Arc Fault Detection going global ...

[Cookie]

Serial arcing is the end stage of joule heating, that is assuming combustion has not already ensued.

 

[DPG]

Parallel arc faults involve very high currents, limited only by Zs in domestic installations.

Sorry, I was referring to series arcing. I wasnt very clear there.

 

[Cookie]

Sorry, I was referring to series arcing. I wasnt very clear there.

Its alright

Sadly AFCIs stop looking for serial currents below 5 amps. Not sure about UK AFDDs.

 

[DPG]

Its alright

Sadly AFCIs stop looking for serial currents below 5 amps. Not sure about UK AFDDs.

I must admit I don't know the lower cut off point for UK AFDD devices either.

 

[pc1966]

Recently i saw for the USA market they are selling testers for AFCI (AFDD) such as mentioned here:

AFCI Testers

AFCI testers or indicators for arc-fault circuit interrupters

www.nachi.org

But for now I have no idea if any MFT offer AFDD testing, or even if the EU/UK market has an agreed standard for that (i.e. like the 15-30mA limit for RCD, etc).

Finally it seems those testers are to verify the AFDD, not sure if anything is available to test a circuit suspected of triggering it. For RCD we have low current clamp ammeters that can measure the leakage to know if we are close to tripping, not sure when 9or if) that will also appear on MFT.

Oddly though that article says the testers are less meaningful than the self-test button. Hmm...

 

[Cookie]

Recently i saw for the USA market they are selling testers for AFCI (AFDD) such as mentioned here:

AFCI Testers

AFCI testers or indicators for arc-fault circuit interrupters

www.nachi.org

But for now I have no idea if any MFT offer AFDD testing, or even if the EU/UK market has an agreed standard for that (i.e. like the 15-30mA limit for RCD, etc).

Finally it seems those testers are to verify the AFDD, not sure if anything is available to test a circuit suspected of triggering it. For RCD we have low current clamp ammeters that can measure the leakage to know if we are close to tripping, not sure when 9or if) that will also appear on MFT.

Oddly though that article says the testers are less meaningful than the self-test button. Hmm...

That a whole other story altogether...

 

[Vortigern]

Speaking of arcs, I have a problem in my computer/printer area related no doubt to arcing. I switch on my multiple socket switch and the MCB pops sometimes. So there is a printer, computer, speakers, a couple of lights probably adding up to about 500w max. All equipment is in good condition. I think it is the switch arcing when switched on, so a fairly minor arc is being detected by an older wylex MCB. What need then for AFDD?

 

[DPG]

Speaking of arcs, I have a problem in my computer/printer area related no doubt to arcing. I switch on my multiple socket switch and the MCB pops sometimes. So there is a printer, computer, speakers, a couple of lights probably adding up to about 500w max. All equipment is in good condition. I think it is the switch arcing when switched on, so a fairly minor arc is being detected by an older wylex MCB. What need then for AFDD?

But I'm sure we've all seen evidence of bad connections/arcing which haven't tripped an OCPD. The arcing in your example would most likely be worse due to the amount of switch mode power supplies present after the switch.

Just playing devil's advocate - I'm not convinced either way about AFDDs yet!

 

[pc1966]

Speaking of arcs, I have a problem in my computer/printer area related no doubt to arcing. I switch on my multiple socket switch and the MCB pops sometimes. So there is a printer, computer, speakers, a couple of lights probably adding up to about 500w max. All equipment is in good condition. I think it is the switch arcing when switched on, so a fairly minor arc is being detected by an older wylex MCB. What need then for AFDD?

Electronics has high in-rush, so a bouncing switch is going to hammer home a few high current peaks.

We used to have 10 monitors off a 20A rotary switch (actual load probably no more than 500W) and it burned out the switch contacts after a year or two of daily use. Ended up having a zero-crossing SSR and NTC termistor arranged after the switch so it reduced the peak current to 20A or so and then connected after the first half-cycle on the next zero crossing. Was still working about 10 years later.

 

[DPG]

Electronics has high in-rush, so a bouncing switch is going to hammer home a few high current peaks.

We used to have 10 monitors off a 20A rotary switch (actual load probably no more than 500W) and it burned out the switch contacts after a year or two of daily use. Ended up having a zero-crossing SSR and NTC termistor arranged after the switch so it reduced the peak current to 20A or so and then connected after the first half-cycle on the next zero crossing. Was still working about 10 years later.

Theres a lot to be said for zero crossing switching. I'm surprised it's not used more often.

 

[Vortigern]

a zero-crossing SSR and NTC termisto

Eh? Now I don't actually know what that is. Who thought of that as a solution. I have heard of current limiters but SSR? Solid State Relay? NTC t(h?)ermistors?, the greater the current the higher the resistance?

 

[pc1966]

NTC is negative temperature coefficient, so the resistance starts high and drop as they get hotter. Often used for reducing in-rush currents. But unless you give them around a minute or so to cool down after switching off, you get a high surge again!

So the solution we had used a relay to bypass the NTC thermistor once output volts had risen enough to operate it:

 

[pc1966]

This is the sort of NTC device:

https://uk.farnell.com/epcos/b57237s0150m000/thermistor-ntc/dp/9754202

Just to add: The bypass relay means very little heat is dissipated, and the thermistor stays cool so it can be cycled off and back on quickly while still doing its job of limiting inrush current. You don't absolutely have to use a zero-crossing SSR, but that is a bit better than a mechanical relay as it won't close during a voltage peak.

 

[Cookie]

I know some EU micrwaves have this circuit where as US versions do not. EU equipment seems to have much lower inrush than US equipment- in the US you can see the lights dim when a fridge starts or someone turns on a tool/appliance ect. I'd imagine not so in the UK/EU?

 

[pc1966]

It is not so common to see lights flickering here on load. How much of that is supply impedance and how much the restrictions on surge current I don't know. USA panels seem to be higher current than typically seen here (200A mentioned a lot for USA, here 100A is typically max for domestic, if you need more it is 3-phase 100A) so I imagine they are quite low impedance.

It might also stem from the historic fuse/MCB characteristics. If your supply trips out at x5 rated load for tens of ms sec you would have unhappy customers returning that product as faulty.

 

[LastManOnline]

I know some EU micrwaves have this circuit where as US versions do not. EU equipment seems to have much lower inrush than US equipment- in the US you can see the lights dim when a fridge starts or someone turns on a tool/appliance ect. I'd imagine not so in the UK/EU?

I, ve noticed that effect in houses in the country side where the pole transformers have, nt been upgraded and basically demand (all the extra household appliances) has outstripped supply.

 

[LastManOnline]

Speaking of arcs, I have a problem in my computer/printer area related no doubt to arcing. I switch on my multiple socket switch and the MCB pops sometimes. So there is a printer, computer, speakers, a couple of lights probably adding up to about 500w max. All equipment is in good condition. I think it is the switch arcing when switched on, so a fairly minor arc is being detected by an older wylex MCB. What need then for AFDD?

What size mcb?

 

[Cookie]

It is not so common to see lights flickering here on load. How much of that is supply impedance and how much the restrictions on surge current I don't know. USA panels seem to be higher current than typically seen here (200A mentioned a lot for USA, here 100A is typically max for domestic, if you need more it is 3-phase 100A) so I imagine they are quite low impedance.

It might also stem from the historic fuse/MCB characteristics. If your supply trips out at x5 rated load for tens of ms sec you would have unhappy customers returning that product as faulty.

Thats exactly why AFCIs were created. After it was theorized that 75 amps could be seen at the end of a really long run a 75 amp pickup breaker was created as a concept but soon realization came that certain goods would trip it.

 

[pc1966]

I, ve noticed that effect in houses in the country side where the pole transformers have, nt been upgraded and basically demand (all the extra household appliances) has outstripped supply.

For rural supplies I'm not so surprised!

 

[Vortigern]

What size mcb

20a