Bare busbar

The bare busbars are heavily corroded and fooled a safe isolation test! I knew it to be live but could have caught the unwary especially because it was lost in a maze of inter-connected tails and other redundant switchgear. Apparently there was a fire in the intake room 25 years ago and FRS simply dumped water on the roof above. 

well, i have come across situations like this that fool the safe isolation test, but I guess that's one reason to prove live first. Ours weren't hosed down either, it's just corrosion and years of dust

Its also the reason boards like that shouldn't be readily accessible to the average ordinary person, the ones we have like that are kept locked with a padlock

a bit nippy on the fingers, and I was always told to remove them using your flat cap (whatever one of those is)

I have seen similar installations many times.

Z.

The flat cap is for attending the pigeon fanciers' club on Saturday, or putting out welding fires, (Fred Dibnah like.)  The top hat is only for Ascot race meetings.

Mixing 'em up could cause terrible trouble, or even a fight.

“How many times have you seen this” was not referring to how rare it might be, quite the contrary. I have seen this many times but never where a voltage indicator failed on all reference points, line to line, lines to neutral and lines to earth. 

I'd not be very surprised you cannot get a good contact to a bus bar covered with a layer of oxides and general grot built  up over the years -  it is however quite impressive if it reads totally dead. In terms of the live/dead test it is perhaps an argument for checking with a non-contact 'volt-stick' type indicator, although that  is not without potential to mis-read also.

The microscopic version of the same problem allows folk to get voltage drop and Zs/PSSC readings that do not reconcile, this is just a rather spectacular example.

The saving grace is that the adventitious insulation of the bars in this way may actually make it safer, if a spanner is dropped in the works it may act as some kind of primitive current limit. Mind you I'd prefer a design with some sort of cover, it is funny how your standard of what is reasonable to work in / on changes over the years.

Mike
PS a thought

The comments about flat caps may be a bit tongue in cheek, but there is a serious point here that re-inserting a fuse against a fault or your tools or wrist watch falling into the works may not end well in this sort of design, and a singed shirt sleeve or glove is much preferable to a burn that may need a skin graft.

As many newer folk will not have encountered a traditional skeleton board with lots of bare live metal, it is worth remembering that the penalty for a lapse in concentration is that bit higher than with a modern one, so dress accordingly, casual beachwear is not really appropriate. There is a very real arc flash hazard here, as the not-quite-zero resistance fault that you get as the oxides are blasted away with a blinding flash like striking a welder, is the kind  that creates the most volume of mobile hot metal.

PPS edit. In a resistive case, the absolute worst case arc is where the fault resistance is equal to the loop impedance of the supply - so an energy of half the PSSC of the fault loop, times half the pre-fault supply voltage, times the upstream ADS disconnection time is available to melt and throw metal about, and the volume of that metal can be estimated adiabatically . With older boards like this the risk is heightened as the upstream ADS is often also quite pedestrian by modern standards.

it was a bit tongue in cheek because it sounds utterly absurd now but the guy showing me, on 100a BS3036 boards was deadly serious.

We used a cotton rag, insert it in the bottom half, then push smartly up while looking away

This was only 20 years ago. It is still advice I take to this day, with MCCBs always but I do have a set of insulated gloves that are too cheap not to buy.

I have been known to ream out a terminal tunnel with a drill or rub a flat terminal with a file to tidy things up and I'm sure I am not the only electrician to do so, it can work wonders when it comes to improving earth fault loop impedances and getting things to work.

Well Fred, God rest his soul, once lost his flat 'at on a roller coaster; and he wore a topper when he went to the Palace. 

“How many times have you seen this” was not referring to how rare it might be, quite the contrary. I have seen this many times but never where a voltage indicator failed on all reference points, line to line, lines to neutral and lines to earth. 

Electricians roulette, using a two pole tester such as a Megger which gives a single pole voltage indication rather than a test lamp that needs two points of contact should shorten the odds of what I work out to be eighteen tests failing, by finding one live point of contact.