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Construction Electrician Basic - Electricity handbook for electricians | Next
Figure 1-8.—Wire-rope fittings. |
a 1/2-inch-diameter wire rope. Using the formula
above, you would solve the problem as follows:
SWL = (1/2)2 x 8
SWL = 2 tons
Figure 1-5.—Correct and incorrect methods of measuring
wire rope.
places on a six-stranded, and four places on an eight-
stranded wire rope.
Use the average of the three
measurements as the diameter of the wire rope.
Safe Working Load
The term safe working load (SWL), as used in
reference to wire rope, means the load that you can
apply and still obtain the most efficient service and also
prolong the life of the wire rope. Most manufacturers
provide tables that show the safe working load for their
wire rope under various conditions. In the absence of
these tables, you may apply the following rule-of-
thumb formula to obtain the SWL:
SWL (in tons) = D2 x 8
This particular formula provides an ample margin
of safety to account for such variables as the number,
size, and location of sheaves and drums on which the
wire rope runs and such dynamic stresses as the speed of
operation and the acceleration and deceleration of the
load, all of which can affect the endurance and breaking
strength of the wire rope. Remember this formula is a
general computation, and you should also consider the
overall condition of the wire rope.
In the above formula, D represents the diameter of
the rope in inches. Suppose you want to find the SWL of
WIRE-ROPE ATTACHMENTS
Wire rope can be attached to other wire ropes,
chains, pad eyes, or equipment by splicing, which is
permanent, or by any of a number of wire-rope
attachments. These include sockets and wire-rope
clips. In general, these attachments permit the wire rope
to be used with greater flexibility than would be
possible with a more permanent splice. The
attachments allow the same wire rope to be made up in a
variety of different arrangements.
Clips
A temporary eye splice may be put in wire rope by
using clips. A single clip (fig. 1-6) consists of three
parts: U-bolt, saddle, and nuts. The correct and
incorrect methods of applying these clips to wire rope
are shown in figure 1-6; the second incorrect method
shown is the most common. Notice that the correct way
is to apply the clips so that the U-bolts bear against the
bitter end; that is, the short end of the wire rope. If the
clips are attached incorrectly, the result will be
distortion or mashed spots on the live end of the wire
rope. After a wire rope is under strain, tighten the clips
again. On operating wire ropes, tighten the clips daily
and inspect the wire ropes carefully at points where
Figure 1-6.—Use of wire-rope clips.
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