Monthly intermittent fault

monkfish10 · Apr 5, 2016

I've been having this recurring problem where the RCD will trip (the MCBs don't move) causing power failure on everything in house. I can get everything (apart from sockets) to come back on immediately only if the MCB that controls the sockets is flicked down before I flick the RCD switch back up. The RCD will trip again if the sockets MCB is flicked up (even if everything in the house is unplugged and all the sockets switched off) until after several hours or longer - depending on how many attempts I've undertaken and their time apart - the sockets MCB won't trip the RCD and everything is back to normal......until the next invevitable power failure !

SOME DETAILS

-I live in a first floor flat house conversion
-Total MCBs are: lights, smoke alarm, cooker light, doorbell and sockets
-Power failures have happened at random times of day roughly one month apart
-I am almost certain that power failures happen when I am running hot water from the kitchen tap (activating the boiler), the other appliances tend to be plugged in but not being used at time.
-I have noticed suspiciously inadequete rewiring in the attic, where wires strewn across floor and not clipped on walls and some old wiring clipped off
-My landlord's eletrician thinks its a faulty appliance causing intermittent fault (is organising a PAT test on the appliances) but I think it goes deeper than that and is more likely to be either a faulty socket/faulty boiler/faulty wall wiring/faulty RCD that is causing the problem. I think I would have more frequent power failures if it was a faulty appliance because they are used so much.
-One time the lights MCB blew and became defective after a power failure which remains unexplained.

Given the information that I have listed, can anyone shed any more light on what could actually be causing the problem and give me any advice or information that will help me get to the bottom of this. I'm not an expert and I would like to be able to explain the situation in more detail as well.

Thank you

sparksburnout · Apr 5, 2016

When you say "Landlord Electrician" what sort of electrician is he exactly? I would suggest you get an electrician in to look at this, his comments regarding PAT testing seem very odd and if he is a proper sparky he should be able to sort it.
By the way if you get to the bottom of things can you let me know because my missus has monthly intermittent faults as well.

DPG · Apr 5, 2016

I would get a decent electrician in and explain the problem as you have above. He will probably check do an earth leakage test. You may be sailing a bit close to the wind, ie. the cumulative leakage may be getting towards the 30mA trip value of the RCD. It wouldn't take much then to push it over the edge. He will also test your RCD to check that it isn't tripping at too low a value. Daz

DPG · Apr 5, 2016

sparksburnout said:
When you say "Landlord Electrician" what sort of electrician is he exactly? I would suggest you get an electrician in to look at this, his comments regarding PAT testing seem very odd and if he is a proper sparky he should be able to sort it.
By the way if you get to the bottom of things can you let me know because my missus has monthly intermittent faults as well.

I must admit I assumed he meant Landlord's electrician rather than Landlord electrician. Daz

monkfish10 · Apr 5, 2016

What could be causing the cumulative leakage? How does such a fault occur?

DPG · Apr 5, 2016

Everything has a degree of earth leakage. IT equipment with switch-mode power supplies and filtering components tends to have more noticeable leakage current, maybe 2-3mA per device. If you add this up all fed via one RCD which trips a bit early (say 20mA) and that could be the issue. Especially if there is a fault on a particular appliance as well. Daz

Paul.M · Apr 5, 2016

Well explained Daz.

Leaving this in the General section, not a DIY project by the OP.

monkfish10 · Apr 5, 2016

Sorry but why would the RCD trip a bit early at 20mA? Weak electrics, not being able to cope with a lot of stuff plugged in? I thought it was unlimited.

Are you saying that when enough stuff is switched on/using electricity then the amount of leakage builds up over time causing the RCD to trip? Leakage is different to a surge/overload or a short in the wiring right?

DPG · Apr 5, 2016

An RCD theoretically trips at 30mA - any higher and it would be pointless to have it as it wouldn't save your life! Simplistic view maybe, but you get the idea. Nothing is perfect and it won't trip at 30mA- and it is impossible to say without testing it. The leakage doesn't 'build up over time' but will vary depending on what is plugged in at any one time. Daz

Paul.M · Apr 5, 2016

monkfish10 said:
Sorry but why would the RCD trip a bit early at 20mA? Weak electrics, not being able to cope with a lot of stuff plugged in? I thought it was unlimited.

Are you saying that when enough stuff is switched on/using electricity then the amount of leakage builds up over time causing the RCD to trip? Leakage is different to a surge/overload or a short in the wiring right?

Thats correct. Leakage is different.

An RCD should operate at 30mA but in reality they normally trip at 20-27mA, depends on age and the amount of times it has tripped. eg it may be damaged and a ramp test by an electrician needs to be carried out.

monkfish10 · Apr 5, 2016

In simple terms, what is earth leakage? and why would it trip the RCD?

DPG · Apr 5, 2016

Theoretically all electricity flows between live and neutral and not to earth. An RCDs purpose is to detect any leakage to earth (which is basically a fault) and safely shut off the supply. It compares the difference between current in the live line and the neutral line and checks to see if there is a difference. (Before anybody nitpicks - [you know who you are], I know neutral is also classed as live). Daz

Pete999 · Apr 5, 2016

https://www.youtube.com/watch?v=RnriL5iEmZs

IzzyS · Apr 5, 2016

monkfish10 said:
In simple terms, what is earth leakage? and why would it trip the RCD?

Maybe not so simple terms, but everything you ever wanted to know about RCD "nuisance" tripping is here Marc's Technical Pages: Power Quality Symptoms and Solutions - Nuisance Tripping

sparksburnout · Apr 5, 2016

DPG said:
I must admit I assumed he meant Landlord's electrician rather than Landlord electrician. Daz

Sorry, didn't read it properly. Specsavers.......

DPG · Apr 5, 2016

sparksburnout said:
Sorry, didn't read it properly. Specsavers.......

It's not you - it did say that but he's edited it since! Daz

sparksburnout · Apr 5, 2016

Anyway, is it really likely that the OP will have enough computers or other leaky equipment in use? More likely a duff RCD, he needs to get a decent spark in to sort it. Landlords, in my experience, will get the cheapest nastiest excuse of a trades-person in whenever possible, and it is quite probable that the "Landlord'S electrician"(!!!) was the same guy as the plumber, chippie etc. In my experience most Landlords need sending into outer space.

DPG · Apr 5, 2016

sparksburnout said:
Anyway, is it really likely that the OP will have enough computers or other leaky equipment in use? More likely a duff RCD, he needs to get a decent spark in to sort it. Landlords, in my experience, will get the cheapest nastiest excuse of a trades-person in whenever possible, and it is quite probable that the "Landlord'S electrician"(!!!) was the same guy as the plumber, chippie etc. In my experience most Landlords need sending into outer space.

I rent a house out myself so I am a landlord. Daz

Marvo · Apr 5, 2016

monkfish10 said:
..........-I am almost certain that power failures happen when I am running hot water from the kitchen tap (activating the boiler), the other appliances tend to be plugged in but not being used at time.........

Is your boiler a gas one with electronic ignition/control board that requires power from a socket or fused switch?

sparksburnout · Apr 5, 2016

DPG said:
I rent a house out myself so I am a landlord. Daz

Well, I am sure, given your standing on here, that you are a decent bloke/landlord. Most, sadly, in my experience are not.

DPG · Apr 5, 2016

sparksburnout said:
Well, I am sure, given your standing on here, that you are a decent bloke/landlord. Most, sadly, in my experience are not.

It's OK - no offence taken

You're probably right. On both counts

Daz

Octopus · Apr 5, 2016

Shame the OP can't post a picture of the CU.

But the way I read is is that the main switch is also the RCD - correct?

Davisonp · Apr 5, 2016

monkfish10 said:
In simple terms, what is earth leakage? and why would it trip the RCD?

"https://www.youtube.com/watch?v=5hL13UjRSoY"

This video shows earth leakage from everyday appliances, and the front room of the house tested has a maximum earth leakage of over 3mA. A full house with washing machines, microwaves Etc can have too much natural earth leakage for an RCD causing it to trip occasionally.
Current regulations require newer appliances to restrict the earth leakage, where older appliances from before RCD’s were required on circuits did not have the same restrictions on earth leakage meaning some older appliances have greater earth leakage. Also, as appliances reach the end of their life, the earth leakage can become worse, so some older fridges can start triping RCD’s as the motor’s start to fail.

A 30mA RCD when working correctly should trip somewhere between 15mA and 30mA.

Octopus · Apr 5, 2016

Davisonp said:
"https://www.youtube.com/watch?v=5hL13UjRSoY"

This video shows earth leakage from everyday appliances, and the front room of the house tested has a maximum earth leakage of over 3mA. A full house with washing machines, microwaves Etc can have too much natural earth leakage for an RCD causing it to trip occasionally.
Current regulations require newer appliances to restrict the earth leakage, where older appliances from before RCD’s were required on circuits did not have the same restrictions on earth leakage meaning some older appliances have greater earth leakage. Also, as appliances reach the end of their life, the earth leakage can become worse, so some older fridges can start triping RCD’s as the motor’s start to fail.

A 30mA RCD when working correctly should trip somewhere between 15mA and 30mA.

Not sure I agree with this!

sparksburnout · Apr 5, 2016

I watched that vid, and then noticed this one https://m.youtube.com/watch?v=5CBuLHVxqLI. Good old Al, he's so busy saving money he's not noticed that great big yawning gap in the middle of his CU!! Hehe.....

GETWIRED · Apr 6, 2016

Had something a little bit similiar last week, the lady unplugged everytjing and the rcd still tripped. The boiler was fed off the sockets via a fused spur so she didnt unplug it when she unplugged all her appliances. Was a very slow leak on the water pump inside the combi. Maybe something to think about.