RCD Problem

[burntwire]

Hi All,

Yesterday I tested an RCD in a house with a metrel multi tester, I tested a socket on both sides of the board ( Dual RCD ) and neither would trip, I then tested them using the ramp setting and both tripped out @ 24, they then both worked fine on the normal RCD test, any ideas ?

Also the fuseboard does not contain a brand name only a red circle with a black mark in it any one know where these are from ?

TIA

 

[ricicle]

Possibly a bit of 'stiction'. ?

 

[ban-all-sheds]

http://www.esc.org.uk/fileadmin/user_upload/documents/industry/rcd_research/Final_Report.pdf

• 
  

 

[Spark123]

At a guess you may have these but are a black circle and red triangle, http://www.controlgeardirect.co.uk/

 

[didster]

Possible your tester was set 10ma and not 30ma ? .. i've done this as the figure is in the corner of the screen and defaults to 10 when its been off for a while .. the ramp test would obviously work fine ..

 

[17thman]

interesting link Bas.. quote from it

"One of the principal conclusions of the Italian Research published in 1996 was that operating
the test button at regular intervals had a positive effect on the reliability of the RCDs. The
RCDs had an average failure rate of 7.1% but this dropped to 2.8% if the RCDs were tested
at least once per month."

this could mean 2 things

1) the test button regime can help clear any dust, debris or inhibitants to operation, so improving performance. And Or

2) regular use of the test button would mean that some or all of the faulty ones are replaced, naturally reducing the fail rate percentage.

 

[Spark123]

Wouldn't the rate go up if it was 2?
I'll go with no 1, that exercising a mechanical device helps keep it free.

 

[17thman]

Hi.

No the failure rate would go down. if 607 rcds were tested on site and some of those tested had had some sort of test button regime it is likely that some or all of those previous test button failures would have been replaced, so reducing the fail rate percentage of those tested.

If i tested 607 old balloons for pressure, but some of the balloons had been tested for pressure regularly and repressured. then the fail rate would be lower.

whether 1) or 2). test button regimes are positive. I was trying to make a point about the research. I believe in 1) but 2 is a factor

 

[Spark123]

Do the test button failures not count as a failure (even if they are replaced) thus adding to the number of unit failures (divided by total number of units to give the rate)?
Or are you saying as a percentage in a single snapshot in time?

I'm completely bamboozled by the balloon analogy

 

[17thman]

607 rcds tested on site.. not in the lab.

If i tested 607 rcd on site and had failure rate of 7%. but of those regularly push button tested i had a failure rate of 2.8% then i can assume that either they are mechanically better off for been push button tested or that some of the faulty ones have been replaced, ensuring a lower failure rate

 

[ban-all-sheds]

I'm completely bamboozled by the balloon analogy

 

[Spark123]

Oops, i just put a pin through my laptop screen

17th, I get what you are saying but fail to see how you could just discount one as a failure even if it has been replaced, otherwise you are effectively saying that you have had a 2.8% failure of those tested monthly in one month which equates to 33.6% per annum.

 

[burntwire]

Thanks for your replies, that was an interesting link from BAS,

The strange thing is that both RCD's did fail on test, I turned all circuits off and did test straight onto rcd, Both test buttons worked fine and it wasnt until I did the ramp test that they then both tested OK.

Normally I find that a second RCD test has better results but very rarely do I see a failure even when I have to wipe the cobwebs off the test switch.

My tester was all on right settings.

Good guess sparks123 it is those ones, are they a good board ?

 

[Spark123]

I don't really rate cheap boards highly! Not had the misfortune to work with them but at that price I'd place them in the same band as Chint and the likes.