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Re: [RFI] ISOBAR

To: rfi@contesting.com
Subject: Re: [RFI] ISOBAR
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Mon, 17 Sep 2012 09:46:56 -0700
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On 9/17/2012 3:20 AM, Pete Smith N4ZR wrote:
Our whole-house protector (from the power company) comes with good insurance for things inside the house provided that you cascade a point-of-use surge protector. They seem to assume that the latter will be MOV-based. Is this a way to get around the IR/IZ drop problem so that one doesn't have to spend $200-500 for even consumer-grade Brick Wall products?

I'm not sure what you mean by "get around" the problem. What the whole house solution does is snub a strike coming in on the power line, but voltage and current can still be induced on wiring within the building. The function of a branch circuit protector is to protect against that.

MOVs are REAL CHEAP -- much less than a dollar. Most of what you pay for MOV-based protectors is for packaging and marketing. Series-mode protectors are expensive to build, for reasons that are obvious when you see what's inside. There's a BIG inductor that stores the spike, then discharges it slowly. It costs money to build something that will reliably handle the energy of a strike, which IEEE studies say can be as high as 6kV in a premises that is properly wired.

The big sound systems I designed used racks full of power amps, and often a rack or two of low level signal processing. Often the bigger power amps were only one or two to a circuit, so the cost of protecting them could be a third the cost of the equipment. For that reason, I did not specify protectors for the amps, but did for the signal processing, where an entire 7 ft rack (or even two racks) could be on the same circuit and cost a lot more than the two amps I could put on a circuit.

So the short answer is that I don't know of a good lower cost solution.

73, Jim K9YC
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