causes of electrical fires??

Discussion in 'Electrical Forum discussion & Blog' started by Master Brian, Jan 26, 2009.

  1. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    Maybe there isn't an easy answer to this question, but what are the main things that cause an electrical fire?

    Reason, I ask is that I am going through my house, which was a bank repo, and cleaning up a lot of old wiring. There are a few metal boxes in walls that move around, when you plug stuff in. They have come loose from the lathe and plaster. I have several areas where fixtures where removed and wires just hanging inside boxes with no covers, and metal boxes in basement ceiling that have several connections. I have come across several of these boxes that only have tape covering the twisted connections and on some the wires are so brittle that when you move them, the insulation crumples.

    There is a bit of knob and Tube, I'm not overtly concerned with that, except for portions that are burried under insulation as I read that is a no-no, UNLESS an electrician says it's ok.

    I have a lot of that BX(?), the stuff in a metal conduit, and old silverish/black romex and some that looks like black romex. The house was built in 1915, so if the wire has been made, it's likely in my house.

    While repairing one outlet last night, I came accross one spot where when a coax cable was run, they actually knicked the romex(?) wire and you can see bare wire on both the hot and neutral wires and they WERE (I took it out) right nex to a joist!

    Right after buying the house, my wife was doing a load of laundry and the breaker kept tripping and you could smell burnt wire. I called my electrician, whom was slated to upgrade me from 60amp to 200amp service, and had him come out. He found a wire that had crossed, due to age deteriation, and shorted out. This was the clothes dryer, I might mention...

    In any case, I'm sure you can see my curiousity over what I should look for. I have replaced several runs and even removed lines that didn't go anywhere any longer. I feel very competant in working with elecricity in this manner, but I am curious, what is the major cause. I can't believe some of these old connections haven't failed yet.

    I am also concerned when an inspection is required and when it isn't. I am planning on calling the inspection unit and speaking with them as well, but to be honest, I find some of these areas, I've mentioned and I yank them as soon as I find them. Not tanking any chances....
  2. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    I should probably mention, I fully realize the boxes with hanging wires, should be closed up with a cover. In some cases, I plan on that. In some, I'm afraid moving the wire will crack the insulation, so I'm leaving as is, until I can get to that circuit.
  3. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    My understanding here is that an electric permit is almost always needed. The (possible) exceptions being when you are replacing a device - ceiling lamp, fan etc. If I'm running wire I need a permit. The problem I have run into is that they expire 6 months after issued, the building permit does not expire (per my Dept) so long as work continues.

    A loose wire can cause an arc, then a fire

    Insulation cracking & falling off could cause a short/spark

    Smaller gauge wire on a larger breaker could cause a fire
    IE - lamp cord or 14g on a 20a circuit with a heavy load

    That's what I can think of
  4. drick

    drick In the Trades

    Messages:
    392
    The number one cause of electrical fires is loose connections. Loose connections generate heat, which causes a fire. Even in new construction I saw a case where homeowner installed a dimmer but didn't securely fasten the wire nuts. One was making a weak connection and caused a small fire. Luckily the homeowner was home, smelled it and put out the fire before is spread into the wall. No major damage but it was a PITA to replace all the wiring to that box.

    In another fire it was the knob and tube poorly connected to an outlet. The outlet had a space heater plugged into it. It looked like the conductor to the back of the outlet had broken off due to movement/age but was still just barly making contact to the screw terminal on the outlet. This was a more serious fire causing about $50K in damage.

    The knob and tube I've seen has been in relatively decent condition. The only problem being that 4 to 5 rooms would end up on a single circuit. If you are planning on keeping the knob and tube I would put arc fault breakers on those circuits to be safe.

    If you are planning on doing extensive rewiring take the time to read the portion of the NEC dealing with residential wiring. It covers outlet spacing, kitchen and bath circuits, etc.

    -rick
  5. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    We also had neighbors house that partially burned - Fire Dept said it was a due to a radio that was plugged in. I don't remember if it was on or off.
    Their fire was contained mostly to one bedroom. This was due to the fact that it was a solid wood door, and that they always closed their bedroom doors
    I have hollow doors at this house & will be replacing them with solid wood
  6. Billy_Bob

    Billy_Bob In the Trades

    Messages:
    422
    I don't think there will be an electrical fire at your house! You are doing all the right things and are on the right track.

    You are learning, asking questions, learning about permits, hiring an electrician when needed, and snooping around your house examining/fixing things.

    Good thing to have covers over boxes, but also I think it is a good idea to not move the old wires until you can replace them (especially if insulation crumbling).

    I would say to check the size of the fuses/breakers and that they are correct for the wiring, but the electrician will do that when upgrading your service.

    Insulation crumbles a lot in old light fixtures due to the heat there. Might not want to even peek at these until you are ready to replace the wiring.

    Might want to get a book or two on electrical wiring here...
    http://www.buildersbook.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=bbi&Category_Code=40
  7. iminaquagmire

    iminaquagmire DIY Senior Member

    Messages:
    207
    Overloaded circuits and loose connections are the biggest issues. I was just on a fire call (I'm on the local department) where the leading opinion so far is that the space heater overloaded the circuit. Good advice stated so far. The suggestion for arc fault breakers on the old circuits is a good one.
  8. GabeS

    GabeS Remodel Contractor

    Messages:
    294
    Location:
    Brooklyn NY
    If you have the budget for it, just rewire the entire house. It sure sounds like you need it. Too many different kinds of wiring. That means a lot of different people worked on that wiring in the house and chances are some were not licensed. Too many possibilities for something done wrong. If you are getting a new service then run all new circuits.

    Did you check for aluminum wiring?

    A good electrician could rewire the entire house without creating too much damage. Then just patch everything up after the electrician is done.
  9. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
  10. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    Thanks for all of the feedback. My goal is to have completely new wiring in the house. The service panel has already been upgraded and I had them install sub panels in my garage and my basement.

    I am hoping to be able to do the rest myself and I plan to get everything inspected when I'm done, just so it never becomes an issue down the road.

    Is there somewhere I can pick up a copy of the NEC dealing with residentual wiring? I know the library should have a copy, just hoping there is something online, I can download. The other question is, how hard is that for the average joe to understand? I understand most all of the basics and am learning more each day.

    One question I do have is regarding the Arch Fault Breakers. It seems some people really like them, but most of the local people I speak with say to stay away, the technology isn't very good yet. With that said, I know it is code that the bedrooms have them, so I'm pretty sure I'll need them for my re-wire to be within code. I am just curious why I hear bad things about them.

    Also, can someone clearify this...I understand the Arch Faults to be needed on the outlet circuit for the bedrooms, but what if all the lights are on a seperate circuit, do I need one for them as well?
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,798
    Location:
    New England
    Rumor has it that the original versions of arc-fault breakers weren't all that great...the newer ones are supposed to be better (fewer false or nusiance tripping). I think someone said that future codes may require them nearly everywhere in residential situations. Could get ugly.
  12. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    2008 online:

    http://nfpaweb3.gvpi.net/rrserver/browser?title=/NFPASTD/7008SB

    Yes, Arc faults will be required in a LOT more places as will the Tamper proof receptacles & outside must be TP & weather resistant. I've checked & the costs on these new outlets are very high right now

    Square D had a recall 2 years ago (I think?) on some of their Arc fault breakers - I think they had blue buttons & now switched to green buttons. I do not think all blue button Arc faults were effected - check the link

    Yup:
    http://www.us.squared.com/us/squared/corporate_info.nsf/unid/9CB09A222974952E85256F19005EAE4F/$file/howcanIknow.htm
  13. Thatguy

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD
    High temp. causes fires when in contact with combustible material.
    http://www.tcforensic.com.au/docs/article10.ht
    If heat loss to the surroundings is < heat gain from power in, the temp. goes up until these two are equal.

    10w dissipated in something with the surface area of a wirenut is too hot to touch. The same power dissipated in something with a surface area the size of a watermelon, or a panel busbar, is hardly noticeable.
  14. GabeS

    GabeS Remodel Contractor

    Messages:
    294
    Location:
    Brooklyn NY
    I think they are requiring AFCI on ALL circuits that don't have GFCI. Wait for a pro to clarify, but we had this discussion in prior posts. You could probably do a search and pull those posts up. I think they costs $40 each or around there.
  15. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas

    I think $40 is about where they were when I looked into them one other time, but like I said, I was told by several, even an electrician, not to mess with it if I didn't need to.

    From my city's website, it looks like just bedroom circuits, I just couldn't tell if they were needed for the lights, if on an independet circuit. Hmm... I guess the inspector can tell me and too be honest, this isn't something that should be hard to retrofit....
  16. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    Suba Dave, thanks for the link. Does that whole thing deal with residentual? I am glancing through it and it is a bit overwhelming. Most of that is stuff that I would never get into. It also looks like they do want Arch Faults in many other places besides the bedrooms, but the city's website doesn't say that. Maybe their code isn't there yet. Hmm....

    Anyone take one of these homeowner tests? I am really curious how difficult it is.

    Also, will they actually make me install a receptacle for the 6' rule on any wall space? Some rooms such as the bedrooms, I am working on making openings. However, my dining room already has wallpaper and I do not want it messed up. There are receptacles, just not per code. I didn't install them either. Remember this is a 1915 house.
  17. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    The NEC has been in existence for over one hundred years and uses technical language, not layman's terms. This eliminates confusion.

    It is not easy to read and not the easiest to understand unless you already have a firm grasp on the fundamentals of electricity and electrical work. The NEC is not a DIY manual. There are lots of books out there that are sold soley for the purpose of explaining parts of the NEC.

    Almost every single chapter and section of the book has to do with residential in one way or another. You can probabl skep the 500 series section and some of the 700 section but you will find information that you need in every single part.

    Here is an example:

    A simple item like bonding or grounding the main panel is covered by multiple sections such as 250.50, 250.50(A), 250.52(A)(1), 250.66, 250.53, 250.53(A) & (D)(2), (E)(G)(F) and even more depending on other sections.
  18. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    I understand it isn't meant to be easy for a layman.

    I guess I am curious as to the test. The inspector didn't give me much info, just said, I can look at a copy of the NEC, there or at the library. Supposedly the homeowner test only covers the sections that pertain to residential, but like you say, every section seems to have residential stuff.

    I can't however believe the stuff on bonding would be in there, as the homeowner isn't allowed to do the panel. *there being the test.

    I do wonder how hard 25 questions in open book format with a 3hr time limit could be, but I have taken many 25 question tests in my field that easily take me 1 hour in open book format. So i'm willing to bet anything goes and I wonder how excited they are to actually have a homeowner pass the test. That is the Million Dollar Question!

    I guess the only way to be sure is to take the test. Right now I am trying to draw up my plans and then I'll progress from there.
  19. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    Here is an easy electrical question that a homeowner should know how to figure out as junction boxes are always being tapped into or installed. I recently came upon this situation while conducting a code inspection.

    This may help to prime you for the test.

    Basement, junction box. Metal 4" x 4" x 2-1/8" deep with cover and ground screw properly placed. No devices, internal clamps, plaster or extension rings on or in the box. Just wires and wire nuts except for the compression sleeve on the equipment grounds.

    There were eight (8) 12/2 NMB cables entering the box.

    Questions:

    1) Is the box properly sized?

    2) What is the box fill?

    3) What size box needed?
  20. PeteD

    PeteD New Member

    Messages:
    52
    Location:
    MA
    I can't resist taking a stab.

    There were eight (8) 12/2 NMB cables entering the box.

    Questions:

    1) Is the box properly sized?
    NO

    2) What is the box fill?
    17

    3) What size box needed?
    38.25 cu in - not sure of the standard size

    Not an electrician so don't shoot me if I am wrong.
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