AFCI

[securespark]

Been poking around in more electrical regulations, this time the US ones!

Quote:

Another safety device introduced with the 1999 code is the arc-fault circuit interrupter (AFCI). This device detects arcs from hot to neutral that can develop when insulation between wires becomes frayed or damaged. While arcs from hot to neutral would not trip a GFCI device since current is still balanced, circuitry in an AFCI device detects those arcs and will shut down a circuit. AFCI devices generally replace the circuit breaker in the circuit. They are required in new construction on all 15A, 20A, and 125V circuits to bedrooms, where most arc fault fires originate.

Wonder if they'll be heading our way in a future edition of the 17th?

 

[ColJack]

you mean insulation monitoring devices?

 

[securespark]

Yes. They're only mentioned in the regs with reference to IT systems.

It would appear from the US National Electrical Code that they are using them on their domestic supplies.

Just wondered how long before we see them in our domestic installs.

 

[RF Lighting]

Is that not just the magnetic trip part of our MCBs?

 

[ColJack]

not according to my googling..

it's an electrinic circuit that compares the sine wave and decided what's a "good arc" and what's a "bad arc"..

"good arcs" are switches and things opening, "bad arcs" are insulation breakdowns and loose connections..

 

[RF Lighting]

I've only seen them in Canada on Holmes on homes.

Their electrician mentioned that fires caused by arcs are not uncommon there, and it is a requirement for an AFCI for bedroom circuits.

I can't recall ever even hearing of a fire caused by electrical arc in this country. Overheating yes, but not arcs*

Maybe our wiring practices are sufficiently different to prevent this fault from occouring?






*except when I am welding

 

[ColJack]

it's more to do with the great fire of london...

we build in brick and masonary rather than sticks and planks like the yanks do...
we also have very strict rules concerning what to use in areas at risk of fire...
then there's us using 230 and them using 110.. their lighting circuits are 20A over there..

we wire timber frame houses and such in MICC..

from what I've read of them, the AFCI's don't work until the current is 75A anyway..?

 

[securespark]

Dunno...but the quote above mentions 15 & 20A circuits.

 

[Adam_151]

I assume it means like bursts of 75A during an arcing connection, a computer will pull a burst of somewhere around this (if not higher) when first switched on, and if we were talking UK side kit, this would perhaps trip a B16 type if it was sustained long enough (but chances are its too short lived for that... particulay likely if the L-N loop at the outlet is lowish, so that the burst is big, but short lived)

Now, if you imagined high current bursts due to insulation failure many times a second, fleeting too fast for the magneti part of the circuit breaker to detect (if yank CBs even have a magnetic part??), it could purhaps aidapate enough heat to cause a fire, granted RMS current will rise, but unless the circuit is near its limit anywhere, unlikely to trip it on a thermal overload breaker

Newer ones also detect series arcing faults as well, 110v out there as well, so max zs values will be lower (perhaps having higher currents, and more risk of arcing faults is just simply the price they pay for a voltage thats less likely to electrocute them than our 240v...)

Not knowing a great deal about electrical installation practice across the pond... I don't know what tests they do, so cannot say wether they do an IR, but their equivelent of T+E; romex, sounds more likely to fault than ours... they have paper in it , and there is no requirement to sleeve the ground AFAIK

Anyway, certainly a lot better than the old federal panels they used to install a lot of our there in the 70's....breakers that had a high incidence of not tripping... great!