[Beowulf] Re: Emergency Power Off

Jim Lux James.P.Lux at jpl.nasa.gov
Mon Mar 19 17:05:20 PDT 2007

At 03:19 PM 3/19/2007, Robert G. Brown wrote:
>On Mon, 19 Mar 2007, David Mathog wrote:
>>After looking at the specs I believe that at least 4 of the 5
>>can be wired to shut down instantly.  (Not sure about the one
>>desktop size APC unit in the room, as it isn't mine so I don't
>>have the manual). However it seems that turning off the
>>tripp-lite UPS requires a positive voltage (12V) on the
>>inverter shutdown line.  Which means, that even after the
>>power has been killed (overtemp, red kill button,
>>or building power shut down) the fireman entering this room would
>>still need to smack another (not yet extant) red kill button, and
>>that button is going to need DC power in order to work.

Ahh yess.. but, that low voltage DC (and 12V is actually quite low, 
most industrial controls use 24VDC) and would normally be wired as 
what is called Class 2 power limited, so it doesn't raise any safety 
issues if it gets rained on.

>>   Googling
>>turns up other EPO installations requiring much higher DC voltages
>>than the tripp-lite needs, for instance here:
>>where they specify 56 volts for the EPO, but only 5mA of current when
>>the switch closes.

That's pretty high. I wonder why they chose it. It's also a weird 
voltage.  The only time I've seen that voltage was on a GPS 
time/frequency standard intended for telecom usage, and even there 
it's weird, because the telecom world uses -48VDC.

>>Clearly a second red kill button (EPO for the UPS units) would be a good
>>thing.  Presumably somebody sells an EPO control unit that
>>has all the pieces:

McMaster-Carr or Grainger are your friend.

>APC has a button -- it is spec'd somewhat in the pdf Jim and I passed
>back and forth and you can look it up on their site.  There are some
>other companies that sell them as well.

The actual buttons are sold by all the standard electrical equipment 
companies (Square-D, Honeywell, Allen-Bradley, Omron, etc.)

>They don't look terribly easy to wire up, though, and say that they are
>only to be installed by "professionals".  I asked our "professional"
>electrician today if he'd ever installed an EPO button, and he said no
>and slunk out.

They're easy to wire if you have the beast sitting in front of 
you.  All industrial switches like this are basically built with 
modules that assemble.  You'd have an "operator" which is the part 
with the mushroom head and the spring loading.  This mounts in a 
standard 1-1/8" (I think) hole in an enclosure designed for such 
things with the plastic flap on the front to prevent the "oops I 
leaned on the kill switch" problem. On the back of the operator, you 
stack one or more contact modules, either Normally Open or Normally Closed.

If you need 24VDC power, you get a UL approved Class 2 power supply 
(essentially a little module that plugs in)

Ultimately it comes down to your fire marshall and inspectors.  If they
>say you need one, you need one.  If they say not, then not.  Unless you
>get sued after a fire when somebody gets killed, in which case it will
>almost certainly turn out that you needed one after all.
>I'm still hoping to put one in "needed" or not.  If I can figure out
>how, without spending a fortune.  How as in wiring and full parts
>diagrams, including what we need at the UPS end.

See, for instance page 821 in the McMaster Carr catalog (online at 

or, for a more build to suit, page 811
or pg 813, where they have a plastic shroud, Mushroom operators, etc

Or page 817, in a bigger size

Grainger (http://www.grainger.com/) has similar things.  Look around 
page 288 in their online catalog.

Mfrs like Square D (http://www.squared.com/) which sell through your 
local industrial electrical supplier

For instance...


(If I copied that correctly..)

Near Duke, you might try Consolidated Electrical Distrs. Inc, 
Electric Supply Co of Durham, Graybar Electric Company, Grainger, etc.

Near Cal Tech..  I used to use Royal Electric down in Vernon, 
All-Phase out in Burbank, Grainger all over the place.  I see that 
Consolidated has a place on Foothill in Pasadena.  Dawson Company is 
in Altadena. Norton Wholesale Electric downtown is another possibility.

>    rgb
>>AC in
>>AC to DC conversion

That would be a power supply.. a standard modular component.

>>battery or capacitor backup of the DC voltage

likewise, but you might not need a backup.

>>a bunch of ports to plug in lines to control the EPO devices
>>Who sells it?
>>How much?
>>Or is every EPO controller custom made???

Yes. In the sense that you basically mix and match the buttons, wire, 
and connectors to match your particular facility and your particular 
UPSes, which, as you've noticed, aren't standardized.

Nor is it cheap... The operators will set you back $30, contact 
blocks are $10-20 each, the box you put it in is probably $50-100, 
etc.  But, hey, if you're paying a union electrician $65/hr to do the 
work, the labor will dominate.

Complicating this is that the terminology and nomenclature for 
industrial controls is a bit unusual, so you have a bit of a learning 
curve.  And, of course, it's designed to be installed by 
electricians, not computer installers, so there's nary a 8 conductor 
modular jack/plug to be found.  Your leatherman tool is your friend.

James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875 

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