Ed, I also hate it when I get ambushed.
In the matter of the extension cord: I guess to lessen their liability they
don't want any extra voltage drop from a cord?
I also agree, why would I hook up a UPS that could fry my equipment with a
switching event?
When you find out let me know, as this sounds like something I need to know!
Michael Sundstrom
NOKIA
TCC Dallas / EMC
of: (972) 374-1462
cell: (817) 917-5021
amateur call: KB5UKT
From: ext Price, Ed [mailto:ed.pr...@cubic.com]
Sent: Monday, June 02, 2003 10:19 AM
To: 'EMC-PSTC List'
Subject: Surge Suppressors on a UPS
Hi Group!
Last Friday, I got ambushed in a meeting. I hate it when that happens!
A question was asked about whether it's OK to put a surge suppressor on the
output of a UPS that is supplying power to some expensive equipment. I opined
that I didn't think it should be necessary, but that it also shouldn't hurt
anything either. So then somebody asks me why all the UPS manufacturer's sites
say not to use a surge suppressor. I expertly reply that gosh, I don't know,
but I'll take a look.
The next question nails me again. "Are there any standards for UPS output
power quality?" Uh, well, I'll look into that too.
Now, the market is light industrial, USA, but are there any applicable EN
standards also?
Just for some background, here's a typical entry from Tripp-Lite's FAQ list
for UPS's (not to pick on Tripp-Lite; they just said it most succinctly of
several sites I looked at):
http://www.tripplite.com/support/faq/tech_ups.cfm
Can I plug a surge suppressor or extension cord into my UPS?
No. Using an extension cord will void your equipment coverage warranty, as all
equipment must be plugged directly into the UPS. Tripp Lite does not recommend
plugging a surge protector into a battery backup outlet of a UPS either as
this can overload it. Also, when some UPS systems switch to battery power they
will output a waveform that a surge suppressor may see as a surge and
short-circuit the UPS. Again, this setup will void the equipment coverage
warranty.
Now this is getting to be a big can of worms! What do they mean by "some UPS"?
Is there one kind that does, and another kind that doesn't; and how do you
know which is which? And if some UPS will create a voltage transient (is that
what they mean?) sufficient to trigger a surge suppressor, then why is it OK
to let the UPS apply that transient to my "protected" equipment? All this talk
about uninterrupted power isn't worth anything if the UPS kills my equipment
when it switches to battery power mode.
And who's fault is this? I mean, a surge suppressor is pretty dumb; it just
sits there waiting for the voltage to go over a certain level and then it
conducts. What's this about the surge suppressor "may see" something as a
surge? That's saying the surge suppressor could mis-interpret the waveform it
sees. If the surge suppressor is conducting, then I think the UPS has just
done something very naughty.
I also don't understand the prohibition of an extension cord. Maybe this is a
legal issue, as I can't see any valid safety or regulation issues here. We
regularly put a UPS in the bottom of a rack system, and then wire a stripline
outlet set for the height of the rack. Isn't that the electrical equivalent of
an extension cord? What am I missing?
Thanks in advance!
Ed
Ed Price
ed.pr...@cubic.com
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Systems
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (Fax)
Military & Avionics EMC Is Our Specialty
