TRP on Megger 1553

[lj2909]

Hi all

I was asked to look into an RCD tripping on a dual rcd board.

When carrying out an RCD test I get TRP come up on the megger when I am plugged into the ring circuit.

This happens when the socket mcb is on and the boiler mcb is on.

If I disconnect the the supply to boiler spur and reenergise, plug the megger back into same socket I get my rcd readings (all readings within limits).

Am I right in thinking that it must be something to do with the boiler that’s causing the intermittent tripping of the rcd?

Thanks in advance

 

[Telectrix]

i suspect a N-E fault on the boiler circuit.these faults can really upset RCDs. sometimes they trip when any load is applied, not always on the RCD protected circuit/s.sometimes they inhibit the RCD from tripping even on the test button. a thorough investigation of the boiler circuit is my call.

 

[Murdoch]

Am I right in thinking that it must be something to do with the boiler that’s causing the intermittent tripping of the rcd?

In such cases of tripping RCD's the best thing to do first is unplug all appliances, switch off fused spurs etc (be warned not every fused spur or socket is double pole) and test the RCD. 

If the RCD test comes back "clear" and withing expected tolerances, I would then recommend IR tests on the circuits on said RCD, and these too are good, then look more closely at the appliances. 

With respect to boilers and valves, you have electricity and water in close proximity, so look around and under the motorised valves and for water dripping out of the boiler

Hope this helps

 

[SPECIAL LOCATION]

Here lies the point where a Dual RCD become more expensive compared to a RCBO equipped board.....

Testing & investigations on intermittent faults!!!

Assume everything is faulty until you have proved it otherwise..

Cause(s) of the tripping may NOT be a single item... 

Remember some appliances can have natural leakage.... 

combinations of natural leakage over multiple circuits fed from a single RCD will cause trips that are a sod to track down...

Especially if the RCD operates on the low end of the 15ma-30ma threshold..

Get back to basics... 

Test the RCD independently.. And ramp test it to see how sensitive it is...

Do continuity & IR tests on the individual circuits..

If the circuits appear sound do some IR tests at 230v with all the customer usual stuff connected to get a taster of any potential faulty appliances or any natural leakage issues..

Always with intermittent RCD/RCBO problems double check ALL appliances involving water..

Kettles / Central heating / Imm heaters / Washing laundry / Garden Ponds / Outdoor wiring etc..

Also check over appliances in involving heating elements.. 

then start looking for physical damage...  Rodents - DIY drills & Hammers etc. 

It may be a long process or you may sort it quickly...

but golden rule Don't assume anything is Ok unless you have proved it yourself!

opcorn

 

[Sharpend]

Effectively this is where the customer gets a free EICR without the report itself! 

If the kitchen circuit is in said rcd then that’s the first place to start for intermittent faults. Eliminate that circuit, then look for circuits with outside lights or external equipment attached. As said it’s a process of elimination. 

This boiler spur is that an individual circuit or off of a local circuit. The trouble with boiler circuits is that you then have to be competent to test the whole circuit through heating controls etc. It could be that a valve is sticking and the motor is overloading perhaps breaking down and tripping. I’d perhaps try to initiate the fault by turning on the heating waiting for valves to operate, etc then again separately with hot water to see if the rcd trips. I would also measure the leakage on the remaining rcd attached circuits then individually on boiler circuit to see if this accumulation tips the rcd over. Obviously this may not be conclusive unless you can replicate the usage of appliances when it trips.