RCBO Ratings

[Fleeting]

Pre metal enclosure requirements for dwellings it was always a no no for a metal enclosure on a TT system unless the rcd was prior to the enclosure, seems fine now for some reason. TT and caravan parks are always an issue with selectivity between rcds. It may be possible to replace the main switch rcds with 's' types however you may lose your 0.2 disconnection time if required (cannot see what all the circuits are supplying) but then again this may achieve nothing. It needs establishing why the main switch rcd trips, cumulative leakage or just poor selectivity.

 

[binky]

Pre metal enclosure requirements for dwellings it was always a no no for a metal enclosure on a TT system unless the rcd was prior to the enclosure, seems fine now for some reason. TT and caravan parks are always an issue with selectivity between rcds. It may be possible to replace the main switch rcds with 's' types however you may lose your 0.2 disconnection time if required (cannot see what all the circuits are supplying) but then again this may achieve nothing. It needs establishing why the main switch rcd trips, cumulative leakage or just poor selectivity.

I think it was changed to reflect increasing use of RCBOs in boards/ requirement for 2 RCDs minimum. Need to be 2 pole for the incoming board as they must isolate neutral and line. Apart from improving reliability of the system overall, what I am also tinking is that it makes fault finding much easier, not just for the current issue, but for any future issues that may occur. As this current issue only occurs in specific weather conditions, it maybe rather hard to trace a fault even iwth earth leakge testing as any testing needs to occur when the conditions are just right.

 

[Andy™]

(And why 40A IN the caravan, but only 16A TO the caravan ?

40a on the RCD is simply the current its designed to handle safely and is completely irrelevant to the problem. you could fit a 63, 80 or 100a RCD and it wont make any difference. its the mA tripping current that matters

 

[Red Squirrel]

From starting this thread I have learnt a lot from reading all your replies, so thank you. Although most of it is still slightly over my head!

We have yet again had more tripping issues from the same pitch, with no reason. The 16amp RCBO was replaced outside, this seemed to fix the issue for a while, so it seemed. Now the issue is back again, turn on power to outside box and trips immediately, even when plugged into another neighbouring caravan power point which points to internal caravan wiring I would think…?

With this aside and going forward it would be much more beneficial for the individual RCBO to trip and NOT trip the main board which in turn puts everything off on the entire park…very infuriating to say the least!

Is there anyway (at all!) that we can change the setup or type of RCBO at each individual pitch to ensure 100% it will trip before banging off the main trip? Instead of sometimes tripping the individual rcbo and the majority of the time tripping the main trip.

Thanks for the help guys.

 

[Andy™]

the RCD in the distribution board could most likely be changed to an S type giving some delay. you would need to get someone competent to come and take a look at the setup and decide if its possible or not

 

[Sharpend]

I have just noticed the word Sewage on one of your main board circuits, would this be a below water sewage pump? Possibly cable breaking down?

 

[Red Squirrel]

the RCD in the distribution board could most likely be changed to an S type giving some delay. you would need to get someone competent to come and take a look at the setup and decide if its possible or not

Thanks for the advice. I may bring this up with electrician, I assume using an s type introduces a certain delay in tripping therefore the rcbo before it should trip first? Is this dangerous for electric shocks etc?

I have just noticed the word Sewage on one of your main board circuits, would this be a below water sewage pump? Possibly cable breaking down?

You are indeed correct, well spotted. These come on when the water level rises, which would certainly make the fault random. Although this time it’s looking like a particular caravan causing the nuisance tripping.

 

[Fleeting]

If you put in place an 's' type rcd then you must ensure a 0.2 disconnection time if required is adhered to

 

[Red Squirrel]

If you put in place an 's' type rcd then you must ensure a 0.2 disconnection time if required is adhered to

Yes by all means we would get an electrician to inspect - although everyone we have ever had cannot explain why this happens…

Can I ask a silly question, how can you tell the rcd we have is not already time delayed?

 

[Andy™]

no S on it

 

[David R Connell]

This looks like a gift problem for the qualified electrician a day out to a caravan park!

 

[Red Squirrel]

no S on it

Makes sense

To make matters even more confusing the 'problematic' caravan has now since been plugged back into the supply and now everything is ok - I really do not understand this anymore.

Here are some facts to breakdown the problem at hand:

- 16amp RCBO at 1 caravan trips (no other caravans individual 16amp RCBO outside trips on park)
- Entire distribution board which supplies said caravan and 20+ others trips
- To eliminate bad 16amp RCBO at pitch, caravan is plugged into neighbouring supply - caravan still trips / knocks out main board

With these facts at hand surely it is safe to assume this caravan is the main cause of the tripping?

Now we are faced with the fact that now the supply is fine when plugged into its own supply now, where as the day before it wouldn't stay on!

As far as we are aware there is no electrical item which is used at the time of tripping - its completely random.

Can any electrical appliance or wiring etc cause issues over a period of time? I assumed when something is bad it will happen consistently...

 

[binky]

I really do not understand this anymore.

the 'curse' of RCDs, otherwise known as right twits to fault find.

So it sounds like you have a caravan with an earth leakage issue + earth leakage from around the site where something random is pushing the main board RCD over it's limits, pump sounds like a candidate, but isn't necessarily the whole picture.

Trouble with earth leakage is that virtually every electrical appliance contributes some, couple of mA from a fridge, couple from a PC, couple from an outside light with a bit of damp in it etc etc, all contributing to the build up of earth leakage, and then you turn on one final item and the whole system trips out. OHHH it must be that last item that is faulty, only you can't repeat the issue because that isn't the whole picture. Random tripping is usually an item that is automated / runs itself switches on/ off, fridges and freezers are fave for that as they turn on/ off at any time of day or night, your sewage pump also works that way, but these appliances may not be faulty, just taking the RCD over it's mA limit

As said above, you need to get someone to test for earth leakage on the individual ccts, and as I suggested, get that 300mA RCD removed if possible and push the RCD protection out to the individual ccts / sub mains to make life a lot more relaaible for you.

 

[Red Squirrel]

the 'curse' of RCDs, otherwise known as right twits to fault find.

So it sounds like you have a caravan with an earth leakage issue + earth leakage from around the site where something random is pushing the main board RCD over it's limits, pump sounds like a candidate, but isn't necessarily the whole picture.

Trouble with earth leakage is that virtually every electrical appliance contributes some, couple of mA from a fridge, couple from a PC, couple from an outside light with a bit of damp in it etc etc, all contributing to the build up of earth leakage, and then you turn on one final item and the whole system trips out. OHHH it must be that last item that is faulty, only you can't repeat the issue because that isn't the whole picture. Random tripping is usually an item that is automated / runs itself switches on/ off, fridges and freezers are fave for that as they turn on/ off at any time of day or night, your sewage pump also works that way, but these appliances may not be faulty, just taking the RCD over it's mA limit

As said above, you need to get someone to test for earth leakage on the individual ccts, and as I suggested, get that 300mA RCD removed if possible and push the RCD protection out to the individual ccts / sub mains to make life a lot more relaaible for you.

Thanks @binky it is starting to make sense to me regarding the earth leakage from a combination of sources, its a little daunting knowing where to start as there will be literally hundreds of appliances amassing from all caravans on the park. To top it off our sparky is having 'issues' getting out to us asap.

Sewage pump runs constantly, was taken off timer quite some time ago due to manufacturers instructions to avoid pump damage - apparently restarts cause the pumps more harm

Could a layman like myself with earth leakage clamp meter attempt to measure leakage from each individual pitch? This would save sparky vast amount of time if I could at least identify pitches with leakage which seems higher than average.

 

[binky]

Could a layman like myself with earth leakage clamp meter attempt to measure leakage from each individual pitch? This would save sparky vast amount of time if I could at least identify pitches with leakage which seems higher than average.

Probably, but I don't want to be responsible for encouraging you to piddle about in live distribution boards.

 

[SPECIAL LOCATION]

I assumed when something is bad it will happen consistently...

Incorrect assumption from my experience.. sometimes they do... sometimes they don't...
But it is always easier to identify, locate and rectify when multiple circuits do NOT share a common RCD..

 

[JonesK]

It could be what is called " Accumulative earth leakage". Its the sum of each individual earth leakage from each individual caravan which is insufficient to trip the local 30Ma RCD units but when added together trip the 300mA Main RCD Unit. You need an earth leakage ammeter top measure this leakage current.

OR

It could be a faulty 300mA rcd unit. I would recommend undertaking an RCD ramp test under load and no load conditions to determine this.

 

[Red Squirrel]

It could be what is called " Accumulative earth leakage". Its the sum of each individual earth leakage from each individual caravan which is insufficient to trip the local 30Ma RCD units but when added together trip the 300mA Main RCD Unit. You need an earth leakage ammeter top measure this leakage current.

OR

It could be a faulty 300mA rcd unit. I would recommend undertaking an RCD ramp test under load and no load conditions to determine this.

Thanks for the input @JonesK I have certainly learnt a lot about cumulative earth leakage over the past few weeks and your theory makes complete sense.

Although the only issue is the fact the local 16amp 30ma RCBO at the one pitch trips at the same time, this means quite a massive 'random' leakage I would assume to set off the 300ma RCD OR the RDC is already on the edge before this random leakage raises its head every full moon.

Sparky coming tomorrow so hopefully we will have some answers by then. I am going to put forward the points raised:

To avoid site wide blackouts:
Removing 300ma RCD to push tripping back to the local RCBO's at each pitch
OR Changing these to time delayed
AND in either case test the 300ma RCD for fault

Earth leakage test on 'problem' caravan - Hopefully will pickup a dodgy appliance or wiring - I highly doubt this but fingers crossed

 

[Sharpend]

For how long it would take to walk the site and test each hook up and other supplies for earth leakage, it would be wise to do all then you have a instant map of what’s going on, of course this is subject to change as usage changes but you may find a particularly high leakage that needs a bit more exploratory work. (Pumps) ??

 

[Red Squirrel]

For how long it would take to walk the site and test each hook up and other supplies for earth leakage, it would be wise to do all then you have a instant map of what’s going on, of course this is subject to change as usage changes but you may find a particularly high leakage that needs a bit more exploratory work. (Pumps) ??

@Sharpend it would take quite some time but it would probably be a necessary task - I have wired up a rig (female to male 3 pin) to go between the supply and meter for each caravan making it easier to do leakage test on the live/neutral (exposed the earth).

It just occurred to me that even if a leakage test was carried out on a 'problem' caravan this is most likely not going to show any issue...until it trips again by which point you wouldn't be able to do a leakage test as the circuit wont stay on (keeps tripping RCBO). Can only hope whatever the issue is shows a relatively high reading below the point of setting off the trip I guess...man these RCD's really are a headache