Model 6 Motor Control Centers 80459-641-01E
Section 6—Maintaining the MCC 10/2012
© 1999–2012 Schneider Electric All Rights Reserved66
ENGLISH
Insulation Test
Before an MCC is re-energized (after installation or regular maintenance),
take resistance measurements. Use an insulation tester (megohmmeter)
with a potential of 500–1000 V.
Take readings between each phase and from each phase to ground, with
the branch disconnects off and on. Make sure the main disconnect is off
during all insulation tests.
Readings from a megohmmeter with all disconnects off will typically be
5–20 megohms. On new equipment that has been stored in a damp area,
lower readings may occur during start-up. If the readings are below one
megohm, a few branch units may be energized to help dry out the MCC. If
additional readings are above one megohm, additional units may be
energized. After the equipment has been in operation for 48 hours, readings
should be in the 5–20 megohm range.
When megohmmeter readings are taken with the disconnects on (except for the
main), disconnect all devices completing circuits between phases or between
phases and neutral (for example, control transformers). Although readings may
be slightly different, observe the one megohm lower limit during start-up.
DANGER
HAZARD OF ELECTRIC SHOCK, EXPLOSION, OR ARC FLASH
• Apply appropriate personal protective equipment (PPE) and follow safe
electrical work practices. See NFPA 70E or CSA Z462.
• This equipment must only be installed and serviced by qualified
electrical personnel.
• Turn off all power supplying this equipment before working on or inside
equipment.
• Always use a properly rated voltage sensing device to confirm power is off.
• Replace all devices, doors, and covers before turning on power to this
equipment.
Failure to follow this instruction will result in death or serious injury.
NOTIC
HAZARD OF EQUIPMENT DAMAGE
• Do not use a megohmmeter on:
– adjustable speed drives
– solid state soft starters
– surge protection devices (SPDs)
– AccuSine™ active harmonic filter units
– PowerLogic™ Circuit Monitor units
– PowerLogic Power Meter units
– capacitor units
– any devices not designed to withstand megohmmeter voltage.
• Disconnect all solid state devices such as SPDs, drives, soft starts,
capacitors, filters, and circuit monitors before performing megohmmeter
tests on the MCC.
Failure to follow this instruction can result in equipment damage.
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