More on the 3b2/Lisa software-power-disconnect brouhaha...

[Rael's brother John]

Summary: it's probably legal, but I still don't like it
Line eater: enabled

Well, I have recently had a chance to examine some sections of the National
Electrical Code, it appears that there is probably not a code problem with
the 3b2's software-controlled power down after all.  After rereading section
522, which defines "appliances" and the supplying of power to such, it appears
that the 3b2 and Lisa qualify as "portable" appliances.  The definition of
"portable" is that if isn't bolted down or otherwise attached to the building
structure, it qualifies as portable.  For most 120-volt devices of this class,
the plug at the end of the power cord meets the requirements for a cutoff,
as long as the device has a line fuse or circuit breaker built into it.
The only condition is that the circuit breaker that supplies the outlet which
the computer is plugged into must be "readily accessible", meaning that it
must not: (1) be in a locked area, (2) be above a drop ceiling or under a
raised floor, (3) be too high off the floor to reach without a stepladder
(6 1/2 feet is the suggested limit), and (4) be obstructed by furniture,
crates, boxes, etc.  All construction done within the last 25 years or so
should meet these requirements; some old buildings may have problems.
(One point here, and this comment applies to any computer, not just to 3b2's:
even though the device is UL- or CSA-listed, and the building wiring has
been inspected and approved, it is possible to combine the two in such a
way that a code violation occurs.)

(Incidentally, for people who are wondering where this code comes from:
it is generated by an organization called the National Fire Protection
Association, sort of an ANSI for electrical wiring codes.  Although the
NFPA is not a government body and has no power of enforcement by itself,
the Code is frequently cited in court cases, and local governments often
adopt it verbatim as their local code.  So, it has a lot of influence
in its field.)

There are still a couple of aspects of this which I haven't figured out yet.
I am trying to decipher just what types of things are acceptable as a
"disconnect"; it varies from one class of equipment to another.  (For
example, for some low-power equipment, a screw-out line fuse holder is
acceptable as a disconnect; for others, it isn't.)  There is a section
(762 I think) which defines specific requirements for "data-processing
equipment", but I haven't been able to locate a concise definition of
that term.  Much of that section talks about underfloor wiring, cable
raceways and such, so I suspect that it doesn't apply to micros, but I
can't say for sure.  Also, this section references a separate NFPA document
which specifically addresses wiring concerns for computers, but I haven't
managed to locate that document yet.

I will continue my research and try to solicit opinions from engineers
who are more qualified than I to make these kinds of judgements.  So far,
it appears that software-controller power disconnect is legal.  But I still
don't like it.
---
"I used to be able to sing the blues, but now I have too much money."
-- Bruce Dickinson

Dave Cornutt, Gould Computer Systems, Ft. Lauderdale, FL
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 or ...!{ucf-cs,allegra,codas}!novavax!houligan!dcornutt
ARPA: dcornutt at gswd-vms.arpa (I'm not sure how well this works)

"The opinions expressed herein are not necessarily those of my employer,
not necessarily mine, and probably not necessary."