AC power line question

John Teller jsteller at
Sat Jun 30 16:26:04 CDT 2012

Definitely some sort of fault indicator.  It'll stop blinking once 
everything is back to normal.

Check out this link to SEL (Schweitzer Engineering Laboratories) or 
Google "overhead fault indicator"


On 06/30/2012 04:41 PM, Nan and Sandy Sanders wrote:
> This is the first time I have seen these flash and they have been 
> there at least 3 years. I think they may be some sort of surge sensor. 
> We were taking some really hard power hits here for a while.
>      Sandy
> At 02:59 PM 6/30/2012, you wrote:
>> Those are most probably some sort of potential indicator.  It's kind 
>> of a weird circuit in that one end is physically connected to the MV 
>> line while the other end is capacitively coupled to ground.  At those 
>> voltages you don't need much current to flash an LED - which would 
>> indicate that the circuit is live.
>> It's odd that the power company would put up something that flashes 
>> when everything is powered normally, as this generally prompts calls 
>> from all and sundry who normally associate flashing lights with 
>> problems.  I was under the impression that power companies tended to 
>> use mechanical devices that displayed a red or green flag and were 
>> driven by magnetic flux developed around an MV line that was carrying 
>> current.
>> Here's a link to an image of an install of some current sensors 
>> installed in Australia:
>> In this picture you can see the mechanical indicators - they are the 
>> three devices attached near the dampers just beyond the disk 
>> insulators (the line post insulators on top are actually the current 
>> sensors).
>> That's a three-phase delta system, which is why the transformer is 
>> connected to two lines.
>> ---JST
>> On 06/29/2012 11:52 PM, wb5mmb wrote:
>>> We just had a line of storms blow through Northern Virginia with 
>>> many hard power hits but power never went all the way down. On the 
>>> power pole in front of the house there are cylinders about 3" in 
>>> diameter and 3" long hanging from each of the 3 high voltage lines 
>>> about 1' from the insulators. Each cylinder has a blinking red led 
>>> on it.
>>>  Two questions, what does it mean when the LEDs are blinking and how 
>>> do you power an led on a box hanging on a 13KV line that looks like 
>>> it could handle several hundred Amps.
>>>      Sandy
>>>      WB5MMB

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