1. E4 Electrical Installation
#2 Wire Sizing and Materials

2. ACITY AMPACITY AMP 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 v1.1

3. 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 v1.1

4. 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 v1.1

5. Ampacity and Wire Insulation
Wire size
AWG
Ampacity for
Type TW & UF
Ampacity for 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 v1.1

6. 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 v1.1

7. 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 v1.1

8. 12-2 WITH GROUND TYPE NM-B 600 V (UL)
“Romex”
Type TW insulation
12-2 WITH GROUND TYPE NM-B 600 V (UL)
Two #12 wires with a bare ground wire
Non-metallic cable
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.1

9. MC (Metal Clad) or Armored Cable (AC)
Insulating Bushing
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.1

10. Electric Metallic Tubing (EMT)
Coupling
Connector
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.1

11. 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 v1.1

12. 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 v1.1

13. 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 v1.1

14. Sample A/C Electrical Data
Unit Rating
Voltage
Compressor RLA
Compressor LRA
OFM FLA
MCA
MOCP
7 ½ Tons
208/
19.0
142
1.9
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 = for OFM = 25.6 MCA
LEGEND
RLA – Rated Load Amps FLA – Full Load Amps
LRA – Lock Rotor Amps MCA – Minimum Circuit Amps
OFM – Outside Fan Motor 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 v1.1

15. 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 v1.1

16. 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 40
# 8 60
# 6
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.1

17. END OF Wire Sizing and Materials
© 2005 Refrigeration Training Services - E4#2 Wire Sizing and Materials v1.1