RCD Plug Trip

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Con81a

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I have an issue with my consumer unit RCD randomly tripping, it happens anything between months, weeks and hrs.

I have bought a few RCD plugs and started installing them in the hope they might trip first, is that the case or would the main RCD trip as well?

It tripped the other day and one of my RCD's was also tripped, would this indicate the source of the issue or could they just randomly trip if they are on the same circuit?

Is it worth while swapping out the consumer RCD module, could it be over sensitive, currently it has an 80amp 30mA module (Crabtree RCCB 380/S030)

Any advice welcome

Richard

 
Both questions answer is no...

Adding RCD plugs to an already RCD protected circuit will prove nothing..

Randomly swapping RCD modules without first proving a faulty item is normally an expensive waste of time...

99% of the time when RCD's start tripping they are normally doing exactly what they are designed to do.

i.e. disconnecting the power in less than half a second because they have detected a fault of 30mA or greater leaking to earth..

Although it could be oversensitive, it is actually more common for faulty RCD's to stop tripping rather than start random tripping..

Any competent electrician can test an RCD with a suitable meter and verify if it is operating correctly or not in probably less than 10mins..

IF the RCD is proved to be working correctly then the nest step is to test the circuit wiring..



However is does sound as though you probably have a bad design of CU with a single RCD protecting multiple circuits...

which can be a bit of a pain in the bum to diagnose the exact cause..

Guinness

 
RCD plugs are a waste of money if used on an already rcd protected circuit. They are meant for use where fixed protection is absent or unknown.

It's just luck which will trip first, but often the fixed rcd will already have other loads connected which increases the chances of the fixed one going first. 

If you experienced simultaneous tripping of a plug in one and its fixed counterpart there is some chance that indicates a dodgy appliance, but nothing is guaranteed.

 
TBH unless you have proper test kit you are only guessing.

I would recommend you keep details of what trips and when to see if you could narrow down any likely causes ...... 

 
Some RCD plugs can only be energised while the power is on..

So if the power is disconnected at the CU the RCD plug would also turn off anyway!

i.e. If the power supplying the RCD has been disconnected, you need to press the reset button to re-energise the socket..

You would need to verify exactly what type you have so you don't go leading yourself to a wrong conclusion..

Guinness

 
I have an issue with my consumer unit RCD randomly tripping, it happens anything between months, weeks and hrs.
There can be any number of reasons why an RCD trips with the trip frequency you state is it an odd random trip or has it become progressively more frequent indicating a developing fault

Other observations you could make, does it trip more if it rains or if you use a particular appliance, it could be that the cumulative earth leakage of a number of appliances is the cause

Generally faults like this need the right test equipment to locate the fault which means getting an electrician in

 
it could be that the cumulative earth leakage of a number of appliances is the cause




This is a very important point that UNG mentioned..

and you MUST keep it in consideration when trying to establish why an RCD is "randomly" tripping..

Your RCD is most probably a 30ma device that MUST operate when it detects a leakage current of 30ma or greater..

But must NOT operate if it detects a leakage current of 15ma or less.. 

And RCD's tripping can be due to a combination of more than one item failing..  NOT just a single cause! 

i.e.  Some appliances have what is known as "natural leakage" where a small amount of electrical current will flow to earth during normal usage..

So..

If you have four appliances that all have 9 milliamps of natural leakage...

individually they must NOT trip an RCD...

But if all four are all on simultaneously connected via the same RCD the RCD must trip, as 4x 9ma = 36ma..

And any three appliances all on simultaneously "will probably" trip a 30ma RCD, as 3x 9ma = 27ma..  (but possibly may not trip the RCD)

Or any two appliances on simultaneously "could possibly" trip a 30ma RCD, as 2x 9ma = 18ma, which is greater than the 15ma minimum operating threshold!!

Basically..  It may not always be just a single fault cause you are looking for!

Any half-decent electrician will have meters that can measure the actual tripping currents of RCD's

and other meters than can measure leakage currents...

which can give some very useful hints as to the best direction to investigate and solve the actual cause..

It's not  impossible for DIY investigations to work out an RCD tripping problem...

But is can be a bit of a "Pi55ing-in-the-wind" exercise, which is not always successful!!!

Guinness    

 
raandom tripping is usually a fridge or freezer, they are the only appliances that switch on and off all day and night at random times. However, they might not be the root cause, just the final bit of earth leakage that finally trips the RCD.

Get a sparky to test the circuit to prove the cct is good or not, then you will have an idea if it is an appliance. It might also be worth changing a single RCD covering multiple ccts to RCBOs, ie a combined RCD / MCB as this gives you 25-30mA per cct and is far less prone to appliance issues. 

 
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