[Top] [All Lists]

Re: [TowerTalk] Shack wiring

To:, "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] Shack wiring
From: jimlux <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Mon, 15 Mar 2010 18:11:48 -0700
List-post: <">>
Pete Smith wrote:
> I have to disagree, on two counts.
> First, all the outlets in the house, as well as those in the string of 
> surge protectors, are in parallel with one another, on one of the two 
> legs of the 220 feed.
> Our whole-house protector is very robust, but it is only rated to drop 
> the surge voltage to a level that, while OK for non-electronic devices, 
> could kill most solid state devices.  for that reason, the power 
> company's warranty on their surge protector says that it is only valid 
> for damage to electronics if they are on a properly rated line-end surge 
> protector.
> 73, Pete N4ZR

Not all protectors are just a MOV across the line.  Good ones have some 
form of series L, shunt C, the idea of which is to turn a narrow high 
transient into a longer, lower transient.  Furthermore, MOV based 
transient protection has the fundamental problem that MOVs wear out.

It is exceedingly unlikely that a decent clamp at the service entrance 
would let a transient through that would actually damage solid state 
devices.  Some 10 years ago (or more.. mid 90s, I think), a study was 
done in Canada on consumer electronics and basically all of them can 
tolerate 1000V spikes on the power line with no damage.  The input EMI 
filters needed to meet Part 15 type requirements (obviously, Canada has 
different EMI/EMC rules) do a lot of good at flattening out that 1 
microsecond kilovolt pulse, and after that, it's mostly a matter of the 
off-line rectifiers toughing it out.  The secondary side is going to be 
immune because it's regulated.

Even a dorky unregulated wall wart is going to do pretty well on a 
several kV pulse: it had to pass HiPot testing for line to case and 
primary to secondary to get the UL mark, and after that, you're looking 
at a bridge rectifier and a capacitor.  The series L and R of the 
transformer limit the peak current.

A typical ESD safe input (which is anything you can touch, including the 
prongs of the power cord) can take a several kV pulse without too much 
trouble, as long as the energy isn't there to destroy junctions.

Much, much more likely is to kill your electronics with a transient 
coupled from some other source.  A nearby lightning stroke will do.  A 
pretty small Marx generator in your garage can do amazingly bad things 
(it's that fast nS rise time).  Folks fooling with tesla coils find that 
garage door openers are particularly vulnerable (lame design on the 
openers.. they have wires that run to the photo sensors and limit 
switches and really, really bad transient suppression on the inputs to 
the microcontroller.  The fact that folks run their tesla coil in the 
garage doesn't help.


TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>