Arc Fault Detection going global ...

[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

 

[loz2754]

I believe that anyone considering fitting AFDDs should give serious consideration to David Savery's videos on how to build your own AFDD tester. ?

 

[LastManOnline]

20a

That does surprise me. For a 500wt load to take that degree of inrush current. Is there any possibility there may be some small transformers built in to the appliances you are or using? (or low voltage lighting on the old wire wound trafo, s)

 

[LastManOnline]

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.

You lost me a little with that post. AFCI, s were created to detect arcing? No?

 

[Cookie]

You lost me a little with that post. AFCI, s were created to detect arcing? No?

In the US a short circuit which produces sputtering of any kind (most faults do) is considered arcing per UL's definition. Paschen's law need not apply.

 

[nicebutdim]

Seems as though Metrel believe AFDDs are going to become much more common...