What makes a cable VFD rated?

What makes a cable VFD rated?

VFD cable offers the proper shielding needed to reduce EMI/RFI noise and to provide a low-impedance signal return path — preventing the common-mode or stray voltage that leads to premature cable and/or equipment failure. Smaller-sized VFD controllers are even more susceptible to charging currents.

Which cable is applicable for VFD application?

To avoid these issues, it is important to choose an electrically balanced, shielded cable with NFPA 79 compliant crosslinked polyethylene (XLPE) insulation when specifying cable systems for VFD applications.

Can VFD cable be run in conduit?

Use metal conduit that has a grounding strap on the outside of the conduit. Inside of the conduit, run a grounding conductor connecting the motor ground to the VFD ground. A shield is preferred over the cable, connecting the shield to the ground bus in the drive and terminating the motor end to the grounded motor.

How do I choose a VFD cable?

To calculate AWG size, three factors must be known: motor HP, motor voltage, and full load current (FLC). For a 30 HP and 460V motor, the FLC is 40A. Per NEC, FLC x 125% is required to calculate AWG size. 40A x 125% = 50 A, therefore the right AWG wire is 6 AWG per NEC Article 310.15.

How do I terminate a VFD cable?

Both ends of the VFD cable need to be terminated in order to allow the high frequency common mode current to flow back through the shield to the drive 1 . To terminate this shield with a gland, use an EMC style cable gland which will provide a 360° connection to the shield at both the inverter and the motor.

How do I wire a VFD drive?

How to Wire a VFD

1. STEP 1: Make sure everything is correctly sized and accounted for.
2. STEP 2: Make sure you have a properly-sized circuit breaker rated for your amps and VFD.
3. STEP 3: Run Wires – (3) power wires and (1) ground wire from your breaker panel to your VFD.
4. STEP 4: Run wires from VFD to motor.

Do you need a special motor for a VFD?

Output voltages are available for VFDs to match almost any existing motor voltage. However, very few, if any, VFDs have a direct 13,800-volt output for very high-voltage motors. For these cases, using a step-up transformer on the output of the VFD is often necessary to match the motor voltage.

What is the current rating of a motor cable?

The motor current protection function in the drive is approved (e.g. by UL) for thermal protection of the motor and cable in the event of an overload. Therefore the basic current rating of the motor cable is the same as for a motor connected directly on line.

Why are long cables between VFD and motor?

For long cables, the combination of cable impedance, high frequency input impedance of motor and VFD switching frequency can lead to reflection of voltage pulses that gives origin to large voltage overshoots on motor terminals.

What’s the maximum cable length for a variable frequency drive?

On the other hand the maximum motor cable length depends also on the switching frequency used due to the charging effect of the motor cable capacitance (this is a limitation on the variable frequency drive side, not on the motor isolation).

How does a cable sizing code work for a motor?

Cable sizing codes used by electrical installers, including cable planning software packages, often have special provisions for motors. These would be based on a standard industrial induction motor started by direct connection to the power line (“Direct On Line” DOL starting).