removing main fuse for changing consumer unit

[sparkyspike]

There's no point breaking a seal and pulling the fuse (which could fall apart as you do so) when you can break the seal on the meter and disconnect the CU tails.

Not that I recommend you do that either.

You get the DNO to isolate it for you.

Of course.

 

[Roo]

1) Cut-out fuses are not designed for use by unskilled person.

This is a particular skill they teach is it, how to pull a fuse? does it come with a certificate?

Have you not got yours then?
I have, it says I'm allowed to work to OP3 and WI3 and if you don't know what they are then you shouldn't be pulling the fuse.

2) Any professional would first assess the condition of the cut-out - can you do this.

What, you mean look at the fuseholder and see if it looks like it is likely to fall apart or break?
Yes an ordinary person with a good level of competence should be able to assess that just as well

I totally agree and I'm sure the owner of the hand below did just that.

5) Removing the load will not prevent arc flash if the cause is a fault. The sort of flash you get from a load is peanuts.

So what your saying is that these things are badly designed & highly likely to fall apart when removed.

Surely the DNO's should be changing them to a safer design as they are obviously not safe?

Your telling me an IRON CLAD type cutout isn't badly designed?

I can't really be bothered arguing that pulling the main fuse is dangerous.

I'll just say that when I do it I wear LV gloves and a visor because I think I look good in them, not to protect me from a cutout which a lot of people here believe is as safe as houses.

 

[Space cat]

It's time to bring this long-running argument over the dangers of pulling service fuses to an end and move on ---

--- to what might happen when you put the thing back!

 

[mattylad]

Now that is a horrible picture, but was that through removing the fuse though?

Space cat has however bought up the best point about all this & that is replacing the fuse.

Do the DNO's charge for removal/refitting?
DO they insist on seeing test certification when doing this?

 

[plugwash]

I totally agree and I'm sure the owner of the hand below did just that.

any more detail on what happened there or did they just put that image out to shock people into complying with thier rules rather than giving them real information.

5) Removing the load will not prevent arc flash if the cause is a fault. The sort of flash you get from a load is peanuts.

Well pulling it out if there was a fault that bad the fuse would already have blown from pulling out the fuse.

I agree reinserting the fuse against a fault is likely to be pretty dangerous though. Only an idiot would do that though right

 

[Roo]

I totally agree and I'm sure the owner of the hand below did just that.

any more detail on what happened there or did they just put that image out to shock people into complying with thier rules rather than giving them real information.

I'll be honest I just pulled that off a well known search engine.

Have seen pictures like that in work tho due to faults but that was the closest I could find.

But I still don't understand why people would chance getting something similar to that and risking having their supply terminated due to tampering with DNO equipment, just because they can't wait a day or 2 to have an Isolator fitted?

 

[NotHimAgain]

plugwash wrote

Well pulling it out if there was a fault that bad the fuse would already have blown from pulling out the fuse.

Your missing the point here - the act of pulling the fuse out might cause the fault.

EG: phase to earth fault on a metal cut-out or failure of the fixings for the cut-out or the meter board causing strain on the supply cable.

It would appear that some of you lack imagination - you can't imagine yourselves in casualty .

 

[Click-Sure]

I posted these recently, this is what happened when a colleague on a site replaced a solid link into the cutout assembly onto a dead short.

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• Click-Sure
• 29 Aug 2008
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• 29 Aug 2008
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It could have been much much worse.

 

[MeterMan]

This is a subject that has been debated since the time that cutouts were fitted. What amazes me is that all of the people that say "i pull the fuse" never explain the procedures they employ. Some will say "i always wear 1000v gloves" but do you carry out the relevant checks before and during refitting the fuse. For your information, the correct method for disconnecting the supply,

1) Asses you work area for working conditions, hazards, access and escape routes.
2) Ask the customer to save all data and power down PC's and turn off sensitive equipment at the plug.
3) With a socket tester check the polarity at a socket outlet.
4) Confirm with customer that it is safe to proceed.
5) Put on 1000v gloves after testing that they are sound.
6) With a glow lamp, check ALL conductive parts that you are likely to come into contact with during the work at the cutout. This includes Henly block screws, trunking, metal enclosures and most importantly the cutout seals. Last year, a meter man was badly injured because someone previously had pulled the fuse without cutting the seals and broke the sealing lugs on the main body. When he put the fuse back in, the excess wire on the seal went into the body and made contact with the live terminal. Remember to prove lamp before and after each test.
7) Turn off/remove customers protection devices and main isolator.
8) Still wearing your 1000v gloves and wearing a face shield (not goggles), firmly pull the fuse carrier. If the fuse will not come out, stop all work and call the DNO. I have had 3 old bakalites fall apart on me this year.
9) immediately, fit a cut out cover over the live terminal in the cut out. It has been known to accidently shove a meter tail in the cutout
10) Prove installation is dead with glow lamp, remember to prove lamp before and after test.
11) You can now remove gloves and face shield.
12) Check the fuse lugs for signs of arcing, damage and overheating. Disassemble the fuse carrier and check the correct rating fuse is fitted and reassemble.

The next steps are dependant on what type of work you are doing.

Refitting

1) Ensure isolator is still in off position. Wearing 100v gloves (after proving they are sound) and face shield, bridge out live terminals in cutout with a glow lamp. There should be little or no glow from the lamp. If bright lamp, investigate further and recheck. Remember to prove lamp before and after test.
2) Check fuse holder is assembled correctly and firmly insert fuse holder.
3) Recheck polarity at socket.
4) Reseal.



As like Roo, i am trained in LV single and 3 phase as well as CT meters CAT 1,2 & 3. There are reasons why you should not pull the fuses and i hope i have shown some of these. I am pragmatic enough to know that people will continue to pull fuses but on your head be it. I have seen the picture that Roo posted and was told that this resulted in amputation.

Ever heard of the term COMPETENCY

 

[plugwash]

But I still don't understand why people would chance getting something similar to that and risking having their supply terminated due to tampering with DNO equipment, just because they can't wait a day or 2 to have an Isolator fitted?

Why do people risk getting run over by crossing the road when they think it is clear rather than waiting for the crossing lights?

The fact is if people never took any risks we would never get anything done. Unfortunately finding real information on how high the risk is is impossible because we don't know how many people take the risk and get away with it.

 

[NotHimAgain]

Let's try a different tack - when you carry out work within your property the magnitude of the fault current that might flow if you make a mistake would usually be in the tens to hundreds of amps range.

If you manage to short circuit something close to the CU you could get, say, 2000A. Higher currents are possible but this is the usual range for most domestic installations.

Now if your cut-out is fitted with a BS 1361 type II 100A fuse this would operate in around 0.06 seconds. This fast action will limit the 'let though' energy (I²t) that dissipates in the installation. It is this energy that might cause an arc flash.

If you manage to cause a short circuit on the upstream side of the cut-out fuse your protection would usually be provided by a BS 88 400A fuse. Now if your lucky and its a 'J' (supply ) type - it will take around 5 seconds to operate on a 2000A fault. If your unlucky it might be a gG type (general use) - and this will hold in for around 10 seconds.

Now look at the figures - remember the let through energy is I²t.

When we select cables for fault current performance we generally use the adiabatic equation.

(SK)² >= I²t The (SK)² bit is called the withstand energy and it relates to the energy that a cable can withstand without damage.

Next time you want to pull a cut-out fuse ask yourself - what is your withstand energy

 

[Roo]

The fact is if people never took any risks we would never get anything done.

I disagree.
In my book thats cutting corners and you would get it done if you waited.

Surely theres some on here that go to weigh a job up and go AH! YOU NEED AN ISOLATOR CALL THE DNO THEN I'LL BE BACK TO DO MY BIT AFTER THEY'VE BEEN.

Every day we all see post's on this site of what people have done without being qualified.
Some are perfectly fine and good jobs while others are damn right dangerous.
I too am guilty of doing work I am not qualified to do.
Yet when the tables are turned some people think it's ok to do something they are not qualified/authorised to do?
Some fuses that are pulled illegally are put back perfecly fine no problems, where as others are damaged and left dangerous.

All be it sparks have a better knowledge than the general public of mains but nobody other than a authorised person by the DNO can work on the network.
Working on the network includes cutting seals droping meter tails and removing the cutout fuse.

Rant over getting ready for my holiday.

 

[333rocky333]

A simple case of refitting a loose neutral turned this

Into this in less than ten minutes

This was fed by 400 amp "J" fuses.

There was no isolation between this and the sealed up cut out, one meter away.
All the mcb's were off, usually I megger the spine of the board, before switching on, unfortunately this time I did not.
And as I had only just turned it off, using the test button, I had no reason to doubt it.

As I switched it on It banged and caught fire within seconds and banged and flashed for a further five minutes.

Not something I would like happen again.

The fire brigade took ten minutes.
Edf thirty minutes, by then two phases had eventually blown and one phase was still live.

 

[BQW]

The person at College who taught me the 16th Ed regs, had two fingers burnt away through a accident with pulling the company fuse.

 

[bsr]

Hi, I work for a large electricity company. We have two to four injuries a year through pulling cutout fuses. All meter fitters are trained and required to use visor and gloves (although tbh they don't usually bother).

I've pulled a cutout a couple of times to do a CU replacement. Just be aware it's a real risk.