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#43321 10/10/04 09:19 AM
Joined: Oct 2003
Posts: 289
:andy: Offline OP
Hey there,

would anyone try to answer me some Questions about AFCIs, as they aren't used here in Germany (only gfci).

What interests me mainly is

-How does the AFCI detect arcing? How is the current sensing done?
-How does it separate a light switch arc from a fault arc
-Does it work as it's promised? No trips on switches and plugging, but safe trips on fault arcs?

thanks very much

Joined: Apr 2004
Posts: 201
They work but not well yet. It takes 75 amperes before they will react unless it is a ground fault. In the case of a ground fault, they will trip at 30 to 50 milliamperes depending on who manufactured the device. They will not protect against a series arcing fault at all. IMHO the NEC was used to promote a new technology that did not perform as promised.

The next device is the combination type. The combination type will protect against series as well as parallel and ground faults. It will also protect extension cords that are plugged into the circuit. These devices are now developed and listed but they have no track record and are not even on the market. With all that said, the combination type will be required by the NEC on new construction starting January 1st, 2008 . . . HMMM. [Linked Image]

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Charlie Eldridge, Indianapolis, Utility Power Guy

Charlie Eldridge, Indianapolis Utility Power Guy
Joined: Oct 2003
Posts: 289
:andy: Offline OP
Alright, so it's a good idea but not technically mature yet....

So they do only trip at short circuit arcs, but not on contact problem arcs??

A 16 Amp breaker (standard for Schuko receptacles) here trips instantly at an 80A spike, so this could meet your 75A arc trip demand.

Joined: Jun 2004
Posts: 206
Charlie is right about new technology that does not perform as promised. Square D is now recalling AFCI breakers manufactured from 3/1/04 thur 9/23/04. Date codes CN DN EN FN GN HN JN. The breakers do not trip.

Joined: Oct 2003
Posts: 289
:andy: Offline OP
that's bad...

so did i understand right, the breakers don't trip at a loose wirenut ect fault, but only on "real" short circuit faults?

thanks for your input [Linked Image]

If you are interested, that's a graphic trip diagram for european/german breakers:

time in seconds and minutes on the vertical, current multiplier on the horizontal

B, C and D show the trip characteristics. B Breakers are usual for normal homes and pretty fast. C and D (and K, not shown) are slower for bigger machines with high startup currents). As shown, above 5 seconds they all act the same.

You see that the 16A breaker will sure trip at a 80A spike (16A * 5).

The bottom text diagram shows Thermal tripping on the left and shortcirc tripping on the right.

For the B characteristics, the Breaker needs to stay on for > 1 hour at 1.13*Current, and needs to trip in <1h at 1.45*current.

Short circuit trip is given at 5*current faster than 0.1 secs.
at 3*current slower than 0.1 sec.

[This message has been edited by :andy: (edited 10-10-2004).]

Joined: Aug 2001
Posts: 7,520

The following manufacturer's site gives an outline of how the AFCI is supposed to work:

There were many discussions here about the AFCI a year or two ago. You might find some points of interest in the following threads:

AFCI breakers

afci parallel series

AFCIs and series arcing faults

Joined: Jul 2002
Posts: 8,443
Likes: 3
Good call there mate!. [Linked Image]
I've also been wondering for some time as to what these devices do and how they work.
It's been mentioned that these devices detect arcing, saying that, would a vacuum cleaner using a brush-type motor (Universal) with a bad commutator or brushes, cause an AFCI to trip?.
Thanks for the links everyone, I'm learnin' fast!. [Linked Image]

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