shall be marked to show the maximum surface temperature referenced to a 40°C ambient, or at the higher marked ambient temperature if the equipment
is rated and marked for an ambient temperature of greater than 40°C. For equipment
installed in a Zone
20 or Zone
, the operating temperature shall be based on operation of the equipment
when blanketed with the maximum amount of dust (or with dust-simulating fibers/flyings) that can accumulate on the equipment
. Electrical equipment
designed for use in the ambient temperature range between -20°C and +40°C shall require no additional ambient temperature marking. Electrical equipment
that is designed for use in a range of ambient temperatures other than -20°C and +40°C is considered to be special; and the ambient temperature range shall then be marked on the equipment
, including either the symbol "Ta" or "Tamb" together with the special range of ambient temperatures.
Informational Note: As an example, such a marking might be "—30°C ≤ Ta ≤ +40°C."
Exception No. 1: Equipment of the non-heat-producing type, such as conduit fittings, shall not be required to have a marked operating temperature.
Exception No. 2: Equipment identified for Class II, Division 1 or Class II, Division 2 locations as permitted by 506.20(B) and (C) shall be permitted to be marked in accordance with 500.8(C) and Table 500.8(C).