Interesting video on testing type "A"'s RCBO and issues with MFT 's

[LukeD]

 

[Pretty Mouth]

Now what happens in a real world fault where someone is relying on an RCD for fault protection but there is a large Cap load. Will they be able to get the disconnection time the need for safety?

I was told that when this happens, the RCD does disconnect in its usual time, but the capacitor fools the tester into thinking the circuit is still live until it has discharged.

Can someone more knowledgeable than me please confirm or deny that this is what happens?

 

[WallaceP]

I was told that when this happens, the RCD does disconnect in its usual time, but the capacitor fools the tester into thinking the circuit is still live until it has discharged.

Can someone more knowledgeable than me please confirm or deny that this is what happens?

Thanks! Thats good to know.
I feel testing is way behind with current tech. The guy from meggar touched on it too, when saying they aim for 5% for earth loop testing but the requirement is to be within 30%. We are worrying about 0.1 ohm and the machines we are getting the values from can way out on this. Don't get me started on some 2 lead No trip tests. completely useless....

 

[timhoward]

Finally watched it, interesting!
I was wondering at first how the guy from Megger could possibly come out of this looking good, without losing the "You need one of our newest and shiniest machines to test type A RCD's" selling point in spite of the both test and acceptable results not matching the manufacturing standards.
To give him his due, I didn't see the "Test them twice" line coming. Pure genius. Once for BS7671. And once to justify the extra cash we've just spent for a test that isn't actually required.

 

[Risteard]

Finally watched it, interesting!
I was wondering at first how the guy from Megger could possibly come out of this looking good, without losing the "You need one of our newest and shiniest machines to test type A RCD's" selling point in spite of the both test and acceptable results not matching the manufacturing standards.
To give him his due, I didn't see the "Test them twice" line coming. Pure genius. Once for BS7671. And once to justify the extra cash we've just spent for a test that isn't actually required.

To be fair that advice has been around for a while, e.g. with a Type B RCD to test as AC, A and B.

Although the ECA view on this was interesting to note, and suggests that all of these tests really aren't all needed for BS7671 compliance.

 

[goasis]

An interesting video, with intelligent input. Does make you think about how much you do "because that's what we do" without thinking too much about it.

 

[Lister1987]

Device standards should be dictating testing regimes, they don't so there is your route problem, OEM/Testers should be ensuring they test to the same standards otherwise there is no unified approach, it's that "It's a 6, not it's a 9" argument all over again.

 

[SparkySy]

Trouble is that then we would probably end up having to buy a copy of the manufacturer standard as well as the BBB on site guide and appendicitis and that's getting expensive! Or (and I'll try not to laugh while typing this) the manufacturer standard should be free to anyone with an interest!

 

[Markyd]

Yep the Megger man just came across as someone punting testers

 

[SparkySy]

but the megger man also said that their testing standard had wide tolerances compared to the manufacturer standard and that their testers although boasting they can test all types of RCD is greatly overstated, aaaannnddd that we only need to test the AC part of the trip so don't really need all the other fancy stuff they have sold us! I can still use my trusty Mft1552 and didn't really need to buy a new 1741+ at all?

 

[WallaceP]

only needing to test the ac part is crazy, unless it just to proven the mechanism works? at that point just use the test button and hope it will disconnect the same way we are hoping it will disconnect in a 'type a' fault

 

[loz2754]

only needing to test the ac part is crazy, unless it just to proven the mechanism works? at that point just use the test button and hope it will disconnect the same way we are hoping it will disconnect in a 'type a' fault

I think the point was that the only test that we can record results for is the AC test, as that's the only table in BS7671 that is available to compare with.
Then we need to do the test again with the instrument set for type A,B, or F. Just to show that it will trip.