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Rockwell Automation Publication 2100-IN012D-EN-P - September 2010
Chapter 7
Final Checklist Before Energizing
Required Minimum
Electrical Spacing
.
Table 7 - General Spacing Requirements for MCCs
(1)
(2)
(3)
(1) Reference Underwriters Laboratories, Inc. Standards for Motor Control Centers, UL 845, Tables 16.1 and 16.3.
(2) Spacings at all horizontal and vertical buses, at incoming terminals, at the plug-in portion of all units and at
feeder units consisting of fusible disconnect switches or circuit breakers only, having other than horsepower
ratings, shall be as specified above. (See 17.2.2 from UL 345.)
(3) An isolated dead metal part, such as a screw head or a washer, interposed between uninsulated live parts of
opposite polarity or between an uninsulated live part and grounded dead metal is considered to reduce the
spacing by an amount equal to the dimension of the interposed part along the path of measurement.
Voltage
Min Spacing, in. (mm)
Between Live Parts of Opposite Polarity
Between Live Parts and
Grounded Metal Parts,
Through Air and Over
Surface
Through Air
Over Surface
125 or less
1/2 in. (12.7 mm)
3/4 in. (19.1 mm)
1/2 in. (12.7 mm)
126...250
3/4 in. (19.1 mm)
1.25 in. (31.8 mm)
1/2 in. (12.7 mm)
251...600
1 in. (25.4 mm)
2 in. (50.8 mm)
1 in. (25.4 mm)
(4)
(4) A through-air spacing of not less than 1/2 in. (12.7 mm) is acceptable at a circuit breaker or fusible
disconnecting means and between grounded dead metal and the neutral of a 277/480V, three-phase, four-wire
MCC.
Table 8 - Spacing Requirements within MCC Units
(1)
(2)
(3)
(1) Reference Underwriters Laboratories, Inc. Standards for Motor Control Centers, UL 845, Tables 16.1 and 16.3.
Voltage
Min Spacing, in. (mm)
Between Uninsulated Live Parts of
Opposite Polarity and Between an
Uninsulated Live Part and an Exposed or
Uninsulated Dead Metal Part other than
the Enclosure
Between Uninsulated Live
Parts and the Walls of a Metal
Enclosure
(3)
, Including Fittings
for Conduit or Armored Cable
(3) The enclosure refers to the section enclosure.
A
metal piece attached to the enclosure is considered a part of the enclosure
for the purpose of this note if deformation of the enclosure is likely to
reduce the spacing between the metal piece and a live part.
Through Air
Over Surface
Shortest Distance
125 or less
1/8 in. (3.2 mm)
(2)
(2) The spacing between wiring terminals of opposite polarity shall not be less than 1/4 in. (6.4 mm) if the terminals
are in the same plane.
1/4 in. (6.4 mm)
1/2 in. (12.7 mm)
126...250
1/4 in. (6.4 mm)
3.8 in. (9.5 mm)
1/2 in. (12.7 mm)
251...600
3.8 in. (9.5 mm)
1/2 in. (12.7 mm)
1/2 in. (12.7 mm)
