[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
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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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