Blowing Board Fuses

Tom Durham · Feb 4, 2011

Three phase supply has been sound for a number of years but has now blown the Blue Phase fuse three times in the past 6 weeks

None of the distribution board or isolater fuses have gone and are rated at the correct sizes

The internal load of the premises has if anything decreased and on every occasion the fuse has popped when the premises are locked up and powered down

Local Utility company are now saying that it may be the meter (reasonably recent replacement)

Anyone had a similar problem

Knobhead · Feb 5, 2011

If the meter is the only thing to have changed then that is the prime suspect. Get it changed before it fries the whole place. To blow the service fuse there’s a lot of energy (heat) on the loose.

mechelec · Feb 6, 2011

I would have thought that if it was the meter it would have shown some sign of distress by now. Never say never though. Do the tails run through trunking? I have seen this before when mice have chewed throught the tails and blown CO fuses.

BlueToBits · Feb 6, 2011

Tom Durham said:
.......The internal load of the premises has if anything decreased and on every occasion the fuse has popped when the premises are locked up and powered down ...........

Ok so it's (only) 3 occasions but seems strange that it has never taken out the fuse with the building occupied or under load. If it were my job I would check out:

Is is always overnight or could it have been over a weekend?
Could this be caused by a drop in ambient temperature resulting in contraction of cables causing a fault in trunking, conduit or enclosures?
What is the IR like?
What goes on in the building next door? Pot farming?
Is it really a power down? or are things left running such as FLT chargers, air compressors, outside lights, Artic Truck power etc? Is there anything that anyone could easily tap into overnight?
Is there any equipment that may be switched off by it's control circuit but not the power circuit?
Rats eating cable insulation?
Can you set up some current monitoring/logging equipment. Both my multimeter and clamp meter can be connected to a laptop and be left sampling current every second. Even a cheap plug-in time switch will at least give the time the fuse went. Maybe a cheap CCTV and recorder (not on the blue phase!) if foul play is suspected? You could even hook up an auto dialler to phone someone's mobile as soon as it goes off if they can get there quickly.

It must be costing your client dearly in downtime so he would likely be prepared to speculate in paying for some investigative work.

Tom Durham · Feb 6, 2011

Thanks for the response

Having seen the lengths the building owner goes to re switching off all equipment and water supplies before they leave I am sure that there are no switched loads other than a Combi boiler being used

Next door there is a pizza house (Big Ovens ) and on the other side a re-hab centre for junkies (Nice area?).

There has only been one fuse failure in the past and that was down to a water leak through the roof which has been sorted.

The only thing that has changed in the building was that the meter was swapped out at the back end of November last year.

The moot point is why does the 100amp fuse pop but leave the 30amp and less on the DB and Isolaters intact

If it tracks out to earth then there should be a trip and a telltale at the sub station and unless the current draw is through the actual 100amp fuse why would it fail

In lots of ways I am trying to duck out of the situation as the owner is as tight as a ducks rectum and wants everything done for free.

I am going to backheel it to her and tell her to get the meter checked over otherwise I am going to put a lot of time in for zilch as I have done on other work she has had done in the past.

Minted but squeaks when she walks!!!

Tom Durham · Feb 6, 2011

The tails are from the meter to a connector block then to the isolators etc so rodents are out of the picture.

It is the fact that it leaves the next fuse in line intact and there are no signs of anything getting warm