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Sources of fire hazards:
–rodents chewing romex. Seen it in several renovations. A general contractor friend who lives in a rural area had his house half burn down. The fire inspector verdict–a rodent chewed the jacket and insulation and this resulted in an arcing short. The new arc fault circuit interrupters are designed to protect against arcing faults.
–unqualified people messing with the wiring. Saw a twin, 100 watt security floodlight on a motion sensor that was wired into a garage circuit with bell wire (20 gage, red-and-white). When I asked the home owner who had put in the fixture, she proudly reported that her 20-something grandson had done it.
–people who think that electrical wiring lasts forever. As Jeff Clarke discovered with the waterpipe ground, things do wear out. Busbar and breaker terminal screws loosen from repeated heat-cool cycles. It’s a good idea to have an electrical “checkup” (by a specialist/electrician) on any building that’s 30 years old or older, even if there’s no overt problem. That’s not a easy sell to your average homeowner.
As for the metal box question, yes, they are safer. That’s why they are required in places of assembly and certain other occupancies.
The best wiring method as far as I’m concerned is conduit. Highly safe, very flexible (pull in any wires you need at any time).
Replies
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On the rodent chewing: recently replace about six feet of romex in an attic where squirrels had chewed all the sheathing and insulation away, leaving only three bare copper wires. Homeowner tripped the breaker every time he turned on the outside lights. Luckily there was direct hot-to-ground contact so no continuous arcing occurred.
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As a firefighter by trade I'll throw in my 2 cents. I tend to agree with Bill about the socioeconomic comment. I have run many more electrical fires on older rundown homes, than homes built in, say, the last 20 years. I think a lot has to do with the abuses the house has seen rather than whether it has plastic boxes. I have seen pennies put behind screw-in fuses. "The space heater kept blowing the fuse!" IMHO adequate wiring, with proper overcurrent protection, properly installed and used for the proper purpose will seldom fail to the extent of causing a fire. The one exception I have seen around here is aluminum wiring. We burned several homes in a tract that were all wired with aluminum. It seems that on hot summer days, the wiring in the attic to the A/C unit would overheat and presto; Instant ripper.
I wired my home with 12 ga. 20 amp. I used good "spec grade" recepticles and plastic boxes. I feel comfortable that it will take whatever I throw at it, although I do tend to err on the side of safety. Call it a hazard of the job.
*Bill, I think you're mistaken... EMT conduit must include a green ground conductor in the run... and be made in with ground screws at each box.Overall... knob and tube (for a 2-conductor system) was safe. Very safe, as the conductors were separated. Problems from a fire investigative viewpoint came where the "old work" was made in with "new work" often 14 ga. romex. Add a 30 or so amp slow-blow screw-in fuse... well, you get the drift.
*Good move.
*I thought that rigid, imc, and emt were all permitted to be used as the ground. Perhaps that has changed; the reorganization of the '99 NEC is a little disorientating. I think that article 250-118 says that emt can be used - but I'll admit I'm not positive. Also, the articles on non-metalic tubing note that a separte ground conductor is required; not so for metalic. (Flexible metallic being a special case.) If you think I'm wrong - please help me find it in the NEC. Thanks in advance.That being said, I think that separate grounding conductors are a good thisng, should be required, and are required by amendment in may jurisdictions (mine included - I voted for it as a member of an advisory panel to teh building codes department.) Also, most electrical engineers I have workedwith require a separte conductor.My search in the NEC reminded me that the box fill issue with plastic boxes is the pigtails that are necessary for the grounds if there are downstream devices - the requirement that removing a device cannot interupt downstream grounding. Thus, the ground of the romex in and out and a pigtail from the device are required to be joined whereas in a metal box, both romex grounds can be connected to the box and the (appropriate) device is grounded - no wire nut and pigtail.All that said, I've used emt, metal boxes (all 4X4 deep boxes with single gang plaster rings), separate ground conductors in the emt, and pigtails to each device. Belts, suspenders, the whole shebang.
*Overkill kills too...something I learned...One note from one of my inspectors...use all the 12 wire you desire but he still wants you to use 15a breakers where called for, (bedrooms, receptacles for lighting, etc) as to protect lamp wire shorting etc. things that are plugged in....And only use 20a breakers where they are called for...appliance circuits, kitchen counter, bath....near the stream, thinking it's definitely time to check my sealed attic for pests and chewed wire...maybe bx would be better in rodent prone areas...aj
*Thanks A.J. I've been kicking that around. 20 amp seems like a lot for general lighting circuits. I knew that it was o.k. for my 12 ga., but I hadn't thought about those 18 ga. zip cords on lamps. I think I'll pick up some 15 amp breakers while I'm in the big town tomorrow.
*Always glad to share the liter side, near the stream,aj
*Very good point AJ...A 20A receptacle or 2 in the garage/workshop is kinda nice though...
*I agree...put them where you need them,,,use the twenty amp receptacles with the extra side slot to ease in identifying them or mark em if ya don/t mind the mark ...Mine are in my garage.near the stream, raining raining rainingaj
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Food for thought: Table lamp with 100W bulb pulls less than 1 amp. 18ga cord is adequate.Short in the lamp? You'll pass several hundred amps though the 18ga and the 12ga, but only for a few microseconds until the OCPD breaks the circuit. Final answer? 15 or 20 amp breaker doesn't matter.
Fire hazard occurs because: a)18ga cord is frayed and arcs, b)12A heater is plugged into 18ga extension cord, c)30A breaker is used on 14ga wire to run a 25A load, d)loose connections anywhere.
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15a breakers and smoke detectors in bedrooms for me no matter what ya say.
near the stream,
aj
*I was surprised that our furnace called for a 15-amp fuse quite specifically -- I decided to read the manual (!) when i wired it for the dedicated circuit it was supposed to have. For that matter, the code tells you to give the refrigerator and garbage disposer their own circuits, but they don't need anything near 20. When a motor starts to go bad it may decide to get really hot first.It's probably best to install a breaker based on the maximum load plus some margin. I think 15 versus 20 IS a big difference -- that over 500 watts right there, and 500 extra watts means that much more heat, that much more risk of fire before the breaker even knows there's anything wrong. The fires aren't coming from sudden catatrophic overloads -- a recent experience with a berserk GFCI showed me that 14-guage Romex will simply melt even before the plastic melts or the (brand-new) 15-amp breaker goes (the GFCI was flipping on and off rapidly, so the breaker didn't trip even though the load was abnormally high -- here's where an AFCI would be nice). Despite the interesting charred wire, I don't think it would have started a fire.)
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>Can anyone answer this question. My wife's uncle hooks up high voltage systems for skyscrapers in New York City and I was picking his brain about the 15 amp/20 amp issue and he advised (as uncles do) that he never wasted his time with 14 wire. That 12 wire, even for circuts that wouldn't be running 20 amps was the way to go due to the risk that at some point in the future, someone would use the circut in an inappropriate manner and having exceeded the exspected use of the circut in terms of hardware would prevent failure. Does it depend on the outlet or the breaker? ( I am not an electricion so forgive me if I make conceptual mistakes)
>I'm trying to understand what would be most likely to burn the wire. I thought the aplaince only draws as much power as requrired to run it; that if you had 20 amp outlet/wire/breaker there would be no problem as long as the appliance/light load didn't exceed 20 amps. Why would you use a 15 amp outlet in this case. Why limit your self or risk that the outlet would fail if over taxed in some way. Isn't it that if you have 20 amps of power potential, all your hookups should be able to handle that as well? I feel I have fuzzy comprehension of this load to hardward issue. Can someone please clarify? My Sunset "Easy Electrical for Morons" was of no help. Thanks Chris
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Chris....I'll give it my best....
Circuits are designed by taking your average lights and appliances and their average locations of use, into consideration ...residentially speaking....
Lighting circuits are low amp and use 15a breakers (usually have low amp items plugged in) Appliance circuits are higher amp and use 20a breakers(most dedicated though on kitchen counters there may be more than one receptacle on a 20a appliance circuit.)
0-Bedroom receptacles are generally thought of as lighting circuits for lamps to be plugged into. A few lightbulbs draw very little amps...So too with tvs, radios, computers. However computer desk areas seem to need a zillion plugins. Most people use the plug strips with surge protection built in. It's still nice to service these areas with an extra circuit and hopefully "clean" power.
1-Any one appliance will usually draw less than 15amps continuous...
2-So when we string six outlets together in a bedroom circuit, we are serving an approximate sqftge of area to be lit, etc. One outlet every six feet, rule of thumb(there's more to it than that), lots of outlets near computer/desks(and maybe an extra circuit or two).
3-Twelve wire can be used in place of 14 and often is...The limit of the breaker for a bedroom lighting circuit is best at 15a, so a 15a breaker should be installed regardless of wire size.
b The breaker is limiting all six receptacles and the 12 or 14 wire to a max of 15a of load. This 15a limit helps protect the home from problems past the receptacle(problems with electrical items and wire plugged into a receptacle.) and of course it is protecting your choice of either 12 or 14 wire along with your 15 or 20a rated receptacles. The basic circuit breaker protection is for overloading causing overheating causing fire.
3- The whole circuit cares not that a larger wire was used except for the following two points...point 1)As Uncle Inlaw says, people do add on to circuits and do make mistakes and or wish a twelve wire was run to begin with....This however is not the best idea as the circuit still should never be changed to 20a (unless you have triplet girls that are starting to blow dry their hair all at once) and point 2) Long runs of wire are prone voltage drop...12 wire will handle 15a using more feet than 14 wire.
So to sum up all...Run enough 15a circuits with either wire size to handle all the anticipated 15a loads...If you want to really understand this you may have to spend a bit more time studying and working with electricity...I still really have to chew over every move I make when designing or working on electrical challenges but I do really enjoy it, probably as much as any of the trades. I learned tons from super nice inspectors and firemen/part time electricians...
near the electrons (or the wholes if you're into quantum physics),
aj
*A couple of almost related short blurbs on the dangers of improper fuse substitution and on the dangers of high voltage induction (from a website on how the Darwinian un-fit are eliminated from the breeding pool...):http://www.iit.edu/~sinfook/darwin7.htmlhttp://www.iit.edu/~sinfook/darwin3.html
*LMAO!!!Thanks Caseyaj
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I appreciate the in depth response. I need a bit of clarification still. In section 3, in bold, you seem to be saying that even if you are using 12 wire and even if you have up to a 20 amp outlet, you still need the 15 amp breaker. The reason being that unless you are running your 13 amp Skisaw and the computer off the same circus, you'd probably never need all 15 maps at once, but if you did, it's better to trip on the low side than the high side. The fire risk in this case is the breaker not tripping while the wire or outlet or lamp was burning up due to too much load or some other problem undefined. Is that it? Do I understand you correctly? Thanks so much. Chris.
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Chris...you pretty much are understanding all...The idea is cirlce saws aren't plugged into bedroom lighting receptacles as a norm...lights and other small load devices are the usual...And there's a greater chance at tripping the breaker with these thinly wired, and low amp designed switches...etc...
near the stream helping ya fish; have we caught or limit? I have.
aj
*Gotta love it!I agree with the logic that a shorted lamp would be plenty to trip a 20 amp breaker, but 15 is still more than enough for gen. lighting, so the little margin of safety appeals to me anyway.
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I've also seen smoke detectors checked with a candle. Light the candle, blow it out and let the smoke drift into the detector.
Just be careful with the open flame!
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I need to wire for an electric stove. 25 feet from box to panel. My electrician friend who helped me spec out my cabin (cant get ahold of him) said to use 50amp breaker, 8-3 w/ground wire. My question is - where does the third wire go at the panel? I assume its a 110 for the stove lights/controls but it doesnt seem like it would need a separate breaker just for that.
jl
*Jim...first safety...Your question is so basic that I have a vision of you blowing yourself orbital and messing up my freshly mowed lawn...One hand in the box, one tied behind your back, dry feet, dry shoes on dry wood, do not touch anything in the box.Wires...go to double pole breaker...two of them...the others go under two separate holdowns on the neutral and safety ground bus bar..Main panels ussually have neutral/safety grounds bonded (wired to each other and interchangeable and subpanels are separate...If ya need to know all this, then I would elect to invite friend to dinner early and convince him to give you the lesson in person...And get some DIY books!!! They illustrate all so well.near the blow me to orbit 200a 220v stream,aj
*Thanks AJ, neutral and ground, duh. My other double pole circuits - well, wall heaters, just needed a 12-2 (no neutral). I got the neutral and ground bars wired to each other - all been inspected. Haven't had the PUD run the feeds into my box yet.I'll try not to blow myself up ;-)
*Sounds like you won't be ariving via airmail anytime soon!Glad to help Jim...near the stream with less fall-out anticipated,aj
*Yes Bill, section 250-118 does allow EMT as the grounding conductor. As you mentioned there always seems to be a loose set screw or locknut somewhere.Why nonmetallic box covers are so much more expensive than metal covers is a mystery to me.Please note if a cover mounted receptacle is attached to a surface box the bonding jumper must be installed between the device and the box. A bonding jumper is not required if the receptacle is mounted directly to a surface box or if a grounding type receptacle is used in a flush mount box, but I put them in anyway.For those of you interested there are some very good electrical forums out there. Two are: http://www.electrician.com http://www.contractorcafe.com
*This will be easier:http://www.electrician.comhttp://www.contractorcafe.com
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Are metal receptical and light boxes considered safer than plastic in terms of fire safety?
More generally, what has been your experience with electric fire hazards? I've seen the back of gypsum wallboard charred from where a nail pierced romex behind a wall, but it died in that bay. I've seen melted plastic boxes from an overheated receptical, but it never threatend to start a fire. Newspapers report of homes burned down due to "faulty wiring", but I'd like to know the gory details. What did the electrician do?! Anyone shed some light on sources of information like that?
*I think shock hazards are worse. When we first moved into our 'new' old house, it had the following simultaneous deficiencies:1) Corroded (fell off) main ground lead to cold water pipe - no contact.2) Bad (corroded) neutral wire top of utility pole in street (little contact, arcing)3) No GFCI's.Item one took 3 years to find, by accident. Item 2 took bugging the utility for 2 years - we knew something wasn't right. Any faults in that period would have been catastrophic.PS - Not to hijack your thread - I prefer metal boxes but you can't get the volume you need for certain common combinations of conductors or at least that seems to be the rationale.Jeff
*Teo: The faulty wiring that would most likely start a house fire includes the following:The use of aluminum wire with receptacles that aren't approved for aluminum or without the anti-corrsion goo. (especially true in older mobile homes).Undersized wire - often the result of someone upsizing ("supersizing" to the McD's crowd) the fuse or breaker without upgrading the wire. More likely with old fuse installations - they are undersized compared to modern electrical usage and have had many years and tenants over which to be upsized.Extension cords: undersized (running a 15 amp heater on 18-gauge lamp cord), frayed, run under carpet, all of the above.Less common possibilities: Those cheap, spring clip, no-screws receptacles. A piece of spring steel carrying 15 amps?! People have reporting seeing them glowing red. Get real! And spend more than 39 cents on your receptacles.Faulty breaker that heats up in the panel - you should periodically feel them for heat.Kinked and nail-shorted Romex.
*Metal boxes are safer but take longer to install and cost more....For those who like lots of room in a box, you can use double size junction boxes fitted with single gang fronts....tons of wire fit in and are also allowed by code....You get what you pay for....the budget is key too.near the stream,aj
*Worst hazard: no boxes at all! (Secret splices concealed all over the place in my house, including aluminum to copper, insulated with tape and a prayer.) And then there was a metal box that was hot and gave me a shock ... dipwit wrapped the BX with tape so, god forbid, it wouldn't touch the clamp.The fires are usually caused by stupidity -- a faulty connection that overheats and starts a fire ... or, my recent favorite, sticking 100-watt bulbs in fixtures clearly marked as limited to 60 (also a feature in my house, thanks to the renters). A metal box won't stop the heat and eventual spontaneous combustion, but it will trip a breaker quick when the wire insulation melts and grounds out against it. (Saw this happen recently when a GFCI got wet and went berserk.) Note that code requires metal conduit and boxes in commercial buildings, metal is definitely a higher standard but probably overkill in residential.I worry about electrical fires a lot. I've rewired, BTW. The split-bus load center may be the last to go. I recently switched to plastic, it's just easier, especially the boxes that adjust to the depth of the wall surface. Those 39¢ receptacles are an atrocity.
*Sources of fire hazards:--rodents chewing romex. Seen it in several renovations. A general contractor friend who lives in a rural area had his house half burn down. The fire inspector verdict--a rodent chewed the jacket and insulation and this resulted in an arcing short. The new arc fault circuit interrupters are designed to protect against arcing faults. --unqualified people messing with the wiring. Saw a twin, 100 watt security floodlight on a motion sensor that was wired into a garage circuit with bell wire (20 gage, red-and-white). When I asked the home owner who had put in the fixture, she proudly reported that her 20-something grandson had done it.--people who think that electrical wiring lasts forever. As Jeff Clarke discovered with the waterpipe ground, things do wear out. Busbar and breaker terminal screws loosen from repeated heat-cool cycles. It's a good idea to have an electrical "checkup" (by a specialist/electrician) on any building that's 30 years old or older, even if there's no overt problem. That's not a easy sell to your average homeowner.As for the metal box question, yes, they are safer. That's why they are required in places of assembly and certain other occupancies.The best wiring method as far as I'm concerned is conduit. Highly safe, very flexible (pull in any wires you need at any time).
*I wince when I see "it's code" as an arguement that it's better or correct or even good. I've been to a lot of code meetings, am on several committees, and generally deal with them daily in planning and spec writing. The steel versus plastic is strictly a matter of the steel manufacturers and suppliers versus the plastic manufacturer's. I may or may not agree with the position steel boxes are better than plastic, but what the code says is not a reason.Personally, in locations where moisture or other corrosives are present, like underground, I think plastic is preferrable. For surface work, it would seem metal is more resistant to mechanical abuse. Inside a drywall and stud wall or through floor joists is less clear. I'm leary of systems that use emt and metal boxes as the ground because I've seen too many emt connections separate; plastic with a separate ground would be better for that problem. As far as rodents eating the plastic - I've heard about it (especially from steel people at code hearings) but have never seen it. May happen. But if they are eating wires won't they eat plastic dwv too?But the compromises required to get a code published and adopted make it not a good source for justification.
*Bill...I too had never seen rodent chewed romex until I helped build a 6000ft addition in Weschester...The house had been wired first with bx then re-mudeled with romex twice more...When ripping out some drwall to accommodate new runs of heating and wire we found a rodent condo and several wires totally chewed up. the moral of the story....get a cat.near the stream, petting the tiger as I type,ajPS..using romex and fiberglass boxes mostly with some mix of other types where called for....Checking into arc fault breakers...And I do like the idea of tightening the main lugs and doing whole house check ups...Also, make sure the smoke alarms work and put them in your bedrooms, not your kitchens with all linked...
*I wonder what house fire statistics indicate as far as the frequency of electrical fire vs the age of the residence.As far as plastic vs. metal boxes, plastic has the advantage that you won't have problems with connections on your receptacle, etc shorting out against the box.
*I think when you check a smoke detector, you are only checking the battery. Smoke detectors wear out in ten years or so, though it might vary by type. So don't just check them, replace them.Of course, what we do with a bunch of used up but radioactive smoke detectors, I'm not sure.One other advantage of plastic boxes is that they don't have to be grounded, unlike the metal ones. Which can mean one less connection to be made and one less ground wire taking up space in the box.I don't think I would use plastic underground though. Too easy to chop through, although the no corrosion is attractive.
*I think I recall reading fine print thatthe manufacturer has to take them back for disposal - assuming you send them to them and have the original reciept - yup.Actually, with emt, etc., you may have one less ground wire because emt is ground. With plastic, you must have ground wire. In actuality, I suppose you may find that the termination on the box takes up more space than just terminating on the device. Not sure since I seem to always live in jurisdiction that don't permit plastic anything - all emt and steel boxes in our house - or knob and tube.
*I believe last time I read statistics from NFPA electrical was cause of about 20% of house fires. (Smoking was number one - near 40% - working on memory. Heating appliances was also high frequency cause.)I don't recall age but the value - or neighborhood - or more succintly the socio-economic status of the residents - correlated very well with fires from all causes. The poorer you are the more likely you'll experience a house fire.
*You can check smoke detectors with a "poke stick" which is this thing that looks like a big joint and smokes thick white smode whan burned, or you can get an aerosol can that sets smode detectors off. This is what's usually used by maintenance departments on monthly inspections in hotels, hospitals, schools, etc.