[Chris K]

Allegedly there some problem with using a different cabling practice at the time, maybe the original installers were not competent with it. It has been troublesome from the start - we were on a generator for a few weeks some years ago while they did some major work on it but it didn't seem to fix the problem long term.

Come to think of it, it must be wired as some sort of ring as when they have dug it up upstream in the past we did not lose power while they worked even though we are at the end od a cul-de-sac.

Chris K

[Broadland Wanderer]

Who is it, if you don't mind letting us know?

saying that over the next

Different companies used different types of lv distribution cables which is why I was curious about the company. There was a type of lv cable known as consac, which was notorious both for occasional problems with manufacturin g QC, but also was quite critical with installation techniques.

I would expect them to lay new mains cable in the footpaths then either joi nt existing services onto the new main or lay new services into properties.

If you have a contact number, I'd ask them is it just the mains distributio n cables they're replacing, or are they proposing to replace service cables as well.

[Broadland Wanderer]

Not for lv distribution. Surge protection - 'lightning arrestors' - are used

11kv and above.

[Broadland Wanderer]

Only usually ducted at road crossings. Long lengths of ducted cable runs seriously de-rate the cable!