Rcd tripping issue.

[Pauldicker]

Can someone shed some light on a problem I'm having.
I changed a CU today as there were only 6 circuits they are all now rcbo's there was no rcd protection prior to that.
On the ground floor circuit the rcd test was x1@ 147ms and x5@ 23ms.
However now when the customer turns the heating on its fine and if they turn the hot water on at the same time it's tripping the rcd.
It is run from a fused connection unit and upon looking all looks good in the fcu.
It's a valiant ecotecplus 618 and the controller is a lifestyle lp522
I'm not a heating engineer but I may be missing something obvious.

 

[Pauldicker]

Hi - just having nice cup of tea and reading this interesting post. Without seeing anything and tin hat on etc : trips when hot water asked for ... I'm liking the 2 port valve? As Lee says, there's likely 2 two port water valves near hw tank, one for supplying heating and one for hw. And a boiler with its own internal divertor valve and pump (sorry, I'm just imagining the set up there). Both the 2 port valves have moving parts, water and power connected and so may cause current leakage? I've not had a valve do this to me, but it would be any easy one to check if you're onsite. Anyway, I would ramp test the new RCBO to see exactly what current fires it and then start measuring the earth leakage current for the circuit - step by step. Hope that helps. Cheers, David.

Yes it has a hot water cylinder.
So im assuming that its leaking an earth somewhere. Which with the old Circuit breaker would not have been picked up as it did not trip the cb.

 

[Pauldicker]

Yes it has a hot water cylinder.
So im assuming that its leaking an earth somewhere. Which with the old Circuit breaker would not have been picked up as it did not trip the cb.

It only trips if you ask for heating and hot water at the same time.

 

[Wilko]

Understood - can you ramp test the RCBO ?

 

[Pauldicker]

Understood - can you ramp test the RCBO ?

Sorry to sound stupid but how do you ramp test?

 

[telectrix]

to perform a ramp test you need a MFT with that feature. on the megger ones, it's indicated with a triangle, like a steep slope road sign. you just connect to the RCD outgoing terminals with the circuit dissed, press "test" and it tells you the mA value that trips the RCD. it applies leakage currents in 3mA steps till the RCD trips.

 

[Pauldicker]

to perform a ramp test you need a MFT with that feature. on the megger ones, it's indicated with a triangle, like a steep slope road sign. you just connect to the RCD outgoing terminals with the circuit dissed, press "test" and it tells you the mA value that trips the RCD. it applies leakage currents in 3mA steps till the RCD trips.

Ah right i use a kewtech kt65mft

 

[Pauldicker]

Ah right i use a kewtech kt65mft

Im also wondering if the rcd tripped at x1 in 147 with all circuits open could this be a reason that the reading was higher.

 

[telectrix]

a neutral fault on a circuit could possibly account for erroneous trip times.

 

[Midwest]

OP. Think you need to start at the beginning again for this particular circuit What trip times are you getting on other RCBO's.

Start again with a fresh head, test circuit to FCU, dead tests, live tests, and then test house wiring to stat etc. Then having ruled them out, it could be something within the boiler, or zone valves etc.

PS you could test RCBO at CU with circuit disconnected to see how the RCBO functions independently. As telectrix, neutral earth faults can have an effect on trip times.

 

[Pauldicker]

a neutral fault on a circuit could possibly account for erroneous trip times.

I spoke to the customer this morning and they have said it is working ok however the controls are opposite. I.e hot water is working the heating and heating is working the water.

 

[Midwest]

Ah right i use a kewtech kt65mft

The KT65DL has a ramp test feature.

If you've only altered the supply, how can the controls be operating visa versa?

 

[Pauldicker]

The KT65DL has a ramp test feature.

If you've only altered the supply, how can the controls be operating visa versa?

I have no idea.

 

[The Ghost]

Think I would defo check that out. Maybe customer has done something ?

 

[Deleted member 72666]

Think I would defo check that out. Maybe customer has done something ?

....or the plumber!

 

[telectrix]

sounds like wet-pants has had his grubby mitts in something that does not carry water or shyte. recipe for disaster.