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-   -   AFCI vs GFCI Receptacle for Bedroom (http://www.houserepairtalk.com/f9/afci-vs-gfci-receptacle-bedroom-17334/)

curtish 02-09-2014 01:53 PM

AFCI vs GFCI Receptacle for Bedroom
 
Hi,

I have an older house built 1938 which has mostly 2-wire BX wiring throughout.

I plan on replacing a few polarized 2-prong outlets to 3-prong... and was considering an AFCI receptacle for added safety. I read that some new construction requires this and also because my daughter uses her hair dryer and curling irons in her room I feel that I'd like the extra protection from circuit overloading / fire... with the older house wiring. The outlets I would be replacing with an AFCI are all BX wire with metal boxes.

My thinking is to us an AFCI receptacle for added safety but then I was reading information that seemed to suggest there were other considerations with how the house was wired from a branch, etc.

QUESTION: is it appropriate to use a AFCI in a bedroom for this purpose?
QUESTION: Should I use an AFCI over a GFCI? Think I saw on this old house once where they used a GFI in a bedroom.

Thanks!

speedy petey 02-09-2014 02:53 PM

Neither AFCI nor GFCI will protect from overload or short circuit. This is the job of the breaker.

Now...GFI on ungrounded circuits DOES provide an added level of safety, AND on the LOAD side of a GFI breaker or receptacle you can install 3-prong receptacles. This is a code complaint alternative to re-wiring.
That said, AFCI will provide an even additional level of safety, but with such older wiring you may get more than normal nuisance tripping.
If you want it all, you can use an AFCI breaker, and a GFI receptacle at the first receptacle in the circuit. One major problem I find in this scenario is that many older homes like yours are wired in such a way that there is a junction box, typically in a basement light or box in the attic, and the rest of the circuit continues from there with several legs. Similar to a wagon wheel hub and spokes. With this wiring setup you CANNOT use the LINE and LOAD function of a GFI receptacle. You'd need a GFI at nearly every spot.
Using a GFI breaker, and NOT an AFCI at all would solve this problem and still add a decent level of safety over what you have now..

Wuzzat? 02-10-2014 08:33 AM

My wife has a hair dryer with a GFCI built into the plug and the wall outlet is also a GFCI. So, with these two GFCIs cascaded we get nuisance tripping - but - always with the wall outlet and never with the dryer plug.

I guess the dryer plug is less sensitive or maybe it doesn't work at all.
Testing the plug GFCI would require me to run a 16 kilo-ohm resistor from the dryer insides to a ground. Since we already have a GFCI in the wall this is a pretty low priority job for me.

Anyway, since organizations are somewhat less likely to BS the Patent Office than the general public
I'd do an online search for patents for GFCI designs that specifically address this tripping problem and
hopefully you can find a GFCI in a store nearby that incorporates the improved design.
But, everybody wants to use up old stock first.

curtish 02-10-2014 11:21 AM

Thanks guys,

I hear what you are saying but I don't fully understand why an AFCI Receptacle is of no value over a GFI in this situation... (by the way, the curling iron does not have a GFI oddly enough)

I get that the AFCI can't prevent a circuit overload and that would be the function of the circuit breaker.

EDIT: It occurred to me that I may be confusing two different kinds of AFCIs. As you know, there are Outlet AFCI Receptacles and AFCI Breakers. I was considering a Outlet AFCI Receptacle...

QUESTION: What is the proper use of an AFCI receptacle? Should I just be replacing my breaker with a AFCI breaker instead?

If I can get a AFCI Breaker to replace my SQUARE D breaker, should I assume that would protect the entire circuit? that would be preferred since the same circuit feeds 3 bedrooms.

From my reading over at Leviton, it would seemed that AFCI Receptacle have circuitry specifically designed to reduce the chance of shorts... whereas a GFI is used to reduce shocks from a poor ground or near water surfaces...

I'm not worried so much about shocks... I'm thinking more about shorts and a possible poor ground that wouldn't trip the breaker

Thanks, I think I know my answer just trying to be clear.

Wuzzat? 02-11-2014 09:05 AM

Quote:

Originally Posted by curtish (Post 100031)
I was considering a Outlet AFCI Receptacle...

If you can get such a thing I'd prefer that over a breaker because it will be much easier to troubleshoot.

An arc is supposed to be a fourth state of matter: plasma, as distinguished from solid, liquid or gas.
These gadgets are supposed to distinguish between "good" arcs and "bad" arcs. Practically what this means is that this device will be telling you when to replace your arc-producing appliances and fixtures: motors with brushes and commutators, and switches.
I'd prefer to make my own judgements of when things are worn out.

The accuracy of measuring or testing instruments is supposed to be traceable to the NIST, so I asked them if they have "a standard arc", something to compare to.
They did not reply, probably because it would be bad for business to have official opinions made public about good or bad arcs, false positives/negatives and all kinds of other worms that would climb out of this can.

I doubt that you will find the truth about how reliable these things are and if they significantly improve fire safety over the base rate of fire danger here in the U.S..
If I were close to a Tech Library I'd look in the IEEE Transactions on Power or whatever journal is likely to post a study on this.
Online patent texts may also talk about the shortcomings of earlier AFCI designs.

nealtw 02-11-2014 10:11 AM

If you were going to protect the wiring with AFCI you would want to change the breakers to include all the wires not just the outlet. With and older house that is likely going to include a new breaker box.

curtish 02-11-2014 11:09 AM

Sounds like there are no solid believers in AFCI receptacles for older homes... as it would only protect a device plugged into the AFCI outlet and any extension cords for shorts.

Although I'm wanting to shore up my older wiring without rewiring the house, seems like a waste of money unless I can determine where the first outlet of a supply branch is and whether there was "wagon wheel hub" extensions in the house.

I have already run new dedicated 20 amp circuits to bedroom A/Cs and bathrooms. Perhaps I shouldn't worry too much about the other older wiring in the walls.

I think that's correct anyway, perhaps I will just install a GFI as Speedy Petey recommends.

Thanks for the advice.

nealtw 02-11-2014 11:38 AM

You might spend some time and check the condition of the wires in boxes and map the system then you could intall welll placed gfis.
In an older house you likely have places that you may be concerned about, extention cords and the like then maybe an afci outlet would not be a bad idea.
The other thing to watch for in old house. If you had a short from a wire to cast iron or copper or steel pipe it would be grounded and blow the fuse or breaker, but as time goes by and people change parts of the plumbing to plastic and ground is lost. A pipe could be live for years waiting to kill someone.

gottodo1 02-19-2014 05:35 AM

Wuzzat, I'm sure there's information about an Arc. Do you know what AFCI's are certified against, is it an ANSI, ISO etc etc standard? I can find out what the criteria are or at least how they test it if they don't have design criteria.

Wuzzat? 02-19-2014 07:48 AM

Quote:

Originally Posted by gottodo1 (Post 100600)
Wuzzat, I'm sure there's information about an Arc. Do you know what AFCI's are certified against, is it an ANSI, ISO etc etc standard? I can find out what the criteria are or at least how they test it if they don't have design criteria.

I was unable to find it.
And as I recall, even the online patents that I searched did not shed much light on exactly how their "signature analysis" is supposed to work. The maker can always claim a Proprietary Method.

Surely at the end of the assembly line these devices are tested, go/no-go, before sold. I'd hope they are tested against bad arcs and good arcs, but I'd like to see that test setup. And how closely do the test arcs match the real world?

And it's not just bad arcs. If you know some programming languages, apparently AFCIs work according to
IF (more than 5A flowing AND bad arc) THEN trip ELSE (don't bother the home owner).
The current flow is another variable in this arc detection strategy.

More generally, and knowing about this
http://en.wikipedia.org/wiki/Sensitivity_and_specificity
as a limit on how well these things can possibly work, I'd like to see the numbers for AFCIs. Numbers are harder to spin.

Let's say you have a genuine bad arc inside a lamp switch.
Well, the switch is housed in a fire resistant shell and a bad switch will make itself known with how the bulb behaves.
So how many house fires did we have before these things and how many do we have now?

With GFCIs there is probably a bias in favor of tripping if the thing is in doubt. I've never heard complaints about a GFCI not tripping and the person continuing to get a shock.


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