RCBO Ratings

[binky]

...man these RCD's really are a headache

Yep, they are designed to be sensitive to protect people, but that also makes them sensitive to lots of little faults aswell.

 

[Red Squirrel]

Ok have an update...earth leakage test was done by myself (sparky couldn't carry this out dont ask)

I noticed when the electric heater (build in heater) was turned on the reading was not steady, the average reading for the caravan was around 2.4mA, now when the heater was on the reading was slightly more erratic hunting between 3.8mA and approx 6mA, it would then seem to lower after a while, then after a period would start to deviate again. Is this normal?

Also this may seem stupid and perhaps the problem is obvious however there was a point when the meter peaked out at 20mA! It did not do this again and I thought it was myself doing something with the clamp meter (position / moving it etc) which caused this? For example would touching the earth wire on the outside of the clamp while neutral/live are clamped cause a weird reading? I assumed it was me doing something silly however if there is no way a simpleton like myself cannot use one of these clamp meters then perhaps this was a genuine reading which would give me a result!

 

[Tulip Spark]

Your sparky is probably pissed off with being told how to do his job. Others have mentioned you have accumulation of leakage current causing the 300mA rcd to operate. Get the earth leakage tested at source. You may have to rejig the main incomer to sub boards to get rid of this fault. Chasing it around the campsite haphazardly and telling the sparky your findings will lead him up the garden path. Start from the beginning and let him design the install better is the direction I would go in. The fact that hes to busy to attend tells me hes had enough of this job.

 

[Sharpend]

Either that, or he didn’t know what he was doing?

 

[binky]

Ok have an update...earth leakage test was done by myself (sparky couldn't carry this out dont ask)

I noticed when the electric heater (build in heater) was turned on the reading was not steady, the average reading for the caravan was around 2.4mA, now when the heater was on the reading was slightly more erratic hunting between 3.8mA and approx 6mA, it would then seem to lower after a while, then after a period would start to deviate again. Is this normal?

this sounds fairly normal, so add in a few mA from other appliancs in the caravan, and times that by 20 pitches and you can see how earth leakge can accumulate rapidly.

Also this may seem stupid and perhaps the problem is obvious however there was a point when the meter peaked out at 20mA! It did not do this again and I thought it was myself doing something with the clamp meter (position / moving it etc) which caused this? For example would touching the earth wire on the outside of the clamp while neutral/live are clamped cause a weird reading? I assumed it was me doing something silly however if there is no way a simpleton like myself cannot use one of these clamp meters then perhaps this was a genuine reading which would give me a result!

Jiggling test leads can cause false readings, if the earth wire is bare copper and you touch it, you just discharged any static from your clothing. If you can't get a repeat reading, it's usually non-sense - it's the sort of thing that experience teaches.

 

[Red Squirrel]

Your sparky is probably pissed off with being told how to do his job. Others have mentioned you have accumulation of leakage current causing the 300mA rcd to operate. Get the earth leakage tested at source. You may have to rejig the main incomer to sub boards to get rid of this fault. Chasing it around the campsite haphazardly and telling the sparky your findings will lead him up the garden path. Start from the beginning and let him design the install better is the direction I would go in. The fact that hes to busy to attend tells me hes had enough of this job.

Either that, or he didn’t know what he was doing?

I truly do get where you are coming from @Tulip Spark but he simply doesnt have the equipment to do leakage tests….also caravan parks seem to be a specialised area to which certain regs need to be applied and I don’t think he wants to put his neck on the line.

this sounds fairly normal, so add in a few mA from other appliancs in the caravan, and times that by 20 pitches and you can see how earth leakge can accumulate rapidly.

Jiggling test leads can cause false readings, if the earth wire is bare copper and you touch it, you just discharged any static from your clothing. If you can't get a repeat reading, it's usually non-sense - it's the sort of thing that experience teaches.

Thank you @binky. I realise the clamp meter I have is probably not great by any Sparky’s standards on here but it seems to also deviate when the meter is at different positions or angles relative to the neutral/live? It can change by 3-4ma by turning it 180 degrees!

I’m getting to the end of my tether and can only do as much as I can not being in the trade. Until a contractor is sourced who deals with setups such as this I am determined to get to the bottom of the fault!!

 

[Sharpend]

Sorry red, did you say where you are based?

 

[binky]

Thank you @binky. I realise the clamp meter I have is probably not great by any Sparky’s standards on here but it seems to also deviate when the meter is at different positions or angles relative to the neutral/live? It can change by 3-4ma by turning it 180 degrees!

all test gear is merely 'an indicator' but some are more accurate indicators than others... LOL! 3-4mA is too bad, if you find something showing a steady 30-40mA, or more, then it will have sufficed it's function. As I said before, it really is worth altering your set-up to get rid of the 300mA RCD and oush the RCd protection onto the submains / dist boards around the site.

I encountered a similar set up many years ago whilst quoting for solar panels on a caravan site down Cornwall. I was glad not to get the job becuse the way the solar inverters start up is good at upsetting RCDs, and the site owner wasn't going to fork out for a complete new cable run of 300m, or interested in paying to change what he had. It made fitting the panels uneconomic anyway.

 

[Red Squirrel]

all test gear is merely 'an indicator' but some are more accurate indicators than others... LOL! 3-4mA is too bad, if you find something showing a steady 30-40mA, or more, then it will have sufficed it's function. As I said before, it really is worth altering your set-up to get rid of the 300mA RCD and oush the RCd protection onto the submains / dist boards around the site.

I encountered a similar set up many years ago whilst quoting for solar panels on a caravan site down Cornwall. I was glad not to get the job becuse the way the solar inverters start up is good at upsetting RCDs, and the site owner wasn't going to fork out for a complete new cable run of 300m, or interested in paying to change what he had. It made fitting the panels uneconomic anyway.

Sorry been cut off with the recent storms we have had recently...Thanks @binky I think i was experiencing interference with other wires, still trying to source the culprit, finding this device very interesting actually!

We have a employed the help of a main contractor to do a full check of our entire power network, this should hopefully resolve our issues, although when this happens may be some time yet. In the meantime my investigating continues...

I have drawn up a part plan of the setup that involves the most recent issue we have had with one pitch cutting off the entire park, hopefully it makes sense

I have marked up the particular RCD's which trip. To me it seems the main RCD is tripping as per the previous suggestions of cumulative leakage, with a spike at the highlighted pitch putting the it over the threshold for every RCD in the line, it just seems quite 'unlucky' for this to be happening unless the culprit caravan has a huge spike in leakage at some point as I cant see the main 300mA RCD being on the edge but further testing will conclude this.

As mentioned from a few people you suggest pushing the RCD protection out to the circuits - as an example does this mean replacing the 4 breakers on the distribution board below with RCBO's? And then remove the 100mA RCD completely? And I also assume the main 300mA RCD would also need to be removed?

 

[binky]

ideally we would get rid of the 300mA and 100mA RCDs in favour of replacing the 32 and 40A MCBs with RCBOs, however, I don't work much with TT systems and I'm not sure if we have to have RCD protection on the sub-main between the main board and distribution board. I believe we would still need a type S time delay RCD for the sub main, but I believe we can get rid of he 300mA regardless, hopefully someone will correct me on that shortly.

 

[SPECIAL LOCATION]

In all your "investigations" you have to keep in mind you are looking at some very very small current values..
i.e. 30ma is approx 7watts..
100ma is appox 23watts
300ma is approx 70watts..

so the amount of current needed for a traditional 100watt lamp would be enough to wipe out all three RCD's if it was leaking to earth...

And if you are using a clamp meter to try and read these ma values..
you do need to check its %tolerances to assess the accuracy of what you are reading..

I haven't actually been back to re-read the whole of the thread..
BUT have you done 'Ramp-Tests' on all of the suspect RCD's to see what actual leakage current will make them operate??

You may be progressing and going in a forwards direction with your investigations..
BUT.. it is also very easy to make a wrong assumption and lead yourself up the garden path when trying to solve these types of faults..

And your layout doesn't look to be the best design to "Minimise Inconvenience In The Event Of A Single Fault"..
(which is a requirement in BS7671 wiring regs)..

P.S.
I can understand a bit of what Tulip is suggesting..
Sometimes it can be a pain in the rear trying to work with a customer who may not agree with your working methods..?

BUT.. also, any half decent electrician likes to get the satisfaction of solving a tricky problem for a customer..
And providing both customer & contractor are happy to work together to track down the cause of an intermittent fault..
It can be very rewarding for both parties..

Over the years I can recall a few "real-head-scratchers" that basically needed someone on site 24/7, (the customer)...
To make a few notes of times/dates/what what was happening when the power tripped off!

All I can say is keep going..
be prepared to work along side a local electrician..
And please come back and tell us of any updates to what you find..

 

[binky]

And your layout doesn't look to be the best design to "Minimise Inconvenience In The Event Of A Single Fault"..
(which is a requirement in BS7671 wiring regs)..

Improving the setup is the approach I would take for long term reliability as well as making it easier to find current fault.

Could you do me a favour and check the above advice about RCD protection on TT sub mains is correct - I don't get involved with TT very often.

 

[Red Squirrel]

@SPECIAL LOCATION thank you. I understand what a ramp test is but do not have the equipment or knowledge to carry out such a test - I hope the contractor will undertake this in due course.

For if or rather WHEN this happens again ...can we safely assume that (going back to the scenario which I have illustrated above) shows 100% that the individual pitch is causing the fault, there cannot be any other influencing factor which would trip the individual RCBO on the pitch other than this caravans load and/or earth leakage?

Thanks for all the help on here its been great

 

[Murdoch]

@SPECIAL LOCATION thank you. I understand what a ramp test is but do not have the equipment or knowledge to carry out such a test - I hope the contractor will undertake this in due course.

For if or rather WHEN this happens again ...can we safely assume that (going back to the scenario which I have illustrated above) shows 100% that the individual pitch is causing the fault, there cannot be any other influencing factor which would trip the individual RCBO on the pitch other than this caravans load and/or earth leakage?

Thanks for all the help on here its been great

OP - you need a decent, competent LOCAL spark to advise you on this - a single up front RCD tripping is a VERY BAD thing to have

 

[mainline]

OP - you need a decent, competent LOCAL spark to advise you on this - a single up front RCD tripping is a VERY BAD thing to have

I had this fault the other week 300ma time delayed sub main feeding a main building from there 100ma time delayed feeding 4 other buildings each having their own CUs all rcbo
Kept randomly tripping the 300ma turned out that there was n to earth leak on the main swa cable and a n to earth fault in one of the buildings on a light circuit ... The problem was that they were not DP rcbos so when rcbo tripped in building the n to earth fault still remained.

 

[Murdoch]

I had this fault the other week 300ma time delayed sub main feeding a main building from there 100ma time delayed feeding 4 other buildings each having their own CUs all rcbo
Kept randomly tripping the 300ma turned out that there was n to earth leak on the cable and a n to earth fault in one of the buldings on a light circuit ... the problem was that they were not DP rcbos so when rcbo tripped in building the n to earth fault still remained.

100% agree but the OP thinks they can solve this without spending money

 

[SPECIAL LOCATION]

[...can we safely assume that (going back to the scenario which I have illustrated above) shows 100% that the individual pitch is causing the fault,

Erm.. NO..

from what I understand and have read.. you haven't actually PROVED much so far..

Basic essential rule is..
"Assume EVERYTHING is faulty until you have PROVED otherwise"..

So far without any ramp tests you haven't actually PROVED that you don't have an oversensitive RCD, (or multiple oversensitive RCD's).

So..
IMHO you have got to test and prove the FULL operating characteristics of each & every RCD..
Plus the insulation resistance values for each and every circuit supplied by those RCD's..
Then look at what is regularly connected and if any natural leakage is evident...

(Sorry if I have missed something you have already stated..
But I think there are still too many unknowns that need to be resolved.)

 

[mainline]

Erm.. NO..

from what I understand and have read.. you haven't actually PROVED much so far..

Basic essential rule is..
"Assume EVERYTHING is faulty until you have PROVED otherwise"..

So far without any ramp tests you haven't actually PROVED that you don't have an oversensitive RCD, (or multiple oversensitive RCD's).

So..
IMHO you have got to test and prove the FULL operating characteristics of each & every RCD..
Plus the insulation resistance values for each and every circuit supplied by those RCD's..
Then look at what is regularly connected and if any natural leakage is evident...

(Sorry if I have missed something you have already stated..
But I think there are still too many unknowns that need to be resolved.)

Was this

100% agree but the OP thinks they can solve this without spending money

He's going to spend money, even if he decides to have a go himself and buy a cheap mft and then learns how to use it.

 

[mainline]

@SPECIAL LOCATION thank you. I understand what a ramp test is but do not have the equipment or knowledge to carry out such a test - I hope the contractor will undertake this in due course.

For if or rather WHEN this happens again ...can we safely assume that (going back to the scenario which I have illustrated above) shows 100% that the individual pitch is causing the fault, there cannot be any other influencing factor which would trip the individual RCBO on the pitch other than this caravans load and/or earth leakage?

Thanks for all the help on here its been grea

@SPECIAL LOCATION thank you. I understand what a ramp test is but do not have the equipment or knowledge to carry out such a test - I hope the contractor will undertake this in due course.

For if or rather WHEN this happens again ...can we safely assume that (going back to the scenario which I have illustrated above) shows 100% that the individual pitch is causing the fault, there cannot be any other influencing factor which would trip the individual RCBO on the pitch other than this caravans load and/or earth leakage?

Thanks for all the help on here its been great

The first thing to do is IR test the supply cable from the 300ma rcd to the dis boards.
Is there a TN earth at the cut out ?
Is the cable 2 or 3 core ? swa ?
Is there tails you can clamp around at the source of the 300ma rcd
I'm assuming it's swa buried to the caravans then a post with earth rod and mcb/rcd feeding the caravan into cu with a main switch and rbos ?
I havent read every post so maybe repeating what others have said.

 

[David R Connell]

Always, always "start from the source of supply and work forward" has been my motto. When distracted and or ignored it has cost me time and money.