Baldor MN1851 manual System Grounding Ungrounded Distribution System, Input Power Conditioning

System Grounding Continued

Ungrounded Distribution System

With an ungrounded power distribution system it is possible to have a continuous current path to ground through the MOV devices. To avoid equipment damage, an isolation transformer with a grounded secondary is recommended. This provides three phase AC power that is symmetrical with respect to ground.

Input Power Conditioning

Baldor controls are designed for direct connection to standard single and three phase lines that are electrically symmetrical with respect to ground. Certain power line conditions must be avoided. An AC line reactor or an isolation transformer may be required for some power conditions.

•If the feeder or branch circuit that provides power to the control has permanently connected power factor correction capacitors, an input AC line reactor or an isolation transformer must be connected between the power factor correction capacitors and the control.

•If the feeder or branch circuit that provides power to the control has power factor correction capacitors that are switched on line and off line, the capacitors must not be switched while the control is connected to the AC power line. If the capacitors are switched on line while the control is still connected to the AC power line, additional protection is required. TVSS (Transient Voltage Surge Suppressor) of the proper rating must be installed between the AC line reactor or an isolation transformer and the AC input to the control.

Power Disconnect A power disconnect should be installed between the input power service and the control for a fail–safe method to disconnect power. The control will remain in a powered-up condition until all input power is removed from the control and the internal bus voltage is depleted.

Protection Devices The control must have a suitable input power protection device installed. Input and output wire size is based on the use of copper conductor wire rated at

75 ° C. Table 3-1 and 3-2 describes the wire size to be used for power connections and the ratings of the protection devices. Use the recommended circuit breaker or fuse types as follows:

Circuit Breaker: 1 phase, thermal magnetic.

Equal to GE type THQ or TEB for 115 or 230 VAC

3 phase, thermal magnetic.

Equal to GE type THQ or TEB for 230 VAC or GE type TED for 460 VAC.

Time Delay Fuses: Buss FRN on 230 VAC or

Buss FRS on 460 VAC or equivalent.

Recommended fuse sizes are based on the following:

UL 508C suggests a fuse size of four times the continuous output current of the control.

Dual element, time delay fuses should be used to avoid nuisance trips due to inrush current when power is first applied.

For European installations, you may want to consider the following fast acting fuse: Gould Shawmut Cat. No. ATMR15 for up to 15 amperes.

3-4 Receiving & Installation MN1851