Siemens: How to Design a Variable Frequency Drive (VFD) Panel

A drive is needed to turn control the motor at variable speeds.

Determine the correct drive family select by using the Drive Selection Guide flowchart

We do not have a requirement for communication, but our drive is over 20HP, so the selection guide suggests we use the G120 family

Series: G120

Select drive power module based on Voltage and Rated HP.

Select 480VAC, 25 HP Power module

Select Control Unit based on preferred communications protocol.

No communication protocol is specified for our application.

Select RS485/USS/MODBUS RTU Communications Module for the most cost efficient option.

Note that the drive control unit has onboard I/O. Digital I/O is 24VDC

Part Number: 6SL32440BB121BA1

A drive operator panel allows for basic operation and commission-ing directly from the drive

Select the IOP-2 for easy programming

Part Number: 6SL32550AA004JA2

A line reactor helps keep the drive running longer by absorbing power line disturbances between the incoming power and the drive.

The Design Guide Best Practice tells us that the PM240-2 power module that we selected includes a DC Link Reactor, and thus we don’t need to select a separate line reactor.

A load reactor helps keep the drive running longer by absorbing power line disturbances between the drive and the motor.

Select the load reactor based on the HP of the motor.

Select the 50HP load reactor

Part Number: RLW-006503

A Hand-Off-Auto (HOA) switch, is a 3 position maintained selector switch that allows for starting a motor manually (Hand), turning off manually (Off), or allowing a separate control circuit or PLC to con-trol the motor (Auto).

Part Number: 3SU1150-2BL60-1NA0

A Run light is typically Red and indicates that a machine is running

Select a 22mm Pilot Light based on color (Red) and match the lamp type to the application control voltage (24 VDC)

Part Number: 3SU11526AA201AA0

The main circuit breaker provides overcurrent protection to the entire panel based on the total current consumption of the entire circuit, by preventing the wires in the panel from conducting more current than they are rated for. All power to the panel can also be turned off via the main circuit breaker.

The main breaker also protects the panel from a short circuit (which can generate MUCH more current than a typical overcur-rent situation).

Select the main circuit breaker based on 1.) Short Circuit Interrupt Rating (determined by the main electrical power from the utility company) 2.) Total Current Consumption of devices using 480 VAC multiplied by a factor of 150%

Total Current Consumption = (Motor FLA (33.7) X 150%
= 50.55
Select a 60 A circuit breaker.

Part Number: 3VA51604EC310AA0

Lugs are used to physically connect the wire to the line and load side of the circuit breaker terminals.

Size lugs based on the compatible frame size of the transformer.

Select Qty 2 compatible with 3VA51 circuit breaker frame

Part Number: 2 x 3VA91330JB11

Terminal blocks allow for easy wiring and distribution of power and signals throughout the panel.

Select feed through terminal blocks wire gauge to be used for I/O (18AWG control circuit) – UT 2.5

Part Number: 3044076

End covers electrically isolate groups of terminal blocks. Select based on compatible blocks (UT 2.5)

Part Number: 3047028

Wire is sized based on current capacity.

We will typically use different wire colors based on the circuit.

Size the wire for the main 480 VAC circuit based on the chosen main circuit breaker (60A) using the “Wire Size and Selection Criteria” blog post – 4 AWG wire

Select colors using selection criteria:

480VAC Phase 1,2,3 – Brown + Orange + Yellow
480VAC Neutral – Grey
480 VAC Ground – Green

Part Number: WITHHN04STRBRW, WITHHN04STRORN, WITHHN04STRYEL, WITHHN04STRGRY, WITHHN04STRGRN

Select the 24 VDC circuit wiring

20 AWG – MTW (based on its recommended use inside panels)
24 VDC+: – Red
24 VDC-: – Black

Part Number: WIMTW20STRBLK500, WIMTW20STRRED500

Wireway allows for routing of wire inside the enclosure in a neat manner.

Select wireway based on dimensions that allow required wire amount to fix, and desired color.

Part Number: 3240199

Select an enclosure with an outdoor NEMA rating (3R minimum) that fill allow for all components to fit with ample space for airflow and wiring.

Part Number: WM483612NC