Branch On Power Lines Caused Fire in My Basement


  #1  
Old 05-02-21, 07:08 AM
A
Member
Thread Starter
Join Date: Mar 2003
Location: USA
Posts: 100
Received 0 Votes on 0 Posts
Branch On Power Lines Caused Fire in My Basement

Hi all. I had a situation where a small branch on my lines caused the neutral and hot lines to touch and it caused a small fire in the basement. I'd like to know how to keep it from happening again.

The line from the street to the first pole on my property is triplex. From the first to second pole, it's three bare individual lines and then goes down the pole underground and into my home.

The branch must have gotten between the lines as it fell and twisted them together. Inside the house, the power went out and we heard loud popping sounds from all over. I ran to the main fuse and pulled it. After a couple of minutes, the smoke alarm went off in the basement and my daughter and I saw smoke and then a small flame coming out of my cable TV splitter. The thing was actually glowing red. I grabbed a pair of linesman pliers and cut the cable.

It turns out that the short on my lines caused the neutral on the power company's triplex to disintegrate. Still not sure how the coax became energized. PECO fixed their cable and we only have a few electrical casualties.

My questions is, is there some device I could put in-line on the coax to stop this from happening again? A fusible link maybe?

I shudder to think what would have happened if I wasn't home at the time.

Thanks.
 
  #2  
Old 05-02-21, 07:38 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 62,651
Received 1,611 Votes on 1,483 Posts
The incoming poco neutral is connected to a ground source in your panel.
The cable tv is connected to the same ground source.
When the poco neutral opened.... the current from the service line short was directly passed thru to the ground.

You need to have the house grounding system checked. It could be the incoming water line if metal.
It could/should be at least one ground and two is better.
 
  #3  
Old 05-02-21, 07:59 AM
T
Member
Join Date: Oct 2005
Location: USA
Posts: 1,740
Received 56 Votes on 53 Posts
PJ has this correct; my only add is that the service entrance system in common use doesn’t accommodate shorts well. It is expected to “burn down” to an open. Even in the best of cases, issues will result. I see many legal installs with the service pvc cable clamped to sided, frame homes. I personally would not accept such an install. Other codes require the service to be in rigid steel conduit, or surrounded by 2” of concrete. Even then, you can see what happens when the neutral fuses before the hot legs. Its also a shock hazard in the home with this slow burn in process. You could be forcing a thousand amps into your grounding rods, plumbing, and cable systems.
 
  #4  
Old 05-02-21, 10:28 AM
L
Member
Join Date: Sep 2019
Posts: 54
Received 16 Votes on 12 Posts
This is a terrifying situation and it's hard to predict exactly what will happen. It would help if the main disconnect also disconnected the neutral, but this isn't standard. When you pulled the fuse, the energized neutral was still connected to everything in the house, including the cable TV lines. By the way, the cable TV should be grounded where it enters your home (although they use a wimpy 12awg wire), which should help at least some to equalize the voltage on the cable TV and neutral.
 
  #5  
Old 05-02-21, 03:43 PM
A
Member
Join Date: Mar 2010
Location: USA
Posts: 4,508
Received 139 Votes on 128 Posts
... could be forcing a thousand amps into your ...
Did you mean volts?

A small branch or a large branch?

Could have formed a short circuit or pushed other wires together to cause a short circuit up on utility pole lines..

One of the wires being a medium tension (primary; typicaly around 7000 volts hot to ground)) line from the top of the pole and another being one of the lines (secondary) along the middle of the pole delivering 120/240 volts to homes.

Not unheard of. Capable of jumping right through and melting insulation on wiring in the walls causing multiple hot to hot and hot to neutral and hot to ground short circuits. Possible rationale for Chicago area codes to require rigid conduit. Has resulted in the need to completely rewire a house.

You would need to have circuit testing done on all branch circuits using a device called a megger, which makes resistance checks to evaluate the likelihood of melted insulation of wiring in the walls.
 
  #6  
Old 05-02-21, 04:09 PM
T
Member
Join Date: Oct 2005
Location: USA
Posts: 1,740
Received 56 Votes on 53 Posts
I did mean amps. A 50kVA transformer should be able to deliver a kiloAmp for a while out its secondary. Lots of melting potential, for sure.

Nothing in this story leads me to believe the primary was involved.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: