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nuckolls.bob(at)aeroelect
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 Posted: Mon May 25, 2009 4:20 am Post subject: Military style external power receptacle question |
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At 04:15 PM 5/24/2009, you wrote:
| Quote: |
<johngoodman(at)earthlink.net>
Looking at Bob's wiring diagram in Appendix Z, 31A, for a military
style external power receptacle, what is the function of the smaller
third pin? Just guessing by the schematic it's hot power, just like
the middle pin.
Inquiring minds want to know........
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It's a pretty subtle thing . . . not obvious without
some attention to the little details.
The third pin is much shorter than the other two
fat pins. This means that as you push the socket
onto the pins, the two fat ones are electrically
engaged before the third pin mates and current
flows.
Similarly, assume you're pulling the plug out of a
ground power connector that is loaded. The
third pin breaks first and de-energizes the system
before the fat pins break.
In some applications, this connector can be loaded
to hundreds of amp at 28V. That kind of power makes
for long hot sparks during a slow make/break operation.
The pins of the connector are not designed to work
like a contactor and are subject to damage if not
made or broken "cold".
Using the third pin to control the ground power
contactor prevents damage to the connector from
a hot make or break of the main power pins.
Finally, the smaller size of the third pin provides
"polarization" for the mated connector halves. If
on tried to plug it in backwards the differences in
sizes prevents any form of engagement from taking
place.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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johngoodman
Joined: 18 Sep 2006
Posts: 530
Location: GA
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| Posted: Mon May 25, 2009 10:26 am Post subject: Re: Military style external power receptacle question |
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Bob,
Thanks!
John
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