On the two occasions it has happened to me I was!
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Company fuse.
- Thread starter DavidWard
- Start date
On the two occasions it has happened to me I was!
What's going to be creating an arc? Anyone who tries puling a DNO fuse whilst it's carrying current is clearly asking for trouble and would be well advised to don some serious PPE!
Kind Regards, John.
Probably when I retire
(or more immediately after the next glass of wine
)How are you ensuring there's no current flowing?
If there's no isolator at the immediate location of the fuse (not uncommon), how do you know someone hasn't gone and turned a heater on? Of course, you could have locked it off.. I've never actually seen a domestic electrician do that. I have, however, seen many people cut locks off.
There could even be a high resistance fault in the meter causing current to flow which you'd be unable to detect or stop.
Pulling the fuse might go fine 99% of the time. The other 1%, you've just permanently damaged your eyesight and lost half the skin on your hands and arms, and probably face.
These days the highest rating fuses I pull are 100amp and sometimes 125amp on sub-mains. I "almost" always put a current clamp on the tail first to ensure no appreciable current. But I am the first to agree with your comment that most of the time its fine but just that 1 in 100 time it could lead to serious regret.
Still up to several kA PFC though, and you can't always access the tails for a clamp! I've seen quite a few installs with the meter butted up to the cutout with no access to the supply side tails at all.
One of the biggest issues we have surrounding this is that we are not strictly allowed to operate customer's switchgear!
So, a call to a local night club for loss of two phases, 250A fuses with two operated.
Of course I'm thinking why, there are no really obvious signs
Before replacing them I ask the consumer to open his 400A (note the lack of discrimination) incommer.
He does, but it was stiff to operate
Replace fuses
He tries to close his switch and it won't
Cut-out fuses removed at this stage!
Further investigation shows a lot of fluid in his distribution board and black marks around the main switch.
Turns out we are below the stage and they had a "water dancer" in the night before and rather a lot of the water had leaked onto the electrics!
It cost a lot of money to clean that up I understand
So, a call to a local night club for loss of two phases, 250A fuses with two operated.
Of course I'm thinking why, there are no really obvious signs
Before replacing them I ask the consumer to open his 400A (note the lack of discrimination) incommer.
He does, but it was stiff to operate
Replace fuses
He tries to close his switch and it won't
Cut-out fuses removed at this stage!
Further investigation shows a lot of fluid in his distribution board and black marks around the main switch.
Turns out we are below the stage and they had a "water dancer" in the night before and rather a lot of the water had leaked onto the electrics!
It cost a lot of money to clean that up I understand
Good point. I ran into what I would call a coaxial arrangement a few weeks ago (not knowing what else to call it) The main incoming cable was armoured 3 phase 4 wire (TN-C-S) The three 100 amp service fuses where, as usual, part of the main structure. Each phase and an accompanying neutral were split out into single phases supplying three small workshops via individual meters. The cable from the service fuse to the meter was a coaxial cable with the neutral on the outside (at least I assume so) Each one terminated just below the meter into a black-rectangular-blob which separated the line & neutral out again to allow connection to the meter. No access at any point to a single conductor for clamp current measurement.
Have a look here
http://www.diynot.com/forums/viewtopic.php?p=1938924#1938924
http://www.diynot.com/forums/viewtopic.php?p=1938924#1938924
An anti theft device that prevents access to any terminals prior to the meter.
Do not underestimate the amount of theft that takes place!
There are no more reasons why the connections in an isolator should be flaky than the ones in henley blocks, switchfuses or CU incomers.
The only people who ought to worry about installing an isolator because of the possibility of the connections being poor are those who also worry, for exactly the same reasons, about installing henley blocks, switchfuses or CUs.
And if, when you install any of those, you worry that your poor workmanship might lead to a fire then you should probably be looking for a new line of work.
Maybe a torque-setting screwdriver should be part of every electrician's toolkit.
One reason for the DNO fitting an isolator in my new supply is that it provides easy and fast access for the fire brigade to shut of power should they be called to a fire at the property.
I'm just doing the 1st amendment update on line, the NICEIC/Virtual college offering. You won't believe this but one of the interactive questions asks:
"is it correct to state that a cut-out fuse may be withdrawn only by a person authorised to do so by the distributor?" Multiple choice answer of YES or NO.
Help which is the correct answer???
"is it correct to state that a cut-out fuse may be withdrawn only by a person authorised to do so by the distributor?" Multiple choice answer of YES or NO.
Help which is the correct answer???
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