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Sam
Joined: 18 May 2008
Posts: 135
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 Posted: Sat Jul 18, 2009 9:24 am Post subject: Fuselinks & breakers |
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Bob, in several of your Z drawings, you show a fuselink in series with a breaker. For instance, Z-18. You also have a fuselink and a breaker separated only by a relay in Z-18RB.
What is the rationale behind this seemingly redundant layout?
Thanks
Sam Hoskins
(Not related to Hoskins fuel systems)
[quote][b]
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Sam Hoskins
www.samhoskins.blogspot.com |
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 19, 2009 8:57 am Post subject: Fuselinks & breakers |
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At 12:15 PM 7/18/2009, you wrote:
| Quote: | Bob, in several of your Z drawings, you show a fuselink in series
with a breaker. For instance, Z-18. You also have a fuselink and a
breaker separated only by a relay in Z-18RB.
What is the rationale behind this seemingly redundant layout?
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Fusible links are not to be confused or even placed
in the same class as breakers and the run-o-the-mill
plastic fuses. Not all that is offered as a "circuit
protective device" has the same design goals.
Fuses are VERY FAST acting devices compared to
thermal breakers. Fusible links and the ANN/ANL
"current limiters" are VERY SLOW compared to the
breakers and slower still compared to fuses.
In the cases you cited, the protective device upstream
of a crowbar ov protection system needs to be pilot
re-setable . . . but when combined with remotely
mounted fuse blocks, a "extension" of the main bus
bar up to the field breaker, the legacy design goals
call for some form of protection for the extended
bus that drives the one and only breaker. However,
it must be MUCH more robust protection than the breaker
itself. I.e., feeders protected with ANL limiters or
fusible links.
Fusible links and current limiters are SPECIAL,
robust forms of circuit protection which are NOT
interchangeable with fuses and breakers on distribution
feeders. They are recommended for use only in
situations described in the Z-figures.
I had a builder some years ago share his wiring diagram
with me concerning some other issues wherein he had
scattered a number of fusible links around the system.
Your car has one, maybe two fusible links. All other
circuit protection is breakers, fuses or polyfuses
specifically tailored to the protection task. Before
you do anything with links or limiters, let's talk about
it here on the list before you do it. Further, the
short answer to your question is that the buss extension
up to the breakers cited is classically protected by
some extra-robust device at the feeder end.
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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