Trane Starters Engineering Bulletin page 76

Glossary
Ground fault protection—low voltage
Low voltage ground fault protection consists of a ground
fault sensor, a ground fault relay, and a disconnect device
(circuit breaker or non-fused disconnect switch) equipped
with a shunt trip device.
The ground fault sensor is a specially rated current
transformer and must be applied only with a ground fault
relay. Ground fault sensors cannot be used with any other
equipment.
The ground fault relay is designed to work with a ground
fault sensor. The current level required to activate the
ground fault relay is adjustable. The response speed (time
delay) is also adjustable to avoid nuisance trips. All ground
fault relays require a manual reset. The time-current
tripping curve of a ground fault relay is nearly
instantaneous when the current setting and time delay
have been exceeded. The contacts of the ground fault
relay energize a shunt trip device to open the circuit and
isolate the ground.
The shunt trip device is a circuit breaker with a shunt trip
coil. Such a circuit breaker can either be opened manually,
opened by its current sensing element (short circuit), or
opened by energizing its shunt trip coil. A circuit breaker is
used to open the circuit because it is capable of
successfully interrupting fault current; the current to
ground may be catastrophic.
The minimum setting of the ground fault protection
system should be 20 percent of the disconnect rating with
a 10-cycle time delay.
Ground fault protection—medium voltage
Medium voltage ground fault protection consists of a
ground fault sensor and ground fault relay. The ground
fault relay interrupts control power to the main contactors
causing them to open. All medium-voltage starters are
equipped with current-limiting fuses. In the event of a
catastrophic ground, the current-limiting fuses would
react much faster than the ground fault protection relay;
therefore, the fuses would perform the act of interrupting
the circuit and isolating the ground.
The minimum setting of the ground fault protection
system should be 20 percent of the disconnect rating with
a 10-cycle time delay.
Grounding
Electrical refrigeration components such as motors and
control panels must be grounded for the protection of
maintenance and service personnel.
76
Equipment ground connection bolts are provided in the
control panel, the motor junction box, and in the starter of
all CenTraVacs. On those CenTraVacs where the control
panel is isolated, grounding straps are installed to ground
the control panel to the chiller frame. Thus, all pieces of a
CenTraVac are provided with an individual equipment
ground.
It is the responsibility of the installing contractor to ground
the CenTraVac equipment to an earth ground per NEC and
local codes.
"Gutless" circuit breaker
See "Non-fused disconnect" ,
I
Inrush current
The current drawn by a motor during acceleration. Inrush
current for various types of starters (in percent of LRA) is
given in Figure 6, p. 18 (low voltage) and
(medium voltage).
Interlock, electrical
Auxiliary contacts on a contactor, typically used in control
voltage circuits, to monitor the position of the contactor.
These auxiliary contacts may be normally open, normally
closed, or convertible.
Interlock, mechanical
Bars, levers, or catches that physically prevent operation
of a device under certain circumstances. (i.e. a CenTraVac
starter door may not be opened if a circuit breaker is
closed)
Interrupting capacity
The rated maximum current that a device can successfully
interrupt without damage to itself. This applies to a circuit
breaker or a fuse only. It is not proper to refer to a starter
as having an interrupting capacity. Starters have an overall
short-circuit current rating. See "Short-circuit current
rating (SCCR)" , p. 79.
Ionization
Insulated conductors carrying over 2000 volts are subject
to ionization. Ionization results in the formation of gas
pockets between the insulation layers. These gas pockets
form areas of unequal stress that may lead to premature
breakdown of the insulation. See "Stress cone (stress
relief cone)" , p. 80.
IQ digital meters
This is a starter mounted meter that digitally displays
many parameters. It is a starter option, however most
p. 78.
Figure 22, p. 31
CTV-PRB004-EN