RCD tripping dilemma

[2BobSparky]

Hi all,

Cam across a tripping 63A RCD, which is protecting pretty much everything in an office and even the lighting!

The first guy who came out seemed to think that perhaps a spur feeding a AC unit was the culprit and proceeded to change it over, but I didn't really see the point in that.

I reckon it's something to do with the light as I know from the past that lighting is notorious for causing nuisance tripping when being protected by an RCD.

Basically, I would like to be able to isolate the cause of the main RCD tripping, but unfortunately no MCB popped before the RCD!

 

[Plonker 3]

Welcome to the world of fault finding. A MCB wont necessarily trip because the RCD is

Could be one of thousands of things causing this. Is there a particular pattern to when it is tripping like when they boil the kettle, at night when no one is in the building.

Have you ramp tested the RCD to prove that is fine?

What have you done already to try and find the fault?

 

[telectrix]

fluorescent lighting is notorious for leakage. too many fittings on a RCD will cause it to trip.

 

[2BobSparky]

A MCB wont necessarily trip because the RCD is

Is there a particular pattern to when it is tripping like when they boil the kettle, at night when no one is in the building.

Have you ramp tested the RCD to prove that is fine?

What have you done already to try and find the fault?

It would be nice if the MCB tripped first though and considering RCDs are constantly referred to as "secondary protective devices" I thought this might be a sign as to what could be causing the RCD to go, but alas it's not that easy of course.

Doesn't seem to be any clear pattern as to what is happening, conflicting reports from different people in the office. Initially though, it appears as though they have gone to switch on all the AC units in the office and going to turn on the last one that was left off has caused the RCD trippage.

Never heard of "ramp testing", but I am familiar with a RCD test done as apart of an inspection and test, is this what you mean?

 

[2BobSparky]

fluorescent lighting is notorious for leakage. too many fittings on a RCD will cause it to trip.

When you say "leakage" I think I am getting the function of an MCB and a RCD mixed up.

My understanding of an RCD is by the measurement of current on both Active and Neutral wires and any imbalance will cause the RCD to activate. With this in mind, how does earth leakage come into the equation, which I thought was something more associated with an earth leakage MCB.

 

[Plonker 3]

It would be nice if the MCB tripped first though and considering RCDs are constantly referred to as "secondary protective devices" I thought this might be a sign as to what could be causing the RCD to go, but alas it's not that easy of course.

Doesn't seem to be any clear pattern as to what is happening, conflicting reports from different people in the office. Initially though, it appears as though they have gone to switch on all the AC units in the office and going to turn on the last one that was left off has caused the RCD trippage.

Never heard of "ramp testing", but I am familiar with a RCD test done as apart of an inspection and test, is this what you mean?

A ramp test will check how much leakage is needed before the RCD trips. So ensuring the RCD isn't tripping at too low a leakage.

I think maybe you are out of your depth with this, and walk away now or get someone with more experience to help you.

 

[Mr.Ian]

I'm sure AC units (air con???) like fridges/freezers can trip RCDs, there aren't a few of these units and rfc's and lighting all on one RCD is there?

 

[truckster]

If you have got flourescent lighting, a/c units and computers all on one RCD you have probably a fair amount of leakage in normal use, have you got a milli-amp clamp meter? Probably need to divide the circuits across two or more rcds or swap the MCBs out for rcbos and lose the front end RCD

 

[Deleted member 9648]

FFS...... do an IR test.....:banghead:

 

[2BobSparky]

So nobody would suggest taking the MCB feeding the AC units off of RCD protection to prove if in fact, like the office workers seem to believe, that AC units are the cause of the problem?

If the MCB trips without RCD protection then clearly that's the problem isn't it?

 

[Octopus]

So nobody would suggest taking the MCB feeding the AC units off of RCD protection to prove if in fact, like the office workers seem to believe, that AC units are the cause of the problem?

If the MCB trips without RCD protection then clearly that's the problem isn't it?

To save messing around with the CU why don't you simply recommend the air con is left off for a specific period!! or could you use a clamp meter on the Air con circuit? do a ramp test on the RCD, IR the circuit?

Problems like this are frustrating and yes the employees may have a point but you need a clear approach to fault finding or I suspect you'lll go round and round in circles

 

[tony mc]

I would be clamping the tails to see what sort of leakage you have.

By what has been said so far it is possible that the RCD is in fact only doing its job and detecting the leakage.

 

[2BobSparky]

To save messing around with the CU why don't you simply recommend the air con is left off for a specific period!! or could you use a clamp meter on the Air con circuit? do a ramp test on the RCD, IR the circuit?

This is not feasible with the client involved and also the temperature in their office! This is also why something like an IR test is not possible at this very moment as we ware talking about a dead test, which means switching their CU off, it's simply not going to happen during business hours in the West End of London.

So anyway, in the end the RCD MCB was taken off of RCD protection and has been left alone to see if it will inf act trip itself.

 

[Strima]

Looks like it's going to be out of hours testing then. The RCD tripping shows there's a fault somewhere which needs identifying and rectifying, I personally would not have left the circuit without RCD protection as the designer deemed it necessary to have it.

Even a quick test taking 15 minutes could highlight problems and reduce the amount of downtime the office has. Protection is there for a reason.

 

[Darkwood]

When you say "leakage" I think I am getting the function of an MCB and a RCD mixed up.

My understanding of an RCD is by the measurement of current on both Active and Neutral wires and any imbalance will cause the RCD to activate. With this in mind, how does earth leakage come into the equation, which I thought was something more associated with an earth leakage MCB.

Do a little revision on how rcd's work first before you address the problem, its clear from your confusion here your going into a problem slighty blind. For a heads up your are correct in that it monitors any different between the feed current to the load and the return current from the load, if it differs the current has leaked elsewhere and usually to earth.

Also check are the light electronic ballast, how many computers are in the offices etc, read up on natural background leakage currents and their causes.

 

[Des 56]

That well known saying is often used in the electrical industry,

"Its better to be sorry than safe"
or is it
"The Show must go on"




Regardless of safety

 

[2BobSparky]

I'm sure AC units (air con???) like fridges/freezers can trip RCDs, there aren't a few of these units and rfc's and lighting all on one RCD is there?

Yep, that's how it is.

 

[Darkwood]

Looks like it's going to be out of hours testing then. The RCD tripping shows there's a fault somewhere which needs identifying and rectifying, I personally would not have left the circuit without RCD protection as the designer deemed it necessary to have it.

Even a quick test taking 15 minutes could highlight problems and reduce the amount of downtime the office has. Protection is there for a reason.

A tripping RCD does not always mean there is a fault present, alot of modern office equipement have electronics that have a designed leakage current to earth hence the term High Earth Currents which must be accounted for in design when you have a no' of computers or light fittings with electronic ballasts, in the OP case i would first do a earth current test to establish if there is already a high leakage which may be related to designed leakage as opposed to fault leakage.

 

[Strima]

Very true mate, trying to read a post and reply with two screaming kids and a nagging wife running around doesn't help...

 

[vernam616]

Why not call an electrician?

 

[2BobSparky]

Looks like it's going to be out of hours testing then. The RCD tripping shows there's a fault somewhere which needs identifying and rectifying, I personally would not have left the circuit without RCD protection as the designer deemed it necessary to have it.

Even a quick test taking 15 minutes could highlight problems and reduce the amount of downtime the office has. Protection is there for a reason.

What about lights being included as apart of the RCD protected circuits? Isn't this cause for concern? Why did the designer include lighting?

Are lights only likely to cause RCD tripping when a lamp blows or can their componetry do it too?

 

[Darkwood]

Very true mate, trying to read a post and reply with two screaming kids and a nagging wife running around doesn't help...

No worries lol.

Think the OP needs to refresh himself to the workings of an RCD as well as well as what i would class a designed earth leakage before addressing this problem further, it may be the case that it is a faulty item creating the nuisance tripping but going into this with half the knowledge could lead to many hours of frustration and no conclusion.

 

[2BobSparky]

Why not call an electrician?

An electrician is the one who moved the MCB feeding the AC units away from being RCD protected in an effort to see if the MCB will still trip.

 

[Plonker 3]

I think maybe you are out of your depth with this, and walk away now or get someone with more experience to help you.

I will refer you to my earlier answer.

 

[tony mc]

Are you doing the work or just making enquirys 2Bobsparky ?

 

[2BobSparky]

I think maybe you are out of your depth with this, and walk away now or get someone with more experience to help you.

If you don't want to help, which is why I am here, then perhaps you should walk away right out of this thread.

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Are you doing the work or just making enquirys 2Bobsparky ?

I'm making enquiries so I can better understand the situation.

 

[Darkwood]

What about lights being included as apart of the RCD protected circuits? Isn't this cause for concern? Why did the designer include lighting?

Are lights only likely to cause RCD tripping when a lamp blows or can their componetry do it too?

As ive already mentioned i suggest you read up on the working of an RCD and what situations would cause them to trip, rcd's under the 17th it is usual to have an rcd covering all circuits in some form or other, there are exceptions but you should already be knowledgable in this area if you are doing this kind of fault finding, no offense meant here when i say you seem to be lacking knowledge in some basic areas that i would expect an electrician to have, we will try help where the situation has caused you confusion but with re' to replies to this thread you seem to lack knowledge of how rcd's function, designed high current earths, reg's re' rcd protection and when its needed as well as when it can be left out.
Its the fact your struggling with knowledge in several areas which you should already know, if you inform us better on your background we can answer your queries better, but all the help your getting your are answering with another question.
So what is your background, are you apprentice, qualified, etc etc then from there we can head you in the best direction.

EDIT....
Sorry you answered my question before i saw it as i was writing this post.... If you have had an Electrician out already i would of expected the questions you are asking here should have been explained by the electrician, i personally wouldn't leave a customer with a rcd tripping without fully informing him of the possible causes and the steps been taken to eliminate it, that aside this particular issue can get quite indepth and random guesses from other members may just add to the confusion and although you slated another member for suggesting you leave it to a proffesional; i must agree with them and the only hope is the electrician you have is competent in his job.

 

[2BobSparky]

As ive already mentioned i suggest you read up on the working of an RCD and what situations would cause them to trip, rcd's under the 17th it is usual to have an rcd covering all circuits in some form or other, there are exceptions but you should already be knowledgable in this area if you are doing this kind of fault finding, no offense meant here when i say you seem to be lacking knowledge in some basic areas that i would expect an electrician to have, we will try help where the situation has caused you confusion but with re' to replies to this thread you seem to lack knowledge of how rcd's function, designed high current earths, reg's re' rcd protection and when its needed as well as when it can be left out.
Its the fact your struggling with knowledge in several areas which you should already know, if you inform us better on your background we can answer your queries better, but all the help your getting your are answering with another question.
So what is your background, are you apprentice, qualified, etc etc then from there we can head you in the best direction.

I will indeed, but for the time being I was just looking for opinions on what would be the best plan of attack.

I am qualified, but working in the maintenance game, knowledge and skill set is comprimised by any given day's jobs, which can involve heating/cooling/plumbing etc and sometimes very little hands on electrical work. I would rather come in here and ask a load of questions and look like an idiot and be mugged off then do it in the workplace, put it that way!

There is a very knowledgeable and expereinced bloke on site who I often refer to, but in this case he has in fact domne something that to me didn't seem quite the right thing to do and to others on here is downright not acceptable ie. removing MCB from RCD protection to stand alone and see if fault occurs again.

So in closing, after reveiwing the replies in here these are the options:

-ramp test RCD
-divide sub circuits across two or more RCDs
-swap MCBs for RCBOs, thus eliminating need for RCD protecting several MCBs
-insulation resistance test

 

[Darkwood]

Circuits dont need to be RCD protected in all cases, which comes more into play in commercial and industrial senerio's, it relates to there been an instructed person present, although i dont exactly know the circuit design and layout of said building there is nothing wrong with dropping off the A/C from the rcd as a temp' measure or the fact 'depending on circuit design' whether it needs to be covered in the first place. I see now your situe' regarding you limited experience due to your job but would strongly suggest as i have always done that you regulary top you knowledge up on the regs and also visit this site often which will help with the areas you lack in. If you havent already i would suggest you get a copy of the reg's and on-site guide as they apply to commercial and industrial just as much as they do domestic, you obviously have a guy you respect regarding his knowledge but rather than sit back for the next 10yrs catch up to his level and revel in the security that you can walk into any similar job if not take over from him with confidence, ive seen so many resident in-house electricians over the yrs who are just not up to their job because they have slipped so far behind, and must say in these times alot are losing them and its expected to get worse rather than better.
Take it as constructive advice as it not a dig in any form.

 

[Darkwood]

Regarding the other collegue it maybe questionable on his order of approach to this problem but he is classed as you are as instructed ppl and taking it off the rcd is allowed and anyone on site that would need informing of the situe should be, if the cause is proving to difficult to find it is quite acceptable to remove the rcd for fault finding purposes and fitting and putting each circuit through a rcd one at a time, although not a method i would employ as there are many ways to skin a cat but just explaining it can be acceptable to do so as long as any one that needs to is informed of the situe.

 

[2BobSparky]

Appreciate those responses.

 

[i=p/u]

well id say the one rcd monitoring all mcbs sounds a culprit. how many computers are on these cirutits?? earth leakage tester i think may help you.

wouldnt say need todo IR test now if you have disconnected rcd and its working. too many computers , the air con units

 

[Moses]

FFS...... do an IR test.....:banghead:

Nice one!!!

Do an IR test on all circuits.

If that's good, then you have appliance leakage / faulty RCD.

 

[Plonker 3]

If you don't want to help, which is why I am here, then perhaps you should walk away right out of this thread.

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I'm making enquiries so I can better understand the situation.

I understand you are hoping to understand the fault, but before you go any futher I would advise getting a spark in who has a good knowledge of these situations. You seem to have a very limited knowledge of this, I am sure any spark you call in will be more than helpfull should you explain the situation to them.

Not everyone knows everything, and every day is a school day but you need to realise that this Forum as good as it is, isn't the answer to every fault you will discover.

 

[Deleted member 9648]

This is not feasible with the client involved and also the temperature in their office! This is also why something like an IR test is not possible at this very moment as we ware talking about a dead test, which means switching their CU off, it's simply not going to happen during business hours in the West End of London.

So anyway, in the end the RCD MCB was taken off of RCD protection and has been left alone to see if it will inf act trip itself.

I dont get why you cant turn off to properly test....if the RCD's tripping it's going off anyway isnt it?

 

[Knobhead]

I dont get why you cant turn off to properly test....if the RCD's tripping it's going off anyway isnt it?

I wondered how long it would take for someone to ask! :hurray:

 

[2BobSparky]

I dont get why you cant turn off to properly test....if the RCD's tripping it's going off anyway isnt it?

The tenants were reinstating the RCD and the tripping was happening interminttently.

The tenants are high demand and need power to their computers at all times. Something like an insulation resistance test would need to be conducted out of hours, which = overtime payment for labour, which is usually undertaken by subcontractors. It's a pretty frustrating place to work actually.

Since the MCB has been removed from the RCD protected side I don't believe it has tripped.

 

[BMelectrics]

Sounds like it could be an 'accumulative' earth leakage. All equipment has an earth leakage, some more than others, and since EVERYTHING is protected by the one rcd this could be the problem. May be an idea to include a main switch and take some of the circuits off of the RCD, ie: lighting.

In saying that, also perform IR tests on all circuits to ensure that there is not an earth fault actually present.

Just some food for thought

 

[joe j]

This thread going round in circles. 2bob may be out of his depth but life's a challenge and I'm sure he's not going to do anything dangerous. Sounds to me as though the present use isn't what it was designed for, we all see 4g extension leads around offices in converted houses where the design/spec didn't look in their crystal ball.
Sorry it's no help,

 

[SPARTYKUS]

2bobsparky, whereabouts are you in the country?

 

[joe j]

2bobsparky, whereabouts are you in the country?

Now that's what this forum is about. Well done Spartykus

 

[SPARTYKUS]

Now that's what this forum is about. Well done Spartykus

Joe j

Don't follow your train of thought please explain further?

 

[dwardy]

if its a office you might not need all the circuits on an RCD. so can eliminate a few straight away. how is the lighting wired, also are there any outside lights.

 

[SPARTYKUS]

Joe j

Don't follow your train of thought please explain further?

Still waiting joe j.


Just to clarify OP, I was asking where you are based in case someone reading this thread could pop in and have a look for you. Not quite sure how that fits with joe j :rolleyes2:

 

[Tonkatoy27]

How many pc workstations are fed from the circuits protected by this RCD? If it's a 30mA RCD you can only run abot 10 workstations before it trips and thats without leakage from any other equipment. Have they recently added any PC's? There's only one real way to fix it and thats dead with insulation resistance tests at the CU with all the neutrals disconnected from each other.
If you're trying to fix it trial and error by removing bit's and pieces from the RCD then you be weeks instead of hours.

I hope the office is shut at weekends or you'll need a free night and a big torch!
Good luck

 

[Darkwood]

This thread is a week or so old, all this ground has been covered and the OP has been made fully aware of design leakage by lighting computers etc, the limitations of removing the RCD from circuits and what needs doing if it is done for fault finding purposes, also he has been made aware of the testing sequences and the quickest way to identify problem. As recently mentioned its just going around in circles.

note what hasn't been mentioned here is if the leakage is designed high earth then the RCD could be changed to a Main switch and a SI unit 30mA put up front of board, this recognises and ignore certain design frequencies and allows for a greater no' of computers etc.

In reply to Tonk a design allowance of 3mA per work point is advisable thus making a circuit only six workstations at max, 10 workstations leaves you open to the occasional nuisance tripping.

 

[Darkwood]

With regards to my SI-RCD unit suggestion, its may be a quick fix but only if it is high earth design currents, but the installations is poor by design and its this that should be addressed, with all the hours spent searching the fault, a few hundred quid to fit rcbo's and front end with main switch would be cost effective and also will identify the problem circuit if genuine fault leak exists.

 

[Silly Sausage]

Seems to be an IT high earth leakage thread!
I've I&Ted loads of Banks and virtually all of them had RCD sockets on standard ccts.
Made sense to me.

 

[joe j]

Joe j

Don't follow your train of thought please explain further?

I'd assumed you were possibly offering to help. Poor 2bob was getting a bit of a hammering.

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Joe j

Don't follow your train of thought please explain further?

I'd assumed you were possibly offering to help. Poor 2bob was getting a bit of a hammering.