This calculator estimates the pulling tension necessary to install a bundle of one or more low-voltage ( <= 600 V ) power conductors in a steel RMC conduit system. The dimensional variations of other conduit types and materials from those of rigid galvanized steel are not significant in these calculations.
When the calculator icon appears above the 'Results Summary' box, data has changed and you need to click on that icon to recalculate the sheet. After a recalc, as you change data, some of the 'Results' may be invalidated by the data change - those will be 'greyed out'. For example, changing the raceway size of a segment affects the pulling tensions of that (and suceeding) segments, but not the pulling tension limit.
You can specify that the conductors are in a cable. You must supply the cable quantity, weight, and diameter ('O.D.'). Note that the weight is in pounds per thousand feet. For a cable, the conductor quantity and size governs only the max. pulling tension - the expected pulling tension is governed by the cable weight and O.D.
To change the number of rows in the 'Conductor groups' table, use the dropdown field at the top of the table, beside the 'Conductor groups' heading. Likewise, the number of rows in the 'Segments' table can be changed with the dropdown field at the top of that table.
Use the checkbox at the top of the 'Conductor groups' table to indicate that the conductor assembly is tri/quadru-plexed. This can also be used to force the calculator to assume a triangular lay even when other data would indicate that the conductors/cables will be cradled. A cradled lay creates the greatest pulling tension - so you should not force triangular lay unless you are certain that is what you will have.
The pulling tension is always calculated with the bundle entering segment No. 1. After entering segment data, you can use the 'INVERT PULL' button at the top of the 'Segments' table to reverse their order. This will sometimes result in dramatic differences in estimated pulling tension - as can be seen with the 'Example' data set.
Bookmarking this page will not save your data for later recall. Instead, use the 'Save' and 'Recall' links to the right of the 'Results Summary' box. You can save one data set. The cable/conductor data that is saved on this page can be recalled in the Raceway Fill and Voltage-Drop Calculator page - and vice-versa - it is the same data set. A method to save and recall multiple data sets may be provided in the future, if there is any demand for it.
!ERR! in a 'Result Summary' field indicates that - no RMC raceway is large enough for the conductor configuration specified.
Calculations are per NFPA-70 [1999, 2002, 2005, 2008, & 2011] data and requirements.
Pulling Tension The 'Segments' table compacts a lot of data. First-time users may find it helpful to review an example by selecting the 'Example' link under 'Data set', near the top of the sheet.
Each row details either a straight section of conduit or a bend. Enter data in the fields on the row as follows:
'Ins'(ert) - Check this box to insert a blank row above.
'Del'(ete) - Check this box to delete the row. Checking both 'Ins' and 'Del' on a row will clear all fields on the row.
'Description' - anything you want to record to identify the segment.
'Size' - The trade size of the raceway - you can select any size, however, the calculator will enforce a minimum equal to the Code-required size calculated in the raceway section at the top of the sheet. The heading text of this table column is a link which - when selected - will allow you to copy the value from segment No. 1 to all the others - a confirmation box verifies your intent before making the copy.
'Bend' - Check this box if the row is for a bend.
'Deg' - If the 'Bend' box is checked, enter the bend angle (in degrees). If the bend is a sheave or rollers, and you want to assume it is frictionless, enter 0 degrees here - or enter 0 in the 'Friction Coeff' field for this segment; otherwise, enter the angle turned by the sheave or rollers and the appropriate friction coefficient.
'Length/Radius' - If the row describes a straight segment, enter the length of the raceway. If the raceway is on a slope, enter the actual raceway length, not it's projected length (as in 'projected on the floor'). For example: a pull that is upwards through a 10 ft section that is perfectly vertical has a 'Length' of 10, and also a 'Change Elev.' of 10. The same raceway installed horizontally will have a 'Length' of 10 and a 'Change Elev.' of 0. If the row is being used for a bend, enter the centerline radius of the bend.
'Change Elev.' - this field is available only for straight segments. Enter the end-to-end change, in the direction of the pull: indicate elevation drops by prefixing the value with a negative sign: in the preceding example, if the pull were from top to bottom, the 'Change Elev.' would be -10.
'Friction Coeff.' - Typical values are 0.5 (dry) down to 0.05 ('Yellow' synthetic, under perfect conditions). This value has a dramatic affect on estimated tensions and consequent sidewall pressures, so you need to enter reasonable values based on your pulling lube, raceway conditions, and knowledge from experience. The heading text of this table column is a link which - when selected - will allow you to copy the value from segment No. 1 to all the others - a confirmation box verifies your intent before making the copy.
'Lay' - though it appears you can choose this, you cannot - the field is informational only, and indicates the bundle configuration the calculator chose to use. You can force the calculator to use a triangular / diamond configuration using the checkbox at the top of the 'Conductor groups' table.
'Clear'(ance) - the distance between the topmost conductor in the lay and the conduit wall. Some manufacturers recommend a minimum of 10%.
'Pulling T' - the calculated estimate of the tension necessary at the end of the segment. The 'Limit' value in the next column is the maximum allowable value, based on the tnesile strength of the largest conductor(s) in the bundle.
'Sidewall P' - The calculated estimate of sidewall pressure in a bend. The maximum allowable value is displayed in the 'Results Summary' section at the top of the sheet.
beside a 'Results' field indicates the estimated pulling tension or sidewall pressure exceeds the limit.