Strange fault. Time delayed mcb trip.

[littlespark]

Fault finding. Good to systematically and logically investigate the problem, then the culprit has been staring you in the face...

phone call from new customer- no power.
get there, split rcd board. “It’s that big switch that won’t stay up”, says the woman
Ok, the rcd. Unplugged everything I could find, did some initial dead tests... everything seems ok. Powered up RCD, it holds... turn on each mcb in turn... all holding... Great!

Two minutes pass, then click! First mcb trips, downstairs sockets. Damnit.
Wasn’t the rcd at all, was the mcb!

She’s on the phone to her husband, “try this, try that!” It’s ok.... I’ll find it!

Split the ring, still everything is ok. Can’t find a fault, but there must be one.
Changed the the mcb, just to rule that out.

clamp ammeter on the outgoing legs.... wildly fluctuating between .5, 1, 5, 7A.... keeps jumping up and down.... not a steady rise.

The husband comes home at about 4pm.... he’s an industrial boiler engineer, but hell he needs to stay away from electrics!

“hmm, I’ll have to run an extension into the garage for the freezers.“

“Freezers!?!” As in plural?


Turns out there’s a single socket in the garage, looks like it’s spurred from a double in the kitchen, back to back.
From this socket is an 8! Way extension lead with a fridge freezer, a chest freezer, a tumblr dryer, a couple of battery chargers and.... wait for it.....



a 3kW immersion heater!!

Seriously!


So all these appliances turning on at once is stretching the 13A fuse in the extension lead, but something still has a fault to take out a 32A breaker at random.


I’m going back tomorrow. It’s fixed and working just now. I’ve told him to try each freezer in turn in the socket, but I’ll have to do something else with the immersion, it’s own radial circuit.

 

[Baddegg]

Before you pop the immersion on its own radial throw it at him he deserves it!...good luck though mate and keep us posted ?

 

[littlespark]

I knew it was going to be a struggle as I went round unplugging badly made extension leads upon badly made diy extension leads....

 

[Baddegg]

I knew it was going to be a struggle as I went round unplugging badly made extension leads upon badly made diy extension leads....

?....as soon as someone rings they other half when you trying work logically round the place and starts giving you advice you know it’s gonna be a ball ache ?....especially if they are an.....”engineer” ?

 

[littlespark]

Aha.... now that boiler man has moved the freezer and various other objects from in front of the water tank, I can see what’s going on.
The single socket is actually a double, spurred from another one in the garage.
He was just telling me a load of lies as in where it was supplied from.

The immersion heater on the tank has its own switch and timer, which was behind the fridge... he could have told me that was there.

The plug that was marked “water heater” plugged into the extension lead actually went to some for of pumping equipment for the hot water... unit also hidden by the fridge.
Flex was the same colour and size of what I could see of the immersion... I just couldn’t see the cable route yesterday.


so the increasing amps has been this pump trying to get up and seizing, causing the overload.

I told him to get the pump unit repaired/ replaced, and not overload the extension lead with freezers

3 hours of searching, which could have been found sooner if he’d answered the question “is everything unplugged” correctly.

 

[Rockingit]

If anyone remembers watching 'House'...... one of his catchphrases was 'The patient always lies'