Buying Guide
Table Of Contents
The Joule rating should not be a method for specifying or
comparing SPD’s
Due to the ambiguity of this SPD/joule conundrum, there is no recognized
standard for SPD joule ratings. Joule ratings do not correlate with the
performance or let-through voltage of the SPD. Because a joule is dened with
time (Watt-second), there may be various numerations based on time. These
may include joules based on small leakage currents over years, joules based
on time specications of industry accepted wave shapes, or joules based on
time before SPD failure.
• A Joule is a unit of energy dened as a Watt-second.
• Joules could appear to be an satisfactory unit-of-measure for SPD’s,
however, industry associations, such as the National Electrical Manufacturers
Association or the Institute of Electrical and Electronic Engineers do not
recommend using joules as the only method of selecting a SPD.
• While consumer class SPD’s use Joule ratings for marketing purposes, this
is a problematical way to compare suppressors. There are fundamental
deciencies using Joule ratings for SPD’s.
Joules
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