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Discuss Type A RCDs Vs Type AC in the Electrical Forum area at ElectriciansForums.net

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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?
 
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I have seen that and have taken note however if an RCD even a type a is rated at 30ma should it not operate as if it were also a type ac. If for example joe bloggs plumbing and heating services touched a live cable and it’s only going to trip in o.4 seconds when 250ma is applied it doesn’t sound great. The same RCD then fails to Operate if 150ma or 30ma is applied. Which are potentially lethal levels of leakage current, surely the risk of electrocution is increased. If the rcds fail to trip at 30 or 150ma then surely there’s an issue with the manufacturer not recognising that the devices they are manufacturing are not operating correctly at 30-150ma I’m not yet convinced that Hager has sorted this. writing an article where they have quoted a reg from bbb saying “it’s ok that it doesn’t trip in 0.4 seconds with normal test conditions the bbb says we can make up our own test parameters so just stick a heap more current than what it’s actually rated at through it.”
Don’t know about you but I’m struggling to understand why that’s acceptable you wouldn’t stick lights on a 32A fuse so why test 250ma when logically we should be testing much less to ensure the operation is correct
 

Wilko

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Hi - I might have missed something - but an RCD with 30mA rating on its faceplate should operate when ramp tested with AC at a value somewhere between 15mA and 30mA. Whatever the RCD type, I'd have thought (?).
 
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Exactly this is the point I’m making why is it that hager are then saying we need to test the type a rcds at 250ma in order to obtain the type of result we want. The amount of leakage current we are then testing with has changed significantly and if it’s not performing below that level then surely it’s not fit for purpose?
 

Wilko

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Then if an RCD is for Additional Protection it needs to be 30mA or less operating current (Reg 415.1.1) and achieve 40ms or less operate time with 5 times operating current or higher (a note in Reg 643.8).

This does seem a bit odd, as you say. It is a new section in BBB and replaces 612.10 in BYB which made no mention of "or higher". I could perhaps read it as "hit it as hard as you like till it operates within 40ms", which can't have been the BBB intention :) .
 
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Best set the tester to 500ma test and test the 30 on that, it’ll trip out in no time at all, I’m sure that’s how your supposed to test rcds
 

Charlie_

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Arms
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.
 

Dobes_88

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Arms
I've used a number of the Wylex Type A miniature RCBO's, have had no problems whatsoever testing at 30mA & 150mA.
 

NDG Elecs

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I'm not saying I agree or disagree with the guidance, and I was always taught that anything greater than 30mA is not good for the old ticker.
However, Hager are just using what is stated within 61008 according to the link I posted. I agree with Charlies post in the aspect of goal post moving. Don't think it is just one manufacturer though, they would all do it. And yes they are all in cahoots with each other IMO.
 
D

Deleted member 26818

One of the things I don’t understand, is the tripping times of 200ms and 300ms.
Older RCDs BS 7288 and BS 4293 had tripping times of 200ms at 1 x I delta n.
Whereas the three standards listed as being acceptable for additional protection in the 18th edition, BS EN 61008, BS EN 61009 and BS EN 62423, all have tripping times of 300ms @ 1 x Delta n.

Maximum disconnection time for final circuits in TT installations is 0.2s (200ms).
 

Strima

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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.
Wasn't that to do with them only being single pole isolation only? Some manufacturers now produce double pole RCBOs but you need to check their instructions as some state whether or not they're suitable for use with TT systems.
 

Charlie_

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Arms
Yes that was the case and is the one I’m referring to, they have now backtracked on that and have stated there is no need to disconnect/switch the neutral ; this has also been backed up in the regs..
A lot of the regs is written to accommodate the needs of the manufacturers
 
There has never been a requirement for a circuit protective device to disconnect the neutral in the event of a fault on a TT system, just that it disconnects the circuit.
 

Charlie_

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There was and is a requirement to disconnect all live conductors for a circuit protected by an RCD

And now they have rigged the rejigged the regs to allow single pole RCBOs
 

davesparks

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Manufacturers specify a maximum earthing resistance for their RCBO's, this may not always be met with TT systems.

For example schneider specify a max earthing resistance of 100 ohms.
 
There was and is a requirement to disconnect all live conductors for a circuit protected by an RCD

And now they have rigged the rejigged the regs to allow single pole RCBOs
Can you point me to it. Are we talking rcd or a circuit protective device such as an rcbo.
 

Charlie_

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Arms
Can you point me to it. Are we talking rcd or a circuit protective device such as an rcbo.
I am talking about RCDs but in doing so that also includes RCBOs and other such devices
 

Charlie_

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Arms
Manufacturers specify a maximum earthing resistance for their RCBO's, this may not always be met with TT systems.

For example schneider specify a max earthing resistance of 100 ohms.
Hager used to stipulate no sp RCBOs for tt systems and now it’s all ok..
Why?
Because it suits what they are selling
 
D

Deleted member 26818

There was and is a requirement to disconnect all live conductors for a circuit protected by an RCD

And now they have rigged the rejigged the regs to allow single pole RCBOs
If they have rejigged the regs, they did it back in the 1980s.
 

davesparks

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Hager used to stipulate no sp RCBOs for tt systems and now it’s all ok..
Why?
Because it suits what they are selling
Or maybe they have changed the design of their RCBO's to be suitable for use on a TT system.

I don't fit Hager so I don't know, do they have functional earth's for their RCBO's or are they the type without?
 

Charlie_

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For years I have used dp RCBOs on tt systems - MG or Hager and will carry on doing so..
Seems strange that the regs are ok with not disconnecting the neutral on a tt system even though it’s not tied to earth.
 
Maybe but BS7671 only stipulates it for isolation not circuit protection.
 

Charlie_

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Arms
It stipulates RCDs shall disconnect all live conductors for the protected circuit except for protection against electric shock
 
D

Deleted member 26818

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?
 

Strima

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Stop picking holes you lot!!! :D
 

Charlie_

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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

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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_

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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

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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

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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. :(
 
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 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)
 
N

Nigel

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

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

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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

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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.
 

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