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
> 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.
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