Question:

What is the maximum three phase power cable length between the motor and PCS/PF Soft Start controller? Is there a need to connect a line reactor to eliminate grounding capacitor effect in long cable or wire runs?

Answer:

The PCS/PF products are designed to handle up to a maximum effective load capacitance of 0.15uF, which is equivalent to about 762 meters (2500 feet) of cable or wire between the motor and the load side of the PCS/PF controller. In a Line or Wye connected motor this means the motor leads can have a maximum length of 762 meters (2500 feet).

The problem with using long motor lead runs is the capacitance of the longer leads can appear to the PCS/PF controller as a short circuit. This typically will only occur on a corner grounded delta power system. In this type of installation, the sum of the length of all the motor leads running from the PCS/PF controller to the motor must be less than 762 meters or 2,500 feet.

There is no actual test data or verified application history, but motor leads with distances beyond 762 meters (2500 feet) should not be a problem on a center grounded power systems (Y) or a Delta power system with a separate neutral.

Beyond 2500 feet, the actual distance or length of motor leads would be difficult to estimate since there are a number of variables including the type of wire or the way the wire is run in the conduit. In addition to installation variables, it is also difficult to estimate the impact of the increased impedance and switching noise on the back EMF wave, which could cause nuisance trips.

The addition of a line reactor will increase the maximum length of the motor power leads.

For additional information please contact your nearest authorized distributor, sales representative, or call our customer service or technical support lines.