Power keeps tripping out, how to diagnose?

jpaul said:
I'm not a qualified electrician ! - but in the picture you posted I couldn't see any reference to rcd's or is it before the consumer unit.

( I googled earlier but can't see whether officially/legally you change an MCB yourself, if you follow the appropriate checklist )
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He doesn't have an RCD in that little consumer unit. As for legality, it's a little bit complicated but the bottom line is that it's not illegal to change it yourself, it's just dangerous.

Personally, I would upgrade the CU as it's missing a few tick boxes including age, lack of RCD, plastic composition (should be metal).
 
jpaul said:
I'm not a qualified electrician ! - but in the picture you posted I couldn't see any reference to rcd's or is it before the consumer unit.

( I googled earlier but can't see whether officially/legally you change an MCB yourself, if you follow the appropriate checklist )
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There is an RCD in the consumer unit, no6, you can only just barely make out the 0.03A marking in the photo.

I have just replaced the MCB in any case, so will see if there's any joy.
 
As said before. Get an electrician in to diagnose the fault and replace the consumer unit at the same time as its looking pretty tired.

Also if that is an rcbo then you have no rcd’s for anything other than your lighting circuit.

Mcbs stop your house burning down but rcds Will save your life.
 
NoobCannon said:
As said before. Get an electrician in to diagnose the fault and replace the consumer unit at the same time as its looking pretty tired.

Also if that is an rcbo then you have no rcd’s for anything other than your lighting circuit.

Mcbs stop your house burning down but rcds Will save your life.
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Electrician has already been and has echoed the earlier suggestions that each device needs to be ruled out on the circuit.
 
So number six is an RCBO and this provides protection only for the lighting - looks like this was an addition at some point and perhaps required after lighting work in say the bathroom etc to comply with newer regulations. Regs have moved on a little bit and this protection should now be continued to have RCD protection on all circuits.
I wouldn't rush out for a new consumer unit - it doesn't require immediate action.

As for the MCB to be tripping, above what has been said on this overcurrent isn't just simply plugging in too much and 'overloading' the circuit with too much current draw. Overcurrent can also be caused by say a short circuit between live conductors.
An example would be a failing heater element that has short-circuited line and neutral and this can get quite complicated as something like a heater can change resistance as it heats up.

As said, you need to narrow down what is plugged in but as you say it happens at 4am when nothing is in use it should be easy to figure out as it wont be things like the kettle etc.

String said:
I'm putting my reputation on the line here; you've installed a new MCB and it's problem solved. :)
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I wouldn't be so sure - electrician of 15 years and I can count on one hand how many 'failed' MCBs i've seen. Fitting a replacement of a different rating or type doesn't count either ;)
 
mattyy said:
I wouldn't be so sure - electrician of 15 years and I can count on one hand how many 'failed' MCBs i've seen. Fitting a replacement of a different rating or type doesn't count either
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Really, yet you think a short circuit on a heating element could be a repetitive fault?

One word to that... Bang! ;)
 
String said:
Really, yet you think a short circuit on a heating element could be a repetitive fault?

One word to that... Bang! ;)
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Yes, if you cannot understand that resistance isn’t a constant and will change depending on temperature of the dielectric or what ever insulation media that is used then don’t read any further.

Obviously using ohms law will tell you that altering the resistance will also alter the current draw at a given voltage.
So as a element gets hotter and it’s resistance changes or maybe the material alters in such a way with temperature that the resistance is reduced then it will slowly start to draw more amperage and thus eventually drawing more current than the MCB can with stand for a given period of time. Over time this will cause a element to completely fail and will be a at a very low resistance to flow enough current to trip the MCB immediately. As many elements are small and do not draw enough amperage to start with the failing process of an element often goes unnoticed until it is a dead short.


This is why why have different cable sizes etc. Let’s take the heater wire in a toaster as the wire becomes thinner with use - what happens? The resistance changes...
 
@mattyy

1. He already said that there's no heating appliances in the circuit.

2. A short circuit happens under the conditions you describe, but it happens once. It happens once because the fault current will melt the heating element to the point of open circuit.

He isn't hearing loud bangs at 4am and all his appliances remain functional. The only time you'll see consistent overcurrent without a short circuit is likely to be inrush current from a motor; and contrary to your previous statement, this would be solved by swapping out the MCB for a type D which would allow the starting current for the short period of time that it requires.

If this isn't a faulty breaker, I would be looking for current spikes from a motor or transformer... Maybe the UPS he mentioned earlier?
 
Energize said:
Electrician has already been and has echoed the earlier suggestions that each device needs to be ruled out on the circuit.
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if electrician visited he must have assessed the devices connected to tell you what he thought (indeed how many are there)
- obviously dangerous if it's tripping in the night. insurance company would hold you negligent to not identify source.

can get an rcd plug adapter and see if that will isolate the problem device .. reasonable chance high current is not being returned
 
If there is a short to neutral though rcd won't trip will it? I think we have a plug adaptor that records peak current draw would that be useful?

I wasn't there there at the time, but I was told that he said what is connected (various computers, tvs, an amplifier, low power consumer electronics and led lamps) was well below the 32A limit, only thing he mentioned was that sometimes UPS devices can cause trips due to the transformer, but turning the UPS on and off at the socket hasn't caused the breaker to trip so far.
 
Energize said:
If there is a short to neutral though rcd won't trip will it? I think we have a plug adaptor that records peak current draw would that be useful?
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Yes, it would trip with neutral short - that's one of the main advantages. However, disregard "RCD plug adapter" comment as it makes no sense. If you really want RCD protection then change out the consumer unit.
 
why don't you think an RCD plug adapter would be a good diagnostic device ?
... if the problem is intermittent then it could just sit there and fire if the the appliance throws a fault ?
 
jpaul said:
why don't you think an RCD plug adapter would be a good diagnostic device ?
... if the problem is intermittent then it could just sit there and fire if the the appliance throws a fault ?
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An RCD trips on earth leakage, this intermittent fault is lifting a 32A MCB which only trips on overcurrent. There could be 100 amps running through that circuit and it wouldn't trip an RCD.
 
yes - as I suggested 'if the device is also not returning the current' , the RCD would identify it, and isolate it before the MCB

both the devices (albeit heating elements) that I have had fail, kettle , coffee machine, threw the RCD, but with a break down in the insulation/MgO in the element, may have also drawn a high current, tripped mcb id the rcd were not present.
 
String said:
Yes, it would trip with neutral short - that's one of the main advantages. However, disregard "RCD plug adapter" comment as it makes no sense. If you really want RCD protection then change out the consumer unit.
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I thought they tripped when there was a difference between the current supplied to the device and the current returned? If all the current in a device was going from the live and shorting so that all that current went back to the neutral there would be no delta n would there?
 
Energize said:
I thought they tripped when there was a difference between the current supplied to the device and the current returned?
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They detect earth leakage, so yes. MCBs do not detect earth leakage, they detect overcurrent. Using an RCD to diagnose why an MCB keeps tripping would be like using a thermometer to take someones blood pressure.

Energize said:
If all the current in a device was going from the live and shorting so that all that current went back to the neutral there would be no delta n would there?
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That would result in short circuit fault current, which would trip your 32A MCB. An RCD would not trip under L-N short circuit fault current.
 
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