100amp 3 Phase isolater blew up in my face today...

[Crosswire]

So here's what happened.......

Was in a main intake room for a school comprising several outbuildings, and in the process of upgrading the entire switch room. The installation was ancient, and had rows of switch fuses all unlabelled.

Had to identify them for the upgrade so turned one off, which we found was isolating the kitchen block. So far all well and good. Turned it back on , only for the caretaker to tell me his fridges weren't on any more, but the lights were. Turns out somehow by turning it on and off, 2 of the three 100A HRC fuses had blown

I put this down to startup current on aged fuses, as there was no bang or any other indication of a fault

Ok , so we had lost two phases, which needed to be reinstated so the food in the fridges/freezers didn't spoil. Didnt have the correct specific fuses on my person (who would?), so put standard 30 amp fuse wire into the fuse holders to give a temporary supply overnight until I could get to the wholesalers tomorrow.

Went to turn the isolater back on and found the handle was a little stiff, but then they sometimes are... I gave it a more forcefull turn ( in hindsight not a good idea) and KABOOM! The isolater burst into flames which burned blue for a good five seconds and ran up the wall, and the entire switchroom filled with smoke!

When it all cleared (and after I changed my trousers) Only 1 200 amp fuse had gone in the main isolater, and the 400's in the head were all intact. Needless to say the isolater was completely cabbaged, so I disconnected it from the main bus bar until I can get my tester onto the submain it supplied (currently away being calibrated), although I have a hunch the fault was inside the isolater which was a make I've never seen before (DB was the make)

Anyway , hope you guys had a better day than me

 

[oldtimer]

Had the same 25 years ago with the 12 way 100A consumer unit taken off a 700A busbar. I put the board cover back on not realising that the tail were coming through a 25mm ungrommeted hole and it went bang. At first the main fuse did not trip the cable just arced then it went bang.

With great bravadoe me thought that was lucky got a bit stunned and went home woke up with my eyes stinging and blind at 1:00 in the morning turned out I had welders flash and could have been blinded so lesson learned.

 

[Guest123]

Did you get any flash blindness......I hate that!!!

 

[Crosswire]

Did you get any flash blindness......I hate that!!!

Thankfully no.... But I hope I don't wake up tomorrow with it, like what happened to oldtimer

 

[jeremy]

Sorry to hear of the botty squinting episode. Reinforces the importance of regular inspections. Council H&S might be interested therefore more regular inspections therefore more work , oh and better safety!

 

[Knobhead]

I had this little mess to sort out

An night shift electrician was doing preventative maintenance on a motor control centre (MCC). At some point in the past the incoming terminal shrouds to one starter cubical had been removed for testing and not replaced. Along comes our electrician and shorts one of the incomers to earth with his screwdriver. Almighty flash and bang and the arc continued as the driver was still in the terminal. He returned and knocked the driver out of the terminal with a wooden chair. Only then did he go for first aid and then a very rapid trip to hospital!

Severe burns to his face and hands (his eyes were saved by his safety glasses) along with all the trauma that would go along with this.

Morning electrician arrives and is told of the accident along with being told to get the faulty drive going! What did he do, simple run 6mm singles out of the adjacent cubical door and in to the faulty cubical! OK He surrounded the area with bunting tape. Drive running management happy.

Enter Tony in the afternoon! Once I’d come out of orbit I was told to prepare plans to return the MCC to normal service the following weekend!

First off a survey of the panel (it was one I’d had little to do with before)

Supply either 1000A or 1200A ACB’s from the plant main board via 400mm singles to 1200A interlocked fuse switches (one on one off). Fed from the 1200A ACB.

Bus-bars 2” X ¼“ Al (under size)
Feeder drops to large drives 2 X 50mm Cu singles
Feeder drops to small drives 1 X 6mm Al singles (supper under size)

First idea, there were lots of spare cubicles so mount a 250A MCCB in one to feed all the small drives using 16mm double insulated singles to each drive. Management loved the idea and put it forward as safety suggestion of the month.

Enter “senior authorised person” “you can’t do that, it will set a president for all other panels”. We want safety but at no cost!
Safety suggestion of the month withdrawn.

Told to make the panel as safe as I could.

After being threatened with disciplinary action I was lumbered with the job. Rollicking No.1

• Replaced all small drive feeder drops with 16mm double insulated singles
• Remove all redundant feeder drops
• replace all live terminal shrouds
• Swap ACB’s to the lower 1000A feeder and adjust the O/L’s to 750A

Rollicking No.2 I didn’t inform accountancy of the change of feeders!

 

[Knobhead]

As a follow on from the above I later found out the “senior authorised person” was involved in installing the panel

 

[Guest123]

Poshly dressed crooks thats all they are.

 

[Knobhead]

I was rereading this thread and spotted this;

“Didnt have the correct specific fuses on my person (who would?), so put standard 30 amp fuse wire into the fuse holders”.

If you look inside most plastic cartridge fuse holders you will see “Do not use wire fuses” the reasoning being if the fuse blows it creates ionised air. Ionised air is conductive so along with the atomised metal particles you effectively have a bomb. A wire fuse holder has a shaped arc path to dissipate heat, absorb the atomised metal and slow down the spread of ionised air.