Clarification of Answer by
28 Sep 2003 13:21 PDT
Certainly! The recommendation of a 50% safety factor is also to be
found on the following webpage, in Chapter 3 of a manual discussing
'Marine Electricity, circuits, and theory', under 'Power Rating':
"In most circuits, the actual power a resistor uses is considerably
less than the power rating of the resistor because a 50 percent
safety factor is used."
However, it is easy to find citations which recommend utilizing
a resistor with a power rating 2 or more times the expected
wattage. Given that the resistor is often the least expensive
component in the circuit, it can't hurt, and it allows for
atypical fluctuations in the circuitry, such as might be
found, e.g., during power-up:
Play-Hookey.com is another goldmine of information on several
topics. On a page about resistors, from their discussion of DC
theory, the following is noted:
"A general rule of thumb is to always select a resistor whose
power rating is at least double the amount of power it will
be expected to handle. That way, it will be able to dissipate
any heat it generates very quickly, and will operate at normal
temperatures." (about the middle of the page):
Likewise, at the site of Power Technology Incorporated, who
design and manufacture high-quality lasers, they have a
technical library which includes a page on ballast resistors:
"...we recommend de-rating the resistor wattage by 50% or more."
Which is to say, if a resistor is rated at 2 watts, use it in
a circuit calling for a 1 watt resistor.
And, for an even 3, here is a page from the Staco Switch site,
titled 'StacoSwitch's rugged duty Keypads' Lighting and
Switching Overview' which also recommends doubling:
"It is good idea to at least double the power rating of the
If anything is unclear, or the links don't work, please
feel free to post another Request for Clarification.
Search results were obtained from the original search:
resistor "power rating"