Tripping RCD on main disribution board - Help Requested

Hi all

I am wondering if somebody would help me out.

Over the last 3 weeks the main RCD fuse on a Crabtree Starbreaker domestic distribution board has been tripping out randomly - most often when we are not home and there is no serious load active. (All of the other circuits never trip).

I have done some research and I understand that sometimes these fuses can get over sensitive and I was hoping that I could buy another one and replace it to see if that helped.

Unfortunately I don't have the instructions for the Starbreaker - and so I was hoping somebody could explain what I need to do to replace the main RCD switch (30mA).

A photo of my Starbreaker can be found here:

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'd be grateful for any advice and guidance. I expect it's a simple excercise but I'd rather be sure what I was getting into in case I do something wrong and electrocute myself!!! I had assumed the fuses pulled out - but there isn't much to grip onto - so I am not at all sure that this is the case.

Thanks for any help, and regards to all.

Reply to
Steve Reeves
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On Fri, 21 May 2004 18:31:55 +0100, in uk.d-i-y Steve Reeves strung together this:

There is no 'RCD fuse, it's one or the other. In this case it's an RCD.

It's not a fuse, and the scenario you describe is highly unlikely. More likely to be a fault with an appliance somewhere.

Leave it alone.

They aren't fuses, they're not meant to pull out.

Not meaning to sound rude, but you seem to be clueless as far as electrics go. I'd get someone in who know's what they're doing if I were you. With the RCD covering all of the circuits the fault could be anywhere.

Reply to
Lurch

as the other poster mentioned, if you don't know how to get it out, then you don't know enough to be messing with it!

You'd need to unscrew the whole box iirc, and they then unscrew behind there and unclip, but don't go messing in there as it's dangerous!

Reply to
Alex Threlfall

On Fri, 21 May 2004 20:04:17 GMT, in uk.d-i-y Alex Threlfall strung together this:

Nearly, the new Starbreakers are plug in MCBs so no screwing involved, apart from the cover. Are you sure you should be offering advice! ;-)

Reply to
Lurch

In message , Lurch writes

:) Hi guys, thanks for the information. I do have "some" clue about household electrics but I've never touched a distribution board before. I don't plan to go messing anywhere that needs a professional!

I had done some research (via google etc.) and had gotten the impression that the RCDs can get hypersensitive and just wanted (if a safe and simple job) to see if I could change the trip switch to see if it cures it. If it didn't then clearly I have a fault somewhere. Clearly I shouldn't mess!

It's a strange one - only started a couple of weeks back and appears to happen once a day at random times - particularly when there is no one in the house. Maybe it's a fridge motor or something kicking in.

Clealry I want to see if I can find an obvious culprit before I spend money on getting an electrician in - so I guess it's a process of elimination job - unplug a load of stuff and see what happens. Any better ideas?

If I did get an electrician in, how easy it is for them to trace these kind of faults? Used to be a test engineer (marine umbilicals) and we had Time Delay Reflectometers to test for shielding shorts and stuff. None of it was AC though - and it was all over much longer cable distances than used in the home. Does the modern electrician have some magic gizmo like that?

Thanks for your replies - I would be grateful for any suggestions.

Reply to
Steve Reeves

On Fri, 21 May 2004 22:40:12 +0100, in uk.d-i-y Steve Reeves strung together this:

Could be, without a bit of testing I couldn't say for certain.

And switching everything unneccesary off, that's about as far as you can go before calling someone in.

Depends what it is, sounds like your fault is somewhat intermittent. The type any electrician dreads. It could be found in 1/2 an hour, it could take hours\days. Until everything is tested we shall never know!

Something like that, I'll leave whoever it is you get in to explain how he's using it and what it is he's looking for.

Reply to
Lurch

Sorry if this sounds cheeky but, If you've done some electrical work around the house, could it be something you've changed yourself in the passed two or three weeks ?

It would mean disconnecting each circuit supplied by this CU and testing each one with meters to determine if it is showing fault or not. You can't really use small DIY multi-meters for this type of thing. if the circuits themselves are testing OK, then the next things to test are each individual appliance that you leave connected when you're not home.

Something like a rodent attack on the insulation of cables somewhere can also be the problem, because you say it is mostly happening when the house isn't occupied, so rodents could be having a run around in the quiet house and chewing your cables. This could also be the random part in the timing I suppose.

A few thing to have a look at would be the flexes from the fridge and or freezer. Any other appliance that is left connected on the circuits should also be checked for damage to the flex or connection points.

It could also be spiking currents from the mains side of the supply that are causing your unit to trip out, so it doesn't have to be something on or in your house that's causing this to happen. The only way to find out if this is the cause, is to have the supply company fit a recording meter on the system for a week or so, to see if it picks up on surges in the supply lines.

There are a few other situations that could be causing this to happen, so it's best to start with your supply company and ask them to check their side of things, then you can start to eliminate from there.

Reply to
BigWallop

i did say iirc - if i recall correctly, i'm not familiar with starbreakers anyway, but i've seen the boxes/breakers in catalogues so i can see how they normally go together... ;)

Reply to
Alex Threlfall

On Fri, 21 May 2004 22:57:22 GMT, Alex Threlfall strung together this:

It was tongue in cheek, I usually keep quiet if it looks like I might get it wrong! Even that plan doesn't work most of the time!

Reply to
Lurch

The main switch on the Consumer Unit in the pic is both a switch and an RCD. An RCD switches off when it detects earth leakage. You almost certainly have earth leakage somewhere in your house. It could be anywhere, in a portable appliance or the fixed wiring.

Dont contact the power company, that is really not an appropriate course of action unless you want to pay them to come sort it out.

Your install is unsatisfactory, because you have everything on one RCD, and exactly this problem is almost bound to occur some time.

The relevant question is do you have time or money?

If money, you can get an electrician to PAT test all appliances in the house, and check the wiring for leakage. Problem will be located and probably fixed in a day - but it will cost.

The free option is to narrow down which appliance it is (it is >90% likely an appliance). I'd start by unplugging everything not essential. Now if it trips again your fault is among the things still plugged in. If it doesnt, the fault is among what you unplugged. Note that items must be unplugged, not just switched off. A process of elimination will probably find the problem. But its not guaranteed, as sometimes the trip can be due to accumulated fault currents from several items.

A split load CU would have been a much better choice, and the use of RCBOs better still.

Regards, NT

Reply to
N. Thornton

In article , Steve Reeves writes

But suggesting a time delay reflectometer.

Have you de-frosted it recently, does it have defrost heaters? Check the drip tray they often overflow onto the motor protector blocks. Any water pen to the house or flat? Heavy rains? Rodent infestation? Any joinery work done recently in the house? Any electrical work done recently in the house? New computer? PCs and other modern equipment use switched mode power supplies (SMPSs) which often have high leakage currents.

You'd be cheaper buying an RCD tester than having an Electcian check all your appliances. Unfortunately the RCD testers wouldn't be much use for offshore earth monitoring systems for umbilicals like those made by Bender.

After having confirmed the RCD is not tripping at too low a leakage current and insulation resistance testing of all circuits protected by the RCD they'd have to do the same as you - check suspect appliances which can take hours, days for which they will gladly bill you but IME not gladly do.

Who were you a test technician with - Simrad, Perry, Hydrovision?

LOL, very unlikely. Most electrical contracting companies do not even have enough basic test gear (insulation resistance meters, loop testers, rcd testers) to go round. An ETDR, OTDR tester as you use in underwater umbilicals would be of little use anyway as once one find the distance to the fault one would have to find how the wiring is routed. If you know about domestic wiring and you know about RF, which the TDRs use you will know a spur or switch drop will act as a stub.

The test gear you need is

eyes for visual inspection, please do check your appliances. RCD tester and with every load removed check the RCD does not trip at too low a current or in too short a time. Insulation resistance tester - with all loads removed check there is a high IR between live conductor and earths.

Reply to
Z

Hi there, cheers for the reply.

Is it not possible that the supply to the distribution board could cause this problem?

I see - the other switches then are simply circuit isolating switches then? Doesn't surprise me - the electrics were done by the original house builders/contracters - has always been this way since we moved in

5 years ago.

Well, I'll make time and I'll find the cash if absolutely necessary - I'll see what I can do first.

I hear what you're saying - will do this.

Sorry, what's a RCBO?

cheers

Reply to
Steve Reeves

Hi Z

:) Well I was using it as an example of a magic gizmo - but if you insist - OK OK - I am CLUELESS!! :))

Good point, will check.

Nope.

Nope.

I'll double check the garage where the supply comes in but I don't think so.

Nope.

Nope. And, you'll all be glad to hear - never any done my me!!

Nothing new certainly.

Ahh, godammit :) RCD tester is a good idea as other posters have suggested.

Understood.

A company called Jacques Cable Systems (Littleport, Norfolk) - about 15 years ago. Not sure they still exist now - may have gone or been taken over. We used to do marine cables, ROV umbilicals etc. for the likes of the MOD and Snamprogetti (sp?) - An Italian outfit if I recall. We did one HUGE umbilical - very long and wide for some offshore rig - treble armoured - huge numbers of comms, power cables and hot/cold water hoses

- that one was a pain to test! Took weeks!

Thanks for your help.

Reply to
Steve Reeves

Hi,

One way to help diagnose the problem would be to put a high value variable resistor across live and earth, adjust it until the breaker

*almost* trips, then switch in the house wiring and plug in appliances etc to see if they make a difference. This will tell how sensitive your RCD is and give some idea how much earth leakage there is elsewhere.

cheers, Pete.

Reply to
Pete C

Well we will know where to come if someone on here starts building a ROV in the back garden and gets in a fix .

Dave

Reply to
dave

Actually asking your supply to monitor the supply for a week is a good idea and will determine if there are outside sources of interference, (street lights can trip an RCD etc) and it's free.

Reply to
Jb

Crucially, they're not *isolating* switches: in a domestic consumer unit the individual-circuit MCBs are *single*-pole, so they interrrupt the live ("phase" if we're being all modern-n-pedantic) when operated manually or on an overload, but they leave the neutral path still connected. Since your RCD is a current-balance device, roughly "I counted the milliamps out and I counted them all back in, and they all (well, all bar maybe 20 of 'em) came back)", if you give enough of those pesky milliamps a different route back to earth through a low resistance between N and E - yes, even on a circuit you think you've "isolated", since its N conductor is strapped to the N conductors of all the still-active circuits through the N busbar in the consumer unit - the RCD will trip. Hence, when you're fault-finding, you need to *isolate* appliances and/or whole circuits, not just operate their on/off switches or the (typically single-pole) switches at sockets.

As Nick T says, and as your background tells you, you're in for a b****r of a time tracking down an intermittent/only-just-there threshold fault such as this one. If you have the house to yourself (or for better safe working practice, one other person with you who won't want to turn on kettles, central heating, TVs and the like ;-) you could try "binary chop" to speed up your fault-finding:

suspect-circuits = all-of-them; REPEAT cut all power; isolate half the suspect-circuits; reapply power IF RCD pops suspect-circuits = the-ones-still-connected ELSE suspect-circuits = the-ones-you-just-disconnected UNTIL number-of-suspected-circuits = 1

(As noted above, to fully do the "isolate" thing means not only operating the MCB, but disconnecting the circuit's N conductor(s); so you need to be sure you're competent to fiddle in the guts of the CU, and realise that the incoming L terminal is STILL LIVE when you've operated the main switch; and "reapply power" in the above is not best implemented by using the main switch alone if there are significant loads (immersion, other kitchen kit, spindle moulder in the garage without no-volt switch ;-) still connected.)

Once you've narrowed it down to a single circuit, you can try repeating the approach to find the appliance or section of wiring which is causing the fault.

But Sod and Murphy are ready to give you grief. We already know the condition is marginal: it's positively likely that there's a a little bit of L-to-E leakage going on in multiple circuits (interference suppressors have capacitors running from L to E and N to E, and yer woshdosh, washmosh, 'puter, prolly CH boiler, and other things will all have one, pushing up the "baseline" leakage to the point where the main culprit is enough to unbalance the RCD, but isolating these other leakers will reduce the the "baseline" leakage so that the main culprit no longer makes the RCD pop reliably. If you're competent to do V = IR and P = IV calcs, you could knock up a "leak-inducer" to add, say, 10mA deliberate leakage from L to E as part of faultfinding using a suitably-rated (for both voltage and power - go overboard on the power rating as the nominal rating on wirewounds allows for a surface temp of 100 degs C or more!); if not I certainly won't put you in harm's way by doing those calcs ;-)

Likely sources of increasing leakage are: immersion heater elements; leccy cooker elements (rings, oven, grill); kettles, irons, dishwashers, washing machines. Less likely but quite possible is cable damage in some out-of-the-way place - one "sodit" factor can be wiring whose insulation has been damaged (rodents, original install cockups, whatever) which are very-close-but-not-usually-touching but which move enough when warm (either ambient heat or through passing a load) to cause a fault; once they've done it a couple of times they accumalate a little layer of carbon making further faults less spectacular and so (in the case of an L-to-E) more likely to make the RCD pop than the relevant circuit's MCB.

RCBO = all-in-one device incorporating the functions both of an RCD (the "current balance" thing) and an MCB (overcurrent and short-circuit protection). They're still pricey (hard to find retail/undiscounted-trade-counter at under 30 quid, compared to MCBs at 5-6 quid a go), but are coming down (were more like 40-45 quid only 3-4 years ago). Since each one protects just one final circuit, they make nuisance tripping less likely, as there's only one circuit's worth of "baseline" leakage for each one, and you know right away which final circuit is faulty. (Some even have a different indication for an imbalance-trip vs. an overcurrent trip; and most take up twice as much room side-to-side as an MCB). With a whole-house RCD as you seem to have, nuisance tripping is maximally likely and maximally inconvenient: with a split-load CU only selected circuits with a higher likelihood of safety-problematic leakage are on the RCD, while "boring" circuits (e.g. lighting) are fed from the non-RCD side - keeping the lights on contributes materially to overall, practical safety!

I wouldn't spend forever trying to track this one down: if you get stuck, find a smallish local electrical contractor, be helpful to your sparks, tell them which circuits seem still to be suspect and so on, bring tea and non-manky biscuits, and the combination of test-gear-in-hand, and experience in using it, may well result in 50-80 quid more effectively spent than similar money on a used (and how well calibrated and cared-for?) RCD tester wot you get off some guy on eBay and won't use ever again. Guy I got in in the previous house did this for me as part of an inspection after I'd done multiple bits of surgery on the house electrickery over a few years, and quite quickly tracked the nuisance trips on the then-fashionable whole-house RCD to the combination of 'puters (which I knew), ageing grill *and* one hob element on the cooker (needed his leakage tester for that), and a just-a-bit-too-sensitive RCD (again requiring use of his RCD tester; a 30mA nominal RCD is supposed (a) to let a 15mA imbalance pass for an unbounded time, (b) to trip within small-number-of-millisecs for a 30mA imbalance - ours was tripping at 13mA.) And a sparks will be a bit less phased (merely eyebrow-rolling rather than dangerous-to-self incredulous "they couldn't have done THAT, could they!?) if the root cause comes down to miswiring in the original install - sadly not unknown even (or expecially!) in new builds...

HTH, and let us know how you get on - Stefek

Reply to
stefek.zaba

Hi Stefek,

Many thanks for your very detailed and helpful post. I will indeed let you know how I get on. Currently eliminating items around the house in an orderly fashion at the moment to see if I can find a pattern. So far no joy - but early days. Will review your comments and improve tactics.

To complicate things (like I need that!!) today, again whilst we were out, we had a power cut (RCD did not trip!) But was back on by the time I got home.

You know what would be really handy, is an electric analogue clock without battery backup) that would stop working when the power dies and start again when it come back on without resetting. This would at least give me some indication of:

a) When the power went (maybe be a pattern) b) How long me sausages have spent defrosting in the freezer (to prevent food poisoining!!).

You'd think there'd be something around an average house that could do that - but nope everything is electronic and resets after a power outage!! Ah well....

Thanks again for your (and everybody elses help).

Reply to
Steve Reeves

Hi,

One of those thermometers with a remote sensor RF sensor might work OK, they usually store min temperatures.

cheers, Pete.

Reply to
Pete C

In article , Steve Reeves writes

Heh heh, I was working in a place today that hires out subsea equipment, ROV tooling, TMSs and winches. I'm doing the portable appliance testing and I'm just happy I'm not testing the umbilicals !

They are hiring BTW. Aberdeen based.

Reply to
Z

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