54 Product Manual PM WSC/WDC
Options for Low Voltage Starters
Canadian Standards Association (CSA) certification and label
Circuit breaker as a control disconnect
Fuse block (fuses by others) with disconnect
Ground fault protection
Medium Voltage Starters (2300 to 6900 Volts)
Standard Equipment
Medium voltage starters are NEMA Class E2 continuous duty AC and include isolated vertical line contactors;
drawout three-pole; gang operated line isolating switch; current limiting fuse block with fuses; drawout three-
pole; vacuum break contactor; control transformer; control circuit primary and secondary fuse block; current
transformers, and phase failure and reversal relay.
Across-the-line starter
Across-the-line starters are very simple and consist of a primary contactor that allows locked rotor amps to
reach the motor when energized. These starters are low cost, provide the highest starting torque, require the
least maintenance and can be used with any standard motor. However, they have the highest starting inrush
current.
Autotransformer starter
In addition to the standard equipment listed above are: drawout magnetic, three-pole, vacuum break shorting
assembly, drawout three-pole, vacuum break starting contactor, and starting auto-transformer. The
autotransformer starter operation was discussed in the low voltage starter section. As with low voltage
starters, the 65% tap is used for centrifugal compressors providing 42% starting torque with 45% inrush current.
The time for the starter to transition from reduced current to full voltage as the motor reaches the proper speed
is critical to get a relatively shock free transition.
Once the starting sequence begins, the motor is not disconnected from the line which prevents a second inrush
“spike” from occurring. Autotransformer starters are a good choice because of their efficiency and flexibility. All
power taken from the line is transmitted to the motor except for some transformer losses during starting. They
are not smooth starting, they may shock machinery if the timing cycle for the motor and starter are not closely
matched.
Primary reactor starter
In addition to the standard equipment listed above: drawout magnetic, three-pole vacuum break shorting
assembly and three-phase starting reactor factory set at 65% tap. These starters are similar in operation to the
autotransformer, however they provide 42% starting torque with 65% inrush of locked rotor current.
Additional Options for Medium Voltage Starters
Certifications and Approvals
• UL certification for full voltage starters
• UL certification for reduced voltage starters
• CSA certification for full voltage starters
• CSA certification for reduced voltage starters
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