What kind of switch?

[nerspellsner]

Under 345000 volt power lines, there is an electric fence surrounding a horse pasture. The owner complained about getting shocked when he touched the fence with the fence controller unplugged. The power company installed data recorders at 5 points along the fence. There is between 400 volts and 800 volts on the fence coming from the overhead lines when the fence is off. The power company recommends grounding the fence when it needs to be turned off. The fence needs to be turned off daily. Instead off connecting a wire to it every time to ground it, a switch to open and close the ground to the fence would be much easier. I was laughed at when I asked for a 1000 volt knife switch. I need a high voltage switch but only milliamps will flow through it. Any ideas? Thanks.

 

[peteo]

Re: What kind of switch?

I'd try a latching contactor, such as the 528-2505-9 in the Mouser catalog here. Found the Newark and Digikey sites useless. That will get you two sets of form C dry contacts, so it could (in theory) be used for both fence grounding and electrification functions.

If there's a little sparking, you can add in an RC snubber, thermistor, etc; the relay can be replaced, if it gets pitted. If that's still not capable of interrupting, you may need to go the full interlocked y/delta (motor reversing) relay set. That's what comes to mind.

 

[realolman]

Re: What kind of switch?

I wonder what the handles for the electric fence gate themselves are rated? They might be sufficient. Could you hook a gate handle to ground manually when you open it?

The whole deal sounds kinda creepy.

 

[charlie tuna]

Re: What kind of switch?

consider a three way switch with the fence connected to the feed and one traveler connected to the ground and the other from the fence charging source..............

 

[peteo]

Re: What kind of switch?

On second thought, a simple 'soft start' resistor, such as a 1 Meg to a ground rod, comes to mind. It will bleed off that stray voltage instantly, but lightning will probably destroy it. The only place in the NEC I see equipotential plane mentioned, is for agricultural use.

 

[mario]

Re: What kind of switch?

yo guys..just a thought..Pete I think your Idea is great but also it could get a bit spendy and complicated ... what do you think about a "Basic" "Start/Stop Station" ?? N/O contacts on the start..N/C contacts on the stop ... ... m

Had to add...the grd wire through the N/C and hot(to fence) on N/O ... m

[ February 23, 2006, 06:36 PM: Message edited by: mario ]

 

[nerspellsner]

Re: What kind of switch?

Thanks for all your help so far. Keep in mind that when the fence is powered, the controller is outputing 7000 volts.