I N S TA L L AT I O N , O P ER AT I O N S A N D M A I N T EN A N C E M A N UA L
39
Ambient temperature and circuit loading
MCCs are designed for installation where the
average ambient temperature does not exceed
40°C (104°F). For higher temperatures, derating is
required. The conductor temperatures within the
enclosure may be as high as 90°C (194°F). Some
parts of the circuit breakers, switches, drives and
fuses may run hotter. Make sure you follow the load
requirements for each device in the MCC.
Short circuits
Generally, the overcurrent protective device on the
circuit will prevent any electrical damage except at
the point of the short circuit. Make a thorough
inspection of the entire system after any large fault
current to ensure that there has been no
mechanical damage to conductors, insulation, or
equipment.
Replacing a control power transformer
mounted under disconnect
Use the following procedure to replace a control
power transformer mounted under a disconnect.
1. Turn the power off.
2. Remove the saddle unit from the motor
control center.
3. Remove the top plate from the saddle unit.
4. Remove the handle assembly, as described
on page 15.
5. Remove line and load cables.
6. Loosen the screws securing the disconnect
assembly to the back plate and slide the
assembly out.
7. Disconnect the transformer power and
control leads.
8. Remove the transformer mounting screws
and lift out the transformer.
9. Install the new transformer by following this
procedure in the reverse order. Torque all
electrical connections.
Replacing a compact starter (1/2X)
Use the following procedure to replace
the starter.
1. Turn the power off.
2. Remove the saddle unit for the motor
control center.
3. Remove the pilot device bracket (it is not
required to remove control wiring)
4. Remove overload relay.
5. Use DIN rail release to gain access to line side
wiring of contactor, remove line wires.
6. Reverse to install new starter.
Arcing damage to insulation
Some organic insulating materials carbonize when
subjected to the heat of an electrical arc and lose
their insulating properties. Any insulation found to
be carbon-tracked must be replaced before re-
energizing.
Water-soaked equipment
Electrical equipment exposed to water can be
extremely hazardous if reenergized without
performing a proper evaluation and taking
necessary actions. Reductions in the integrity of
electrical equipment due to moisture can affect the
ability of the equipment to perform its inteded
function.
Damage to electrical equipment can aso result
from flood waters contaminated with chemicals,
sewage, oil and other debris, which will affect the
integrity and performance of the equipment. Ocean
water and salt spray can be particularly damaging
due to the corrosive and conductive nature of the
saltwater residue.
Do not energize equipment that is exposed to flood
or other contaminated water. Consult ABB field
services for guidance.
When equipment has become exposed to non-
contaminated water observe the following points
during maintenance:
• Completely de-energize the switchboard.
• Carefully clean and dry all parts of the
switchboard
• When using heaters, make sure the temperature
does not exceed 180°F.
• Replace all fuses
• Inspect all individual devices for the entrance of
water, dirt, or foreign matter.
• Replace all sealed deviced and circuit breakers.