Cutler Hammer AFCI

[luke warmwater]

I spoke to my CH rep today and asked about Series arcing since I know that this has been debated on this forum before.
Cutler Hammer states in their literature that their AFCI breakers will detect series arcing, so I asked him if this is a misprint or if this is really possible.
His response was "Cutler Hammer AFCI breakers detect all types of arcing faults, including Series arcs."
I asked him to explain.
After some technical terms and abbreviated jargon, I got that the circutry in CH AFCI's detect the 'signature' characteristics of all types of arcs and somehow know what each 'signature' is.
Has anyone else checked into this??

On another note: Cutler Hammer has again re-designed their AFCI's and they are now longer, which puts them even closer to the ground bar, unless you install them at the very bottom of the panel (30-42 sp), which is not always convenient.
I also asked the rep about this change and the extra length. He replied that he is telling customers to wire the breaker before installing it into the bus bar.
We've found that this is still not always possible. The neutrals and grounds must be bent very sharply and cut very close to the bar for the breakers to fit.
Has anyone else come accross this?

 

[harley]

Re: Cutler Hammer AFCI

That is Series Arc's in NM-B WIRE.

 

[alex winkler]

Re: Cutler Hammer AFCI

“His response was "Cutler Hammer AFCI breakers detect all types of arcing faults, including Series arcs."”

This statement is true but somewhat misleading. The arc signature of series and parallel faults are essentially the same. The difference is the amount of fault current available. A parallel fault could have hundreds or thousands of amps of fault current available, limited only by the impedance of the transformer and conductors. In a series faults the current will be limited by the impedance of the transformer, conductors, and whatever utilization equipment is in the circuit, such as lights, TV, clock, heater, ect.

AFCI are programmed to open on arcs above 70 amps +-. Since most 15 and 20 amp circuits in bedrooms would have equipment that would limit series arcs to below 20 amps the AFCI would see the arc but not open the circuit. An example would be a 1500 watt heater plugged into a receptacle with a loose connection. The arc at the lose connection is only 12.5 amps well below the 70 amp trip level. Now if that heater developed a fault above 70 amps and had the same loose connection at the receptacle the AFCI would open on the arcing at the receptacle. So your rep can say AFCIs detect series faults. Possible but not probable.

 

[harley]

Re: Cutler Hammer AFCI

C-H Distribution Products & Services page 4-16
"FIRE-GUARD AFCI responds to series arcs in two conductor plus GROUND fixed premises wiring (Type N-B wire) of Zone 1".
No, I repeat, no two wire or loads are mentioned only in the premise wire.

SERIES ARCs. What about a switch, brushes on a vacuum sweeper or a bi-metal in a Iron or thermostat in a electric heater or a hair dryer. What about those 1500 watt series arcs? Will this be nuisance tripping?

Fault currents. Branch circuit breakers are rated @ 10,000 amps bolted fault. The main breaker is usually rated @ 22,000 amps. In a resi
application A BIG NO to 100s of thousands of AMPS. I have measured many availabe short circuit currents in homes and found 1500 amps @ the nearest receptacle to load center and 70 amps @ the furthest. This availabe fault current is not realated to loads but to length of wire, small voltage drops @ connections such as back stabs of receptacles and not twisting wires together for wire nuts.

 

[harley]

Re: Cutler Hammer AFCI

Fault Currents. The 70 amp availability fault current is a RMS value 16.6 millisec. An arc is not symmetrical in nature and may miss positive or negitive peaks. The arc last 2 or 3 milliseconds and measurement are peak amplitude.
These peaks amplitudes are lower than the 70 amp availability of source.

 

[alex winkler]

Re: Cutler Hammer AFCI

I believe the reason they set the arc signature trip level at around 70 amps is to prevent nuisance tripping, it is a trade off between protection and nuisance tripping. The testing I have done on AFCI indicates that the 70-amp level is peak not RMS.

I agree with you on fault currents. My post was not worded very well but I said (hundreds or thousands) not (hundreds of thousand).

 

[harley]

Re: Cutler Hammer AFCI

Actuality there are 6 RMS short circuit availability currents that are tested. These are
500, 300, 200, 150, 100, and 75 amps. Usually a scope and ct are used for measurement. Another way is using a nice load (300 watt light bulb) and measure the voltage @ the receptacle then apply my light bulb load and measure the voltage
drop. Take 2.5 (light bulb load current) and divide by the voltage drop then multiply by the unloaded source voltage. I use a Fluke RMS meter which is pretty accurate. A 3 volt drop @ 120 volts is approx. 100 amps rms short circuit availablility.