Light rain after a long dry spell raises the possibility of power poles catching fire

by: Graham Johnson Updated:

After 55 official days without rain in Seattle, things are a bit dusty.

One of the places dust has settled is on power line insulators.

If our first rain after a long dry spell is a big, soaking rain, Scott Thomsen of Seattle City Light says there won't be a problem.

"That's what we want," Thomsen said. "If you could dial up about a quarter inch of rain or more that would be really nice."

But if our first rain is light and misty, which is what we mostly get around here, there's a higher risk that parts of power poles might catch fire.

It happened in 2003, when it rained after a similar dry stretch.

That's when a power pole fire in South Seattle led to an outage for 2,600 customers.

The problem comes when there's not enough rain to wash the dust away and it turns into a thin coat of mud on the wires and insulators.

"It gets just damp enough to stay there, but it's wet enough that it becomes a conductive surface instead of a non-conducting insulator," Thomsen said.

That means electricity can escape the wires and move past the insulator.

Power pole fires don't happen often, and they tend to involve only the horizontal cross arm at the top.

In fact, you're more likely to hear some sizzling and buzzing from moistened dust on the line.

Seattle City Light says this is one reason crews regularly trim tree branches away from power lines.

Utility officials say they are prepared to fix any outages if they happen.

Officials say if you hear a line buzzing, there's no need to call that in.

But they do suggest you report an outage.


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