Volital Varnish Vapor??? We had a 50hp motor burn up the other night. When the electrician turned off the main disconnect (for lockout/tagout) it blew the door off the box. Nothing in this box was burnt or damaged, the motor circuit shared a conduit with this box, the motor was down in a pit (maybe 15ft lower) the conduit runs up to a Tee which is connected to the box that blew. I assume that turning off this disconnect provided the spark for ignition... but what was in the box that was explosive????
Motor Enclosure Blast
- Thread starter danw@sor
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
perhaps the motor was stalled when he opened the circuit.
could be a loose wire touched something when he messed with the disconnect handle.
maybe something volitile was in the box and a small spark set it off.
does the electrician often have hallucinations?
could be a loose wire touched something when he messed with the disconnect handle.
maybe something volitile was in the box and a small spark set it off.
does the electrician often have hallucinations?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
That would be my bet. Are you certain that the disconnect switch's knife blade or contacts show no signs of damage?petersonra said:
Bob NH
Senior Member
- Location
- The "Live Free or Die" State
Had he turned on the switch just before turning it off? I would expect that the locked rotor current of a stalled motor would trip the breaker in very few seconds. Was the motor powered and rotating when he turned off the disconnect?
Perhaps I wasn't clear enough... The controllers for the burnt motor were not in the box that blew. It simply shared a common conduit that T'd fairly close to and under the box. The motor was already fried and tripped, the electrician was turning off a disconnect to a soft start and small control transformer. This was a disconnect with fairly open contacts (I think an ABB with the throgh the door operator) so a small current arc would have occurred (normally not an issue). He was turning this disconnect off for lockout/tagout as he was going to start working on the failed motor and would be working in close proximity to other equipment.
So... we have an ignition source... nothing was blown up in the box and is currently all running... but it did flash enough to straighten the clamps on this Hoffman NEMA12 enclosure. So again, my question is... what burnt? While in the process of failing (or "burning up") does a motor give off ionized volitile fumes that travelled up the conduit to the enclosure?
I am pretty sure there was no hallucinations...
So... we have an ignition source... nothing was blown up in the box and is currently all running... but it did flash enough to straighten the clamps on this Hoffman NEMA12 enclosure. So again, my question is... what burnt? While in the process of failing (or "burning up") does a motor give off ionized volitile fumes that travelled up the conduit to the enclosure?
I am pretty sure there was no hallucinations...
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
any pictures?
hockeyoligist2
Senior Member
- Location
- close to greenville sc
You said the motor was in a pit, is there a possibility that flammable gases came from the pit thru the conduit?
Just guessing!
Just guessing!
No... this is at a plywood mill... the motor is for a blower that blows wood chips to a cyclone, the disconnect and box is for a softstart to the chipper that feeds the blower. The pit is outside and fairly open to atmoshere, I mainly mention it because of the elevation change... the motor that failed is approx. 20ft below the control boxes (if there is flamable vapors created by the motor windings smoking and burning, would they be lighter than air?). There is not enough accumulation of dust in the air to ignite and the ambient temp. was mild (70degF) as it happenned on graveyard shift.
Bob NH
Senior Member
- Location
- The "Live Free or Die" State
Some sources that I can think of for flamable gas:
1. Wood chips or particles in a motor could have gotten heated to charcoal level and given of carbon monoxide, which is lighter than air.
2. Biodrgradable matter in a pit, decomposing, could give off methane. That sort of thing happens in land fills.
3. Turpentine fumes from pine tree chips if the get into the pit
1. Wood chips or particles in a motor could have gotten heated to charcoal level and given of carbon monoxide, which is lighter than air.
2. Biodrgradable matter in a pit, decomposing, could give off methane. That sort of thing happens in land fills.
3. Turpentine fumes from pine tree chips if the get into the pit
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