Thermally protected outlets

[Robert Green]

Does anyone have any working experience with thermally protected outlets like these:

The information seems a little off:

I own several AFCI's in standard outlet form, so . . .

[philoÂÂ]

The AFCI can distinguish between a "normal" arc such as would be detected when a circuit is energized as compared to arcing conditions that would be caused by faults. Paragraph 7 states (in a perhaps confusing way) that it does not protect against a "glowing condition" which the thermally protected outlet is specifically designed to handle.

Possibly you were thrown by their use of the word "signature"?

I have a good friend who once had a job designing circuit breakers and he explained to me the amount of sophistication those devices have. The AFCI's are designed to recognize wave-form variations other than overloads and "trip" if such a fault is detected. They cannot remotely detect heat though...and thus the reason for the thermally protected outlet.

BTW: He explained to me the an AC breaker "trips" at the zero point of the sine wave and FWIW a completely different type of device from a DC breaker.

[Robert Green]

Sorry, I was unclear. The site said AFCI's were only available in breaker box form, not outlet form. Since I have a number of AFCI outlets I know what they're saying is either false or way out of date. Either way, it makes me suspicious about all the other claims on the site if they got that wrong.

Yes, we've have a lot of discussion here about how AFCI's work. I believe it was postulated that the outlets cost half of what an equivalent breaker costs because the breakers have to be small enough to fit in a circuit breaker slot. There's a lot more room for the arc detecting electronics in an AFCI outlet.

Agreed. The modern circuit breaker is a very different beast than the first breakers to hit the market which, IIRC, were basically bi-metallic strips that broke contact when an overcurrent heated them to the tripping point. I believe the problem with those sorts of breakers is that they can become welded in the closed position. Newer breakers work magnetically: current through the breaker flows through a small magnetic coil. At a certain threshold, the magnetic field is strong enough to actuate the trip arm, tripping the breaker. This detection method is almost instantaneous and doesn't have the contact welding problem of older breaker designs.

AFCI breakers incorporate not only the elements of a standard circuit breaker, but elements of GFCI's in addition to arc detection capabilities. Despite all those capabilities they may be unable to detect a condition where a space heater or toaster plug is only partially plugged in, creating a glowing connection.

I bought the AFCI outlets primarily to make sure that the space heaters I use don't start a fire through a bad, high-current connection. However in reading some of what Bud posted I believe I would have been better off with thermally protected outlets.

Now that I know about them and the limitations of AFCI outlets I will be adding thermally protected outlets to all of the circuits where devices that draw more than 10A are plugged in. (And yet more annotations to the circuit panel legend on the inside of the panel door reminding me to check those outlets if the space heaters or the toaster oven stops working!) At least they are less than half the price of the AFCI outlets. I will equip all potentially high current outlets with an AFCI at the first outlet in the branch and use TPO's at each outlet that serves space heaters, toasters, hairdryers, etc.

Ideally, the AFCI outlets should incorporate thermal sensors to protect against glowing connections but there may not be enough room in this generation of AFCI outlets to add that sort of protection.

Thanks for your input, Philo.

[philoÂÂ]

All very interesting, I'll have to check to see what's available the next time I'm in a hardware store...looks like the technology is changing pretty fast.

As of late I've been working on the lighting in my old house and phasing out the incandescent bulbs.

[bud--]

In addition to that out of date information, the BSafe site has information on a product with planned delivery 2010. Seems like they could keep the site up to date.

FAQ 10 Can a BSafe outlet be "daisy chained" for wiring outlets downstream? It appears that the outlet has only one set of terminals, so a connection to a downstream load is made with external wirenuts. Wire-through connections with loose connections cause some of the glowing connections. BSafe just avoids wire-through. (This is also in FAQ 2.)

FAQ 5 AFCIs can't detect a glowing connection? The UL investigation for Cutler Hammer found that the ground fault feature in AFCIs may (or may not) detect a glowing connection that carbonizes the plastic resulting in a path to ground in the receptacle.

The UL investigation for Cutler Hammer is at: May 31, 2001 UL SPECIAL SERVICES INVESTIGATION ON BRANCH/FEEDER ARC FAULT CIRCUIT INTERRUPTER INCORPORATING EQUIPMENT GROUND FAULT PROTECTION

Another piece from Cutler Hammer

talks about a UL carbonized path test for AFCIs, and glowing connections.

AFCI detection can be done without ground fault detection - then the neutral would probably not have to connect through the AFCI. The ground fault feature (usually at 30 mA) adds to the fault problems the AFCI will detect.

I doubt the UL test for the BSafe receptacles tests the thermal feature.

That feature may provide additional protection. It should be a lot faster than an AFCI trip on ground fault through carbonized plastic.

[bud--]

AFCIs may (or may not) trip eventually on a glowing connection.

IMHO there is a lot more room in an AFCI circuit breaker. The second link in another post shows the inside of an AFCI breaker

The breaker also trips on overload and shorts, part of the cost. But you need to get an AFCI breaker from the manufacturer of the panel, a controlled market.

Electronic switches can open at zero voltage (or zero current, which is not the same time with an inductive load). The circuit breakers we use have a mechanical trip and are not likely to open at a zero crossing. But zero crossings help extinguish the arc from breaker contacts opening. DC arcs are harder to extinguish. If contacts have both AC and DC ratings the DC ratings are almost certainly lower voltage and/or current.

I don't know of major differences in DC breakers. DC switches are fast acting "snap" switches. AC switches can be slower "silent" - the zero crossings help extinguish the arc. I think AC breaker operate fast. There are techniques for blowing-out the arc which may be used more on a DC breaker.

The circuit breakers we use are thermal-magnetic (and have been for a long time). Trips on overload are thermal (bimetal). For high fault currents the "instantaneous" trip is magnetic. (Instantaneous means there is no intentional time delay.) Adding AFCI or GFCI features, the trip is magnetic through a solenoid coil that unlatches the breaker.

If they work like the web page says they should increase the protection. (I don't think a very high percentage of failures are glowing connections at a receptacle.)

As you probably read, if they trip they can't be reset.

[Robert Green]

That's an interesting point. I looked at both units (actually, I compared a typical non AFCI breaker because I had a spare lying around with the dimensions of the AFCI breaker) and concluded they contain roughly the same number of cubic inches of volume, albeit in very different geometries. The AFCI breaker has to be a circuit breaker as well, so some of the internal space is already spoken for. I might have to break out the vernier calipers for more accurate measurements. (-:

Hmm. That would probably better explain the serious cost differential. The issues with the AFCI breakers, aside from cost, is that they all take pigtails and, from what a poster said in another thread, they tend to run warm since they have to incorporate a power supply for the arc detection electronics. In my circuit panel, the last thing I need is to have to make more connections to the neutral bar(s). So I played around with one and then decided that outlets were the way to go because of cost and pigtail requirements. And because I knew where the outlet closest to the panel was by simple visual inspection so protecting all downstream outlets was simple.

Now that I can hunt down the first outlet in the older circuits with my X-10 meter, I think it was the right decision and will save $100's if I choose to protect all the circuits (I probably won't - I am no longer convinced they're the hot stuff they have been made out to be).

That explains something I've always wondered about - why switch ratings and such always seemed to indicate DC was more powerful. I suppose when you consider the total number of seconds that AC is at 0 volts it makes a difference. Interesting.

More reading by me is definitely required here. I didn't know there was going to be homework. )-:

Thanks. I can see my understanding of their function was incomplete. I am sure I read that one of the reasons the magnetic operation was adding was to prevent the welding of the bimetallic contacts when faced with extremely high trip currents. Even *more* reading required! (Not that I will retain anything I learn about it. Oh well.)

capabilities.

I have two melted outlets that inspired this whole journey. It would be nice to know if they would have tripped the AFCI outlets instead of melting.

No, I just posted that as an example and stopped reading when they claimed AFCI outlets didn't exist. That's good to know. I suppose the price is low enough that it's not much of an issue, but I would have expected them to operate like GFCI/AFCI outlets with a reset button. A little disappointing. Maybe in the four years or so that have passed since there have been improvements in thermally protected outlets and resetability is possible. Before I buy any TPO's I will be sure to do a more thorough scan of what's out there.

Thanks for your inputs, Philo and Bud.

[Robert Green]

Today the big multipage Harbor Freight catalog arrived and I looked through it and decided I didn't really need *anything* (which is quite something - there's usually always some doodad I can't resist). The saddest part about not needing anything is that I've already purchased $100's of dubious stuff that I may never use but somehow feel that I might. Wait - step drills! - don't have any and someday I may need to enlarge a pre-existing hole. Someday. Let's see how much money I actually spend just going to HF for a set of drills.

[Robert Green]

Who knows if they're even still operating? Last night I went to order take out from a local Chinese place that's been here since I got my master's - about 30 years ago - and got the do DO DEE sound of "the number you have dialed is not in service." Checking Yelp confirmed they are gone with the wind, in just one week since I last ordered from them just like the little family owned Thai restaurant of equal age. One day, they just weren't there anymore and the new restaurant was selling papusas. Oh well. Tempus fugit.

That's pretty ironic.

I am not sure I follow. Is this saying that I could connect the AFCI breakers without the pigtails and still have arc but not ground fault protection? Surely this would give the AHJ conniptions.

One thing I discovered a long time ago with worklights from China is that there's a thriving market in China for forged UL hologram stickers. Is it really possibly that the UL would bypass testing the safety function that would be the reason people bought the TPO in the first place? That's pretty incredible.

The price is low enough that I will probably pick up a few to test, although the testing is going to be destructive. If it does catch a deliberately "half plugged" line cord then I suppose I'll use them in the high current outlets in the kitchen and where I have space heaters operating. The melted outlets I've experienced probably would not have started fires (fingers crosses) but they did make an awful smell and scared my wife quite a bit. There's just not a lot of flammable material inside outlet boxes - mostly meltable stuff.

Thanks for your input again, Bud. This has been a most informative thread for me.

[Robert Green]

You know a guy like me that measures the cold water inlet temperature is going to break out the vernier calipers . . . (-:

The Leviton AFCI outlet is 1.5" deep, 1.5" wide and 2.5" tall = 5.625ci of space.

The Square D QO breaker is 2.5" deep, 3" tall and .75" thick = 5.625ci of space.

Doesn't seem possible but we both were wrong. (-: Same room inside each. Measurements are approximate because of the designs. The outlet has a "pod" behind the topmost outlet that's .25 thick and 1" square and will seriously crowd a shallow outlet box, but that's offset by some hollows in the design. I suppose I could always build a little tub and submerge them both, Archimedes-style, to calculate the true displacement from the overflow but that's not going to happen. I wouldn't have believed they were so similar in volume had I not measured them.

So it definitely seems that you're right about the cost differential being far more attributable to proprietary design than size since there's no appreciable size difference.

[bud--]

My thinking is in a breaker you can move the current-trip mechanism to the side (as was done in an internal picture in my second link). A receptacle has contacts for the plug all over the inside. A GFCI I looked inside put the trip solenoid and plunger between the ground contacts for the plug.

Wouldn't think you would need another neutral position. The circuit needs a neutral connection, but it goes through the AFCI. The AFCI neutral replaces the circuit neutral at the neutral bar.

AFCIs are also intended to protect the circuit wiring. For new construction, protection can be an AFCI receptacle with the rest of the circuit wired through it (like you did), but the wiring from panel to receptacle has to be in some of the metal-walled wiring methods.

Wiring through the first receptacle actually protects the upstream wiring from a series arc (loose connection) since the arc current will flow through the AFCI (to the load) and it will trip.

Cute idea.

I would figure out what is on the circuit and make a guess which receptacle is first - a PITA. And something else could be first, like a ceiling light box.

Would be interesting to see data on how many fires are caused by arcs vs. glowing connections.

Code change proposals are often denied because there is no data to show the change would result in safer wiring. I have never seen the data to support AFCIs. There was a change proposal to allow smoke detectors in bedrooms to not be on an AFCI protected circuit. (At that time only bedrooms had to be AFCI protected.) It was denied for a reason something like there was no data to show that would be safer. But the code panel had no data to show AFCIs were a significant fire source. (The next NEC greatly expanded the locations where AFCI protection is required.) (I believe that line-operated smoke alarms that are on AFCI circuits must have a battery backup.)

[bud--]

It is easier to make an AFCI that does not have ground fault protection; I don't see why the neutral would have to go through then. But the UL standard requires ground fault protection, which means the neutral has to go through the AFCI (else it would trip on any load).

UL tests to a standard. I doubt the standard for receptacles has any tests for a thermal trip. The standard could be revised, or a different standard written, but I doubt that has happened.

Hey - great idea for a new device - a SFCI (stink-fault-circuit-interrupter).

[philoÂÂ]

I have quite a few step drills, they come in handy for light jobs such as sheet metal. If you get one, don't use them for any heavy duty drilling.

Speaking about *not* getting anything...my wife tells me she managed to get in and out of Macy's without buying anything.

THat must be a first.

[Robert Green]

Clearly figuring out which device is actually more spacious is something I'll leave to someone with the actual engineering specs of both devices and LOTS of time on their hands. I was just surprised that they were so equal in my rough measurements.

The images at the top all have pigtails. Mine had a pigtail. I assume it's looking for some difference in something but I was unable to find out why they required the pigtail the last time I looked. I should have researched it further but that was a dealbreaker and once I discovered the outlets that were much cheaper I didn't care much *why* the pigtails were there.

This time I looked harder for the reason for the pigtails. (-:

(Although this wasn't posted a year ago when I was looking. So it seems they might be there for subpanel use - damn, I guess I can just look at the installation instruction for the breaker.)

says

Which does not inspire confidence but they also say:

Whatever the reason for the pigtails I decided the outlets are a lot easier to deal with. (-:

It seems that the AFCI's don't require more neutral buss bar real estate after all, they just require that the neutral wire from a branch circuit to be directly connected to the breaker (which has two terminals) and then the pigtail wire from the breaker goes to the spot formerly occupied by the neutral branch wire on the neutral buss bar.

I assume that's because of the fear that the unprotected segment of wire will spark so they contain in conduit which makes the outlet method less cost attractive in new work, as perhaps it should be. Protection of branch circuits is best done at the panel, I would think.

I assume the conduit (or is that word misapplied - is "metal-walled" more inclusive of other types of wiring?) is required to protect against other types of arcs that can occur?

In practice, there's often a device in a circuit that attenuates nearby X-10 signals so it's not foolproof. It's a better strategy than pulling all the outlets, though. Still not sure proceeding any further with AFCI's is worth the time or expense. I'll do the circuits I added, but not the older ones (which probably need them more)

I have a screw in outlet adapter for just those sorts of occasions. I once had a fluorescent shop light that had been very X-10 friendly for years suddenly starting "singing" with over a 1 volt noise emission precisely at X-10 transmission frequency. One volt was a lot for stock X-10 to contend with and since that light was very close to the breaker panel, electrically, it stomped most X-10 transmissions.

There's a lot of clamor about it here and I think they're talking about you (-:

They do make an interesting point about GFCI's going through the same birth pangs:

In other words, Bud, come back in 20 years and they'll tell you if it was all worth it.

[Robert Green]

I just saw this message - the dog unsubbed me from the group which did a lot of nasty things. It explains the pigtail. Thanks.

With the evidence for AFCI being so sketchy, I am sure there's even less evidence that TPO's prevent fires.

Don't laugh. A meltdown of an early model Lights Of America (made in China) CFL burned out with a horrific smell that freaked my wife out for days. Spousal Foul odor Circuit Interrupter. No fire and no realistic probability of one, but the stink was sure a black mark for CFLs in her book.

[bud--]

The size of the AFCI receptacle can make it harder to install if there are a lot of wires in the box. The AFCI is larger than a simple receptacle. (Same is true for a GFCI receptacle.)

For determining how many wires can connect to a box, a receptacle or switch volume is factored in. I am surprised the larger volume of a GFCI/AFCI is not accounted for.

AFCIs require the neutral be wired though the device for the same reason GFCIs do. For the ground fault feature the AFCI runs the hot and neutral through a current transformer and looks at the difference in the current between them. If it is 30 mA or more the AFCI trips.

Also may include metal sheathed cable - MC and AC.

It adds safety for parallel arcs (L-N, L-G). With romex you can get a parallel arc from a nail or screw driven through the cable. A lot harder to do with metal walled, and the metal provides some fire protection if you manage to do it. There is much higher current available for parallel arcs.

[Robert Green]

I am probably going to pass. I am trying not to acquire any more junk unless the need is urgent.

I was surprised at all the stuff my wife bought at HF. Garden stuff, dollies, etc.

[Robert Green]

Not only is it larger, one end is 1/4" thicker than the other, so you have some space to tuck wires but not an awful lot. I had no troubles with new(ish) 12/2 Romex using them as pass throughs but this is new work and I always try to use roomy metal boxes for RTE - room to expand. I've never had to take stuff OUT of boxes. The only time I gained any space in a wiring box was replacing the failing 40 year old light switches with newer ones that were remarkably small in comparison. But soon afterward I was cramming large X-10 devices into smallish boxes. Fortunately they used pigtails which meant wire nuts but a lot of flexibility in wire cramming. Unfortunately wire nutting stranded and solid wire is an artform and skill at it evolves slowly. )-:

For the really critical stuff I once chiseled out the whole thing but that turned out to be a project that I immensely underestimated, time-wise and since then I tend to choose any other method. Even installing a new box in a plaster and lathe wall is easier than working around an old box. The damn Reader's Digest book made it look a lot simpler than it turned out to be. I can still see the faint outlines of the canal I dug to string new wire after the old one broke right at the entrance to the switchbox. The front porch light switch is where I learned to be very gentle with old wiring and the toilet shutoff valve was where I learned to be very gentle with old plumbing.

Really? I assume you're talking NEC.

I know of several problem outlet boxes in My Very Old House that those units would not fit into because X-10 devices of similar dimensions did not fit. Twisting and fussing with those old, cloth covered wires is very dicey business if you hate chiseling plaster as much as I do.

"Some difference in something" I was right! (-: So the effect is that the neutral of the load isn't mixed into the pool of shared neutrals directly - it has to pass through the breaker so the GFCI component can determine if the neutral from the load is or is not at ground potential. I assume that is what the white pigtail is always at because it's connected to the neutral buss bar which is bonded to ground at the panel.

The latest thing I read about AFCI operation is that they captured the signatures of over 100 different arc sources and try to pattern match any detected arc to their internal arc sig library. That's how they exclude the arcs produced by motors, switch contacts, vacuum cleaners and other "good arc" creators.

Rather than my inept paraphrasing, I'll just post the URL and the abstract.

A Method for Parallel Arc Fault Detection and Identification

Some interesting diagrams . . .

Was it ever called armored cable or BX? That's what I seem to remember from NYC wiring codes. That and my poor Dad regularly cutting himself on that coiled sheath.

Is that because L and N are directly connected with no intervening load?

[bud--]

AC is "armored cable" and a brand name is BX (allegedly made by the Bronx Cable company in Bronx NY). I've usually heard it called BX.

Romex was developed by the Rome Wire Company in Rome NY. It is another brand name that has become a common name for the product (which is NM).

Yup.

[Robert Green]

[re: ]

Worse than that, it appears you can't even buy them. They list Smarthome as a distributor but they don't seem to sell them. I'll call around in the AM.

I wanted to get a few for testing for a Hometoys article to see whether the thermal outlet or the AFCI outlet upstream (if either) would trip if I plugged in a 1500W space heater into one of a (preburned ) outlet strip's remaining good outlets part way. That's what's cause two outlet meltdowns so far - accidental partial insertions - so I know there's a need for the protection.

The question is whether it will actually do what it says. If it exists. That 2010 date on the website gives me a queasy feeling . . .