[RFI] ISOBAR

[Jim Brown]

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