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Discuss Main Isolator blowing in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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evo666

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Hi All

I have just been asked to have a look at a Fridge that keeps blowing the Main isolator. It is one of those big American style fridges and everytime the things fires up it pops the main breaker. (she has also had the same thing with a breadmaker, steam iron)It is not a new fridge but worked fine in the old house.

I have not seen the job yet but wondered if anyone had any ideas as to why it would happen.

Thanks

Rog
 
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WarrenG

  • Thread Starter Thread Starter
  • #2
Rog,

If we are talking about the circuit breaker for that particular circuit then I would check to see what type of circuit it is i.e. Ring / Radial and then check the load thats on it.

If the circuit breaker is tripping then it is going to be an overload or short circuit and by the sounds of it, when the fridge fires up there is an inrush which may be causing the breaker to trip.

When you say that the breaker trips when the fridge fires up indicates that the breaker is holding out untill this point which would suggest to me that its an overload problem.

Fridges are know to have an inrush to fire up and then calm down when running. Check the fridge loading?

I would check the loading of the circuit, unplug everthing off the circuit and plug one item at a time back into the circuit on its own one by one to see if this trips the breaker. If for example the breaker trips when you plug the fridge in on its own, it stands a chance there is a fault with the fridge.

If all plugged in and breaker holds for a while then trips when the fridge kicks in I would say there is an overload problem.

The circuit may be ok on loading and when the fridge fires up pushes it over the limit. A way to solve this would be to use maybe a 'C' type breaker instead of a 'B' Type but to be honest you wouldn't normally have this problem in a kitchen. More like a garage with a welder.

Hope this makes sense.

Warren
 
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evo666

  • Thread Starter Thread Starter
  • #3
Thats helps thanks, it is the main isolator that blows not the circuit breaker :)
 
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uksel

  • Thread Starter Thread Starter
  • #5
main breakers can trip.

if there is a problem with overload (which it sounds like) and it's the main breaker (100A or 60A) which is tripping out, then it is not solely due to the current demand of the final circuit in question (ringmain), this would only be the straw that breaks the camels back, it is the accumulation of current from all circuits overloading the main breaker, this should or would really be obvious to you if you have any experience or qualifications.

I think WarrenG is right, although, as opposed to unplugging every accesory on the ringmain i think i would opt to turn off all the breakers and just run the ringmain with the fridge on it as the breaker protecting this circuit is only 32A and should trip well before the main breaker. If this 32A breaker trips then unplug your appliances all around the house (or just turn everything off by the socket switches)

If the circuit breaker doesn't trip initially with the fridge plugged in then turn on each circuit one at a time, leaving a few seconds in between.

It could also be worth looking to check if your main breaker is 63A, 80A or 100A. if it is less than 100A then consider what the demand is from the installation and wether upgrading the main breaker would be an option.

what do you think...?

also it could be worth just checking the flexible cable for the fridge or putting your meter across the plugs pins to see what sort of resistances you get, as it could easily have been damaged in transit if it's been moved from their old house.

I have heard that old fridges dont like being moved much...
 
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uksel

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  • #7
i think he is, but it's an easy one to be fair :D
 
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eskimo39

  • Thread Starter Thread Starter
  • #8
We recently had to put a C rated MCB into a lighting circuit. The startup on a fancy light fixture just kept popping the B rated one.

These are usually classed as Motor breakers, but who knows what the americans use to power their fridges.
 
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uksel

  • Thread Starter Thread Starter
  • #9
you're spot on there about your breaker types young man, C type breakers are used for items which induce a high start-up current (just like motors) and they prevent nuisance tripping while still keeping the overload ratings of the device low enough to protect the installed equipment/circuit.
 
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chrissyh

  • Thread Starter Thread Starter
  • #12
Dont want to teach anyone to suck eggs but bear in mind when upgrading breakers from B-C-D that each time you go up, you reduce the maximum Zs permitted for the circuit.
 
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geecam

  • Thread Starter Thread Starter
  • #13
Dont want to teach anyone to suck eggs but bear in mind when upgrading breakers from B-C-D that each time you go up, you reduce the maximum Zs permitted for the circuit.

and cant be installed with quite a few domestic installation methods

geecam
 
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