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Michael Walker

RCD problem

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Michael Walker

Hi, my names Mick. I live off grid in 7 acres of woodland near Chepstow. I've been here 3 years now and can't imagine life anywhere else. 

I have a spring for water and 640w of solar supplying 3x100w deep cell batteries. 

I also have a 3kw diesel generator to run my washing machine and at this time of year to up my batteries. The genny has been performing perfectly well for 16 months but last week the 16amp RCD kept flipping. 

I checked the extension from the gen and the wiring to the washer(&water pump). All good. After resetting for the 10th time, the RCD stopped working. I have replaced it with a 25amp unit and it was still the same,even with nothing plugged into the gen.

The original RCD unit had the earth and negative wired into the same side of the RCD which I have copied onto the replacement. 

Today I tried it one last time and it is working perfectly. I know these intermittent problems are the worst but winter is the when the batteries, therefore my,for want of a better word 'house's, needs it the most.

Thank you for taking the time to read this, and for any advice you might have to offer.

Mick

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Michael Walker

Hi all, it's happening again. 

Genny ran for 5 hours yesterday, no problem until RCD threw. Wouldn't reset.

Genny housed and dry.

Question: Can I bypass the RCD? The power comes to the dwelling via a jcb extension  with built in breaker. The plugs that go into it all have 13amp fuses. Surely they would protect my devices. 

Thanks for your patience, hoping my idea for a fix will float. Mick

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Murdoch

Unplug all the devices you have. 

 

Reset rcd

 

Plug in devices one by one and you may find one device is the culprit

Edited by Murdoch

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Michael Walker

Hi Murdoch, thanks for getting back so quickly. 

The RCD throws with nothing plugged into the gen.

It was the same with the original RCD, I can't for the life of me figure why it's happening 

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Murdoch

Disconnect solar and batteries,

 

please dont start multiple threads

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Michael Walker

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. 

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Blue Duck

Is it actually an RCD? 

 

Fuse takes longer to blow in an overload situation, lucky dip on a short.

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Murdoch
20 minutes ago, Michael Walker said:

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. 

 

ANY load downstream of an RCD, with a fault can and most likely trip the RCD

 

if you don’t disconnect the solar / battery system you haven’t isolated everything connected.

 

and by isolating it means switching off live and neutral 

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Onoff

Can you perhaps post a picture of the 16 & 25A units?

 

You may not have posting rights yet but can post a link to another photo upload site or the mods here can give you posting rights.

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Onoff
2 hours ago, Michael Walker said:

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. 

 

Is the extension lead a reel type and is it unwound? Wound leads can actually melt together in the middle but look perfectly OK from the outside. They will generally have two ratings on them  wound and unwound.

 

On another note things like cables and generators, motors etc can take time to heat up in use and only then "go down to earth" and "trip" when hot and things have expanded. Photos of what you have would ascertain whether its RCDs or MCBs you have. 

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apprentice87
16 hours ago, Michael Walker said:

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.

 

Ok, from this it can be seen that you have no idea at all about the function of RCD's or MCB's.. You need an electrician..

You seem to think that the 13A fuses in your BS1363 plugs will protect your devices, maybe they will, but they will NOT protect you..

 

Photos would help..

 

john..

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kerching

Not wishing to urinate on your fried potato products BUT a 25 A RCD will not trip at 25A or even 50 it may possibly melt BUT it won't TRIP whereas it WILL TRIP as it senses an earth fault approaching 30mA

 

 

you seriously need to,get someone in who knows what they are doing AND how to,test when completed

Edited by kerching

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apprentice87
3 hours ago, kerching said:

you seriously need to,get someone in who knows what they are doing AND how to,test when completed

 

Definitely.. especially as your setup is powered with a generator, bypassing the RCD would be a lunatic thing to do.. You say you are near Chepstow?? I understand the burns unit closed down some time ago.. Shame that, you may be needing them soon..

 

Please listen to Kerching.. [above..]

 

john...

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apprentice87

Hi all,

 

As in interesting point that just popped into my little brain.. Say you have a setup powered by a small generator. Presumably the ONLY earth fault protection you have will be an RCD, as, i would imagine, if you relied on an OCPD to provide fault protection, the generator would be physically incapable of providing a PEFC high enough to provide ADS within the required disconnection time????

 

john..

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Michael Walker

Hi. Yes, extension lead is real type completely unwound. RCD original unit and the one used now both have RCD printed on them. Genny trips, or doesn't with nothing plugged into it. 

It's ex-army from a surplus outlet. Very basic 3kw,diesel Lambordini. It is pull start and simply has the RCD and the blue, 3 pin outlet. Nothing has been fiddled with and the replacement RCD is wired identically as the previous unit.

I'm a mile from the nearest car,across farmland, including 3 streams. 

The problem with it being intermittent, as I'm sure you're aware, is that unless the problem shows its face to a professional, it remains a mystery. 

It has run trouble free for over a year.

Not being a fan of burns of any kind  I will heed the advice to leave the unit in place.

Many thanks to all for your input. M

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kerching

Get elctrical work wrong and at the least it will not work correctly....at the worst it will kill you and possibly others and whilst you are  dying it will hurt a lot

 

just saying 

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Michael Walker

Anyone live near Chepstow looking for a job? I can deliver. M

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Phoenix
On 27/12/2019 at 11:04, apprentice87 said:

Hi all,

 

As in interesting point that just popped into my little brain.. Say you have a setup powered by a small generator. Presumably the ONLY earth fault protection you have will be an RCD, as, i would imagine, if you relied on an OCPD to provide fault protection, the generator would be physically incapable of providing a PEFC high enough to provide ADS within the required disconnection time????

 

john..

 

While undoubtly true, I think for a small machine like this, it wont be as bad as it looks on paper. The lack of PEFC is going to be down to two reasons:

 

a) the high impedance of the generator winding, as compared to the grid, we can, at least measure one with this with a loop tester, the saving grace with high proportion of the impedance in the source windings, is that under fault conditions the output voltage will collaspse down quite a lot.

 

b)The ability of the machine to actually produce enough energy to feed into the fault, you can't generally measure this, and a loop test won't show any hint of it, unless you test with quite a high test current, it does again have its advantages that under a hard short the machine is likely to stall.

 

So I would expect if the RCD providing fault protection was inoperative, then under a fault that wasn't sufficent to operate the OCPD then the volatage would likely dip  down to whats probably a safe level, the machine would slow right down, it would try and ramp up to compensate, but that could just cause even more current to be drawn and it would soon stop. Probably wouldn't want to be holding a class 1 appliance at the time becuase you cant guarentee it'll be under 50v, but I don't think the fault would be able to persist for ages until it got someone, in quite the same manner that a fault on a TT system with a failed RCD / VOELCB can

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apprentice87

Great answer!!

 

john..

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Michael Walker

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

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apprentice87
2 hours ago, Michael Walker said:

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..

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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

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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..

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Geoff1946
1 hour ago, apprentice87 said:

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.

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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 

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