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AFDDs - when do they work?

alanblaby

I'm struggling to see the benefots of fitting AFDD's.

I've searched the web, but cannot find any compelling evidence that they actually help in safety.

 The Proffesional Journals all say they are a good thing, but with little content to show the data used to show they make a difference.

As we know, many fires are not caused by arcs, the build up of fluff in a tumble dryer is a typical example.

When I did my Social Housing work, I found many burnt out shower switches, along with washing machine sockets and occasional cooker switches that were totally burnt around the terminals, yet, in many cases would still work until the switch finally fell apart. Clearly some of these switches had been arcing, then had fused the cable to the terminal, others showed black terminals with only a small contact area, thus heating the terminals and causing the 'fishy' smell, which was quite typical.

Is there any evidence that AFDD's would stop these failures?

What about internal appliance faults?

Wasnt Grenfell started in a fridge? If so, would AFDD detect that fault?

And, what are appliance manufacturers doing to make their goods safer? From what I see, there are still thin tin plate terminals on cookers,and poor, loose spade terminals inside firdges and other appliances.They are made to be as cheap as possible, and it shows when you tighten up a terminal, and it bends the back plate as it is so thin.   

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    SPD are easier. Testers exist, only in the lab generally, but it is quite possible to use pulse power techniques to create a fairly well controlled current pulse, and verify that the SPD either does or does not clamp to the voltage it should.

    It is a smaller version of the EMP emulating thumpers that are used to qualify nuclear bunkers and similar, (well understood since the 1960s) and testing immunity to voltage pulses is called up in product standards like IEC/EN61000-4-2

    (this webpage has some pics about 1/3 of the way down showing the method of ESD testing which is the baby version, and then further down transient injection to IEC/EN61000-4-4 and -5 in mains leads etc. )

    For a domestic SPD you need a similar sort of test rig,  but bigger. Mind you, I'd be very wary of testing a whole house SPD with the house still connected at full zap, just in case it was not a pass, and I'd want to be keeping my fingers out of the way, and anyone else's ;-)

    I'm not sure if really we need SPDs as much as some folk think, or not, as I think the estimates of typical transient voltages and their probability of occurrence is a bit uncertain,  but at least what they do and how to verify it is working as it should, is not shrouded in mystery.

    The absence of AFDD testers and equivalent data is more interesting.

    Mike.

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  • 0

    SPD are easier. Testers exist, only in the lab generally, but it is quite possible to use pulse power techniques to create a fairly well controlled current pulse, and verify that the SPD either does or does not clamp to the voltage it should.

    It is a smaller version of the EMP emulating thumpers that are used to qualify nuclear bunkers and similar, (well understood since the 1960s) and testing immunity to voltage pulses is called up in product standards like IEC/EN61000-4-2

    (this webpage has some pics about 1/3 of the way down showing the method of ESD testing which is the baby version, and then further down transient injection to IEC/EN61000-4-4 and -5 in mains leads etc. )

    For a domestic SPD you need a similar sort of test rig,  but bigger. Mind you, I'd be very wary of testing a whole house SPD with the house still connected at full zap, just in case it was not a pass, and I'd want to be keeping my fingers out of the way, and anyone else's ;-)

    I'm not sure if really we need SPDs as much as some folk think, or not, as I think the estimates of typical transient voltages and their probability of occurrence is a bit uncertain,  but at least what they do and how to verify it is working as it should, is not shrouded in mystery.

    The absence of AFDD testers and equivalent data is more interesting.

    Mike.

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