Type A RCDs Vs Type AC

[tmus1]

I understand why the increased use of type a rcds are recommended however there’s something I don’t understand. If these type a rcds aren’t tripping at 1x on a normal 50hz ac cycle or at x5 then surely they can’t be fit for purpose because they are not detecting a potentially critical fault. In my understanding an MFT simulates a fault at a specific leakage current in order to trip the rcd. Type ac rcds trip without failure most of the time. But carry out exactly the same test under the same conditions on a type a RCD it fails to interrupt the supply. Obviously there’s a type a test on the mft but why is it acceptable that they fail the ac test when the circumstances and requirement for them to trip under fault conditions on an ac circuit hasn’t changed?

 

[Charlie_]

If we need double pole protection in TT installations, then fuses can’t be used.
So we have to condemn all those BS 3036 and BS1361 fuse boxes.
What about the DNO fuse, or plug top fuses?

Wait, what about single pole light switches?

What does any of that have to do with circuits protected by RCDs ?

 

[richy3333]

Hager will move the goal posts to suit themselves..
Before metal boards it was stipulated by the manufacturer that RCBOs must not be used on TT systems and now it’s suddenly all ok..
When Hager done their Amd3 roadshow I quizzed them on quite a few things but he couldn’t break out of script, kept repeating the same nonsense.
Even the regs are guilty of it, would appear they are in cahoots with each other.

Not sure I agree with a lot of that comment.

I really don’t see the issue with A typeRCBO’s. I’ve probably fitted at least 100 and all have tested out fine.

 

[Charlie_]

Not sure I agree with a lot of that comment.

I really don’t see the issue with A typeRCBO’s. I’ve probably fitted at least 100 and all have tested out fine.

What parts don’t you agree with?
I don’t have any issues with testing them either

 

[mattg4321]

I've fitted a load of Hager Type A RCBO's and had no problems testing the RCD part of them as normal with my Megger MFT1553?

 

[freddo]

Had some unusual things when testing the last 2 type A RCBOs I stuck in, set test meter to type A RCD, and both tripped at 1/2 IΔn, replaced them with new ones from a different place and still the same. The readings were the same with outgoing conductors connected and disconnected. Testing them with the meter set to type AC RCD gave normal results. I have previously tested quite a few type A RCBOs without issue. Perhaps meter is faulty.

 

[Clarkyj2k]

Getting the Same as you @freddo on the last two Split load Hager Boards fitted...Both have tripped at 1/2 on all RCD's and giving me well over 40ms (X5) on the last board. I'm using a Kewtech Tester (KT64DL) which I've had no problems with before? Spoke to both Kewtech and Hager about this and both party's seem blame each other?!?

 

[freddo]

Hmm, Kewtech KT65DL here.

 

[mydigitalhome]

What about the DC leakage side?

 

[Clarkyj2k]

@freddo Well Kewtech Tech told me they were trying to get info out of Hager in regards to what mA @ X5 is needed if its between 150mA - 250mA the Kewtech cant do it at the standard setting and Kewtech units are not Variable (unlike the meggers are)?! So was told to carry out X5 @ 100mA??!!?? Which could possibly damage the RCD?! So not sure what the point of that is as this would be putting 500mA through the device? But also reading up people have suggested carrying out 1/2 @ 500mA (Giving you 250mA) which I believe Hager are saying is the recommend value needed for there Type A Devices. (CD285U)

 

[Nigel]

How many of us own the appropriate DC RCD tester to test Type A RCDs?

 

[mattg4321]

Not enough information from the relevant manufacturers. Quelle surprise.

 

[Nigel]

The reason we should install DP (switched neutral) RCBOs in a TT system is only when an up-front RCD (100mA S Type) is installed so that we achieve selectivity and avoid nuisance tripping from a neutral - earth fault which would then trip the up-front RCD in fault conditions.

 

[davesparks]

How many of us own the appropriate DC RCD tester to test Type A RCDs?

You'd hope everyone who needs one does, though this is unlikely to be the case.

My MFT (Megger 1730) is capable of testing types AC, A and B RCDs and I think most common testers are capable of AC and A type.

 

[Andy78]

How many of us own the appropriate DC RCD tester to test Type A RCDs?

Me. Even though it is a bottom of the range Metrel MI300 of 8 years age.