Rated Load Amperes (Rla) And Maximum Continuous Current (Mcc) - Carlyle 06D Series Application Manual

This discharge temperature sensor will operate as an
automatic reset device. However, because the trip setting
is at a high enough value, any trips should be investigat-
ed by service personnel. For that reason, Carlyle recom-
mends the discharge temperature thermostat be wired
into the control circuit in a manual reset mode. While a
number of alternate wiring arrangements for manual
reset are possible, one possible alternate is shown in
Figure 19.
L
1
TYPICAL MANUAL RESET CONTROL CIRCUIT
CYLINDER HEAD SENSOR
Lockout Low High
Relay Pressure Pressure
Control
R Control
1
Time Delay
Relay
Reset
Button
R
2
Lockout
Relay
Figure 19 – Alternative Wiring Diagram
Branch Circuit Protection
Branch circuit protection may be obtained by use of time
delay fuses or by circuit breakers selected at110% to
125% of compressor motor overload trip current.
4.3 Rated Load Amperes (RLA) and Maximum
Continuous Current (MCC)
Rated Load Amperes or Rated Load Current is defined in
Paragraph 440.3 of the National Electrical Code which
states: "The rated-load current for a hermetic refrigerant
motor-compressor is the current resulting when the
motor-compressor is operated at the rated load, rated
voltage and rated frequency of the equipment it serves."
It is also stated that: "The Rated Load Current in
amperes of the motor-compressor shall be marked by
the equipment manufacturer on either or both the
motor-compressor nameplate and the nameplate of the
equipment in which the motor-compressor is used." The
relevant UL Standards also reflect this position.
FOR
Oil Safety Switch
Heater Circuit
Oil
Pressure Safety
Switch
C
Compressor
Time Delay
Contactor
Relay
Coil
Coil
TDR
Lockout
Cylinder
Relay
Head
Coil
Sensor
R
The above RLA value is established by the equipment
manufacturer at their standard rating condition or on a
calorimeter test with the unit's compressor at or near the
condition representative of unit operation. In unitary
equipment, that condition has been defined as the ARI
Standard Rating Condition for the class of product
involved. These products require the tests be run with
the complete unit: compressor, condenser and evapora-
tor. In refrigeration systems that are not completely
defined (i.e., compressor or condensing units that can
L be applied with various evaporators), the calorimeter
2
conditions have been arbitrarily selected and appear in
UL 303 in classes of high, medium or low suction pres-
sure applications. In these refrigeration applications, UL
will allow the equipment manufacturer to use the com-
pressor manufacturer's determination of maximum con-
tinuous current (MCC) as the basis for calculating mini-
mum RLA values.
As a compressor manufacturer, Carlyle does not publish
certified RLA values. We publish a maximum continuous
current value (MCC) which UL certifies. This is verified
by operating a compressor at a specified condition with
a specific refrigerant. The voltage is then lowered until
the compressor's protection system trips. The amperage
value just before the point at which the protection trips
is considered the MCC value.
Determining RLA From MCC
The UL standards provide the equipment manufacturer
with the option of using a motor-compressor Rated Load
Amperage established by testing the equipment or deter-
mining the RLA value based on a certain percentage of
the MCC value.
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