E4 Electrical Installation
#2 Wire Sizing and Materials
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AMP
AMPACITY
ACITY
• Ampacity is:
The AMPerage handling capACITY of wire, fuse, or CB
• It is the amperage draw PLUS a 25% safety factor
Or, the amperage load x 1.25 = Ampacity
• Example: Name plate amperage is 12 amps
12 amps load x 1.25 = 15 amps ampacity
• Ampacity is the value used to determine the correct
size of wires, fuses, and circuit breakers for inductive
(motor) loads
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Wire Insulation
• The insulation on a wire is a factor in its
rated ampacity
• Examples of wire insulation descriptions:
• TW
– Thermoplastic, Wet (and dry) locations
• THHN
– Thermoplastic, High-Heat resistant, Nylon
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Wire sizing
• Wire is rated in AWG (American Wire
Gauge)
• The lower the number, the thicker the wire
• The lower the number, the higher the
amperage capacity
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Ampacity and Wire Insulation
Wire size
AWG
Ampacity for Ampacity for
Type TW & UF Type THHN
Maximum
Amp Ratings*
# 14
20
25
15*
# 12
25
30
20*
# 10
30
40
30*
*According to the electrical code, the overcurrent protection
shall not exceed 15A for #14, 20A for #12, or 30A for #10
(However, insulation is a factor in locations above 86 F)
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Wire Marking
• Marking on the cable usually indicates wire
type, insulation, conductor size, and application.
Following are some examples:
– NM: Non Metallic casing enclosing the wire
– MC: Metal Clad casing enclosing the wire
– UF: Underground Feeder
– SEC: Service Entrance Cable
– #12 AWG: Size 12 American Wire Gauge
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Some Examples of Common Indoor
Wiring Materials
• Non Metallic cable (NM, Romex®)
• Armored cable (AC, MC, BX)
• Rigid Metallic Conduit (EMT, “Thinwall”)
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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“Romex”
Type TW insulation
Two #12 wires with
a bare ground wire
Non-metallic cable
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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MC (Metal Clad) or Armored Cable (AC)
Insulating
Bushing
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Electric Metallic Tubing (EMT)
Coupling
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
Connector
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Outdoor Wiring
• For outdoor condensing units, the wiring
materials must be flexible, liquid tight, and
damage resistant
• Following is one example of the wiring
used
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Flexible Liquid Tight Conduit
Coiled metal for
flexible strength
90 °
Connector
Plastic sheathing to
make it “liquid tight”
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Unit Ratings
• The unit data plate contains important
electrical information
• Based on the information on the following
slide, wire and circuit breaker sizes can be
determined
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Sample A/C Electrical Data
Unit Rating
7 ½ Tons
Compressor Compressor
RLA
LRA
208/230-3-60
19.0
142
Voltage
OFM
FLA
1.9
MCA
MOCP
25.6
35
What is the wire size and circuit size for the above unit?
A unit with 25.6 ampacity (MCA) requires:
a minimum 30 amp circuit
# 10 wire
The circuit may be fused at a maximum of 35 amps (MOCP)
Note: For ampacity calculations of a multi-motor assembly, 25% is added only to the
largest motor. Example: 19.0 x 1.25 = 23.75 + 1.9 for OFM = 25.6 MCA
RLA – Rated Load Amps
LRA – Lock Rotor Amps
OFM – Outside Fan Motor
LEGEND
FLA – Full Load Amps
MCA – Minimum Circuit Amps
MOCP – Max.*Overcurrent Protection
*Note: The overcurrent protection device must be a fuse or HACR breaker.
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Common HVACR Ratings
• The following table is a useful guideline for
determining the wire and circuit breaker
sizes for the most common motor
amperages
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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Wire and Circuit Breaker Sizing
for Motor Loads
Total Unit Amps Circuit Breaker Amps
Wire Size
0 – 12
15
# 14
13 – 16
20
# 12
17 – 24
30
# 10
25 - 32
40
#8
33 - 48
60
#6
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.2
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