ANSI UL 458 - Maximum Output Without Fan Operation; Zero Clearance

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37.1.11 A temperature is considered to be constant when three successive readings taken at intervals of
10 percent of the previously elapsed duration of the test, but not less than 15 minutes, indicate no further
increase.
37.2 Maximum output without fan operation
37.2.1 A converter or inverter employing a cooling fan, the operation of which is controlled by a
thermostat or other thermal sensing device or component, is to be operated under the conditions
described in 37.1.1 – 37.1.11 except that the load is to be reduced to the maximum load it can carry
without resulting in operation of the cooling fan. The converter shall comply with the temperature limits
specified in Tables 37.1 and 37.2.
37.2.1 effective April 13, 1993
37.3 Zero clearance
37.3.1 A converter or inverter mounted in a wooden enclosure as described in 37.3.2 and 37.3.3 shall
comply with the requirements in 37.1.1 – 37.2.1. In addition, the surface temperatures on parts exposed
to contact on a converter or inverter for flush-wall installation shall not exceed those specified in Table
37.3.
Exception No. 1: A protective device may cycle during the test.
Exception No. 2: A temperature rise may be 20°C (36°F) greater than that specified in Table 37.1.
37.3.1 revised January 27, 1995
Table 37.3
Maximum acceptable temperature limits
Degrees
CF
A. Surfaces
Bare or painted metal 67 153
Porcelain enamel 71 160
Glass 78 172
Plastic
a
83 181
B. Handles and knobs
Bare or painted metal 55 131
Glass 65 149
Plastic
a
75 167
a
Includes plastic with a metal plating not more than 0.005 inch (0.13 mm) thick; and metal with a plastic or vinyl covering not
less than 0.005 inch thick.
JANUARY 27, 1995 UL 458 55