[RFI] ISOBAR

Pete Smith N4ZR n4zr at contesting.com
Mon Sep 17 06:20:45 EDT 2012


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
The World Contest Station Database, at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com,
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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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