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Table 28.2
Spacings for converters or inverters intended for use within a protected environment
Table 28.2 effective April 13, 1993
Involved in V
RMS (Peak)
Minimum spacings, inch (mm)
Between any uninsulated live part and an uninsulated live part of
opposite polarity, uninsulated grounded part other than the
enclosure, or exposed metal part
a, d
Between any uninsulated live
part and the walls of a metal
enclosure including a fitting for
conduit or armored cable
b
,
shortest distance
Through air Over surface
0–50
(0 – 70.7) 3/64 (1.2)
c
3/64 (1.2)
c
1/16 (1.6)
c
51 –125
(70.8 – 176.8) 1/16 (1.6)
c, e
1/16 (1.6)
c, e
1/4 (6.4)
126 – 250
(176.9 – 353.5) 3/32 (2.4)
c, e
3/32 (2.4)
c, e
1/2 (12.7)
251 – 600
(353.6 – 848.5) 3/8 (9.5) 1/2 (12.7) 1/2 (12.7)
a
For printed wiring boards, see Exception Nos.2–4of28.1.1.
b
For the purpose of this requirement, a metal piece attached to the enclosure is considered to be a part of the enclosure if
deformation of the enclosure is likely to reduce spacings between the adjacent metal piece and uninsulated live parts.
c
The spacing between field-wiring terminals of opposite polarity and the spacing between a field-wiring terminal and a ground
dead-metal part shall not be less than 1/4 inch (6.4 mm).
d
On printed wiring boards, their connectors and board-mounted components, wired on the load side of line filters or other
similar-voltage-peak-reduction networks or components, or both, a minimum spacing of 0.023 inch (0.58 mm) plus 0.0002 inch
(0.005 mm) per volt peak shall be maintained over surface and through air between uninsulated live parts and any other
uninsulated conductive part (live or dead) not of the same polarity.
e
At closed-in points only, such as a screw and washer construction of an insulated stud mounted in metal, a spacing of 3/64
inch (1.2 mm) is acceptable.
28.1.7 With reference to Exception No. 2 to 28.1.1 concerning conformal coatings, minimum spacings of
1/32 inch (0.8 mm) between adjacent foils shall be maintained. A conformal coating on printed wiring
boards is not considered as insulation in lieu of spacings between a foil on a printed wiring board and
uninsulated live-metal parts of opposite polarity or to uninsulated dead-metal parts.
28.1.7 effective April 13, 1993
DECEMBER 14, 1993UL 45840
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