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sohandy_gw

Intermatic Wall Timer Shoots Sparks, Trips Breaker

sohandy
10 years ago

I have an Intermatic wall timer, model 885L that controls a single heat lamp in a bathroom. The house and timer (20 amp rating) are about 32 years old. Tonight while switching on the timer, a large spark shot out of the wall and (fortunately) the breaker tripped immediately before anything else happened. Very exciting!

Are there any known problems with these timers? It is easily replaced, but it gives me an uneasy feeling that this happened. I'm curious why something would work fine for years and suddenly fail like that. If it is a timer issue, I will have others in my house replaced too. Is there a safer brand to use than Intermatic?

Kudos to the circuit breaker designer, it may have prevented Intermatic from starting a fire!

Comments (6)

  • ionized_gw
    10 years ago

    That is what junction boxes and circuit breakers are for. Few things last forever. I'd just inspect the damage to see if there is any damage outside of the timer and replace the timer. I might bypass the switch temporarily and turn on the breaker just to see if there is another problem with the wiring.

  • cold_weather_is_evil
    10 years ago

    >> I'm curious why something would work fine for
    >> years and suddenly fail like that.

    Sounds like a description of my brother-in-law...

    There's no way to tell from your info. It could be the timer has failed; 32 years is a good run. Replace it anyway if just for peace of mind. In any event when the timer comes out you will have to check to see if the house wiring has failed in some way. Perhaps a clamp has finally made contact with the hot leg of the wiring? Maybe a screw just came loose enough to touch the metal wall box?

    Trust your ability to find a black sooty smudge somewhere in the box. Then you'll mount a new timer and not worry any more. The other devices in the house are all hooked up to a fine working breaker system, so just wait until there's a new problem (that may never come).

  • bus_driver
    10 years ago

    It is possible that the timer has not failed but that some of the conductors in that wall box are loose or have other problems. Examination by an experienced eye is advisable.

  • ionized_gw
    10 years ago

    You might examine the switch carefully as well as the wiring. If you can identify the switch as the point of failure it will be of some comfort, but does not rule out collateral damage inside the box.

    That brings me to something else. Switch failure does not usually result in visible sparks shooting from the wall or switch plate. Where did this spark come from, more precisely. If it did come through the switch plate, is this a real, approved switch plate or some home-made decorative item?

  • sohandy
    Original Author
    10 years ago

    The wall plate is part of the timer package, and is labeled Intermatic with the timer clock positions printed on it. It is metal and held on to the timer control shaft with a nut. There is nothing else in the timer's box, the regular room light and fan switches are in their own box underneath the timer box.

    Everything happened in less than a second as the room went dark, but I'm fairly certain the spark shot out of the middle of the plate as I was moving my hand away.

  • sohandy
    Original Author
    10 years ago

    Update:

    Finally was able to start working on this during daylight hours. Upon removing the timer from the box, I discovered the wire connected to the Load terminal was nicked about 3/8" from where it enters the timer. The timer has a funny design that uses internal screw terminals, so the wire feeds along the side of the timer before entering it.

    On the box itself, there was a lot of evidence of arcing near where that nick would be when in place. Just in front of the arc spot, there is a metal box clip.

    I determined that the wire became nicked from the clip when the timer was inserted into the box (it's a fairly tight fit).

    This is original equipment and timer, so that nick likely was there since 1980. I wonder how many times past owners reset the breaker. I have not used the heat lamp until using it a few times in the past week.

    For now, I put electrical tape around the nick, and protected the metal clip/box as well with tape to prevent any more chafing as the timer is inserted back in the wall. I tested it by temporarily turning on the timer/heat lamp and all appears normal.

    This is a temporary repair only, will have everything replaced soon. In the meantime, I will not use the heat lamp. Assuming that the wire really is on the Load side (i.e. wired correctly to the timer as labeled), the damaged wire is not energized when the timer is off.

    There isn't much excess wire to begin with, so cutting off the nicked section will make this a challenging project, because there won't be much free wire available to connect to a new timer.

    Fortunately the original electrician DID ground the box properly. I've seen many metal electrical boxes that are not grounded at all, and others that rely on a ground connection via the screw holding a switch or socket into the box--even when the device is not approved for that type of grounding.

    I hate to imagine what could have happened if that box had not been grounded. I also wonder what other surprises are inside other boxes in the house.

    This post was edited by sohandy on Fri, Mar 28, 14 at 18:00