Compressor Mcc Values; Compressor Contactor Selection; Compressors: Wire Sizing - Carlyle 06D Series Application Manual

The percentage of the MCC value used is a function of
the type of motor protection device, as outlined in
Paragraph 440.52 of the National Electrical Code. Briefly,
the National Electrical Code allows:
A separate overload relay that trips in response to
motor-compressor current and selected to trip at
not more than 140% of the marked motor-
compressor Rated Load Current.
A thermal protector or protective system which will
not permit a continuous current in excess of 156%
of the marked Rated Load Current.
A fuse or inverse time circuit breaker response to
motor-compressor current and rated at not more
than 125% of the marked motor-compressor Rated
Load Current.
4.4 06D Compressor MCC Values
Carlyle 06D compressors are provided with overcurrent
and over-temperature protection that comply with UL
and NEC definitions of inherent motor protection. The
overcurrent protection for 06D compressors is provided
by supplementary overloads and these compressors have
now had MCC values approved by the appropriate Code
organization (UL,CSA). The UL Standard allows the MCC
testing to be done in five different suction temperature
ranges (in addition to different refrigerants); from
refrigeration conditions (-40°F to +10°F, -40°C to -
12°C) to normal air conditioning evaporator ranges
(+32°F to +53°F, 0°C to 12°C). While changes in suc-
tion ranges and refrigerants will result in slight changes
in MCC values, Carlyle's policy is to certify with UL only
the largest MCC value for each individual 06D compres-
sor. Therefore, there is only one MCC value independent
of the suction range or refrigerant used.
4.5 06E Compressor MCC Values
On larger 06E compressors, Carlyle requires that the
system manufacturer utilize an approved and UL rec-
ognized overcurrent device to protect the 06E compres-
sor against overcurrent conditions. These overcurrent
devices may be magnetic overload relays or circuit
breakers where the must trip setting is in effect, the
maximum continuous current at which the compressor
can operate. Since the overcurrent device can be select-
ed to match the load, this policy gives the systems manu-
facturer greater flexibility in selecting and sizing the
overcurrent device and the associated electrical compo-
nents. Since the overcurrent device can vary, there is no
single MCC value which Carlyle lists with UL. Therefore,
Carlyle will not be listing any MCC values with UL on any
of the 06E compressors. Carlyle does specify the maxi-
mum must trip current which can be used with the 06E
compressors and these values are shown on the 06E
electrical tables (see Pages 27 and 28, Tables 6 - 9).
4.6 06D Compressor Contactor Selection
Because contactors are not tested to determine their life
performance acceptability under the above 156% rule,
Carlyle does not recommend that contactors be sized to
this rule. Carlyle recommends that contactors be sized to
a current determined by dividing the MCC by 1.40.
As an example, for the 06DR228, 208/230 volt model,
the minimum contactor sizing amperage equals:
MCC/1.40 =55.5/1.40 =39.6 amps.
It is obvious that using the 140% rule results in more
conservative contactor selections, therefore enhancing
contactor and compressor reliability.
The RLA value that is stamped on the compressor or unit
nameplate is left to the system manufacturer's discretion.
Carlyle does not stamp RLA values on their compressor
nameplates, thus allowing the system manufacturer the
greatest flexibility in optimizing contactor, branch circuit
conductor (wire) and disconnect sizes. In the above
example, the 208/230 volt 06DR228 compressor could
be stamped with an RLA value of 35.6 amperes, provid-
ing you meet Carlyle's contactor sizing requirements
shown above.
4.7 06D Compressors: Wire Sizing
The standard external overloads and internal ther-
mostats currently supplied with all 06D compressors are
considered a combination overcurrent and thermal pro-
tection system which complies with UL and NEC defini-
tions of inherent thermal protection. Carlyle compres-
sors that comply with this definition have the statement
"Thermally Protected" stamped or printed on their
nameplates. This would allow a system manufacturer to
use 156 as the specified percent to determine the com-
pressor minimum rated load current. The minimum RLA
can be computed by dividing the MCC by 156% or 1.56.
For the same 06DR228, 208/230 volt model:
Min. RLA (to meet codes)
MCC/1.56 =55.5/1.56 =35.6 amps
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