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nuckolls.bob(at)aeroelect
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 Posted: Tue Mar 01, 2011 7:58 am Post subject: Toggle switch keyway convention: up vs. down |
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| Quote: | | I would take "keyway conventions" with a grain of salt! |
It's been about 15 years since I did much writing
about switches but I think the context under which
keyways are oriented has become a bit muddled.
Most switches are symmetrical . . . they function
the same no matter which side the keyway faces.
Further, the right and left sides can be interchanged
with no observable differences in functionality.
When we began to study the application of progressive
transfer switches I published drawings with numbered
terminals to assist the neophyte technician in getting
wires on the right terminals the first time. I discovered
that the way Microswitch and Carling built their progressive
switches was not the same. I had to publish this piece to
make folks aware of the differences:
http://www.aeroelectric.com/articles/Carling_Micro/Carling_Micro.pdf
. . . right and left hand columns were functionally
swapped between the two brands. In later years,
I think Carling swapped their progressive transfer
switches to conform to what the mil-spec guys
were doing.
Microswitch had numbers molded into their switch
housings as did the other high-end suppliers. So
I adopted THEIR convention for speaking to terminal
' numbering versus functionality.
Once you venture out of the purely symmetrical
world by adding spring loading to one side (or
single pole switches with only two terminals)
then there is risk that the desired functionality
cannot be achieved with the keyway oriented any
particular direction.
This is one reason why I've always recommended
that keyway engagement washers (shipped on all
products offered by AEC and I think B&C) . . .
be used on the BACK side of the panel. This way,
the hole in the panel for the keyway engagement
washer can be under a switch labeling placard . . .
or be so shallow that it does not penetrate the
panel. This allows one to have them above, below
or even changed after initial installation
causes one to discover the need to change it.
[img]cid:.0[/img]
Speaking of 'conventions' . . . you'll note
that the panel tab and keyway tabs are on
the same side of this locking ring. But
I've seen them on opposite sides too.
So the premise of this tread is correct, there
are no industry-wide "conventions" for marking,
functional orientation, or installation of
switches. There ARE standards . . . many of
them mil-specs that speak to widely adopted
configurations. But it's a free-market decision
by designers and manufacturers as to how
their particular product comes into the
marketplace. In the case of switches,
one would do well not to stray far from
what the majority of your competitors are
doing . . . a Croatian market street
vendor will find himself at a decided
disadvantage hawking wares in Swaheli.
Bob . . .
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roee
Joined: 28 Feb 2011
Posts: 6
Location: San Diego, CA
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| Posted: Tue Mar 01, 2011 10:31 pm Post subject: Re: Toggle switch keyway convention: up vs. down |
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This appears to be a duplicate thread, the above posting being a response to this original thread: http://forums.matronics.com/viewtopic.php?t=79809
The message above has been re-posted to the original thread, and additional subsequent messages have been posted there.
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mmayfield
Joined: 09 Oct 2009
Posts: 40
Location: NSW Central Coast, Australia
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| Posted: Wed Mar 02, 2011 4:19 am Post subject: Re: Toggle switch keyway convention: up vs. down |
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| roee wrote: | This appears to be a duplicate thread, the above posting being a response to this original thread: http://forums.matronics.com/viewtopic.php?t=79809
The message above has been re-posted to the original thread, and additional subsequent messages have been posted there. |
Yeah. Unfortunately the structure of Matronics Email Lists does that frequently. It's the price you pay for having a jack-of-all-trades email list. It bugs the living hell out of me because it often makes it hard to follow a thread chronologically through all the responses.
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Mike |
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nuckolls.bob(at)aeroelect
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| Posted: Wed Mar 02, 2011 6:33 am Post subject: Toggle switch keyway convention: up vs. down |
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| Quote: | All things being equal, where an industry-wide convention exists,
whether formal or informal / de facto (e.g. keyway down, I think
we've now established), then that would be the default first choice.
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I don't think I implied that. There is no convention
for mounting switches into the product, only a few standards
for orientation of the keyway for purposes of describing
functionality of any given switch. That can vary from
manufacturer to manufacturer EXCEPT for a preponderance
of respect to some mil-standards. The heavy hitters
like Honeywell, Cutler-Hammer, et. als. got their
growth spurts during WWII. If one intended to
to supply a switch, it WOULD be to a spec This
set some trends but it certainly didn't drive
the whole industry nor did it drive design goals
and outcomes for product.
| Quote: | And finally, having a mix-and-match hodge-podge throughout would be
the least desirable, though granted, occasional well-justified
exceptions to a convention may still exist.
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Depends on circuit design requirements. I've seen
test fixtures at Beech that would have had switches
mounted both ways on the same panel. And as others
have noted, in some cases, CONTACTS closed is not
SYSTEM on.
We've seen that not all switch (and CB) manufacturers and product
lines meet that criteria,
the 'criteria' is non-existent . . .
and I would factor that into my component selection process.
How? You would reject some device because of keyway
orientation? How about designing YOUR project
so that orientation doesn't matter and ANY functional
device can be used irrespective of orientation?
Bob . . .
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roee
Joined: 28 Feb 2011
Posts: 6
Location: San Diego, CA
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| Posted: Wed Mar 02, 2011 2:44 pm Post subject: Re: Toggle switch keyway convention: up vs. down |
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| Quote: |
There is no convention
for mounting switches into the product, only a few standards
for orientation of the keyway for purposes of describing
functionality of any given switch.
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I don't entirely agree. There seem to be multiple conflicting conventions out there, each with varying prevalence in different areas, hence this discussion. While there may be no formal standard conventions for mounting orientation in the form of mil-specs, etc., there do seem to exist de facto standard conventions. You yourself established one (keyway up) by your statement in the AEC, which granted is not a formal standards document, but nevertheless is referenced and adhered to by many amateur aircraft builders. And on the flip side, the switch specifications themselves from prominent manufacturers do often make direct references equating the keyway side to "down", which while certainly doesn't force the system designer to use the switch that way, does imply a de facto convention (keyway down) to their installation orientation which many system designers will adhere to, all else being equal, to avoid confusion. I don't know how commonly that's adhered to in the field of GA, and I'm curious to find out. I'll survey a few different aircraft types next time I'm at the airport to satisfy that curiosity.
| Quote: |
Depends on circuit design requirements. I've seen
test fixtures at Beech that would have had switches
mounted both ways on the same panel. And as others
have noted, in some cases, CONTACTS closed is not
SYSTEM on.
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Yep, as noted, some well-justified exceptions to a convention may exist in a system. But there too, an exception can often be just as easily avoided. For example, as has been noted, in many cases one can use a symmetric switch where one isn't technically needed, and thereby be able to maintain a uniform keyway orientation convention, as well as minimize unique part count. An example of this would be a magneto P-lead, where contact closed is system off, versus switching power to a load, where contact closed is system on. In both cases, use a three-terminal ON-ON switch instead of the two-terminal ON-OFF switch, and you can stick to your chosen keyway orientation convention, whatever it might be. The ON-ON switch might be slightly more expensive, but in this case I would consider this a good trade-off.
| Quote: |
and I would factor that into my component selection process.
How? You would reject some device because of keyway
orientation?
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Not as a hard rule, but all else being equal, yes. How? Well, where there does exist a de facto standard for the contact numbering and the keyway orientation relative to the contact numbering, then I would favor a component whose specification conforms to that de facto standard over one that does not. Helps avoid future confusion such as that created by the early Carling switches, as you described.
| Quote: |
How about designing YOUR project
so that orientation doesn't matter and ANY functional
device can be used irrespective of orientation?
|
With few exceptions, yes.
-Roee
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nuckolls.bob(at)aeroelect
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| Posted: Wed Mar 02, 2011 6:11 pm Post subject: Toggle switch keyway convention: up vs. down |
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At 05:44 PM 3/2/2011, you wrote:
| Quote: |
>
> There is no convention
> for mounting switches into the product, only a few standards
> for orientation of the keyway for purposes of describing
> functionality of any given switch.
>
I don't entirely agree. There seem to be multiple conflicting
conventions out there
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. . . if there's more than one and they do not conform to each
other, is this not prima-facie demonstration that no such convention
exists?
Bob . . .
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roee
Joined: 28 Feb 2011
Posts: 6
Location: San Diego, CA
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| Posted: Wed Mar 02, 2011 7:23 pm Post subject: Re: Toggle switch keyway convention: up vs. down |
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| nuckolls.bob(at)aeroelect wrote: |
. . . if there's more than one and they do not conform to each
other, is this not prima-facie demonstration that no such convention
exists?
Bob . . . |
No, I don't think it is. Even if there doesn't exist a single universally-adopted convention, there can still exist one or more conventions that are adopted within more limited scopes. And it appears to me that that's indeed the case here.
Anyhow... We don't need to debate the semantics of what constitutes a convention, nor the merits of employing one. My original query, fundamentally, was about what non-obvious practical factors may exist to favor one choice over the other (keyway up vs. down) when the choice appears otherwise arbitrary. And that question is pertinent whether making the choice on a case-by-case basis or in adopting a broader convention. The question of whether or not conventions exist in industry, and whether they're driven by practical considerations or arbitrary aesthetics if they do exist, is actually ancillary to the core issue. I wrote my original posting as an inquiry to what was behind the convention expressed in the AEC, since no further explanation of it was offered there (your explanation here regarding the Carling switches cleared that up). In retrospect, I should have phrased my query differently such as to avoid making the discussion convention-centric.
Anyway, I think I've got the answers I needed. I do appreciate your input.
-Roee
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