Fault finding help

[Cirrus]

Ok chaps, a customer calls you saying he has a 'tripping problem' on his CU. Apparently it is totally random and no rhyme nor reason to it. No work done recently etc etc but the RCCB trips every now and then and the guy is worried as he is going on hols soon and naturally doesn't want fish to die etc should the power go off.
Now, where would YOU start? I reckon best way is to change RCCB for a new one and then go from there but what are your thoughts chaps?

 

[London Luke]

tell him to take the fish on holiday with him.

 

[greekislandlover]

Try to isolate the circuit that's causing the tripping by leaving each breaker in turn off would help narrow it down. Or try unplugging appliances one by one. But if the tripping is very spurious this is a long job to prove what the problem is.

I'd start with unplugging everything and doing the continuity / IR and RCD tests on the wwiring system alone to see if that gives any clues. Also, consider how it's wired. Our RCD used to spuriously trip with no appliance conclusively to blame, but we suspected something or other in the kitchen. Wen the buliders did our kitchen some 15 years back they wired it themselves. They took two radials off of the ring, and we were plugging all of the big power users into one of these radials. A new ring in the kitchen solved that one.

If the tests shed no light, I'd be inclined to suspect kitchen appliances, or items with a motor as the most likely culprits. Not easy I know!

But if his concern is the fish, then does he have any non - RCD supplies that have sockets on them?

 

[stevie h]

Check for outside- pond pumps,sockets,lights wired off the ring ect ... water often causes sporadic nuisance tripping

 

[Reg Man]

Have that problem with the old stone walled houses. Walls get very damp and cause nuisance tripping randomly.
I would do Insulation resistance test. You could try Earth leakage clamp on each circuit if you have one.

Have also had the problem several times when washing machines run and ten mins into cycle or so when the heaters come on...the trip goes. Common fault with heating elements in a washer.

 

[Cirrus]

Have that problem with the old stone walled houses. Walls get very damp and cause nuisance tripping randomly.

Yes, this is an old cottage too with cotswold stone walls. Trouble is, I can't leave circuits off for too long because it doesn't happen daily but just now and then.

 

[tony.towa]

It's a difficult one as from what you say there is no common denominator with regard to why or when it trips. If it is a true intermittant fault even using a clamp may not show where they problem lies initially.

If the customer would accept the cost etc you could always replace the cu with one containing rcbos and atleast you could then identify the faulty circuit when it tripped.

This is going to be a bit of a brain tease

 

[Cirrus]

Expensive option changing the board for one full of RCBO's but I suppose 2 days scratching my head trying to find the fault is just as expensive. Don't have an earth leakage clamp either

 

[mdavismccoy]

Hi, I have the same problem now and again intermittent tripping. Now I only found out it was the RCD it's self found it by a ramp test with my new meter, tripped at 15mA, it mainly trips when the kids plug in the power supply for the laptop, this can cause a residual current enough to trip sometimes. I will change the RCD soon, it's just extra sensitive for now.

 

[London Luke]

trouble is as suggested. tracing the fault could cost a lot and not be seen as "good value"

get use to RCBO's !

 

[spark-doctor]

I get this problem a lot where i am as a lot of the houses are made of Portland stone that gets very damp. I start with a ramp test on the RCD and if OK then IR test the whole house 95% of the time i find the fault by these two tests.

Failing that i would turn every other circuit other than his fish tank of. Someone must be coming in to feed the fish so they can check the RCD has not tripped.

 

[Spudmiester]

Have had this exact problem.RCD on whole house. Changed RCD to no avail, Meggerd everything, set about PAT testing appliances and found two with a small amount of earth leakage that on their own would not trip the RCD, but together they did. RCBO's would have narrowed it down a lot quicker.

 

[luke teague]

Try the dish washer or washing machinee sometime they trip curcuit in mid cycle they are a pain to find sometimes tell him to leave them off an see if it still does it!!!

 

[lee mcgregor]

circus have you made sure that the neutrals of the rccb's and the neutrals of normal breakers are in seperate blocks in side the consumer
???

 

[jeremy]

even if the problem doesn't occur all the time, an ir test would indicate which circuit was more likely at fault. if this is a socket bearing circuit a temporary extension lead supplying the fish may prove useful. ( what does he have ? Electric eels?)