84 Publication 2100-IN012C-EN-P - April 2009
Chapter 7 Final Check List Before Energizing
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General Spacing Requirements for MCCs
(1)
(2)
(3)
Voltage
Min Spacing, in. (mm)
Between Live Parts of Opposite Polarity Between Live Parts and
Grounded Metal Parts,
Through Air and Over
SurfaceThrough 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)
(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.
(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.
Spacing Requirements within MCC Units
(1)
(2)
(3)
Voltage
Min Spacing, mm (in.)
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
Through Air Over Surface Shortest Distance
125 or less
1/8 in. (3.2 mm)
(2)
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)
(1)
Reference Underwriters Laboratories, Inc. Standards for Motor Control Centers, UL 845, Tables 16.1 and 16.3.
(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.
(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.
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