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Topic Title: A HEAD SCRATCHER
Topic Summary: A VERY LARGE HOUSE IN THE COUNTRY
Created On: 16 April 2013 11:34 PM
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 16 April 2013 11:34 PM
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John Peckham

Posts: 7371
Joined: 23 April 2005

Call today from a contractor saying, What are you doing today are you busy?"." No I am home not feeling well with man flue so I am not going to work and I have to teach tonight". "Good" says contractor I will be round to pick you up I need you to look at a house with a big problem".

Anyway I arrived at this very large house with many outbuildings, you know the sort of thing Grade 1 listed with a gardeners shed bigger than my house, swimming pool, separate buildings with gym, office, garage and games room.

Anyway there was a smell of burning with cable and flex to the immersion heater melted, £120K worth (yes £120K) of Lutron. Cresstron and AV kit
cream cracker-ed and some T&E cable from the Lutron melted.

Spotted the pole at the gated entrance to the drive to the house with the overhead supply on my way in. So me thinks not another neutral loss on the overhead as I had seen one 3 days earlier with lots of melted wiring in the house.

So single phase supply in to Gym building near the road via underground cable from the pole. Lots of switch fuses and consumer unit for gym building SWA feed from supply to generator and back to switch fuse to feed the Henley block with tails and SWA cable away to house.

Take a quick look and say to contractor with me. " What sort of earthing have we got then?" He says, "PME off the head". I say no. He looks and says must be TT. I point and say, MET with earth to that board and those 2 switch fuses and no front end RCD or sign of earth going outside so what is it then. He says, " F**k me it's unearthed". I say lets go and have a look at the generator house to see what is there. The SWAs to and from the generator house are not glanded and armour is not connected but there is a 3rd core connected to the MET. 2 X generators and change over panels in the generator house. No earth on either panel with panels mounted on wooden walls. One generator panel guts are all burned up.

Look in nice big house and find second supply on concentric cable also no connection of earth to head. 1/2 the house is on one supply and the other 1/2 is on the other supply with no connection at all to earth or incoming neutrals. No gas supply. Plastic water main. Oil supply to plastic tank. No main bonding at all in any building.

I isolated both supplies and 240V ish line to neutral with voltmeter at the origins. Nice dull light with trusty Drummond line to neutral on both supplies.

Clamp meter on one supply says 90A on line but around 5A on neutral. Isolate 2nd supply on double pole switch and it is still the on same on supply 1. Isolate all the boards in all the buildings and no change.

Answers on a post card please?

I did get to college in the nick of time feeling less well than this morning.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 17 April 2013 12:01 AM
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Parsley

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Struggling to understand the set up John, are the two supplies on different phases with a common neutral at the genie change over panels resulting in 400v when one of the neutrals went open circuit?

Regards
 17 April 2013 08:42 AM
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John Peckham

Posts: 7371
Joined: 23 April 2005

One single phase supply from the pole with a single concentric down the pole then underground. A concentric cable emerges in the Gym building nearest the road and another concentric in to the house.

Both have Series 7 heads with 25mm tails. No connection to earth at either head and no earth rods. Both installations un-earthed.

Both supplies go in to 100A switch fuses then SWA out to a generator (2 gens. one for each supply) in to a change -over panel (one for each gen) then SWAs back to each installation in to another 100A switch fuse.

I forgot to mention there is a wire running around the boundary of the garden for a dog electric fence/ electric collar system. I noticed that on a fence the wire had parted with a blob on the end of each conductor where it went in to the ground. Clearly lots of current had gone down there.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 17 April 2013 09:14 AM
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AJJewsbury

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First thought - any thunderstorms in the area lately?

Clamp meter on one supply says 90A on line but around 5A on neutral. Isolate 2nd supply on double pole switch and it is still the on same on supply 1. Isolate all the boards in all the buildings and no change.


No chance of there being a 3rd supply lurking unknown somewhere is there? (and some borrowed Ns).

Either that or there's a N-PE fault and a decent path to true earth somehow - some pretty hefty buried metal somewhere (pool?) - or electric fence electrode has hit a buried service?

- Andy.
 17 April 2013 01:08 PM
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statter

Posts: 124
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From what you say could be a combination of installation issues and subsequent fault (N-PE ish on imm htr?).
Did you notice if the meter was registering kWh compatible with 90A? If it wasn't might point to reactive current and problem on generator or change over or with pump motor in swimming pool plant.
 17 April 2013 01:30 PM
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BigRed

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SWA feed from supply to generator and back to switch fuse - change over switch/ auto change fail?
crispy lutron etc might suggest a fault current trying to find its way down signal earths or thgrough supression ccts
but crispy gen panel? someone bieng testing failure modes on supply and a fault occured, with no earth, the fault current finding its way to earth through the path of least resistance? Just a thought, any other IT kit dead with in line filters or switchmode psu's?
no earth and potential dodgy Neutral? thank goodness for the dog collar....
:-)
 17 April 2013 04:02 PM
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dbullard

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Both the same phase JP. ?? and is the damage to the installation restricted to one supply ?? or to both supplies, smells like an over voltage problem for a short while, causing havoc, not affecting the genny side of things due to the changeover switches.

I would ask locally if any other property locally has been affected as it may well have been a "Networks issue" further away causing the issue in this property

Regards


Daren

-------------------------
..... Dont pee in my pocket and tell me its raining ......


www.quest-electrical-sw.co.uk
 17 April 2013 08:21 PM
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weirdbeard

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Hi John, as AndyJ's post earlier my first thought was lightning, (plus stabbing in the dark I also heard something recently on the radio about some kind of solar flare that can affect electrics? )

Another thought was the possibility that an HV overhead cable had come into contact with the LV cables? (up the road from me there's some that cross and are only stopped from contact upon the HV dropping by a flimsy looking (earthed?) conductor above the LV cables.

How badly melted were the damaged cables - was it possible to identify which conductors caused the damage?

How did this issue get reported initially to your contractor? were there any whole power losses reported by the customer at the same time or just the smell of burning, lights failing etc?

Has the contractor worked there before?
 17 April 2013 09:09 PM
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baldelectrician

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Any polatity issues?
All the gennys wired correctly?

-------------------------
baldelectrician.com
 17 April 2013 09:22 PM
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slittle

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If the two generator panels and supplies are not connected to each other which your post suggests they are not then my first thought of the DNO's network feeding parts of the village through the house isn't going to happen.

So I'm going for a "proper" N-E fault as a result of a problem in the generator panel (maybe welded contacts) which leaves the machines N-E link visible to the DNO supply but the mains supply neutral disconnected.

Any current used in the house is then flowing through the melted generator panel and it's N-E link and back to the transformer via any available routes including the dog fence until it melted.

Stu
 17 April 2013 11:04 PM
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John Peckham

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Well after lots of head scratching on the day at the 1st supply position when the SWA comes back from the generator it goes in to a 100A switch fuse as I said. From the 100A switch fuse 25mm tails to a Henley Block. Henly block supplies consumer unit above then some more tails and a 3 core 25mm armour . The SWA armour is not earthed and not glanded. Straight in to the Henley block. No circuit protection other than supply fuse. I have already tested this supply and there is a line and neutral and as I said the installation is unearthed. So we disconnect all the tails from the Henley and re-conect one at a time with the clamp meter in place. Guess what the SWA is drawing the line current with little neutral current? Disconnect SWA and test end for IR with all DBs on site isolated. Dead short line to earth core and low IR neutral to earth core.

No the fun and games start as SWA goes along the bank of a stream on the surface (nice job) and then goes in to the ground serving half the house and some of the out buildings but a 25mm SWA does not appear in any of the buildings. Smaller SWAs in the outbuilding and 16mm T&E in the house.

Stu I think is the closest with his answer and spookily also geographically (Matching).

Contractor still on site but I cannot get back as I am HM the Queen needs me for a few days.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 18 April 2013 07:56 PM
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slittle

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I'll add it wasn't one of my installs John !!!

We've got lots of customers in that part of the world but not domestic.

If you want a third pair of eyes I'm always up for a nose around.


Stu
 18 April 2013 10:12 PM
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paulskyrme

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If I could get there for a reasonable cost I'd be up for a nose around too!
Also nothing to do with the value of the property, I'd love to have a look into what the heck is going on!
 20 April 2013 03:09 PM
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John Peckham

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The contractors merry men have found where the underground cables are joined and have identified the rogue cable and dis-connected it.

All of the underground cables are run directly off a Henley block inside a panel in one building which is supplied from the origin. The underground cables spider out from this central building. Of course there is no circuit protection or earthing what would you expect. The faulty cable is dead short line to earth and a near dead short line to neutral. As the whole installation in not earthed to either supply cable or an earth electrode I assume the burning of neutrals and Band 1 cables is due to the fault current returning via these unintended paths. This would account for the immersion heater flex and cable going up in smoke and the damage to the Lutron and Crestron with 90Aish flowing down the CAt 5s.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 20 April 2013 03:26 PM
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slittle

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Damn lucky it wasn't any worse then.

It would be interesting to know what the client's insurance company say about it. "keeping premises in good condition etc" springs to mind.

Also the contractor who installed all the lutron etc without ensuring the installation was earthed ??


Stu
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