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Topic Title: "people who dont have a clue" peteTLM
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Created On: 02 February 2011 10:52 PM
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 03 February 2011 11:23 PM
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John Peckham

Posts: 7520
Joined: 23 April 2005

Antric

I understand that the person killed was a very experienced person close to retirement. He had gone to the site to hand wind a tap changer that would not change by remote operation. The tap changer was faulty and resulted, as Alan said, in an exposion and fire. I understand the HSE took the transformer and associated equipment away on a low loader to their own test site for examination. I have seen the photos of the incident and they look horific.

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John Peckham

http://www.astutetechnicalservices.co.uk/
 04 February 2011 07:20 AM
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zeeper

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who think its ok to draw fuses on DNO networks which are installed in DNOs customers properties to risk life


Sorry cant see it, can someone explain the danger of removing a fuse that has no load on it.

I think the risking to life bit comes from working with live tails because of the lack of installed isolators.
 04 February 2011 09:06 AM
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normcall

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"Sorry can't see it, can someone explain the danger of removing a fuse that has no load on it. "

Let me think. Bottom of cutout is still live, meter board riddled with woodworm or similar, the pitch has migrated onto the fuse contacts due to a contact slightly looser than when installed 50+ years ago or just at the bottom of a hill/slope..

Yep, you are right, no problem at all as it would never happen (must get out more!!).

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Norman
 04 February 2011 09:36 AM
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Jobbo

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We had a situation yesterday were on of our clients called us out because they lost there supply, turns out that next door were having a DB change and the electricians carrying out the work had pulled out the wrong fuses!! To make matters worse, they damaged the cast head so couldn't reinstate the supply. Guess what? The network supplier wasn't informed; that was until we arrived. Wouldn't want to be that contractor, our clients are an asset management company, they are going to sue.

Jobbo
 04 February 2011 09:58 AM
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ant1uk

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What did they do to it to damage the cast head? and why are the fuses in someone elses property sure this is not right?
 04 February 2011 10:05 AM
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Jobbo

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Ant

Common basement with 6 cast iron heads, very common in London. They forced out the fuses damaging the housing. The carriers were ceramic and approx 50 years old

Jobbo
 04 February 2011 10:12 AM
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ant1uk

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Oh right I see is the building divided into flats? Round here the cast iron heads are replaced free by the DNO.
 04 February 2011 10:17 AM
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Jobbo

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Ant

No these are small commercial offices. It's a minefield of distributor equipment

Jobbo
 04 February 2011 10:29 AM
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Jaymack

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Originally posted by: John Peckham
He had gone to the site to hand wind a tap changer that would not change by remote operation.


A tap changer is probably the most dangerous part on a power transformer to cause injury, I wonder what the supplier's procedure is, for live manual operation of an automatic changer, I don't want to stay too long near any live transformer, I have seen the effects of a divertor rod failure on an automatic tap changer for a 33kV, 30MVA rectiformer, fortunately with no one around.

It's not just the blast, it's the disgorging of burning oil at high velocity. Pressure release diaphrams can be fitted to the winding tank, I doubt if they are feasible on tap changer housings. They would limit the damage but are still dangerous to be around.

Regards
 04 February 2011 01:09 PM
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alancapon

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Originally posted by: zeeper
. . . Sorry cant see it, can someone explain the danger of removing a fuse that has no load on it. . .

Having the bottom (live) contact come out with the fuse carrier can also be "exciting". In the end of the day, the fuse is the property of the supplier, and only they (or their appointed contractors) should be removing them. I can tell you that standing before an H&S inspector and saying that you didn't call them in to remove the fuse for you because the procedure was difficult to use will not get you very far in terms of an excuse for something going wrong. The only real option is for the UK DNOs to "wise up" and start taking action against anyone intefering with their equipment. All the regulations are already there, it just requires them to begin looking in the right direction.

To some extent, the introduction of smart metering will be a distinct advantage in this regard, as all meters will be able to report "no incoming supply". If a single meter reports, then recovers itself a little while later, it will be pretty obvious what has happened and an investigation could then take place into seals etc.


Regards,

Alan.
 04 February 2011 01:24 PM
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intrinsic4225B

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Alan,

Its also interesting when the whole DNO cut-out comes away from the wall, twisting and distorting a rather elderly service cable!

It is possibly time that the DNOs made a short film showing the effects of a fault on a DNO cut-out or service cable.

Unfortunately I think a lot of people out there don't have a real appreciation of the kind of fault enegy available in a distribution system and assume that the effects are not much worse than those experienced cutting a live installation cable by mistake and ruining your best side cutters!
 04 February 2011 01:41 PM
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John Peckham

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Alan

It might work Ok in your part of the world but in the EDF area the whole thing is pants. You have to remember the contractor is trying to earn a living by installaing a new consumer unit etc. If they have to enter a non-productive loop of being passed from DNO to Meter Operator to supplier each denying resonsibity and then around the loop again of call centres the contractor is going to remove the supply fuse and if present cutting the seal. If they do manage to get a response for a temporary disconnection when will it be done, how long will the customers supply be off and then getting the supply restored plus the costs.

The fitting of smart meters should include the fitting of an isolator after the meter at the same time. Problem solved. No need to remove supply fuses or interfer with the meter again.

I changed by consumer unit some years ago and fitted an isolator at the same time. Foutunatly there was no seal on the company fuse and had been in this condition for at least 20 years from when I moved in. I had a new meter fitted a couple of years ago and seals are now fitted.

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

http://www.astutetechnicalservices.co.uk/
 04 February 2011 01:54 PM
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zeeper

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In the end of the day, the fuse is the property of the supplier, and only they (or their appointed contractors) should be removing them


I suspect its more about revenue than safety.

Although now that I think about it I wouldnt what a DNO worker rewiring my house due to them not having a working knowledge of BS7671. So maybe your point is fair.

Having no local isolation from the supply cable is bad by design.
 04 February 2011 02:07 PM
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mikejumper

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Are there any statistics on how many people are killed or injured removing the main fuse?
 04 February 2011 02:20 PM
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intrinsic4225B

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Whilst I can see both sides of this argument and recognise that some DNOs are rather more organised that others, there are still a couple of things to think about.

What do you do if the cut-out or fuse begins to break up as the fuse is withdrawn or replaced, with the risk of exposure of live parts, or the creation of a fault?

What if the cut-out begins to come away from the wall, twisting and distorting what may be a rather elderly service cable, again with the risk of exposure of live parts, or the creation of a fault?

Are you aware of the effects of a fault on a service cable, protected only by the fuses in the distribution substation?

What personal protective equipment (PPE) do you use when withdrawing fuses? Is it adequate for the fault energy likely to be encountered?

What if there is an incident causing damage (or worse) to persons or property as a result of withdrawing or replacing the cut-out fuse? How will your insurers view the matter?

Just for the record, I do not work for a DNO - just playing devil's advocate here!
 04 February 2011 02:44 PM
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perspicacious

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"You have to remember the contractor is trying to earn a living by installaing a new consumer unit etc."

One assumes that "contractors" don't just start a rewire as soon as they go to estimate the job and that they advise the consumer to contact their supplier to get a DP switch put in during the "quote acceptance" period.........

Regards

BOD
 04 February 2011 02:52 PM
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ant1uk

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I can't believe what I'm reading here..... The whole thing is unlikely to self destruct by removing the fuse. I wear gloves and goggles when removing the fuses with insulated pliers. I see this is enough care to take in a domestic house. I pull the fuse gently and not force it out. make sure the loads are removed first from the DB.

I come across more dangers on industrial sites than this doing live testing on 185mm SWA's in panels. So I see pulling a fuse in a domestic house alot less risk.
 04 February 2011 03:09 PM
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OMS

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I come across more dangers on industrial sites than this doing live testing on 185mm SWA's in panels. So I see pulling a fuse in a domestic house alot less risk.


Being lucky doesn't mean it's not risky.

There could easily be 630A or 800A fuses behind that piddly little bit of service cable backing up the distributor cable in the road (remember the DNO's don't play by the restrictions of BS 7671).

If you've never had one go nasty then that's great - but do be aware that there is an awful lot more risk in cut out's than would be apparent.

If you ever get the chance to talk to a few seasoned DNO jointers, they will tell you that they feel safer live jointing in the road than they do removing or replacing distribution fuses (and for good reason).

Regards

OMS

-------------------------
Failure is always an option
 04 February 2011 03:35 PM
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ant1uk

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If I said I could get hit by a bus does that mean I would never go outside? I'm taking care in what I do and if there is a danger present which needs the main fuse isolating I will pull the fuse straight away without question.
 04 February 2011 03:41 PM
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OMS

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Up to you Ant - I'm just pointing out that it can be more dangerous than you think - and I'll miss our little chats whilst you are having the skin grafts done and learning to use a braille keyboard

Regards

OMS

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Failure is always an option
IET » Wiring and the regulations » "people who dont have a clue" peteTLM

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