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Topic Title: RCD types.
Topic Summary: What will we use and find?
Created On: 11 May 2018 07:12 PM
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 11 May 2018 07:12 PM
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sparkingchip

Posts: 10706
Joined: 18 January 2003

Is this list of RCD types correct?

AC

AC-S Time delayed

A

A-S Time delayed

F

B

B-S Time delayed

Andy B.
 11 May 2018 08:01 PM
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sparkingchip

Posts: 10706
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Another to add the list:

A-EV

Andy B.
 11 May 2018 08:04 PM
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AJJewsbury

Posts: 16813
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Is this list of RCD types correct?

AC

AC-S Time delayed

A

A-S Time delayed

F

B

B-S Time delayed

Looks to be correct, although I'm not sure it's complete...

- Andy.
 11 May 2018 08:05 PM
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Weirdbeard2

Posts: 395
Joined: 29 November 2017

Hi Andy, the test button is said to be ok for upto 10 years after an installation for a domestic consumer to check the safe operation of their RCD, 5 years for commercial, what changes when an electrician turns up with a tester, a millisecond either way suddenly becomes dangerous?

http://www.theiet.org/forums/f...AR_FORUMVIEWTMP=Single
 11 May 2018 08:18 PM
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sparkingchip

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WB. I'm not sure if you jumped topics there.

I'm just trying to establish which RCD types we are likely to encounter in the next few years, not the rare RCDs that we won't come across.

Andy B
 11 May 2018 08:26 PM
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Weirdbeard2

Posts: 395
Joined: 29 November 2017

Originally posted by: sparkingchip

WB. I'm not sure if you jumped topics there.



I'm just trying to establish which RCD types we are likely to encounter in the next few years, not the rare RCDs that we won't come across.



The test button should work equally as well on all types of RCD, current and future
 11 May 2018 08:27 PM
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dustydazzler

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It's the property owners who fail to function
 11 May 2018 09:09 PM
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sparkingchip

Posts: 10706
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I'll try that again

Is this list of RCD types correct?

AC

AC-S Time delayed

A

A-EV

A-S Time delayed

F

B

B-S Time delayed

Andy B.
 12 May 2018 08:24 AM
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AJJewsbury

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 12 May 2018 08:58 AM
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mapj1

Posts: 10778
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aah.The standards meetings seem to have messed it up spectacularly.
The chances of the wrong thing, or worse, what someone later decides is the wrong thing being fitted is going to be too high.

That no false tripping on very short short surges test really should have been in the specs for all of them from the outset . It would have been better to simply up-issue the guidance to one kind, say B type with surge immunity (which I dint think exists yet, but I bet one day it will.. )after a certain date.

-------------------------
regards Mike
 12 May 2018 11:38 AM
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sparkingchip

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Further to the recent discussion on testing type A RCDs and the 6 mA DC rating coming up the hybrid Doepke type A-EV RCD brochure makes interesting reading ">http://www.doepke.co.uk/rcd/rcd-EV.html[/S I am unsure if they discriminate with the upstream 30 mA RCD and why there is not a 300 mA or time delayed RCD shown upfront on the distribution circuits.

I was considering a list of RCD types with tick boxes when I revise my minor works certificates later this year, information that would be additional to that on the model form. It looks like it might be easier to write the type in by hand!

The problem with these new RCDs is obviously the cost, type A are affordable though far more expensive than the AC RCDs, but the others appear to be currently priced at £200 to over £500.

Presumably costs will fall if manufacturers can dramatically increase production, but in the mean time if we fit a RCD costing the customer £250 and in a year or so guidance is issued to use a different type, there is the possibility of some future arguments.

Andy Betteridge.
 12 May 2018 12:16 PM
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Weirdbeard2

Posts: 395
Joined: 29 November 2017

Originally posted by: sparkingchip

I'll try that again



Is this list of RCD types correct?



AC



AC-S Time delayed



A



A-EV



A-S Time delayed



F



B

B-S Time delayed



How about B+ RCDs referenced but not explained in this wiring matters article:

http://electrical.theiet.org/w...ctrician-should-know/


Other questions not answered by the article "RCDs: everything an electrician should know" :

. what type RCD would I want in my home of the modern era?
. do I recognise or look for these symbols when inspecting existing installations/systems?
. how do I know that what we have chosen to install is safe?
. if a USB charger goes faulty what happens to my protection?
. what type device would you choose?
. what is the legal duty of care placed upon me?
. is the split-load consumer unit I bought fit for the work I need to carry out?
. is there any special testing I need to do or test kit?
. how do the new devices proposed in BS 7671:2018 called 'arc fault detection devices' fit in to all this?

 12 May 2018 12:18 PM
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AJJewsbury

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I am unsure if they discriminate with the upstream 30 mA RCD and why there is not a 300 mA or time delayed RCD shown upfront on the distribution circuits.

My reading is that they don't discriminate for a.c. leakage (>15mA) - but will trip on d.c. leakage >6mA - thus protecting the upstream RCD from having its core saturated (D-loc style) and so from the risk of it failing to trip when it should. One example (TT system, two charge points) does show an upstream 300mA unit - the others either seem to have a dedicated RCD upstream (so discrimination isn't necessary) or are fed from a general purpose socket outlet (so no avoiding 30mA RCD upstream protection).

- Andy.
 11 July 2018 05:34 PM
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vstrom1000

Posts: 48
Joined: 09 July 2018

A couple of handy resources regarding RCD's

- The BEAMA RCD Handbook - Guide to the selection and application of RCD's (I provided a link to BEAMA to obtain the pdf but this IET system removed the link, so just googling the title will find it for you).

- https://professional-electrician.com/18th-edition/doepke-consumer-units/

It's annoying because I've only recently purchased a new Megger MFT, so now I've got to scrap it in order to test F types. Oh F.
 11 July 2018 05:44 PM
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mapj1

Posts: 10778
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Do you ? - I think you can still test the normal RCD functional part of an F type perfectly well, which is all the regs require.
For now.

-------------------------
regards Mike
 12 July 2018 01:55 PM
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vstrom1000

Posts: 48
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Perhaps yes, because I called Megger technical, who didn't know the answer off-hand, so they will have to make enquiries and get back to me. The issue is that type F accommodate mixed/multi frequencies, which a type AC and A tester may not accommodate.
 12 July 2018 02:06 PM
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mapj1

Posts: 10778
Joined: 22 July 2004

An F type, and for that mattter all of the other types still have to do the RCD thing in the normal way to 50Hz current imbalances As a bonus it is also designed and tested at the factory, to still work in circuits with high frequency stuff happening as well, a condition where the behaviour of an ordinary A type may or may not be OK, the whole point is the makers don't design or test the other types for that condition.

At least for now, the regs only define the 50Hz test currents and opening times that need to be met, and all RCD types should pass that check equally well.

In the same way although you can test a B type with rectified DC, and get testers to do it, again, at least for now, the regs don't say you must test that in addition to the ordinary RCD tests.

Of course, if you wish to do extended testing of the performance with HF noise on the line as well, then indeed you'd need another tester.

-------------------------
regards Mike
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