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Comment by tibbon | Hacker News Reader

You need a AFCI in most places now. In the 2020 edition of the NEC®, Section 210.12 requires that for dwelling units, all 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets or devices installed in dwelling unit kitchens, family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, laundry areas, or similar rooms or areas shall be protected by AFCIs.

The latest National Electrical Code requires both AFCI and GFCI protection only in kitchens and laundry rooms, but if you're already doing AFCI, why not do it all everywhere as it is clearly to be required at some point

Main downside is they are expensive. I've recently installed a new 24-slot subpanel and I'm using them everywhere required. At $50 a pop, that's a quick $1200.

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"At $50 a pop, that's a quick $1200."

See, this is the part I hate. I bet someone patented the design, then the NEC made it mandatory, and now they just rake in the money on something that likely costs <$10 to make. If something is legally mandatory, it should not be patented.

Looks like you're not wrong: https://patents.google.com/patent/US9577420B2/en

Some countries you have a single one for the whole building, rather than one per circuit.

That dramatically lowers the cost.

The only real downside is that if you accidentally put your finger in the toaster, rather than just the power to your kitchen cutting off, the power to the whole house cuts off. I think thats a fine tradeoff to save $1200.

Well, if the power shuts off and that saves me from electrocuting myself, I couldn't care less how much of the rest of the house lost power.

The annoying part is when I plug in some faulty device that is not immediately dangerous and that shuts down power to the whole house.

> The annoying part is when I plug in some faulty device that is not immediately dangerous

Do you mind, re-reading that statement? I don't even understand that argument. You should not be plugging in faulty devices in the first place...

I guess you don't know if it's faulty until you try to use it. Manufacturing defects are a thing, but kind of a once every 30 years type thing, so maybe not a big deal to worry about. The reason you install circuit breakers and AFCIs is to avoid a fire in these cases; rare, but worthwhile to avoid.

Also because plugging in faulty devices into outlets is something that ought to be safe. Because with probability 1 it will happen in every house. If the way the house is wired makes the only safe action to shut everything off that's the problem and shitty wiring.

Exactly: it's just like computer OSes. You should be able to run a faulty program that divides by zero or dereferences a null pointer without the whole computer crashing. The computer should flag the error, tell you what went wrong and why, and let you continue with your work and the other stuff going on in other windows.

Fault-tolerance is an important and useful thing.

Of course I should not be plugging in faulty devices. But sometimes appliances that were fine before break down, perhaps some insulation broke down or just the ravages of time.

I would absolutely like that to be safe. And like I said, if it's immediately life-saving, then I don't mind the power to the whole house being cut. But if it's "just" a bad appliance, then, well, I do find it a bit annoying that it reset all my electronics, and I would have preferred it if only that specific outlet was effected.

But I would still very much like the protection.

real downside: many things work poorly on gfci stuff. E.g. A miter saw or welder. I had AFCI/GFCI breakers in my garage per code, but essentially no power tools work with those kinds of circuits.

I've noticed the same thing with a cheap lemon juicer in the kitchen. I'm assuming the brushes on the DC motor are the cause.

The bigger downside is nuisance tripping because the breaker doesn't like electrical noise emitted by some device or another in your house. I don't have any AFCIs but I've heard it's pretty common.

You'd rather have one circuit go out instead of the whole house, and if all you have is the one AFCI breaker you're going to have a much harder time identifying what device(s) is the culprit.

I've mostly used them on new circuits, but have put them on a few of my older circuits too. For my small sample size, I've yet to have one nuisance trip.

Yeah I've replaced all of the breakers (to living areas) in my 90s home with AFCI ones. Haven't had any nuisance trips. If I had "nuisance trips" I'd be more worried about my wiring than about my breakers...

This nuisance tripping is the bane of my electrician friend's professional life.

"Oh just err on the site of extremely cautious and sensitive. More safety can't be a bad thing."

And god forbid you use anything with a brushed motor, which has sparks in its normal operation

Some OS's have a single task for the whole computer, rather than one per application.

The only real downside is that if your app accidentally dereferences NULL, rather than just your application crashing, the whole computer crashes.

... Sorry, somehow reminded me of the early days of the Macintosh's OS before it was "true multitasking" (as the Amiga kids would love to tell us).

Don’t even get me started on AFCIs. At least the behavior of GFCIs is well-defined.

The AFCI thing is a money grab.

why's that, is there some guarantee they fail to live up to? Is there something probabilistic to them or something?

AFCI's are of dubious effectiveness at their purpose (preventing fires). They're kinda snake oil because each manufacturer won't tell you under what exact conditions they'll trip. Somehow the law in the USA now requires them on every circuit, although they aren't used at all in Europe (which has a higher voltage yet far fewer electrical deaths).

FWIW, Google says 540 electrical deaths per year in Europe vs. 200 per year in the USA. Whether that's from lower voltage or more GFCI is anyone's guess.

Europe is many different countries with different electric code

That’s definitely lower voltage. It’s just physics.

AFCIs aren't meant to protect against electrocution, just sparking which leads to a fire.

I'm not sure where you are getting this.

According to the CPSC, who analyzed some 10s of thousands of fires, something like 50% of them were caused by wire arcing that could be prevented with AFCI breakers. This is the exact reason why the NFPA is moving the NEC towards eventually requiring AFCI on every circuit in the house.

Key word is could.

Do AFCIs actually do their prescribed function effectively?

They highlight bad appliance design especially hard, while also being somewhat difficult to pinpoint due to the design of many electrical systems.

Arc detection is also basically somewhat complex RF processing, so there are multiple approaches to it and implementations vary.

Plus (detected) arcs are common with for example brushed motors.

Maybe there's something else the person you replied to would like to highlight, but I wouldn't call them a money grab, just made difficult due to some past choices.

GFCIs have a simple and well defined function. What is the current through one lead? What is the current through the other lead? Do they differ by more than x amount? If so, trip.

AFCIs are a whole different thing - the plug is trying to predict when arcing is happening somewhere downstream of it and it has very little in the way of 'processing' power to do it, so generally there is a classical filter that is designed to detect the characteristic harmonics of the current waveform that are inherent to an arcing condition. When you experience a sharp upward or downward step in power draw you introduce harmonics, when you have capacitive coupling between SMPS you introduce harmonics, motors often introduce harmonics, etc.

There's like a zillion things that can create AFCI trip conditions and cause spurious trips and frustration for users, and there's very few documented cases of them doing the thing they're supposed to do. I think it's a case of someone being well intentioned but releasing regulatory guidance to use a product that isn't quite there in terms of technology maturity.

AFCIs are just The Man trying to stop us running Tesla coils.

Agreed on AFCI circuit breakers! They are now mandatory for all 15-20 amp light and plug circuits on new construction where I live - although breakers for large appliances do not require them. But I have several portable tools (eg a carpet cleaner) which will make an AFCI breaker trip every time. AFCI circuit breakers seem to be more fragile (read the box: much smaller range of acceptable heat and limited number of duty cycles) - I apparently killed one just by tripping it repeatedly. And while a regular 15 amp breaker is a few bucks, the CAFCI breaker I'm supposed to use is $45...

Not an electrician, but an observer of tradespeople at r/electricians.

There are definitely bad feelings about these AFCI breakers. The feeling is that the code mandate for AFCI got out front of the reliability of actually-produced AFCI's, and actually-in-use products like blenders that may have small "arcing". This results in expensive call-backs from unhappy customers who are getting nuisance trips.

There are other downsides. For example, actually finding a two-pole or AFCI breaker or, worse, a combination AFCI/GFCI breaker is not so easy.

it is nearly impossible, IME. Good luck finding AFCI 20amp 2 poles for doing shared neutral 120v circuits on a 14/3 wire.

I recently installed some new circuits and was able to find them, but strangely it was $20 or more per circuit cheaper to get an AFCI/GFCI outlet and a regular breaker instead of combo breakers.

Michigan is an exception. No AFCI required.

Is there a site that show what states have adopted what version? looking at my states webpage the official adopted code for my state is NFPA 70 - National Electrical Code, 2008 Edition.

AFCI trips on the smallest thing. Turning on my blender or microwave tripped it. I ended up downgrading to just GFCI in frustration.

Brushed motors in particular are largely indistinguishable from an arc fault. Lots of home motors (in vacuum cleaners, fans, blenders, food processors, garbage disposals, blah blah blah) use them.

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