HomeMy WebLinkAboutFax-9/30/02 (Vos Electric)
. SEp',30.2002 10:03AM VOS ELECTRIC, INC.
NO. 861 P.1/7
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3131 MARKET ST. GREEN BAY, WI 54304
(920) 336"0781 FAX 920~336-0792
FACSIMILE COVER PAGE
DATE: 7 - ao:- o$l.
This transmission consists of 7 pages, including the cover.
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TechnlCBIlnfonnation & Teohnjcal fill.llletlns
B. DERATING FOR AMBIENT TEMPERATURE
All ampacity tables necessarily must use some ambient temperature as a basis and NEe Table 310-16
uses 300e (860F), At the bottom of the table, correction factors are given for situations where the ambient
is expected to be higher or lOwer thall 300c (S60F). Use of these factors Is fairly straightforward; for
example, what is the ampacity of a 1/0 AWG, aluminum. type THHN conductor wilen U1e ambient
temperature is 1 OQ"F? The answer is found by taking the ampacity from the table and multiplying It by the
appropriate correction factor. In ttlis example, we would have 135)( 0.91 -122.85 amperes.
c. DEAATING FOR NUMBER OF CONDUCTORS
Note 8 t(l the ampacity tables in the NEe contains the requirement columns for derating ampacity ~use
of adjacent current-canying conductors. Thts note states that when the number of conductors In a raceway
or cable exceeds 3, the ampacltJes are to be reduced by the appropriate percentage. In the 1999 NEe, a
column of factors is given. Fnr example. what is the ampacity of twelve No. 12 copper THHN conductors
installed in one conduit? From Table 31()..16 the ampaclty (in the table) is SO amperes. From Note e. the
derating factor for 12 conductors Is 50 percent. 30 x 0.5 :;: 15 amperes per conductor.
D. DERATING FOR BOTH AMBIENT TEMPERATUR.E AND NUMBER OF CONDUCTORS
When derating for both conditions is necessary, then both calculations must be made. For example. what is
the ampacity of four 1/0 THW copper conductors when the ambient temperature is expected to reach
110"F? From Table 310..16 tM ampaelty is 150 amperes, derating factor fol' 11 OOF is 0.82, and derating
factor from Note 8 for 4 eonduetots is 80 percent. 150 x 0.82 x 0.8 = 98.4 amperes.
( RECOMMENDED PULLING TENSION)
FOR
PULLING CONDUCTORS IN RACEWAYS
The force required to pull II cable or cables into a raceway depends on the cable weight, the friction
coefficient and the raceway length. The following information is based on a study sponsored by the ICEA:
The maximum puning tension placed on a cable should not exceed tI1e following:
1. ~ cable equipped with a pulling eye or bolt attached to the conductor:
~ For copper of any temper and hard-c:lrawn aluminum conductor 0.008 Ib/cmiJ times the
circular mil area of the conductor(s), and.
B. For 3/4 hard drawn aluminum 0.006 Ib/cmil times the circular mil area of the conductor(s).
2. For cable to be pulled with a cable grip over the sheath:
A. For cable with a lead sheath 1500 Ibs.fsquare Inch of lead cross-sectional area:
A = nt (D-t)
where A := cross-sectional area of lead (square inches)
t = sheath thickness (inches)
P = overall diameter of cable (inches)
o Soutltwjre-
6SOuI/poIra"~ rogIaI8NllWIdelI'IlldC or StM~m ~y.
One Southwll9 Drtv.
Carrollton, GA ~11B uSA
7701832-4242
www.$oulhwife.llom
SEP.30.2002 10:03AM
VOS ELECTRIC, INC.
. -- - --NO.861 . "P.3/7.
Tedlnicat InfQrmatio., & Technical Bulleljns
B. For a cable grip over nonleadjacketed cable, the maximum PLlUlng tension should
not exceed 1000 Ibs. and, of course, may not exceed the maximum tension
calculated per 1 above. The pulling tension for a given installation may be
calculated from the folloWing formulas.
T = ... x W x f (fora straight section) (1)
where T = Pulling tension (Ibs.)
L = Length of Raceway Run (feet)
W = Weight of cable (Ibs./ft)
f :; Coefficient of friction
(Generally taken as 0.5)
T = T\l;;:: T,efl (for a raceway with a bend) (2)
where T 2 = Tension for the straight section following the bend (Ibs.)
T, :; Tension for the sbaight section preceding the bend (Ibs.)
e ::: Natural log base (2.718)
f ::: Coefficient of frietion
a = Angle of bend (radians)
As an aid in solving the above fonnula. Table 1 is offered listing the values of e" for
common angles.
TABLE I: Calculated (eta) Values
Bend Angle f .. 0.40 f .. C>>.50 h0.75
in degrees
15 '.'1 1.14 1,22
30 1.l!3 UO 1.48
4$ 1.37 1.48 1.80
60 1.52 1.69 2.19
90 1.87 2.19 3.25
The maximum sidewall pressure should not exceed 300 Ibslft of radius. I. e., 1I1e tension in the cable
immediately folloWing a bend must not exceed 300 times the bend radius (in feet). For a sampte
calculation. assume th& following raceway plan.
A
iD~..
70' 10'R
450
10'f{ C
B
200'
Cable 3 1/C 500 kcmil. 0.175 wall, shielded, triptexed. Op = 3.02"
Weight::: 6.35 IbsJft. (copper conductor f = 0.5)
Pull from A to F
Normally the tension calculation is a progressiVe one as follows:
Tension at B (T,) ;: 200 x 6.35 X 0.$ = 635 Ibs. (from sq.1)
Tension at C (Ta) = T ,eft = 635 x 1.48 = 940Ibs,
Tension at 0 (T J ;; ~O + (70 x 6.36 x 0.5)1;; 1162 Ibs.
Tension at IE (TJ = T 38" = 1162 x2.19 = 2545Ibs.
Tension at F (Tj) = 2545 + (100 x 6.35 x 0.5) == 286S Ibs. total
o Soathwire.
g .,.,...114 OIl Recydoll Plflltr
~DI1l ,~. 80UlAWh CompOWlY.
AQ RlgI\CG Fl9Hrwd.
61-4
,SEP.30.2002 10:03AM
VOS ELECTRIC, INC.
----NO.B6t"" "P.4/T - .....-
Technleallnformation & Techl'lical Bulletins
0'Illll8
Maximum permissible pulling tension on this cable equipped with a pulling eye bolt is
0.008 x 500,000 x 3 = 12.000 lbs.
Sidewall Pressure (at C);;: 940/10 = 94lbs.lft.
Sidewall Pressure (at E) = 254511 0 ;;: 255 Ibs./ft.
Be<l8Use the sidewall pressure at E is rather high (through not outside design limits) it would be desirable
to investigate the results if the cable is pulled from F to A.
Tension at E (Ts) = 100 x 6.35 x 0.5 = 318 Ibs.
nmsion at 0 (Tt) ;;: 318 x 2.19 == 6961bs.
Tension at C (T,) = 696 + (70 x 6.35 x 0.5) = 9181bs.
Tension at B (TJ :. 918 x 1.48 = 13591bs.
Tension at A (T flI) = 1359 + (200 X 6.35 x 0.5) = 1994 Ibs. total
Pulling from F to A results in considerably less tension both at the bends and overall. While. in this cast,
it would be acceptable to Jlu. from eitherdirectioo, it is pn.adent design to select the direction which results
in the least stress on the cable and equipment provided thereat'e no extenuating Circumstances such as
limited setup or working space at one end or the other.
During the pulling as weR as other operations, it is ffequenUY necessary to re-reel the cable or pass it oyer
pulleys or sheaves. To avoid damage to the cable, It Is imperative t~the cable not be bent over a radius
small enough to cause damage. Tllis is especially important because this type of damage is frequenUy
concealed and therefore may verJ well go unnoticed until a proof test or service failure occurs. Tables
It, III & IV befow give the minimum recommended bending radii for cables of various construction.
TABLE II
Non-Shielded & Non-Af'morecl Power Cables
Cable OD, inches
Thk:lcneness or CanduetO( Up 10 '.000 I ' ,001 to 2.000 1 Over 2.000
Insulation 11'I MUs
MinimUm BellCling Racltt-ls K a Multiple
or Cable OD
1 S5 sod less 4 5 6
155.310 5 6 7
310 and over 7 B
TABLE III
Shielded or Armored Power Cable
Cable Typa
Minimum Bend Radius as Multiple of
Cable CD
12
12
12
7
Flat Tape or Wire ArlTlOracl
Tape Shielded
WR Shlelded
Interlocked Armer tN/o Shielding
<0 Soathwire"
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One Soll"'Wira Drive
C."oll(On. GI\ 30119 USA
770/832-4242
www.sQulhwlr8.com
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'" SEP.30.2002 10:03AM
VOS ELECTRIC, INC.
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CompatibJl) with 811 cable jackets.
Cleans up easily.
EnvironmenlaRy safe.
Operating range ffOnl ~2' . 190" F (O'C . SS'C).
. CompatIble will1 pre-IubriCatecl in"erdUCIs.
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.. ----. 'NO. 861 - --P. 7/7
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