Moved house about 5 months ago, every now and then (about once or twice a month) the RCCB trips for now apparent reason. it tripped last night when there was nothing heavy duty running. checked all the sockets tonight and they look ok. connected to the same circuit is a whirlpool bath and a shower. could the RCCB be playing up, its about eight years old? any other things to check?
Paul
Are you near the sub-station by any chance? Or on a hill or patch likely to get a bit of electrical discharge? Clunky fridge/freezer motor?
I had a friend with this problem. Lived in the middle of nowhere, but the thing kept going off all the time.
Try to work out some common factor between the trips. Has it always happened when someone's in the house? Has it always happened when it's raining/damp? And the more obvious ones -- has it always happened when some particular appliance is running?
What appliances does the RCD protect? Are there a lot of PC's covered by it for example?
It has happened three times when the washing machine was running but since then we have got a new machine and its happened once since then, again the washer was running. it tripped last night when we were asleep the only things that were running were a fridge freezer and a chest freezer. apart from the above there is a dishwasher, two pc base unit's the usual tv,stereo, digibox etc. on the RCD. The washing machine was the common factor until last night.
Paul
I see you used the uncommon term RBBC in your subject line & original post.
What exactly is it you've got? If it's an ancient installation, i'd suggest getting it replaced with a split load CU and a modern RCD just on the circuits that need it (or them plus one or two others if you're paranoid).
A fairly common cause of sporadic inconsistent tripping is an existing earth to neutral short circuit somewhere in the wiring (on any circuit). By itself this won't always trip the RCCB but makes it susceptible to sporadic tripping.
RCD - Least Likely o they can fail, but it seems they either fail "on" or refuse to ever turn "on" o my MEM 100A 30ma RCD was confirmed faulty, it was 8-10yrs old, lots of trips/usage
N-to-E wiring interaction - More likely o typical area is inside a socket or switch
---- even PVC insulation will cold-creep if two wires are pressured together
---- this is one reason why the Earth conductor in FTE is insulated o less likely is a damaged cable during installation or other finishing
---- nails or screws can be knock thro a cable, and damage insulation o temperature/humdity/vibration can all cause triggering
---- cables move slightly with temperature & vibration (floorboards)
---- during an RCD trip insulation may carbonise re-insulating for a time
Appliance fault - Equally likely o Appliances with mineral insulated heating elements can suffer leakage
---- the insulation breaks down (eg, washing machine, dryer, storage heater) o Appliances leak more than others
---- PC PSUs used to leak by design quite an amount to the earth rail
---- suppression etc could cause 3.5ma to be routinely leaked o Cables to the appliance can have breakages inside
---- this more usually make themselves known quite readily & spectacularly o However an appliance MAY leak a bit, BUT is not the actual cause
---- a 30ma RCD may take 20ma to trip, the appliance is leaking 6ma (too much)
---- however that just means a wiring fault elsewhere need be just 14ma to trip it
---- so whilst a washer being on aggravates the fault, it may not be the cause
The method of testing is: o Switch the main-switch OFF
---- inspect carefully every switch & socket in the house
---- specifically check all E bare wires are green-yellow sleeved (not bare)
---- specifically re-position carefully all wires so N & E do not touch in the backbox
-------- this is somewhat difficult, but at least avoid N & E wires crushed together o Unplug all non-essential appliances
---- turning them off just removes their L connection to the house wiring
---- unplugging them removes their L, N & E connection to the house wiring
---- identify if any change/improvement in tripping characteristic o Switch off all non-essential MCB circuits
---- removes L connection to the RCD
---- leaves N & E of those circuits STILL connected to the RCD (touch N to E still trips) o For each switched-off MCB, disconnect & insulate the N & E tails in the CU
---- insulate the tails in simple terminal strip cut-offs for safety
---- now you have removed the L, N & E of those circuits from the RCD o Repeat disconnect MCB (L) & MCB N-&-E for all remaining circuits
---- eventually you will discriminate which circuit is at fault
---- if all circuits are disconnected L, N & E then the RCD/suppy are at fault
The disconnecting of circuits from the MCB & N+E can find faults in the CU itself. Not uncommon to find an N-to-E pressure point in older wiring in the CU itself.
Obviously if you have outside lighting or outbuilding connected to the same CU, then you should entirely disconnect those (L+N+E) first - not uncommon to find a seal has gone on a light and an intermittent leakage path is being created there.
You can also: o Use a megger to measure insulation resistance on each cable
---- you MUST disconnect FIXED appliances which state they are damaged if megger'd
---- typically that is smoke alarms o The problem is you don't have a non-resettable RCD
---- you have an intermittent problem, so testing may not find the fault
---- however typically a megger will indicate suspicious circuits
Meggers can be hired from ~£25-45/week, they can be bought on Ebay for £85 & up. However, frankly I'd at least check all sockets & switches first.
Now, is it an old RCCB or is it a modern whole-house RCD? o If the CU installation is old it is worth replacing with a Split-Load CU
---- split-load is where some circuits are off the RCD
-------- eg, Lights Up/Down + Cooker + Water-Heater + Fridge
---- some circuits are on the RCD
-------- eg, ring-main sockets, cooker sockets etc o Once you have a split-load-CU you can fit RCBOs to individual circuits
---- you move a circuit off the RCD onto the non-RCD side
---- you then add an RCBO to that circuit so that *individual* circuit is protected
---- thus you can create a system allowing circuit-discrimination
You also want to verify Earth Bonding is up to spec - very often it is not.
Finding intermittent RCD leaks can be expensive in electricians time. So some simple checks can be helpful.
Remember RCDs do not necessarily prevent fires - an L-N short will happily heat away until either the MCB trips due to overcurrent or L-E or N-E becomes involved. Found a nice piece of butyl carbonised that had been disconnected at one end, but not the other.
Butyl breaks down due to 1) Ozone and 2) Heat conducted from the plug-pins/socket-grips, particularly so where over 30-50yrs the terminal screws back-off slightly as copper cold-flows. The same applies to PVC - it just takes a bit longer, but rapidly cooks the insulation to brittle. Moisture & temperature is also a factor, I've noticed BASEC PVC FTE cable on unheated areas goes to a hard quite unstrippable material after ~20yrs. Escalate attempts to discriminate which of appliance/circuit/CU/RCD as the problem continues - or itself escalates (ie, RCD doesn't reset).
Thanks for helpful info Dorothy, certainly gave me more idea's as to what to do next. The CU was installed in 1996, and has two bus bars, with 5 mcb's not on the RCCB these have the lights,boiler,alarm on. and 5 mcb's on the RCCB side these have the socket's,shower,spa-bath on. over the weekend I'll have another check off the wiring, one thing that i have just thought of is i have found old evidence of mice under the upstairs' floor's so they could have had a nibble on the cable's. I could borrow a megger from work if need be.
Paul.
So you have a split load in a recent installation - and mice.
o Use the megger if easy access to the wiring
---- mice-to-wiring are like wasps-to-fences or o Buy 1x RCBO & move circuits one at a time over to the non-RCD with RCBO
---- you retain protection & discriminate which trips
RCBOs aren't cheap - but it is worth having one anyway: o You have 2 water appliances - spa & shower o Electrician call-out is £35 - RCBO offsets diagnosis bill component "someday"
Mice are not NIC-EIC trained :-) Cats are due to stage a protest over Reg P as it may take away treats in rewiring.
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