Surge suppressors

Jim Lux James.P.Lux at jpl.nasa.gov
Mon Oct 28 15:12:19 EST 2002


At 01:57 PM 10/28/2002 -0500, Robert G. Brown wrote:
>On Mon, 28 Oct 2002, Steve Gaudet wrote:
>
> > You might want to reconsider how you have your UPS plugged into your surge
> > strips.  Your current configuration is not wired correctly.  The UPS has
> > surge built in and nothing should be between it and the power source.
> > Coming out of the UPS is a surge protector.  Therefore, all you need is
> > cheap power strips with no surge in it.
> >
> > Of course it will work but it is against National Electrical Code.  Any 
> kind
> > of inspector can fine you for this configuration.  Keep in mind that all
> > UPS's have surge protection built into them.  The correct scenario would be
> > to plug PDU's into the UPS for receptacle distribution.  PDU's do not have
> > any surge protection built into them.
>
>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 too, wonder... last week I happened to be studying the 2002 NEC, and I 
don't recall anything about this in there, but then, I was looking for 
information on grounding.  In fact, in general, the NEC is more applied to 
permanent installations, rather than "cord connected utilization 
equipment", which is more of a UL issue (which, in turn, is really more of 
a sales, consumer safety, and between you and your fire insurance company 
(or safety inspector)..)

Sure, ganging chains of plug strips (of any kind) is sort of a "bad thing", 
but I wouldn't be so sure that the NEC covers it.

So, just which article of the NEC covers it?

One might also consider that most surge protectors are a "parallel", 
"across the line" device, as opposed to a "series" or "through" device. If 
so, anything else plugged into the same branch circuit would be protected, 
whether upstream or downstream of the protector, although, depending on the 
lengths of the wires, the inductance might make it moot.

This doesn't go for actual EMI filters, which are series devices.



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