Bang goes the supply fuses any ideas greatly recieved.

[DiscoDave]

Picture the scene,

Last week I replaced a sub main and distribution board on a farm. I left site and about six hours later two of the phases dissappear.

with in half an hour of the supply going down the standby generator was fired up with out problem.

The following day the corp turn up and say that whatever the fault was it has taken two of the 100A fuses in the incomer head and one of the 100A fuses in the installation main switch.

After pointing the finger at me - (last man on the job) no fault was found, the fuses were replaced and all (touch wood) is well.

Today I have run and insulation resistance test on every sub main from the bus bar and have not found any faults.

The only time in the past I have come accross a similar situation was when a cable was cut or rather the thieving pikeys that were trying to nick it tried to cut it but is blew their hack saw to dust.

Can anyone give any ideas of thoughts as to what may have caused this?

The main supply comes from a transformer on a pole that is about 15ft away from the incomer, however the supply at the incomer has a TNS rather than TT. The pole it's self is labeled up as PME.

The Transformer is the last on the line.

Cheers
Dave

 

[Marvo]

You would usually detect a pikey (alive or dead) with a good insulation tester so I doubt it's pikeys this time around. Were the fuses taken out on two different phases or all on the same phase?

 

[DiscoDave]

one fuse one one phase, two fuses on another, although I don't know which two phases because I wasn't there at the time!

 

[nickblake]

Depending on what load was running if any high current three phase machinary or equipment was running ,you may have had a tiard fuse once one fuse goes this could cause the machinary in use to draw higher currents on the other 2 phases possibley causing the fuses to blow

 

[Marvo]

Did it trip any mcb's or take fuses in the distribution board?

 

[DiscoDave]

fuses? distribution board? The main switch is fused before the Bus bar chamber, each out put from the bus bar chamber is fused before it goes any further. All these fuses are fine and in tact. There are a number of small storage/workshop units around the farm, I've a feeling that it's either a problem in one of the ones that i can't get access to or as nickblake has sugested. Problem is that in some of the units people don't go in from one month to the next and the owner has no keys, so if it is a fault in one of those I won't find out for a while!

cheers
guys

 

[nickblake]

could be a herb factory in one of the units , we did up here in an old Jewsons yard , you never know !!!

 

[DiscoDave]

My thoughts are that at some point in the coming months someone will come to the owner and say "i've not got any electric but there's an impressive portal to the next unit where my meter used to be"

I'm satisfied that there are no faults on the sub mains feeding the buildings, all have had 1000v fired down them just to double check, and with the supervision of the owner, the results have been witnessed - very useful those red and green, fail and pass lights on my tester. So for now at least it's just a waiting game. At least i'll be on hand if there's a problem.