Cables Pulling Calculations with ETAP.
ETAP has been one of the most popular software used by many companies and electric utilities worldwide to perform complex electrical systems analysis/studies on different projects.
Before starting to perform any analysis with ETAP it so important to have a good background in all technical aspects in power systems, electrical equipment as well as the different studies that ETAP can perform such as arc flash, harmonics, transient stability, and others.
This article will help you to perform cable pulling calculations with help of ETAP software. basically, cable pulling may seem like a fairly basic process in any construction project. Cables pulling means pull of length of cables through a conduit/pips in order to establish a connection between two separate areas.
Accurate calculations of cable pulling forces are essential for the proper design of cable systems. The possibility of damaged cables during this process can be high when exceeding the cable design limits and that can lead to delays in the project plan, extra resources/cost being needed and additional time needed for removing and replacing damaged cables. Even simple faults like exceed the minimum bending radius or tension can have serious repercussions.
Factors that need to be considered
· Cable clearance
· Minimum Bending Radius
· Sidewall Bearing Pressure
· Weight (Weight Correction Factor)
· Pulling Tension
Cable pulling configurations
for three cable pull:
for four cable pull:
·Jamming Ratio = D/d, where D = is the inside diameter of Duct , d = 1.05* largest cable diameter
If the ratio of the raceway (inside diameter) to the conductor or cable (outside diameter) is between 2.8 and 3.2, jamming can occur. While jamming can occur when pulling four or more conductors or cables into a raceway, the probability is very low.(Read National Electrical Code (NEC), chapter 9)
· Cable clearance
Cable clearance is the spacing between the cable and the conduit's inner diameter and it is equal to D minus d.
· Minimum Bending Radius
The installation of cables requires care in order to avoid excessive pulling tensions that could stretch the conductor or insulation shield, or rupture the cable jacket when pulled around bends. The minimum bending radius of the cable or conductors should not be exceeded during pulling around bends, at splices, and particularly at terminations to avoid damage to the conductors.(Check IEEE gray & IEEE red book, chapter 8)
· Sidewall Pressure (SP) is exerted on a cable as it is pulled around a bend. excessive sidewall pressure can cause cable damage and is the most restrictive factor in many installations.
Cable pulling analysis Using ETAP
In ETAP, you do everything in the context of a project. Thus, the first thing you need to do is create one.
After creating a new project, the first thing to do is create a single line diagram (SLD) of your system/network and set all the parameters to the components that we have devised including power gird, transformer, cables, loads and etc.
On the left-hand side of the ETAP’s window, click on the cables pulling system option.
you’ll see the popup window similar to the following:
You could adjust conduit properties (size, type, ID) By double click on the conduit icon (the blue circle) where it pops up with a conduit window. you will see the conduit window as shown below. Select the type/size of conduit you are specifying.
Then just drag and drop your chosen cables that want to fit in the conduit (either existing or new cables). Once you fit the cables in the conduit, ETAP will automatically calculate the conduit fill percentage.
Calculating conduit fill percentage is an important step to keep your electrical installation safe and to fulfill the NEC requirements.
where NEC establishes that if a conduit only contains 1 wire, the max fill percentage is 53%. If it contains 2 wires, the max fill percentage is 31%. And if it contains 3 or more wires, the max fill percentage is 40%. (Read NEC, Article 314.16(C))
The next step is the cable routing layout, you will perform pulling calculation according to your routing plan and cable paths/length as in the construction site. Let’s say we want to pull the cable from point A to B with the dimensions shown.
In pulling calculations you have to specify the number of bends and segments (straight section) needed in your designs. The above figure show four bends and five segments. To add new segments just select a new segment option on the right-hand side.
After adding new segments, enter your details, segments length, slope, bending radius, horizontal angle. ETAP will create a three-dimensional geometry of the cable path to help you to visualize your design and the cable path before getting started in the implementation stage.
At this point, the last thing to do is to perform calculations by select Calc Cable Pull option.
it will ask you to enter the file name go ahead and type the name you want and hit “OK”.
In order to generate a report that shows results details, select the report manager option on the right-hand side and hit “results” then “OK”. ETAP will generate a report automatically, similar to the following:
In the end, I hope you find this article helpful. If you have any questions, feedback or you want to share more information about the topic discussed above, please don’t hesitate to ask through Gmail or add me on LinkedIn.