Short circuit?

Status
Not open for further replies.
A

alfranken

Member
Location
United states
Occupation
Bricklayer
How can a short circuit fire be started but from outside a home where the utility pole carries electricity to the house? How could a fire of this nature engulf the entire house externally? How might this happen at least in theory? Could an electrician please explain? Could someone give me some feedback please? Thank you.
 
If we can assume that there is a correctly sized main breaker or fuse at the service disconnect, that leaves at least four possibilities for overloading the service drop (wire from pole) itself.
1. The short circuit is in the wiring before it reaches the main breaker.
2. The main breaker is faulty.
3. There is mechanical damage to the service wiring which causes local heating.
4. The utility (POCO) badly undersized the service wire.
 
A bunch of ways... #5 would be a blown xfrmr..which is why many utilities are switching to slo/low burn xfrmrs
 
GoldDigger said:
If we can assume that there is a correctly sized main breaker or fuse at the service disconnect, that leaves at least four possibilities for overloading the service drop (wire from pole) itself.
1. The short circuit is in the wiring before it reaches the main breaker.
2. The main breaker is faulty.
3. There is mechanical damage to the service wiring which causes local heating.
4. The utility (POCO) badly undersized the service wire.
Click to expand...
The main breaker faulty? Please explain...
 
alfranken said:
The main breaker faulty? Please explain...
Click to expand...
The line side of the main breaker when it is the main service disconnect has fault current available that is many times the rating of the breaker. A fault at that point will generate a large arc flash and a whole lot of heat.
 
alfranken said:
How can a short circuit fire be started but from outside a home where the utility pole carries electricity to the house? How could a fire of this nature engulf the entire house externally? How might this happen at least in theory? Could an electrician please explain? Could someone give me some feedback please? Thank you.
Click to expand...
What type of forensic investigation was done to show that the fire was a result of an "electrical short circuit"? Often when non-electrical professionals use the term "short circuit" it is used incorrectly. There are a number of conditions on the utility side of the service that could result in a fire of electrical origin within the dwelling.
 
A fire marshal told me that, because they take it that the fire was extinguished faster than it spread, the point of origin is indicated by the point with the most fire damage.

Electrical arcing can usually melt metal; perhaps that's one thing they look for.
 
LarryFine said:
A fire marshal told me that, because they take it that the fire was extinguished faster than it spread, the point of origin is indicated by the point with the most fire damage.

Electrical arcing can usually melt metal; perhaps that's one thing they look for.
Click to expand...
But only a real forensic engineering analysis can say if the arcing caused the fire or the fire caused the arcing.

Yes the point of origin is often located by the most fire damage, but the exact cause is much harder to determine and it is very rare that the exact electrical cause is ever investigated. There was electrical equipment in the area of the fire origin, therefore the fire was electrical origin.

Unless there was some other circumstance such as a death or suspected arson, a detailed investigation involving an electrical forensic engineer is rarely done.
 
Saw a house that had a short in the cable from the weatherhead to the meter. The wood siding was blackened the entire length. Didn't actually catch the house on fire though.
 
I had a customer that swore up and down that a fire in a truck wash bay was caused by electrical. The problem was, non of the electrical in bay was connected. It had all been disconnected years ago. There was a chase wall between the bay and and the shop. They had large holes in the bay wall, and the employees would toss the trash out of the trucks into the holes. Someone apparently threw a lit cigarette in the hole, and caught all of the trash on fire!
 
alfranken said:
How can a short circuit fire be started but from outside a home where the utility pole carries electricity to the house? How could a fire of this nature engulf the entire house externally? How might this happen at least in theory? Could an electrician please explain? Could someone give me some feedback please? Thank you.
Click to expand...
Am I missing something? That arcing is not "the wires from the pole to the house." That looks like a fault on the broken (bare) overhead primary conductor arcing to ground, like it says in the video description. (Probably 12,470/7200V). Fault protection is the high voltage fuse (cutout) feeding the transformer. Larger fuse, bigger fire....It has nothing to do with the service conductors and breakers. The wires to the house are 240/120V. They don't arc like that. Primary on any ground or secondary conductors can definitely arc and possibly cause fire.
 
Last edited:
meternerd said:
Am I missing something? That arcing is not "the wires from the pole to the house." That looks like a fault on the broken (bare) overhead primary conductor arcing to ground, like it says in the video description. (Probably 12,470/7200V). Fault protection is the high voltage fuse (cutout) feeding the transformer. Larger fuse, bigger fire....It has nothing to do with the service conductors and breakers. The wires to the house are 240/120V. They don't arc like that. Primary on any ground or secondary conductors can definitely arc and possibly cause fire.
Click to expand...
Please note, the observations you made are on the videos posted by LarryFine, not the OP. Your admonition is misplaced.
 
alfranken said:
But if arson was the case, how can police determine this then?
Click to expand...

Someone doing this intentionally would be very unlikely. Damaging the service in some way would likely only result in localized damage to the house because of the way the service is installed. Services are installed so to minimize the possibility of fire damage.

As was said, if the whole house was involved, the cause has to be a primary to secondary cross. That would put high voltage (7,000 to 12,000 volts) on the service going into the house which would put it on all the house wiring which would cause fires to erupt all through the house. All electrical equipment would burst into flames.

Neither of those videos above illustrate this. Those are only downed high voltage power lines.

The only place a primary to secondary cross could occur is out on the street when a high voltage conductor at the top of the poles is damaged for some reason, falls down and contacts the secondary conductors below. There is no way somebody is going to do that intentionally.

We have a video of a whole neighborhood involved but it was a long time ago and I can't find it.

-Hal
 
hbiss said:
Someone doing this intentionally would be very unlikely. Damaging the service in some way would likely only result in localized damage to the house because of the way the service is installed. Services are installed so to minimize the possibility of fire damage.

As was said, if the whole house was involved, the cause has to be a primary to secondary cross. That would put high voltage (7,000 to 12,000 volts) on the service going into the house which would put it on all the house wiring which would cause fires to erupt all through the house. All electrical equipment would burst into flames.

Neither of those videos above illustrate this. Those are only downed high voltage power lines.

The only place a primary to secondary cross could occur is out on the street when a high voltage conductor at the top of the poles is damaged for some reason, falls down and contacts the secondary conductors below. There is no way somebody is going to do that intentionally.

We have a video of a whole neighborhood involved but it was a long time ago and I can't find it.

-Hal
Click to expand...
But how can an entire house exterior assuming it was a small structure go up in flames without gasoline, kerosene, ect... coming into the picture? How can arson be the cause without these fluids being the perpetrator? How could a small house exterior all go up in flames without gasoline being used assuming investigators couldnt find the cause to be arson?
 
hbiss said:
I found the video I was talking about. Watch the whole thing but particularly the 7 minute mark.



-Hal
Click to expand...
I watched it but the whole exterior structure didnt go up in flames! Could dousing with gasoline the outer exterior of a small house be the only way in which it would engulf in flames???
 
Status
Not open for further replies.
Top