RCBO not restting

[sparkside1]

Hi all

Have a problem with a Wylex 32A Type C RCBO that has tripped to a utility room and heating plant room to a west London mid terraced house.
It will not reset even with all loads removed. I tried swapping the line and neutral conductors to an adjacent same rated RCBO and the same happened. I tested the ring between L-N at the utility sockets and incoming spur to the plant room and was 0.42 ohms. I only had time for a quick look on xmas eve and will return on Monday to carry out further tests. But not having had many issues with RCBO's I need some advice on how to test these devices properly and what the possible causes could be. There is no history on this fault as the property is vacant and the problem miraculously appeared!

Cheers

 

[tazz]

Please note debate by all means, but any abuse or bad language directed at any member will not be tolerated.

 

[shanky887614]

do your normal continuity tests etc.

if it keeps tripping there will probably be a short or bad appliance connected somewhere

 

[trev]

or bad appliance connected somewhere

The first thing is to ensure no appliances are connected. They might not like 500 volts up em when the time comes.

 

[Geordie Spark]

The first thing is to ensure no appliances are connected. They might not like 500 volts up em when the time comes.

They don't like it up 'em Captain Mainwaring Sir .. they don't like it up 'em!!

 

[TJ Anderson]

The first thing is to ensure no appliances are connected. They might not like 500 volts up em when the time comes.

250V range. There would be very few occasions when I would be using 500v on fault finding!

 

[shanky887614]

id use my fluke dmm on continuity. it goes a lot lower than the continuity on a megger.

no need for a megger when fault finding

 

[trev]

250V range. There would be very few occasions when I would be using 500v on fault finding!

As a rule I always do the 250 test first but I often use 500 when fault finding. The thing is though, some may not have the sense to do a soft test first

 

[davesparks]

250V range. There would be very few occasions when I would be using 500v on fault finding!

Always use 500V for circuits operating at 240V AC, there's no point testing insulation resistance at a voltage less than the peak voltage of the supply.

 

[Darkwood]

Very good point brought by Davesparks.... if we have 230v RMS then peak voltage is around 320v so exactly what would an insulation test that isn't in excess of this proof because it may not show any issues or failed readings where a 500v would unless its very poor value.

 

[TJ Anderson]

Always use 500V for circuits operating at 240V AC, there's no point testing insulation resistance at a voltage less than the peak voltage of the supply.

On a new install / additions then definitely 500V. Not faulting on an existing installation unless you are absolutely 100% that all loads are disconnected and after 250V has shown clear. Like I said very rare I would use 500v outside new installation. To be honest, in this scenario 500V will provide no benefit over 250V and only the risk of damaging equipment which will give the OP another problem to deal with.

 

[TJ Anderson]

Very good point brought by Davesparks.... if we have 230v RMS then peak voltage is around 320v so exactly what would an insulation test that isn't in excess of this proof because it may not show any issues or failed readings where a 500v would unless its very poor value.

You have answered your own question there, the fault is present at 230v and is operating the RCBO, therefore higher than that is not required to trace the fault. I appreciate what 500VDC testing provides, but in the case of locating a fault that is tripping a 30ma RCD, 250VDC is adequate and with no risk.

 

[TJ Anderson]

id use my fluke dmm on continuity. it goes a lot lower than the continuity on a megger.

no need for a megger when fault finding

Good luck when you get an insulation fault!

 

[telectrix]

1000V kill or cure. shove it up 'em.

 

[PEG]

...Right! i have finally got it...the 0.42 is the duration our poor OP lasted,from original post,1.00 being a full day of 24 hours,corrected for temperature...:icon12:

 

[trev]

...Right! i have finally got it...the 0.42 is the duration our poor OP lasted,from original post,1.00 being a full day of 24 hours,corrected for temperature...:icon12:

Sigh.
Peg, he's already said what the measurement was all about mate. It was a completely pointless exercise as far as fault finding is concerned but never mind.
Actually, thinking about it maybe you've got more of a point.