CASA Modular Systems, New Zealand
Subject:
Some Fuse & Fuseholder Basics
Respecting their Importance
2nd Draft (4 pages for
comment/criticism)
Preamble:
Having been working on
CASA’s fuses consistently for the past 10 days it seems time to reflect upon
their importance… …and upon their value so often trivialised!
CASA probably has 5~10,000,
current,
legacy and special type, fuse elements and fuse-holders ranging from 2mA to 800
Amps and they (perhaps 300
line-items) need to be catalogued
and sold…. …a job that has received
only sporadic/spasmodic attention… …except for some on-a
customer’s apparent need-to-know… …an overview of the assortments and the
beginning of stock-keeping consolidation essential following the various moves
of the past 25 years.
We do have a small
representation of fuse-products listed on our ZenCart eCommerce site under
“Circuit-Protection”:
http://casamodularsystems.com/index.php?main_page=index&cPath=65_137
The maturing lists and
accumulating data/reference resources are on our local server:
http://www.casa.co.nz/Electrics/Fuses/
Introduction:
With the reducing price (higher production volumes) and availability of resettable fuses (PTC), circuit-breakers
and other current limiting and transient-energy absorbing devices, conventional
fuses seem to be less in demand… …furthermore, fuses are being ‘engineered’ out
of electrical/electronic circuitry or internalised rather than visible to the
equipment owner/user. This begs the
question:
Q: Who are the fuse
customers of the new millennium?
A: The multiplicity of
electrical merchants and their shelf stocks may deserve a little recognisance… …and a few pertinent questions to their staff… …and
hand-out a picture-listing of CASA’s galleries to show what CASA has to help
them satisfy any enquiries they can’t meet from their current shelf-stock.
So What is an
Electrical Fuse?
A
fuse is one kind of over-current safety-protection device for electrical
equipment.
An electrical fuse is
essentially a sacrificial energy absorbing short-duration explosive device, contained within a suitable enclosure to eliminate (or
minimise) secondary effects in its near vicinity… …the ‘exploded’ fuse
hereby protects electrical apparatus from bigger explosions or other (extraneous)
destructive effects of the out-of-design condition J.
As described, a fuse must be carefully
chosen so as to ensure that, under conditions that exceed its design-limits (continuous
current carrying rating for the load equipment/apparatus the fuse ‘explodes’
melts or vaporises or otherwise) the fuse becomes a strategic discontinuity,
and the fault condition is rendered safe or minimal damages occur except
to the sacrificial fuse element itself.
The fuse is hereby a
short-duration electrical-energy absorbing device that acts in defence of some
defined or un-defined fault condition. A fuse is an insurance-device with a
premium paid in the equipment-design and fuse-implementation…
..post event, the fuse’s replacement cost is but a tiny fraction of the
potential costs of damages to the otherwise under-protected electrical
apparatus.
Note – an
electrical-fuse does not ‘fuse’ (bond-together or fuze), however, given
the energy that electrical-fuses are often connected too it is not surprising
that the ‘fuse’ was so named…J
Design Diversity
Because the defined and
undefined conditions needing to be addressed in the diverse operational
contingencies, many kinds of electrical fuses have been created and the proven
popular amongst these are widely adopted into international standards and
patronised by industry and others seeking to identify with the specifications
that regularise design integrity and risk-management.
As new generations of
electrical apparatus are invented and commissioned new fuse designs are needed
for the safety of the equipment, its infrastructure, and the safety of persons
using, or near to, the equipment.
Energy Absorption & Fuse Ratings
To be effective a fuse must
be carefully chosen so as to sacrifice itself (by melting or other
discontinuity) under any over-current or transient condition for which the
equipment was/is not designed operate (or safely endure). The
chosen/specified fuse must be capable of dissipating the maximum rated fusing
energy without dangerous consequences to the fuse-holder (or equipment or
container etc.).
The energy is
expresses in Watt-Seconds (Joules) and is a function of the current
flowing, the resistance of the fuse-element and the voltage. The energy numbers
can get very big once we get out of the modest home supply environment:
Volts x Amps x seconds = Joules
250V @ 10 Amps for 1 second (the hypothetical time for a fuse to respond) = 2,500 Joules (2.5kWatt-Seconds)
An arc-welder primary of 400V @ 60A for 3 seconds =
72,000 Joules
Above illustrates that as the
energy gets high we need to adopt the use of HRC (high-rupturing
capacity) fuses which are designed to endure (contain) the dissipation
of large fusing energy. Arcs, flames, fires and plasma are typical consequences
of improper fusing design and implementation or maintenance.
http://arcadvisor.com/faq/electrical-explosion
Note - As an appreciation of 2500 joules we may relate
this to calories:
What Makes up a
Typical Electrical Fuse?
Various pre-fusing and post
fuse-conditions may exist that differ with AC and DC voltages and
Radio-Frequency Voltages and the materials of which the fuse-cartridge and its
container are made and their dimensions and other properties are all carefully
selected to ensure reliable performance and the durability of containers where
re-use by the installation of new fuse-cartridges is practical.
The fuse-cartridge and
fuse-holder manufacturing industries are well practiced in the selection of
materials and the designs that meet recognised specifications required by the
electrical and related industries and appropriated by national and
international standards etc.
According to the Deverell
Filter Theory, “everything is a filter” (or my be considered as such for the purpose
of analysis)… …therefore a fuse is a
filter… …a fuse is a filter with a finite current carrying capacity… …a
band-pass-filter till confronted with an excess of current when it changes into
a band-stop-filter and stays in that state till physically replaced.
Everything in an electrical
circuit is a potential ‘fuse’… …the impedance of any continuous circuit limits
the current that can flow so that in order to ‘act’ any fuse must be of a
resistance less than the resistance of any other component in the circuit… …the
combined thermal and physical characteristics of the fuse needs to be chosen so
that it melts (or otherwise become discontinuous) according to the
strategic requirements of the system-design.
What are the 3 most
critical parameters for fuses?
1)
The working
voltage rating… …must suit or exceed the operational voltage to which the
equipment is connected
2)
The
carrying current capacity… …this rating must provide
continuous/indefinite running of the equipment under its normal (appropriate) functional conditions.
3)
The time/response-characteristic
under start-up and/or fault/transcient conditions
Warning - a fuse that does not ‘fuse’ when needed is a ‘fizzer’
J… …an anti-band-stop filter J …perhaps a bi-stable-filter?
What do others have to say by
way of descriptions or definition?
https://en.wikipedia.org/wiki/Fuse_(electrical)
“…a fuse is an
electrical safety device that operates to provide overcurrent
protection of an electrical circuit…”
https://www.dictionary.com/browse/fuse?s=t
“…a protective device, used in an electric circuit,
containing a conductor that melts under heat produced by an excess current,
thereby opening the circuit…”
A Scotsman tells it all… …or nearly enough to encourage appropriate caution… …and some very pertinent warnings t’-boot:
https://www.youtube.com/watch?v=kx35WN3uLis
Amongst the competition and/or potential wholesale customers are:
https://www.vynco.co.nz/products/circuit-protection/fuse-holders
https://nz.element14.com/c/circuit-protection/fuses-fuse-accessories/fuses/cartridge-fuses
https://nz.rs-online.com/web/c/fuses-sockets-circuit-breakers/fuses/cartridge-fuses/
A few graphics, illustrations, cartoons or real-world examples to further encourage our respect:
TBA
Kind regards - AlanD