I don't think I entirely understand the critique of the CAFCI here (I am not disagreeing, just trying to understand.) I get that, in general, there's offense at the self-interested industry tactics. But setting that aside for the moment, what are the other criticisms? Does anyone claim it's 100% hype, and CAFCI's are good for nothing?
I won't go as far as to say that they are 100% hype, but I don't think they do any where near as much as the proponents want you to believe. One of the biggest issues is the outright lies that were published by the manufacturers in the attempt to get them in the NEC. If you go back and look at the original proposals, in the ROP for the 1993 code, you will find that they claimed to have a device that does what the combination AFCI does...a device that came on the market some 13 years after the original proposal. Because of that I have a major issue believing anything about AFCIs that comes from a manufacturer. Another issue is that the fire cause statistics show that at least 85% of the dwelling unit fires that are said to be of electrical origin occur in dwelling units that are over 20 years old. Do more modern installations have less fires or is just a reflection of aging electrical systems?
Most seem to agree that it's the GFP component of CAFCI's that fires "most" or even "90%" of the time, but so what? Isn't it a good thing to detect those ground faults, and also to detect the 10% (or whatever) occurrences that are actually arc faults?
I don't have an issue with this.
Or is the critique just that its detection of real arc faults is so rare that it doesn't justify the expense?
It doesn't even come close to justifying the expense. If the AFCI was 100% effective in preventing fires of electrical origin (even the manufacturers don't claim that is it possible to prevent 100% of the electrical fires) full compliance with the 2008 AFCI rule would result in the prevention of about 435 fires in the first year, assuming all new homes were built in compliance with the 2008 code. This would give a cost of about 1.5 million dollars for each fire prevented. Over 20 years they could be expected to prevent about 128,000 fires, but at an installed cost of about $170,000 per fire prevented.
What I also don't understand with respect to industry/marketplace is why they make CAFCI's ground fault at 50ma instead of GFCI standard of 5ma. Is there a specific desire to allow some ground leakage in applications where CAFCI's would be spec'ed? (seems not very likely.) I guess I don't understand what the SAVE THEIR BUTT purpose Pierre refers to. I'll search some past posts and try to see if I can answer my own question.
I have no idea why they picked a 30 to 50mA trip point for the GFP in the AFCI.
If the CAFCI's were less expensive than GFCI's, it'd make marketing sense that the manufacturers would not want to undercut the GFCI market, but that's not the case, in fact, CAFCI's are more expensive. If a CAFCI worked as a GFCI, you'd presumably get some people "upgrading" to CAFCI where GFCI required and CAFCI not required (garage, exteriors) and this would be profitable to makers, unless the issue is that the margins are on GFCIs are much greater than on CAFCI's.
I don't think there is much competition between AFCIs and GFCIs in the residential market. Most of the GFCI protection in that market is provided by receptacle type devices. I am not sure if there are any dual listed CAFCI/GFCI devices on the market, but there were dual listed AFCI/GFCIs....at a cost much higher than the AFCI itself.
