Power keeps tripping out, how to diagnose?

jpaul said:
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.
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Your RCD tripped on a fraction of an Amp, 0.3A. If there was a catastrophic breakdown of the insulation that created enough current to trip your MCB (in the absence of an RCD) then that would blow the element. This type of fault happens once and it destroys the element - it doesn't happen intermittently.

Don't forget that in the case of the OP, it was a 32A MCB that was tripping - are you forgetting that there are 13A or even 5A fuses in the plug tops? They didn't need replaced and the much higher rated MCB continued to trip - this is why I diagnosed a faulty MCB. If the new MCB starts to trip, then my next step would be to isolate any transformers in the circuit.
 
String said:
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.

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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Ah right, sorry got confused as to which sentence of mine your original comment referred to. So a plug in RCD will not trip if there is a short to neutral whereas a plug-in current sensing device will show the over current and potentially trip correct?

It hasn't tripped since I replaced the MCB so I am hoping that's all it was.

When I do eventually get around to having the consumer unit replaced I would certainly like to have more circuits so each floor of the house is on it's own circuit, the tediousity of this I cannot tell you!
 
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Energize said:
Ah right, sorry got confused as to which sentence of mine your original comment referred to. So a plug in RCD will not trip if there is a short to neutral whereas a plug-in current sensing device will show the over current and potentially trip correct?
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Could you link to the products or post part numbers?

By the way, I assume the new MCB has held up so far?
 
String said:
Could you link to the products or post part numbers?

By the way, I assume the new MCB has held up so far?
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Actually, could you recommend any particular diagnostic product? With Amazon prime I might as well order something that could come in handy in future for diagnosing similar faults.
 
To be honest, no. The test equipment that I own and use costs £1000+ and it isn't plug and play as such - it requires an experienced technician to use it.

If I were you, I wouldn't invest any more time into this unless the replacement MCB starts tripping.
 
String said:
To be honest, no. The test equipment that I own and use costs £1000+ and it isn't plug and play as such - it requires an experienced technician to use it.

If I were you, I wouldn't invest any more time into this unless the replacement MCB starts tripping.
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Unfortunately after replacing the MCB it has tripped a couple more times. Every device has been now unplugged one at a time so that seems to rule out any device as being faulty and I have checked that the continuity on all the sockets between earth live and neutral is correct, so it looks like we're going to have to call out an electrician again. Wonder if it's a problem with wiring somewhere in the house, maybe damaged insulation on the cables?
 
Having ruled out a faulty MCB, and with no apparent damage to equipment, I would be looking for loads that have high starting current. What have you actually got plugged in?

You could plug each individual device into one of these, set it to amps, and see if anything spikes momentarily as it is switched on.

FLOUREON Power Meter UK Energy Monitor AC 230V~250V Power Consumption Meter Energy Cost Calculator Watt Voltage Amp Meter[Energy Class A+++] - 1pack https://www.amazon.co.uk/dp/B01DSQ30FO/ref=cm_sw_r_cp_apa_i_M3RADb3HR0CM0
 
Did the electrician that came do any insulation resistance tests on the circuit?, if not then get a new electrician!

I would suspect fixed wiring at fault rather than equipment, while a 13A plug top fuse is pretty poor at discriminating with a B32 breaker, at least sometimes a fault would take out both, and if you are saying its happened multiple times (how many), even if it doesn't blow the plugtop fuse, it'll stress it, and eventually it will go alongside the breaker. I would expected that at somepoint the 13A fuse would have gone, the fault would be disconnected and you'd know what is not working.

I'd also rule out inrush in a domestic situation taking out a B32 unless you have industrial kit, or a server farm or something, if it was a B16 i'd be bit more wary, even 3kva site transformers don't take out B32s, the 5Kva ones do sometimes.

I'd suspect cable damage, and you are likely to see a poor IR even when the breaker is holding in, there is a possible fire risk (especially without any RCD protetcion), so it ought to be addressed as a priority

Where in the UK are you? there might be someone on here local who can diagnose it
 
String said:
Having ruled out a faulty MCB, and with no apparent damage to equipment, I would be looking for loads that have high starting current. What have you actually got plugged in?

You could plug each individual device into one of these, set it to amps, and see if anything spikes momentarily as it is switched on.

FLOUREON Power Meter UK Energy Monitor AC 230V~250V Power Consumption Meter Energy Cost Calculator Watt Voltage Amp Meter[Energy Class A+++] - 1pack https://www.amazon.co.uk/dp/B01DSQ30FO/ref=cm_sw_r_cp_apa_i_M3RADb3HR0CM0
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Just consumer electronics and lamps.

A couple of tvs, game consoles, 2x desktop computers and monitors going through a UPS, amplifier + speakers, subwoofer, network switches, external hard drives, a printer. That's about it.

Computers and stuff in the UPS are left on 24/7 so there's nothing really being turned on or off there. Yeah I've got one of those and have thought about doing that, it's just that it doesn't seem to trip at the point anything is switched on.

Adam_151 said:
Did the electrician that came do any insulation resistance tests on the circuit?, if not then get a new electrician!

I would suspect fixed wiring at fault rather than equipment, while a 13A plug top fuse is pretty poor at discriminating with a B32 breaker, at least sometimes a fault would take out both, and if you are saying its happened multiple times (how many), even if it doesn't blow the plugtop fuse, it'll stress it, and eventually it will go alongside the breaker. I would expected that at somepoint the 13A fuse would have gone, the fault would be disconnected and you'd know what is not working.

I'd also rule out inrush in a domestic situation taking out a B32 unless you have industrial kit, or a server farm or something, if it was a B16 i'd be bit more wary, even 3kva site transformers don't take out B32s, the 5Kva ones do sometimes.

I'd suspect cable damage, and you are likely to see a poor IR even when the breaker is holding in, there is a possible fire risk (especially without any RCD protetcion), so it ought to be addressed as a priority

Where in the UK are you? there might be someone on here local who can diagnose it
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Hasn't run any insulation tests as far as I know, but I have contacted an electrician I personally know through a social group to ask him if he can take a look rather than the randomer my housemates got in!

It's not even a 13A fuse in the plugs, it's 3A or 5A for everything connected to the circuit!

It's tripped 14 times in the past couple of weeks according to my UPS logs.
 
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Energize said:
It's tripped 14 times in the past couple of weeks according to my UPS logs.
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still don't understand - you are manually resetting it though - so you know exactly when it happens .? .. obviously you don't see a pattern

still think I would get an rcd adapter and see if that fired under the theory that current is not exclusively being returned to neutral.

I have a (maplin) energy meter wouldn't know if these are fast enough to capture short duration current peaks (they are probably integrating over a period of time)
 
jpaul said:
still don't understand - you are manually resetting it though - so you know exactly when it happens .? .. obviously you don't see a pattern

still think I would get an rcd adapter and see if that fired under the theory that current is not exclusively being returned to neutral.

I have a (maplin) energy meter wouldn't know if these are fast enough to capture short duration current peaks (they are probably integrating over a period of time)
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Yeah I am manually resetting it, and don't see a pattern. Psb.

Month Day _Year_ Hour Minute Event Description
8 30 2019 13 24 Battery backup transferred to AC utility power.
8 30 2019 13 4 Battery backup transferred to battery power due to blackout.
8 28 2019 13 2 Battery backup transferred to AC utility power.
8 28 2019 12 58 Battery backup transferred to battery power due to blackout.
8 28 2019 8 57 Battery backup transferred to AC utility power.
8 27 2019 21 19 Self-test Passed.
8 26 2019 9 12 Battery backup transferred to battery power due to blackout.
8 25 2019 11 49 Battery backup transferred to AC utility power.
8 25 2019 0 45 Self-test Passed.
8 24 2019 11 30 Battery backup transferred to battery power due to blackout.
8 22 2019 20 26 Battery backup transferred to AC utility power.
8 22 2019 20 22 Battery backup transferred to battery power due to blackout.
8 22 2019 10 32 Battery backup transferred to AC utility power.
8 22 2019 10 31 Battery backup transferred to battery power due to blackout.
8 21 2019 20 49 Self-test Passed.
8 21 2019 13 15 Battery backup transferred to AC utility power.
8 21 2019 13 8 Battery backup transferred to battery power due to blackout.
8 21 2019 9 35 Battery backup transferred to AC utility power.
8 21 2019 9 35 Battery backup transferred to battery power due to blackout.
8 20 2019 15 6 Battery backup transferred to AC utility power.
8 20 2019 15 4 Battery backup transferred to battery power due to blackout.
8 20 2019 4 16 Battery backup transferred to AC utility power.
8 20 2019 3 52 Battery backup transferred to battery power due to blackout.
8 19 2019 21 32 Battery backup transferred to AC utility power.
8 19 2019 21 31 Battery backup transferred to battery power due to blackout.
8 19 2019 18 56 Battery backup transferred to AC utility power.
8 19 2019 18 47 Battery backup transferred to battery power due to blackout.
8 19 2019 17 53 Battery backup transferred to AC utility power.
8 19 2019 17 32 Battery backup transferred to battery power due to blackout.
 
Have you continuity tested the UPS lately? the slightest leak from them could cause a neutral fault making it trip.
 
String said:
@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?
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1) I know, it was only an example to help you understand.

2) "It happens once because the fault current will melt the heating element to the point of open circuit." Incorrect, the MCB should trip before this - depending on the load the current flowing could be huge, what you have described is how fires start and not how a circuit should work. Short circuits can be permanent but not always - its al about resistance, resistance generates heat. No resistance has less heat energy and more resistance has more. We use this in its basic form to generate light and heat. This is why electricians test for insulation resistance. What you describe is a permanent dead short circuit with 0 resistance between fault, the worst-case scenario. What I would say is that you would generally need a near dead short on an appliance for it to draw enough current to trip a 32A MCB. As the resistance reduces the current increases...

I think @String is overcomplication things here, there is no need to use a power analyser. An RCD operates on current imbalance and an MCB works on current amount. So a short neutral and earth on a circuit with load on it, part of the neutral current flows through earth conductor instead of neutral. The RCD sees an imbalance and trips. So an RCD trips on almost any live fault, but only trips on neutral faults if the circuit is carrying a load. Any imbalance will also increase the current - which, as we know, overcurrent trips MCBs.

In reality, you need to identify what is fed on that circuit and remove what you don't require or move to a different circuit. Try and narrow it down instead of guessing. As mentioned here, things like fridges and things with motors in are likely culprits because they breakdown often with heat build-up causing short circuits. @String's suggestion of inrush current from a motor is also not good advice in a general domestic application - I very much doubt you have any motors that will generate over 32A on startup suddenly without having a short circuit fault.

After listing the equpiment you have on the circuits it is could be an earth fault generating high current. This would also trip an RCD so the suggestion of an RCD plug for the suspected appliance is good advice. The alternative would be PAT testing to check for low resistance with damage flex - causing short circuit faults and higher than usual current.

As you've said you've disconnected everything and you've still got issues. It could be a cable fault causing an intermittent short circuit or a socket faceplate arcing on the terminals/burning out. Get and electrician to do an insulation resistance test on that circuit and you'll solve your issue.

String said:
A 13A fuse is designed to blow before a 32A MCB, else what would be the point in fitting fuses?

A 32A MCB also has characteristics and tripping curves.
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A plug top fuse only protects the live... is often a slow burn and depending on the current flow the MCB may be quicker to activate... go figure.
 
As you've said you've disconnected everything and you've still got issues. It could be a cable fault causing an intermittent short circuit or a socket faceplate arcing on the terminals/burning out. Get and electrician to do an insulation resistance test on that circuit and you'll solve your issue.
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this would be my current bet given all thats been done so far!
 


So after further testing I found one socket which isn't being used with live and neutral reversed, touching the screw on the socket with my electrical screwdriver lights it up! After opening it up I was shocked to see that there is an uninsulated earth wire connecting to the socket and the backplate which I guess must be making the whole of the backplate and the screws connecting to it live.

Question though, why does my multimeter show 37v ac when only one probe is touching the shorted earth wire?
 
The earth wire is supposed to be connected to the back plate, although it's also supposed to be sleeved.

I strongly advise you to leave the intrusive testing to a qualified electrician.
 
String said:
The earth wire is supposed to be connected to the back plate, although it's also supposed to be sleeved.

I strongly advise you to leave the intrusive testing to a qualified electrician.
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I'm going to, I've got an electrician coming over tomorrow.

Doesn't connecting the earth wire to the backplate create a danger of electrical shock? I mean the screws on the front of the socket have a voltage across them because of it, so touching them could produce a shock. If the backplate was not connected to the earth wire than this danger wouldn't be there surely?
 
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