RCD Tripping on AMF switch-over to generator supply

[qwest]

I suspect you are right. I will try to find someone with the right experience.

I like a challenge and would like to think I could figure this out but reached the end of my patience.

The actuation of the contactors can't be cross wired otherwise under power cut there would be nothing to actuate the gen contactor and the gen would have to be running to get utility supply.

 

[Marvo]

You obviously have a good understanding of the system you have and I'm sure you can work safely but if you're banging your head against a fault and you're at the end of your capabilities there's no shame in getting assistance and saving yourself a lot of gray hairs. The cost won't be prohibitive for an hour or two of time, your biggest problem is finding an electrician who's suitably experienced. If nobody offers their services in this thread I'd web-search for a commercial electrical company that specifically offers back-up power/UPS/generator services.

 

[Engineer54]

Oh Dear, .....this sounds like a real old mess you have here!! First and foremost, does this second hand generator have an AVR (automatic voltage regulation) included, as most genest's of this rating do not!! If it doesn't then i'm afraid your're generator is unsuitable for domestic appliance use, where those appliances include the use of electronics!!....

The earthing arrangement is also a very important aspect to any generator installation, has the alternator neutral been suitably grounded to the frame via an external earth rod/electrode arrangement etc. Somewhere along the line, it seems by the sound of it you have mixed the house and generator earthing systems up. You really do need to get an electrician in to check over this installation, and one that actually knows what he's doing!!

 

[qwest]

Gen has AVR - earth isn't mixed up - I don't think.

we have a PME here so N tied to E at various points upstream.

gen has N tied to E and its own Earth so I have added a further earth - I could switch the earth so the gen and house earth are independent but I can see no reason why this should be necessary. Can a PME also be staked to earth? The electricians did this and I can't come up with a theory of why this would cause an issue.

gen frame, engine, chassis etc all on a common earth too.

Despite the problem the project was fairly well researched.

all sensitive electronics in the house are behind a UPC so AVR.

the AVR produces a more stable supply than the utility from my very brief sample. Any AVR isn't going to be able to fix the momentary drop off when switching to load - they'll all drop a few volts. In any case the issue isn't stability related so far as I can tell.

 

[Engineer54]

You should not be mixing the PME earth with the generators earth rod earthing system.
It's fine to add a rod to the PME earth (and is standard practice in many European countries) at the house MET, but not to then join that earth to the generator earthing system. The generators earthing should be for the generator alone. A separation distance between any PME rod and generator rod should be at least 3 metres distant (more if a deep driven rod) from the generator earthing rod(s) House earthing to be left in place from the change over switch back to the house CU.


Don't forget here that on PME systems (in effect an artificial earthing system) there is a Neutral earth connection at the incoming cut-out....

 

[Darkwood]

Ill reiterate what i said before fully disconnect and get a knowledged competent person in ...Electrician means nothing nowadays with all the short courses and fast track qualifications so ensure who-ever you get is fully experienced with gen' set-ups...You could always fly E5 over and ensure a quality experienced knowledgeable sparks or taxi Marvo over as very good advice has been given ... anyone else you will need to vet them and ensure they aint just your routine sparkies!

As i said before you clearly have a bit of grasp of electrics but i fear not enough for this situation and as you have realised you maybe at risk here ...... a little knowledge is very dangerous sometimes!

 

[Engineer54]

gen has N tied to E and its own Earth so I have added a further earth- I could switch the earth so the gen and house earth are independent but I can see no reason why this should be necessary.

So what do you call this, if not mixing the earthing systems then??

 

[Darkwood]

So what do you call this, if not mixing the earthing systems then??

Suicidal :shame:

 

[Knobhead]

With PME you need automatic earth transfer to safely use a generator. This gets messy and very complicated, if you try to do this on your own.
You can’t use the PME earth for your generator.

You say you now know what DNO means, I think they would love to see this set up. It is downright bloody dangerous and they will remove you’re supply and PME earth immediately.

So you have two options, scrap the generator or employ an engineer that knows what they are doing.

No I’m not offering my services:
YOU CAN’T AFFORD ME!

Personally:
I think this is a very well put together Troll thread. A knowable Troll I’ll grant. There are far too many inconsistencies.

Biff!
It’s time to doff you’re cap!

 

[qwest]

I had guessed the earth may not be set up correctly.

The gen spike tied to the N at the gen is on good copper and is as close to the gen as possible - about 1m away. It consists of a spike about 1.5m long.

What I don't quite understand is what additional risks or benefits are involved in switching the earth system.

Currently because the Utility N is switched then so too is the utility E,

So on gen supply the earth is entirely to the gen spike. There is no utility earth.

On utility feed there is both the gen spike and utility N tied.

Now I could switch out the generator earth but I can't see that being the issue.

Incidentally the earthing system to the gen is on really heavy gauge copper - looks like three core car battery cable - the gen earth was tested by my electrician and they seemed to think it well within spec

I don't have test kit myself beyond a little meter but I have checked if there is any pd between the utility E and the gen E (when the two aren't connected obviously) and there is no pd.

What is interesting is that there is a regulation or best practice in having utility spike and gen spike a set distance apart.

My guess is that this is to prevent a potential backfeed to the grid from one earth to the other - so if a gen fault creates a current to earth it doesn't then find its way back into a nearby earth spike along the utility to a lower resistance E.

The is no chance of that happening since the only earth spike in on the gen.

So what would I gain by switching earth systems? I would gain a momentary period where the entire house has no earth at all.

Am I at risk from a utility fault? Potentially I could now be earthing the grid if their E was not as good as mine?

The AMF I have is 3 phase capable but I'm on a single phase supply so I can easily switch the earth using spares on the contactors but really not sure what I'd be gaining.

Either that or add a furthe spike and earth the PME again?