Help please rcd does not trip.

[ashdail]

Hi folks I have just installed an new mk consumer unit, but I'm having problem with the 63A rcd's. The test button works fine and it does not trip @ x1/2 it trips at 99.0 @ x1 and fails to trip @ x5 (>40ms) Its not the tester as I've checked it on another installation I know to be good. Any ideas? Help much appreciated.

 

[Plonker 3]

Have you carried a ramp test on the RCD?

Sounds like a faulty device so i would just take it back and get it replaced.

 

[Knobhead]

Swap the RCD.

 

[Acer]

I installed two rcbo's on Friday...had to wait until end of day to turn off power...a bit of a fiddle to fit..tested both for trip times the 20amp one was 10ms/20ms the 32amp one was 83ms/125ms !!!! so got to go to wholesaler to get replacement...wait around to turn off supply... then undo Fridays work and replace faulty unit...who pays for that??

 

[ashdail]

Yeah I will head for a replacement in the morning. Just don't really expect them to be faulty brand new! I have never come across this before as I usually use wylex gear. Apart that is from the recall on the dodgey melting mcb's!! But that is another thread!!

 

[Marvo]

... then undo Fridays work and replace faulty unit...who pays for that??

If you supplied the RCD's then the replacement parts would be at the wholesalers expense and the labour and running around would be at your expense. Your price mark-up to the customer would generally cover labour for replacing failures.

 

[cogsey133]

It sounds very much like an issue with the rcd's so they will need to be changed

 

[ashdail]

It sounds very much like an issue with the rcd's so they will need to be changed

Just read some customer reviews on the web and it seems that these units do sometimes arrive faulty. cheers for the feedback folks.

 

[MarkieSparkie]

I installed two rcbo's on Friday...had to wait until end of day to turn off power...a bit of a fiddle to fit..tested both for trip times the 20amp one was 10ms/20ms the 32amp one was 83ms/125ms !!!! so got to go to wholesaler to get replacement...wait around to turn off supply... then undo Fridays work and replace faulty unit...who pays for that??

Hi mate, A point for future reference, when testing RCDs or RCBOs it's a good idea to trip the device half a dozen times on the test button as part of your pretest commissioning to free-up the mechanism before testing trip times. This especially true with new devices which benefit from a little 'running-in'. Those of us old enough to remember the notoriously 'sticky' old Wylex BS4293 RCDs are well practiced at this and do it as a matter of course.

 

[Deleted member 9648]

Hi folks I have just installed an new mk consumer unit, but I'm having problem with the 63A rcd's. The test button works fine and it does not trip @ x1/2 it trips at 99.0 @ x1 and fails to trip @ x5 (>40ms) Its not the tester as I've checked it on another installation I know to be good. Any ideas? Help much appreciated.

Are there any connected loads?...they will slow up the RCD and it's very common for one to pass the 1x but fail the 5x......try testing it at the output terminals with all MCB's off. Despite the slagging off of RCD's on here in my experience it is very rare for new RCD's to fail the time tests,if they do it's connected loads still in circuit 99% of the time.

 

[Acer]

There were/are loads connected when I did trip test on both these rcbo's with the 32amp having 2x fridges and 1x large commercial freezer..would it be prudent to switch these off and test again before driving 40 miles to wholesaler..most of the work here has to be done before or after opening times so maybe I should test again tonight....

 

[plugsandsparks]

For sure, if the compressors were running they provide an inductive load. Inductive loads will slug the performance. I always test new stuff with no load on, its also more polite to not keep the loads going on and off 4 times or more to complete the test

 

[Darkwood]

Just to mention that in agreement with the general jist that its faulty rcd but you said its not the tester because you tried it on a rcd you knew to be good, just be careful here with your method of thinking, the only way to proof test meters is callobration, and relying on the results of other tests shouldn't be how you diagnose the issue, if the meter had a fault then the other install may be giving false positive results.
In this situe try borrow another rcd from a collegue or other electrician you may know if not then an earlier than expected calibration would be the only way to say meter is fine. In your situe though its probably just as quick to replace suspect rcd and see what the meter does then.

 

[Deleted member 9648]

There were/are loads connected when I did trip test on both these rcbo's with the 32amp having 2x fridges and 1x large commercial freezer..would it be prudent to switch these off and test again before driving 40 miles to wholesaler..most of the work here has to be done before or after opening times so maybe I should test again tonight....

Capacitors (as found on fridges and freezers) hold a charge...when the RCD disconnects the supply a capacitor in circuit will fool the tester into not seeing an instantanous disconnection,which will be reflected in your result......Test with all loads out and 99% likely your RCD's will pass.

 

[Acer]

Went back yesterday..disconnected all loads ie switched everything off..tested again and got identical results....the 20 amp rcbo was also under load when tested and was well within limits..went back to wholesalers and they've sold out so will have to leave it situ for a couple of days..the tester is calibrated up to date..incidentally on same job tested another 30ma rcd and got times of 170ms at 0 degrees and 180 degrees...MK rcd...

 

[Deleted member 9648]

I'm surprised......I appear to be the only person on this forum who very rarly encounters faulty RCD's.

 

[Acer]

I have also been surprised by this especially as both incidents happened at the same location...the faulty rcbo is the first I have encountered but the MK rcd is a few years old and in a location which would leave it prone to dampness, dust etc...ideally the board should be an IP56 type enclosure but this would not be easy to achieve...however I do take on board the notion that the tester, once, calibrated may then be used without any further checks on its accuracy, apart from a check box and this would'nt help with the rcd function....?.