big bang

[meercat]

400amp bs88 fuse blown 3 times in a year, building is a school and is feeding submain board, not an overload problem, any1 any thoughts for course of action?

 

[Brightspark2]

Test the circuit?...

 

[alanl]

If it isnt an overload fault, then it must either be a short circuit fault, or poor quality fuses.

You need to narrow the fault and the time it happens down a little, and make some deductions from that.

 

[Pete999]

Nice thread succinct and to the point, maybe a short intro will get some more answers

 

[7029 dave]

Get your tester out, if it is not overcurrent, then must be short circuit?.

 

[Guest55]

i'd be looking very closely at the main switch's contacts , latching prongs , & fuse carriers.

 

[Deleted member 72666]

I'm assuming it's 3 phase, is it the same phase that's going down each time? What is the loading/phase, what is it feeding etc, etc, etc, more info! We demand it!

 

[Darkwood]

Why do you consider it not an overload issue? - have you calculated the submains demand and confirms it is impossible to draw this amount of load?

What are your test results for the submains supply?
What is the fuse cascading down to? (discrimination)
What is the nature of submain 1ph 3ph?
If i have confused you here or even educated you to the basics you should already know and have done then go back to house bashing and give it to a competent Electrician with experience of larger installs.

Harsh i may be but with a short quick question like that and no info' it screams out that you are in too deep! otherwise you would have provided us with relevant info.

Ill happily be corrected if you will be so kind and forthcoming with the info i requested.

Edit - title Big Bang is this what happened did someone hear this - suggesting a short!

 

[UNG]

What type of cable is the sub main and what is the run like to the sub board

 

[sparkdog]

Sounds like a job for Brendon Grace.

 

[Deleted member 72666]

Could be single phasing as Biff is implying due to poor contact(s), if so replace all 3 fuses as the others could have been weakened and you'll just be chasing your tail. Above all you must get your test gear out and investigate!