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Re: [RFI] ISOBAR

To: rfi@contesting.com
Subject: Re: [RFI] ISOBAR
From: Pete Smith N4ZR <n4zr@contesting.com>
Date: Mon, 17 Sep 2012 06:20:45 -0400
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
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?

73, Pete N4ZR
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On 9/16/2012 1:12 PM, Jim Brown wrote:
On 9/16/2012 2:22 AM, Christopher Brown wrote:

On 9/15/12 5:46 PM, Jim Brown wrote:
I can't comment about RF filtering, but it's an MOV box, which is BAD
NEWS on a branch circuit.
Care to explain or provide a ref?

The fundamental problem is that MOVs, like all shunt protectors, attempt to short out the surge, mostly by conducting it to ground. When the MOV is at the end of a branch circuit, the IR and IZ drop produced by surge current raises the chassis of the protected equipment to a very high potential. If that product is connected to ANYTHING that is grounded elsewhere (an antenna, or equipment plugged into a different outlet) the difference in potential is quite likely to fry both pieces of equipment. This used to be a major problem in the pro audio world until we found series mode surge suppressors, and it's still a problem in the computer world. I've seen several well-documented reports of lightning taking out everything connected by Ethernet in homes and offices with no ham radio involved.

MOVs also have a limited lifetime -- after they have absorbed a certain number of joules, they no longer do anything -- and they often fail destructively. In cheaply constructed products, they could even start a fire. The Isobars do not fall into that category, but a lot of power strips with MOVs do.

MOV's are a fine solution at the power service entrance if they are properly installed and the premises follows proper grounding and bonding, but on branch circuits, they're likely to CAUSE as many problems as they might prevent.

I know of two companies making series-mode protectors, both of which license the same technology. Brick Wall sells in the consumer world, SurgeX to the pro audio and video world. About 15 years ago, I started specifying their products to protect racks full of very expensive small-signal equipment in the large and small sound systems I was designing and specifying. As a consultant, I had no part of the sale of equipment, nor did I get a commission on anything -- rather, I was paid by the owner of the building for whom I was designing the system, or by his architect.

About ten years ago, because I was well known as a technical writer, SurgeX asked me to write a tutorial for them on power and grounding for audio and video systems, and since about 2004, I've been teaching classes on that topic at industry trade shows. As a result, I know more about their products than about Brick Wall.

73, Jim K9YC
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