Bad Electrical Luck in a Winter Storm

[cowboyjosh]

A buddy of mine who is on the Fire Department that responded to this fire scene sent me this news link. He asked being an electrical contractor if I had ever heard of this happening and I have, but I have never personally witnessed it. He said when they arrived on scene they kind of had a WTF moment, no knowing why or how 4 houses had electrical panels, wiring, and appliances in the houses on fire.
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MARYSVILLE, Ohio — A transformer was being blamed for fires at a handful of homes early Wednesday morning.
Firefighters were called to Lakeview Court shortly before 4:30 a.m., 10TV News reported.

Authorities said a transformer blew in the area and sent power surging into nearby houses.

The surge started fires in at least four homes, 10TV News reported.

No injuries were reported.

Watch 10TV News and refres





http://www.10tv.com/live/content/lo...rysville-house-fires-transformer.html?sid=102

 

[Busted_Knuckles]

ok, elaborate,,, I get the gist, so does the transformer fail and overcharge the panels, and then what actually is catching fire ?

 

[cowboyjosh]

Its hard to tell, but Ill try and explain, others correct me if need be. It was definately a outside plant failure of the utility, in this case it was Dayton Power and Light. Either the line fuse failed to open when the transformer and outside utility lines failed and shorted and the arcing and surge voltage spikes shot into the homes, possibly 7000 volts, or maybe evn 13k off the offending transformer, or if the overhead lines came down and somehow the ground/neutral was energized, either scenieo is bad news and can cause instant fireworks, explosion, or fire to the associated buildings.

 

[mrb]

either a primary to secondary fault in the transformer or a primary fell and landed on the secondary lines

 

[Jarcese]

Most likely a primary came down on the secondary like the above post says. The fire department calls everything "the transformer", no matter what it is. Its the only piece of equipment that most people know of, so every explosion is a transformer in their eyes. 9 out of 10 times people call about transformers, it has nothing to do with a transformer.

 

[ajaynejr]

If the primary came down on the secondary there is a good chance the transformer will also burn up.

In the houses the hot can arc to neutral and/or ground, right through the insulation of the various wires possibly in the panel, possibly everywhere in the walls of the house where cables run. The plastic insulation on the wires is the first thing to catch fire.

A home can require a complete rewiring since it is not easy to see which wires in which walls got fried.

 

[Busted_Knuckles]

If the primary came down on the secondary there is a good chance the transformer will also burn up.

In the houses the hot can arc to neutral and/or ground, right through the insulation of the various wires possibly in the panel, possibly everywhere in the walls of the house where cables run. The plastic insulation on the wires is the first thing to catch fire.

A home can require a complete rewiring since it is not easy to see which wires in which walls got fried.

Ok, I'm thinking I'm getting this, the hi-voltage wire (you guys keep talking primary and secondary? layman's terms please !) on the pole, falls down and touches a wire after the transformer going to a building and sends several thousands volts into said building, thus arcing all over in the building causing fires ?

 

[ajaynejr]

Primary -- The medium tension lines at the top of street utility poles, may range from 2400 (older installations) to 20000 volts to ground, most commonly around 7000-8000 volts. They can run several miles to a substation where the high tension lines on much taller poles come in.

Secondary -- The 120/240 volt lines out of a transformer and hung about 3/4 way up the pole, and serving individual homes within a few hundred feet. May be twisted around the ground/neutral wires so as to resemble a single cable.

 

[cowboyjosh]

I just talked to the FD friend in Marysville, they are still without power today, that would ****!

 

[ajaynejr]

IT would probably be unsafe to reconnect the services of the affected houses. The panel would need to be inspected for usability. If the panel was okay all of the branch circuit leads could be removed from their breakers and as the various branch circuits were rewired or found to still be good the breakers could be rewired.

Should the service be unusable, the utility would do well to install a temporary service with receptacles outside the house where the family could use extension cords to connect up individual appliances, etc.

 

[Teken]

This is pretty much why I installed a secondary surge arrestor at the meter along with a thicker ground rod.

The main panel is also coupled with a secondary surge protector as a fail over just in case.

 

[Gigfy]

In the panels, my guess is the main breakers are at least toast. I once lived in a house where the main breaker was "frozen" (i.e. welded) shut. I don't know how this happened w/o blowing the breaker. I tried to tap it loose to the point of busting the switch and it still wouldn't budge.

Another time I welded the main cutoff myself. I was working on my own 400 amp transfer panel, and with that type of load, the meter won't disconnect because the load rails are bolted in place. I ended up working the box hot, got in a hurry and didn't tape my tools. Before I realized it, I got a wrench across two leads (or maybe it was a neutral and a lead). Quite a show. It welded the switch to the incoming power feed. Fortunately, it wasn't stuck very bad and I was able to get it loose. I did have to replace some components in the box. Could have ended a lot worse. Went to church the following Sunday.

 

[ajaynejr]

This is pretty much why I installed a secondary surge arrestor at the meter along with a thicker ground rod.

The main panel is also coupled with a secondary surge protector as a fail over just in case.

An ordinary surge protector will not protect against this problem which is a continuous as opposed to momentary overvoltage.

You would need some kind of arc resisting high voltage sensor connected to a battery power activated or spring loaded shutoff switch to cut all power to your house.

Perhaps together with device to attract the arc somewhere else first. It would have two (correction three) thick plates of metal spaced about 1/16 inch apart connected to the main feed (both hots and neutral) outside the house using wires fatter than the service drop. Regular house current won't jump the gap but the 7000 or so volts will. The plates need to be in a stone or other high temperature housing so that, if the plates melt, the molten metal will pool up in a large enough quantity that 200 amp fuses (or whatever your service is rated at) further upstream would blow first. And this device needs to be outside the house as it would get very hot.

 

[hetkind]

Surge protectors are usually heat (current) operated than voltage operated. A primary to seconday fault will sent high voltage (14.7kv distribution power worst case) into wiring and appliances designed for 120 volts. Not enough clearance in internal parts, arc, heat, smoke, fire in that order.

A complete rewire on the power companies nickle would be appropriate.

Howard

 

[foolishpride]

This is pretty much why I installed a secondary surge arrestor at the meter along with a thicker ground rod.

This is a common misconception. Increasing the diameter of the ground rod doesn't materially reduce its resistance. Doubling the diameter of the rod only reduces the resistance less than 10 percent.

On the other hand, doubling the length of the grounding electrodes(s) reduces resistance by approximately 40 percent. But this isn't really practical. The best way is to drive multiple rods, which gives you parallel resistance paths.