If an RCD fails to operate once, should it be considered faulty and replaced?

[Silly Sausage]

Nick,

It's possibly to do with the amount of Energy required to cause them to operate.
With an RCD, it would be tiny compared to an MCB, hence 'gumming up' stopping them from operating.
I think that's why the Max Zs increases with breaker rating.
Further study require, or some of our esteemed members could enlighten us further!

 

[NickD]

It's possibly to do with the amount of Energy required to cause them to operate.
With an RCD, it would be tiny compared to an MCB, hence 'gumming up' stopping them from operating.

I think the energy to operate the actual opening of the contacts is stored mechanically in the internal spring mechanism when you push it up, isn't it?

 

[Rockingit]

OK....I'll fess up.

I honestly can't remember the last time (if ever, for 'routine testing') that I've used the test buttons on any installed in my house......like most people, it's just so dull going around resetting everything.....

 

[Richard Burns]

Just do it when the clocks change, then you were going to have to reset everything anyway!

 

[trev]

Just do it when the clocks change, then you were going to have to reset everything anyway!

Aye, if you live in 1985

 

[NickD]

Aye, if you live in 1985

Bowling For Soup - 1985 - YouTube

 

[Marvo]

Bit uneasy about that. Aren't they meant to be maintenance free? If an RCD requires user cycling every three months to keep it from seizing up, is it a fit for purpose RCD?

Good question and I don't have an answer but they all seem to suffer from increased tripping times the longer they're inactive, even the good brand name units are guilty.

Is there a valid reason why RCDs should be treated differently in this respect from MCBs? We don't rely on the user cycling MCBs every three months in order to keep them from seizing up, we expect them to do their job if left for years and if we found one that had failed to operate under appropriate fault conditions we'd chuck it, wouldn't we? Grateful for your thoughts, maybe I'm missing something here.

RCD's and MCB's have always been treated differently, there's never been a requirement to test that an MCB trips according to the current/time graph for its appropriate curve. You only find out the hard way whether or not an MCB is capable of disconnecting withing the expected time.

I don't think you're missing anything, there's plenty to be uneasy about, it's a point that all the official publications seem to have cunningly avoided giving specific guidance on.

 

[Eddiesparks]

Best thing is to bring in your nan's kettle/oven/fridge/iron and donate it to them. Then they wont have to worry about the test button ever again...

 

[Rockingit]

I think the single largest deterrent to testing MCB's is the practicalities of doing so!!!

 

[Engineer54]

Yep, a Primary current injector test kit can be a little steep to purchase for the average journeyman electrician... lol!!