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,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000
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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