RCD problem

[apprentice87]

In layman's terms please. I'm a retired tree surgeon. Mick

Hi Mick, it was just a load of electrical "electricians" talk. not really related to your problem at all.. It is difficult to explain but i will try..

Basically, in an electrical installation you have to have a means of ADS. That is, "automatic disconnection of supply" which is to take place, [the disconnection that is] within a specified timescale, in the event of an earth fault. This COULD be achieved by means of an OCPD [An overcurrent protection device] like a circuit breaker or fuse.

What we were on about is, say you have a 40A breaker. To get it to operate with the required timescale in the event of an "earth fault" [This is where a phase conductor ["live" if you like, although use of this term in this context is technically incorrect] comes into contact with earth as a result of a fault] [and so, as you can imagine this means that everything else ALSO connected to the earthing system is now ALSO at anything up to full mains voltage] requires a certain amount of current flowing to earth to operate the OCPD in the required time. In the case of the 40A breaker, this would require not be 40A at all, but 200A [or 400A or 800A] depending on the type of breaker you have...

We were on about what would happen if a small generator was the power supply, as your generator cannot possibly put out this sort of current, and so the breaker would not provide ADS, so, therefore, an RCD is fitted to achieve ADS, but in a different way..

What the RCD does is this. It has been established that the MAXIMUM current, [voltage does not matter] that you can have flowing through you, [with a reasonable certainty that it will not kill you] is about 30 milliamps.

Therefore, what an RCD does is this: It compares the amount of current that flows through the one side of the RCD, with that that returns through the other side [thus completing the circuit] In the event that there is a difference of MORE than 30mA it is obvious to the RCD that this current has "escaped" somewhere and so it trips and shuts off the power [hopefully...] I say this because an RCD is a very unreliable device. I believe the failure rate is about 7%.. This is why it is important to test them on a regular basis..

So, as you can see.. The ONLY thing preventing you from being killed by means of electric shock, is the RCD.. Fuses and breakers will not help you at all, [although they MAY prevent overloading and fire] but if you are already dead, this is possibly not much of a consolation!!

Bypassing the RCD would be a BAD idea!!

john..

 

[Michael Walker]

Many thanks John. So,if I understand this correctly, it's throwing, with nothing plugged in at all, because the blue industrial plug socket is at fault.

The 25A RCD is now refusing to reset. Trekking into Chepstow tomorrow for a replacement. 

When I replaced the original one, it had earth and negative in the same slot on the RCD. I repeated this when I fitted the new one. 

Questions:

should I continue to do this with the next?

Should I connect in going from genny, run genny and see what happens before I connect to industrial blue outgoing?

I'm starting to feel that the blue socket might be at fault, so to save time and another trip to town I will pick one up.

Many thanks John, for taking the time, it is genuinely appreciated. Mick

 

[apprentice87]

For the RCD to trip, there is either an insulation fault somewhere, OR the RCD is faulty.. Can you post photos of the RCD and how it is wired??

john..

 

[Geoff1946]

For the RCD to trip, there is either an insulation fault somewhere, OR the RCD is faulty.. Can you post photos of the RCD and how it is wired??

john..

Agree with that, and I think Michael said it trips with nothing connected. In that case there must be an earth leak within the generator.

Presumably the neutral output of the RCD is connected to the machine frame, so bingo! the RCD will detect the leakage and trip.  

As it lives outside I put my money on water ingress into the generator or control box. If so drying it out thoroughly could solve the problem.

 

[Michael Walker]

Ok. So if I put a different earth cable from chassis to RCD and another from chassis to industrial blue outlet socket, might this solve the problem. 

On the other hand, how do I get picture posting rights so that I can show you how it all goes together 

 

[Murdoch]

Ok. So if I put a different earth cable from chassis to RCD and another from chassis to industrial blue outlet socket, might this solve the problem. 

On the other hand, how do I get picture posting rights so that I can show you how it all goes together 

Doubtful TBH

If the set up worked before you started to experience the tripping, then that would point at a fault.

 

[apprentice87]

Now you have made ten posts you should be able to post photos already..

john..

 

[Geoff1946]

IF my (pure guess) theory is correct then re-wiring the earth connections will make no difference at all.  Only fixing the fault, (by guessing again, drying out the machine innards) MAY fix it.

Only finding the fault either by testing, which an electrician could easily do, or by guesswork, as we are presently trying to help you do, will actually resolve it.

I must re-iterate what you've already been told, that if you conceal a fault by disabling the very limited protection which you have from the RCD, you are creating a potentially lethal situation. 

Please be careful, and a happy new year.

 

[Michael Walker]

I'll take some pictures. 

 

[Michael Walker]

I can't upload pics, it says 501kb only.

Think I'll have to bite the bullet and strip the genny.

I will look for and replace weak/bared and lose connections on all three wires coming out. 

Firewood takes priority at this time of year and what with the almost biblical rain and Glastonbury mud its almost a full time task until there's more daylight. 

Thanks to all for your input. I'll let you know how I get on. Mick

 

[Murdoch]

I don't understand what effect that would have on the generator. The RCD trips when nothing is connected. The RCD is 25amp, it has replaced the original 16amp unit that was on there when I picked the generator up. 

If the RCD trips at 25amp, why doesn't the 13amp fuse in the plug blow. Or the trip switch on the extension.

Seriously considering bypassing RCD. 

I don't recall you answering my previous point - have you actually disconnected EVERYTHING downstream of the RCD ? 

Bypassing the RCD isn't recommended if you value your or your families life

 

[Michael Walker]

Hi Murdoch. 

The RCD trips when nothing is connected. 

The generator has 4 wires coming from the alternator housing. 2 earth's, one each pos and neg. 

1 earth and the neg go in one side of the RCD,  the pos goes in the other. 

Pos comes out of the bottom of the RCD into the blue ind socket, single neg comes out the bottom of the RCD and into the blue socket. 

Remaining earth goes into blue socket.

The trip goes with nothing plugged in. 

Sometimes it works for 10 mins, other times it works for 4 hours. When RCD does trip, that's it for the day. But then it might not set for 2 or 3 days after.

 

[ProDave]

Take the 2 wires out of the output of the RCD.  Does it still trip then?

If it is tripping with nothing in the commando socket, that suggests to be a fault in the socket, possibly saturated with water?

 

[Michael Walker]

I'll try that next, thanks Dave

 

[apprentice87]

I would not be taking the generator to bits... There will be nothing much to see in there..

Out of interest, measure the voltage between the neutral and the earth that goes to the socket and then between the neutral and the frame of the machine..

Do you have a facebook page you could put the photos on.. What make and model is the generator??

john..

 

[Murdoch]

Take the 2 wires out of the output of the RCD.  Does it still trip then?

If it is tripping with nothing in the commando socket, that suggests to be a fault in the socket, possibly saturated with water?

Or got an ants nest in it ....

still wondering how the solar panels are connected to this set up 

 

[OnOff]

This was a "blue" plug used outside I found recently,  literally full of water and as you can see a bit rotten! As much as anything it was an IP4* plug when they should have fitted an IP6* rated one. This was causing a 16A circuit breaker to trip. 



Slug, snail? 

 

[Michael Walker]

I've now got a Facebook account. 

I chose a name that should be easy to find

Fnar Brimble

I'll be totally gobsmacked if I'm not the only one.

Thanks in advance, again 

Mick

Pictures posted on Facebook page

 

[apprentice87]

I've now got a Facebook account. 

I chose a name that should be easy to find

Fnar Brimble

I'll be totally gobsmacked if I'm not the only one.

Thanks in advance, again 

Mick

Pictures posted on Facebook page

You need to change your facebook settings so that people can search for you.. I tired but it could not find any entries for that name..

joh..

 

[OnOff]

Not everyone has a Facebook account. 

(Including me).