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101
TECHNICAL INFORMATION
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Technical information
Beam formula
Conclusion
Referring to the load span tables on pages 00-00
for B-905 channel, a 36-inch span has a uniformly
distributed load rating of 1,133 lbs., which is
greater than the 390 lb. load calculated above,
and is therefore satisfactory.
On longer spans or spans with greater loads, use
B-901, B-900-2A or B-905-2A channel or provide an
intermediate support.
Note on conduit support (see Figure 02)
The National Electrical Code
®
states the rigid metal
conduit, intermediate metal conduit, and electrical
metallic tubing shall be supported at least
every 10 ft. See Article 344, Section 344.30 for
exceptions for rigid metal conduit.
Problem (see Figure 01)
Design trapeze to support 8 – 2" rigid steel conduits
and 2 – 3" rigid steel conduits on a No. B-905 channel
span with hangers spaced 5 ft apart.
Weight per Hanger Equals
2" rigid steel conduit with heaviest conductor
combination = 6.625 (lbs/ft).
3" rigid steel conduit with heaviest conductor
combination = 13.415 (lbs/ft).
8 x 6.625 x 5 = 265 lbs = weight of 2" conduits
per hanger
2 x 13.415 x 5 = 134 lbs = weight of 3" conduits
per hanger
Total = 399 lbs
= weight of conduits
per hanger
Beam formula
For calculating deflection and maximum safe load
(Beams of uniform cross section):
I
S = Section modulus – in position of load( l/n), in (in)³.
f
E
L = Length of section, in inches.
W
W Max.
M
D, D1 = Deflections at points given, in inches.
D Max. = Maximum deflection at point given, in inches.
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01 NEC and National
Electrical Code are
registered trademarks
of the National Fire
Steel and aluminum - Modulus of elasticity (E)
Steel and aluminum - Maximum fiber stress (f)
2" 2"
2"
2"
2"2"
2"2"
3"
3"
1
3
/16
1
17
/32
1
3
/16
36"
3
1
/83
1
/8
3
1
/8
3
1
/83
3
/4
3
1
/8
3
1
/83
3
/44
5
/16
1
17
/32
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01
—
02
5"
36"
M
M
L
L
D
W
X
X
½
½
R
R
R
R
M
M
L
L
X
D
D
½½
D
R
R
W W
W W
W
D
36"
2" 2" 2" 2" 2" 2" 2" 2"
3" 3"
3¾ 3¾