Pin Insulator Line End Fitting – Clamped V. Free

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The O-Calc Pro master catalog includes a number of options regarding types of insulators that may be used for modeling accurately. Among these options are Pin insulators, which can be set in O-Calc to either be free or clamped; essentially either allowing the tensions among the attached spans to equalize, or stay fixed.


      Pin Insulator – Free/Saddle                               Pin Insulators in O-Calc

Ideally this pin would be used to model two spans, a forward span and backward span. The tensions between the two spans would equalize, as the wire would be able to slide through the saddle until the point of equalization had been reached.

If however a third span is modeled as being attached to a pin, it would be at a fixed point, or clamped. The tension for this span would be fixed, as a third wire could not slide through the saddle. This would be the case when modeling service drops or taps from the main primary wires.

Crossarm with Additional span on insulator – set to “Free” In data entry Panel

Capacity Display and Data Entry Panel – Line End Fitting Set to “Free”

When this third span is attached to the insulator and the line end fitting is set to free, O-Calc equalizes the tensions of all three spans, resulting in the high reading on the capacity display and the pole overturning in some cases. The tension values can be viewed in the report pictured below.


Under the “Reports Tab”, on page 2 of the “Analysis Report”, the load components can be viewed for each span. Under the “Tension (lbs)” column, the tension for each span on the same insulator has been averaged since the “Line End Fitting” attribute is set to free.

However, if this attribute is changed to “Clamped”, the tension will not be averaged and each span will retain its set tension. Additionally the capacity of the pole being utilized will be diminished.

Capacity Display and Data Entry Panel – Line End Fitting Set to “Clamped”


In the new report, the tensions are not equalized on the insulator that is set to “Clamped” – each span retains its tension value.

Modeling this component of the insulator is necessary for an accurate idea of capacity utilization.