[RFI] ISOBAR

[Jim Brown]

On 9/17/2012 3:20 AM, Pete Smith N4ZR wrote:
> 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? 

I'm not sure what you mean by "get around" the problem.  What the whole 
house solution does is snub a strike coming in on the power line, but 
voltage and current can still be induced on wiring within the building. 
The function of a branch circuit protector is to protect against that.

MOVs are REAL CHEAP -- much less than a dollar. Most of what you pay for 
MOV-based protectors is for packaging and marketing. Series-mode 
protectors are expensive to build, for reasons that are obvious when you 
see what's inside.  There's a BIG inductor that stores the spike, then 
discharges it slowly. It costs money to build something that will 
reliably handle the energy of a strike, which IEEE studies say can be as 
high as 6kV in a premises that is properly wired.

The big sound systems I designed used racks full of power amps, and 
often a rack or two of low level signal processing.  Often the bigger 
power amps were only one or two to a circuit, so the cost of protecting 
them could be a third the cost of the equipment.  For that reason, I did 
not specify protectors for the amps, but did for the signal processing, 
where an entire 7 ft rack (or even two racks) could be on the same 
circuit and cost a lot more than the two amps I could put on a circuit.

So the short answer is that I don't know of a good lower cost solution.

73, Jim K9YC