Surge suppressors

Bob Drzyzgula bob at drzyzgula.org
Mon Oct 28 15:13:46 EST 2002


On Mon, Oct 28, 2002 at 01:57:55PM -0500, Robert G. Brown wrote:
> 
> 
> This is the second or third time I've heard this little-known bit of the
> NEC cited (that one cannot plug surge strips into surge strips).  Being
> the curious sort, I wonder why this is the case (that is, what is the
> hazard avoided by not doing this).  I can't offhand see why plugging a
> surge protector into a surge protector would do anything but provide one
> with marginally greater surge protection and three de facto overcurrent
> circuit breakers in the circuit instead of two.
> 
> Anybody know?  I like to understand this sort of thing, and not just
> avoid it because an inspector would fine me.

I've often wondered this as well. While there may be
something about the addition of the surge filtration,
one possible way to view it is that surge strips
tend to be found at the end of extension cords, and I
believe that simply daisy chaining extension cords is
contrary to code, for a number of reasons. For example,
the gauge of the wire that must be used in such a
cord is dependant in part on the length of the cord,
and plugging them together can result in cords which
violate the spec. Also, unless the mating plug & socket
are secured in some way, it is easy for the connection to
slip apart slightly, exposing bare connectors. Finally,
there may be some defined limit (e.g. 2) on the number
of spring-clamped, metal-to-metal connections in a
single run, possibly based on the higher resistance
(than a screw-clamped connection) they would present to a
circuit. For example, one guide document I found (at SLAC,
http://www.slac.stanford.edu/esh/eshmanual/ESHch08.pdf)
allows a hardwired surge strip to an extension cord to
a device, but not a plug-in surge strip to an extension
cord to a device, see figure 8.1 in that document.)

If there's more to it than that, I'd be real intrested in
the physics of it.

--Bob
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