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Topic Title: NA for AFDDs?
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Created On: 10 July 2018 08:59 AM
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 10 July 2018 08:59 AM
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lyledunn

Posts: 1209
Joined: 13 August 2003

Regulation 421.1.7 in the 18th will not be easy for any designer to wrestle with, especially when the installation falls within the examples listed in the note to the regulation. I suspect that most designers will want to be onside with the national standard and will simply acknowledge the regulation by specifying AFDDs as appropriate.
It is noteworthy that a dedicated column for testing the function of the AFDD is provided in the model schedule of test results. I wonder if it will become commonplace that the box is completed with a response other than NA?

-------------------------
Regards,

Lyle Dunn
 10 July 2018 09:19 AM
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Zoomup

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421.1.7 (18th). "Arc fault detection devices conforming to BS EN 62606 are recommended as a means of providing additional protection against fire by arc faults in AC final circuits."

This reg. comes in the section headed "Protection Against Thermal Effects." I suppose that the "additional protection" provided by arc fault detection devices is in addition to 421.1.6 which requires material used for the construction or enclosures of electrical equipment to comply with the resistance to heat and fire requirements in an appropriate standard.

Of course arc fault detection devices are designed to detect arcing due to faults occurring, so it is a belt and braces situation. They would not of course protect from fire if I placed my coat over a storage heater.

AFDDs are promoted and recommended by whom? The makers?

Z.
 10 July 2018 10:39 AM
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dustydazzler

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Arc Fault Circuit Breakers are wide spread in America and Im not even sure they know why



As you commissioning and testing one , errrr


Im opting for N/A in the schedule
 10 July 2018 12:43 PM
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psychicwarrior

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I asked about AFDD's recently at the wholesalers: what's one of those, I got asked. I tried to explain, but I got the reply...what a farce wasn't an RCD enough. :-)
 10 July 2018 02:25 PM
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burn

Posts: 312
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Originally posted by: Zoomup

They would not of course protect from fire if I placed my coat over a storage heater.


AFDDs are promoted and recommended by whom? The makers?



Z.


A device to protect people from their own stupidity would save thousands of lives, but so far no has managed it.

I'll probably be fitting them in my house when they become widely available, ready for next autumn, when the mice come home

burn
 10 July 2018 02:47 PM
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OMS

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Have you thought about getting a cat ?

OMS

-------------------------
Let the wind blow you, across a big floor.
 10 July 2018 03:46 PM
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sparkingchip

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They bring more mice in.
 10 July 2018 05:45 PM
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mapj1

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It is noteworthy that a dedicated column for testing the function of the AFDD is provided in the model schedule of test results.


!!

OK, has anyone seen an AF tester yet ? I presume hacksawing though a live cable to see if it trips won't really pass muster with the H and S dept.
Actually even the tests in the official standards are pretty rough looking.
There are a few 'testers' for the US market that do what we already have to do for RCDs, but as far as I can see none that actually create an arc-like waveform.

-------------------------
regards Mike
 10 July 2018 06:49 PM
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Zoomup

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A suitable AFDD tester may be a old orange coloured Black and Decker sparky commutator electric drill from the local car boot sale.

Z.
 11 July 2018 09:23 AM
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lyledunn

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Mike,
The test is only to confirm operation of the device by operating its test button. The point is that it has been decided to put these devices full square in the attention of anyone compiling a schedule of test results. That is certainly one way of promoting an intention.

-------------------------
Regards,

Lyle Dunn
 11 July 2018 02:27 PM
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mapj1

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The standards ( IEC:62606 2013) do include proper tests, but they are not suitable for easy table top use.

An arc generator test is an apparatus consisting ,<snip>....one electrode shall consist of a 6 mm 0,5 mm diameter carbon-graphite rod and the other electrode shall be a copper rod. The arcing end of one or both electrodes may be pointed as shown ..<snip>.. It may be necessary to clean and sharpen the rods in order to have repeatable arc conditions.
When inserted in a circuit, the separation of two electrodes at a convenient distance shall generate a consistent arc between two electrodes.When using the arc generator, the AFDD shall clear the arcing fault in less than 2,5 times the break time in Table 1 or 2


and

The insulation across both wires is to be slit 50 mm (or 2 inches) from one end to a depth to expose the conductors without severing any strands.
d) The slit in the insulation is to be wrapped with a double layer of electrical grade black PVC tape and overwrapped with a double layer of fiberglass tape.
e) The conductors are to be stripped at the end farthest from the slit approximately 12 mm (or 0,5 in) for connection to the test circuits. The cable specimen shall be then conditioned to create a carbonized conductive path across insulation between the two cable conductors:
f) The cable specimen is to be connected to a circuit providing 30 mA short circuit current and an open circuit voltage of at least 7 kV. The circuit is to be energized for approximately 10 s or until the smoking stops.
g) The cable specimen is to be connected to a circuit providing 300 mA short circuit at a voltage of at least 2 kV or sufficient to cause the current to flow. The circuit is to be energized for approximately one minute or until the smoking stops.


Not sure how either of those tests can be re-created on a test button, or even emulated with a bench top tester.
So I'm not sure how we could sensibly fault find to see if they are working correctly or not. Clearly the test button is verifies the circuit breaker part, not the arc detection function.

I also have some doubts that devices that disconnect in such contrived tests actually do very much against real faults.
If we fit one and the building burns down, I bet we don't get our money back..

I also think you could fit one, and by and large negate any sensitivity by following it with a suitable mains filter.


A very interesting thesis showing some real results of tests in this is here

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


Edited: 11 July 2018 at 02:47 PM by mapj1
 11 July 2018 04:47 PM
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John Peckham

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I believe the product standard requires AFDDs to carry out a self test every 24 hours and stay tripped if the test fails. I am told that Hager types carry out a self test hourly and trip if the test fails.

In addition most AFDDs have an integral test button which the new 18th Edition Appendix 6 model schedule of inspection and schedules of test results have a box to tick to indicate the button does operate the device in the same way as an RCD test button.

I am also told that the UK test equipment manufactures have no intention of making a test instrument for AFDDs.


If you come along to the Elex shows the IET panel is doing a presentation on AFDDs that tells you all you need to know and gives you the opportunity to ask questions.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 11 July 2018 05:01 PM
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Zoomup

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"..................CWT highlights the broadband noise much better than STFT. However, in the case of the power drill,
one must be careful in order to distinguish series arc from the load." Thus said the scholar in Mike's reference above. So the old car boot sourced orange coloured Black and Decker drill does produce some nice arcing and radio interference?

Z.
 11 July 2018 07:36 PM
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ToniSM

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One advantage American electricians have over UK electricians is each state has to approve each alteration to the NFPA-NEC. A number of states have rejected the mandatory requirement of AFCI's as unreliable technology.

In another thread I asked UK electricians to compare the differences in wiring methods.

Wirenuts.
Pushgrip receptacle and switch connections.
Figure of 8 power leads to appliances.
Higher current draw due to the use of 120V.
No testing when commissioning an installation.

They do have AHJ (Authority Having Jurisdiction) inspectors (BC with teeth). Officially each job should have a permit issued by the AHJ. An inspector can red tag a job as not to code.

-------------------------
The reports of my death are greatly exaggerated.
 11 July 2018 07:57 PM
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dustydazzler

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Most sparks don't use the pishwire tabs as far as I know , they usually use the gold silver and green side screws ?

I have no issue with their methods , in fact some of it makes more sense than ours

Like no soft sheath surface mounted wiring is allowed , it must be in tube or some other form of containment

They use pre-wired copex for surface installation with looks a real doddle to use
 11 July 2018 09:19 PM
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sparkingchip

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To install arc fault devices to every circuit you need to install a consumer unit with a RCBO and a spare way for every circuit.

That puts the job out of the price range most customers are comfortable with, before you have even bought the AFCIs.
 11 July 2018 09:29 PM
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dustydazzler

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You can now buy a combination mcbrcboafdd

It's a 3 wide module from the ones I saw
 11 July 2018 09:56 PM
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deleted_1_vstrom1000

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Joined: 09 July 2018

[text in this post removed]

Edited: 25 July 2018 at 09:56 AM by IET Moderator
 11 July 2018 11:32 PM
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sparkingchip

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Brochures for consumers are virtually non-existent and hard going.

There seems to be the assumption that electricians will do all the work selling these devices to the final customer.

Manufacturers and others, such as the IET are going to have to promote them to the final customers as well as to electricians if they want a serious uptake.
 12 July 2018 12:37 AM
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mapj1

Posts: 11440
Joined: 22 July 2004

Well, that brochure suggests that
A 10% reduction in electrical fires has been reported in countries where arc fault devices are mandated such as USA.

That's pretty useless
Now the chance of an electrically iginted fire in any one home is less than1 in 1,000 per year, so we are suggesting that we need to fit AFDD in more than 10,000 houses where it will not be needed, and in 9 of those there will be a fire that it will not prevent, for every fire it prevents per year.

That's great if it's your house it saves of course, but not really cost effective unless almost free to install, or if the house it saves is very valuable.
It might be better if wylex hurried up and developed that 3 pole think the regs allude to for charging cars on a PME supply instead.

-------------------------
regards Mike
IET » Wiring and the regulations » NA for AFDDs?

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