RCD tripping at half the rating ?

[Kev2632]

Hello, i was doing an RCD test yesterday on half its rating, and the rcd kept tripping everytime, does this mean the RCD is faulty?

 

[chrish_1977]

Did you carry out a ramp test to see what it is actually tripping at

 

[pete555]

it is faulty and requires replacing

 

[bigbaddave]

Did you have anything pluged in at the time or was it off load?

 

[chrish_1977]

it is faulty and requires replacing

Couldn't be anything else then?

 

[Kev2632]

yea i did the ramp test and it tripped out at 17ma :s, there was some things plugged in at the time of the test happening yea?

 

[Octopus]

Best test it again with all MCB's switched off to get a better idea. It could well need replacing - they are not as reliable as people think

 

[Kev2632]

how can you do a RCD test when all the MCB's are switched off?

 

[jamesBoater]

An RCD should trip no less than 50% of its rating?

 

[i=p/u]

Test at terminals of rcd

 

[Kev2632]

Test at terminals of rcd

oh ok yea, i didnt know if that was possible? i take it that is still ok to do yea?

 

[bigbaddave]

yea i did the ramp test and it tripped out at 17ma :s, there was some things plugged in at the time of the test happening yea?

It could be giving a bad reading then, For Example the things you still have connected could be producing earth leakage..

Therefore if its leaking 5ma then the 17 its tripping at will man 23ma

As above retest at RCD with no MCB'S ON

 

[JD6400]

oh ok yea, i didnt know if that was possible? i take it that is still ok to do yea?

Have they started teaching a different way to test a rcd now days then ?

 

[Sintra]

oh ok yea, i didnt know if that was possible? i take it that is still ok to do yea?

That is the correct test procedure for an RCD. Test at device with no loads connected.

 

[JD6400]

Thanks Sintra , was starting to wonder what latest fad they had changed things to this time !

 

[telectrix]

it's these 5 week courses. week 6 is when they were going to mention placing probes on live terminals.

 

[guest119]

Have they started teaching a different way to test a rcd now days then ?

electrical trainee shortform course :dunce2:.

Boydy

 

[pete555]

Couldn't be anything else then?

of course but why mess change it and cure it

 

[shagbite]

of course but why mess change it and cure it

you're confusing me.

are you saying that changing the rcd will cure the fault, even if the rcd isn't the cause of the fault?

 

[bigbaddave]

Sounds like is

 

[Engineer54]

oh ok yea, i didnt know if that was possible? i take it that is still ok to do yea?

Oh Dear, ....It's statements like this that make me wonder what the hell's going on back in the UK these day's!!!

 

[DJ Ovengloves]

Post deleted I can't use multi quote properly!

 

[Octopus]

Oh Dear, ....It's statements like this that make me wonder what the hell's going on back in the UK these day's!!!

E54 - you read this forum everyday and you are surprised??

 

[i=p/u]

Easy when you know how,

 

[AdieB]

If the RCD is MEM then it will not test correctly from the rcd you have to test it downline.
AdieB

 

[Sintra]

If the RCD is MEM then it will not test correctly from the rcd you have to test it downline.
AdieB

Never had a problem with them myself tbh can you explain a bit more.

 

[Darkwood]

Never had a problem with them myself tbh can you explain a bit more.

Most Rcd 's are fine to test at terminals but some are designed in that the coil is connected after the live terminal thus using terminals for testing won't operate the device

Save me explaining it in full read this previous thread ...
.http://www.electriciansforums.net/i...stallations/28288-rcd-testing-no-trip-db.html

 

[AdieB]

As Darkwood says beet me to it . But I have also had no problem with the very latest MEM RCD's but have had a problem with the older units.
AdieB

 

[Darkwood]

Its also the case that some rcd's have remote C.T.'s and this must be tested downstream of these monitors this isnt usually found in domestic but more so commercial and industrial where rcd's monitor over 3ph, i understand this won't ever effect 99% of sparkies out there but just noting it so this thread isn't misleading in saying the RCD's should be tested at the terminals as on occasions this isnt the correct method.

 

[Engineer54]

Most Rcd 's are fine to test at terminals but some are designed in that the coil is connected after the live terminal thus using terminals for testing won't operate the device

Save me explaining it in full read this previous thread ...
.http://www.electriciansforums.net/i...stallations/28288-rcd-testing-no-trip-db.html

Only the one as far as i know. The manufacturers suggestion is to connect 10cm or so of conducters to the terminals and test from the ends these!!

 

[cobrauk]

Yes agree its test at the rcd/RCBO terminals, as its the rcd you are testing not the circuit

 

[Darkwood]

There are plenty that use remote monitoring using current transformers, ive fitted them on occasion and many brands available and yes although this thread is really about Rcd's in standard consumer units i thought it deserves a mention that other rcd devices exist that cant be tested at the terminals in this manor but regarding AdieB noting the older MEM rcd's i believe these were the only one with this issue from a domestic CU point of view.

 

[Engineer54]

There are plenty that use remote monitoring using current transformers, ive fitted them on occasion and many brands available and yes although this thread is really about Rcd's in standard consumer units i thought it deserves a mention that other rcd devices exist that cant be tested at the terminals in this manor but regarding AdieB noting the older MEM rcd's i believe these were the only one with this issue from a domestic CU point of view.

This type of Earth leakage protection where an external CT is used are termed as relay's. The smallest i've seen are 300mA, but most incorporate adjustable settings for both tripping values and time... You wouldn't use a standard RCD tester to test such relay's, a secondary injection test kit is a far more appropriate tool...