Testing, testing...

[kwikfix328]

I recently invested in a new Megger RCD tester , and then set about checking some of the RCD's that i own.
My house doesn't currently have a Modern RCD protected Consumer Unit, I'm having one fitted in the next week or so.

The new Garage CU in my shed works perfectly and passes all of the tests easily.

I then set about checking some of the many RCD plug top type adaptors that i have fitted to many power tools , etc.
I've only checked 4 so far , but depressingly already have had a 50% failure rate. One adaptor failed to trip at all and so would have offered no protection if used.
Also my trusty RCD 25 metre long cable reel that i have used for just about everything for a few years now , also failed the test, ( the test wouldn't even start, the Tester indicated ' Check' ) the Test instrument indictor lights shows it having some kind of internal wiring fault as the N-PE LD is lit and i don't think it should be. The adaptor 'works' if you push the self test button though.

and they say that what you don't know can't hurt you...[/url]

 

[JohnD]

Well done!

"RCD Adaptors" don't seem to me to have a long life

Even proper RCDs and RCBOs have a "fail-to-trip" failure rate which is much higher if they are not tested regularly.

We had a link to a report somewhere showing the high failure rate of "tested never" and "tested less than once a year" RCDs which was much worse than the "tested monthly" failure rate.

The other advantage of testing monthly is that you can spot a fail-to-trip and fix it, hopefully before an emergency occurs.

IIRC the "Test" button introduces a much higher fault current than the rated one, howevere when I have had adaptor failures, they wouldn't trip at 500mA or on the button. On the plus side I suppose they are (if working) better than nothing and fairly cheap. Their downfall is that they are easy for the user to discard if they annoy him by tripping

BTW if you are having a new CU, consider RCBOs if you can afford them. they are far more convenient and actually less prone to nuisance tripping as they individually have less background leakage.

 

[vsynth]

This is good to know, thanks.

 

[kwikfix328]

One of the adaptors that failed is the type that you cut off the original BS plug and replace it with an RCD Plug , rather than a plug in adaptor.

I like to think that i'm quite particular about this type of thing, however my wife and kids aren't perhaps quite so dilligent.
I'd rather the RCD fail safe and pass no current at all , than fail un-safe with no possibility of tripping in case of a crushed/damaged or severed cable , etc.

It was slightly expensive, and a bit of an impulse purchase but I'm glad i bought the tester now.

 

[Chivers7]

I once trimmed a hedge with a plug in type adapator feeding the cable and accidently cut the mains cable as I stumbled on the ladder

The fuse didn't blow and neither did the RCD trip , I guess it was a neat cut. I now use petrol engine powered trimmers though

 

[ban-all-sheds]

I dug up my hedge.

Harder work than trimming it, but you only have to do it once.

 

[Chivers7]

I dug up my hedge.

Harder work than trimming it, but you only have to do it once.

More room for a shed

 

[ban-all-sheds]

No - the council don't like sheds in the front garden. The new shed will be going at the rear....

 

[Spark123]

I then set about checking some of the many RCD plug top type adaptors that i have fitted to many power tools , etc.
I've only checked 4 so far , but depressingly already have had a 50% failure rate. One adaptor failed to trip at all and so would have offered no protection if used.

What trip times do you get for I and 5I? Did you check your earth fault loop impedance before conducting the RCD test (important test which is often overlooked as if there is no loop any exposed conductive parts may become live during the test)?

Also my trusty RCD 25 metre long cable reel that i have used for just about everything for a few years now , also failed the test, ( the test wouldn't even start, the Tester indicated ' Check' ) the Test instrument indictor lights shows it having some kind of internal wiring fault as the N-PE LD is lit and i don't think it should be. The adaptor 'works' if you push the self test button though.

Sounds like a P-N reversal?

 

[kwikfix328]

What trip times do you get for I and 5I?

Sounds like a P-N reversal?

I seem to be getting some mixed results, but specifically from two RCD's of the same Model/Manufacturer . ( Power Breaker bought from B&Q a few years ago).

Basically the fixed RCD in my Garage CU and two Plug in adaptors were within limits and did what i was expecting according to the instructions and other literature that i have. e.g. 0.5 x I = no trip, 1 x I < 200ms ( typ <17 -37ms) 5 x I = <40 ms (typ < 8 -15ms) , ramp current was typ about 20mA.

These two Power Breaker Branded RCD Plugs just don't check out though. They will trip and reset using their own self test. But all of the indications using the tester are just wrong.

I've made up a little test rig using a 2 way trailing socket and short length of new flex, specifically to test them. I fitted a standard plug to this first of all and tested it , everythng was fine ( so the cable and 2 way socket is good). I then fitted the RCD plugs and it won't test. I can therfore only assume that either the RCD plugs are faulty, or their internal wiring circuits are configured in such a way that they give weird indications.
For example they both trip on the 0.5I test when they shouldn't.


I've Physically checked and also used a Martindale Plug socket tester and there are no P-N reversal indications. They were only cheap so I don't plan to waste too much more time or effort with them , I'll just bin them . I'd rather be safe than sorry.

Did you check your earth fault loop impedance before conducting the RCD test (important test which is often overlooked as if there is no loop any exposed conductive parts may become live during the test)?

I haven't got one of these testers, but do plan to buy one and an Insulation/Continuity tester at some point in the future when funds allow.
I don't actually need these tools proffessionally, these are just for personal use and as they are not exactly cheap I decided to get the RCD tester first. It is probably a more expensive way of doing it, but i figured that if I bought a Multifunction Tester if one functon bust , i'd probably lose them all.

Like a lot of Technical/Maintenance Engineers , I can sometimes be a bit of a gadget junkie...