HVAC Equipment Power Rating Calculations – Part Eight

Today, we will list all the summary tables for sizing calculations for Air Conditioning and Refrigeration Equipment as Per NEC Article 440.



Summary Tables For Sizing Calculations For Air Conditioning And Refrigeration Equipment As Per NEC Article 440


 
Sizing Calculations For Air Conditioning And Refrigeration Equipment





First: Sizing Calculations for Disconnecting Means



Summary Of Sizing Steps For Disconnecting Means For
Single Hermetic Motor Only


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Step#1
Select AR of disconnecting means ≥ 115% of the compressors rated load current or branch-circuit selection current, whichever is greater.
Step#2
Calculate the greater value A or B of equivalent horsepower rating for the selected disconnecting means in Step#1.
A
Use NEC Tables 430.248, 430.249 or 430.250 using the greater of either the rated load current or the branch circuit selection current.
B
Use NEC Tables 430.251(A) and 430.251(B) using the locked-rotor current.
Step#3
The Selected disconnecting means from step#1 must have HP rating ≥ the equivalent horsepower rating from step#2. If not, repeat step#1 with higher value of AR.
Notes:
  • In A or B, if the current value falls between two horsepower ratings in a table, round up to the larger HP.
  • Step#2 must be verified to be sure that The horsepower rating of the disconnecting means is capable of safely disconnecting the full amount of the motor locked-rotor current.
  • In case of using a non-fused disconnecting means, non-fused disconnect means AR < 115% of the specified current.
  • AR: Ampere Rating




Summary Of Sizing Steps For Disconnecting Means For
Combination loads


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Step#1
Select AR of disconnecting means ≥ 115% of the sum of all of the individual loads at rated load conditions.
Step#2
Calculate the greater value A or B of equivalent horsepower rating for the selected disconnecting means in Step#1.
A
Use NEC Tables 430.248, 430.249 or 430.250 using the sum of all of the individual loads at rated load conditions, where:

The sum of all of the individual loads at rated load conditions = motor-compressor rated-load current(s) or branch-circuit selection current(s), whichever is greater + fan /blower motors rated-load current(s) + full load currents of other motors + the rating in amperes of other loads
B
Use NEC Tables 430.251(A) and 430.251(B) using the sum of all of the individual loads locked-rotor currents, where:

The sum of all of the individual loads locked-rotor currents = motor-compressor locked-rotor current + fan /blower motors locked-rotor current(s) + locked-rotor currents of other motors + the rating in amperes of other loads.
Step#3
The Selected disconnecting means from step#1 must have HP rating ≥ the equivalent horsepower rating from step#2. If not, repeat step#1 with higher value of AR.
Notes:

  • In A or B, if the current value falls between two horsepower ratings in a table, round up to the larger HP.
  • Step#2 must be verified to be sure that The horsepower rating of the disconnecting means is capable of safely disconnecting the sum of all of the individual loads locked-rotor currents.
  • In case of using a non-fused disconnecting means, non-fused disconnect means AR < 115% of the sum of all of the individual loads at rated load conditions.
  • AR: Ampere Rating





Second: Sizing calculation for Branch-Circuit Short-Circuit and Ground-Fault Protection Devices



Summary Of Sizing Steps For Branch-Circuit Short-Circuit and Ground-Fault Protection Devices For Single Hermetic Motor Only

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Step#1

Size the short circuit and ground fault OCPD AR ≤ 175% of the motor-compressor rated-load current or branch-circuit selection current, which‐ ever is greater.

Step#2
Compare the time current curves for both the motor and the circuit breaker:
If there is intersection, go to step#3,
If not, the OCPD AR is adequate (end of sizing calculations).
Step#3

Size the short circuit and ground fault OCPD AR ≤ 225% of the motor-compressor rated-load current or branch-circuit selection current, which‐ ever is greater.

Notes:
  • AR: Ampere Rating,
  • OCPD: Over-Current Protective Device,
  • The short-circuit and ground-fault protection device for motor-compressor must be capable of carrying the starting current of the motor.
  • The inrush current for motors is calculated from table NEC 430.251(B) @ the operational voltage.
  • for Design B energy-efficient motors, the peak transient current equal 1700 percent of full-load motor current as per NEC 430.52 exception (2).
  • You must provide separate overload protection for the motor [440.52(A)] and over-current protection for the conductors [440.52(B)].
  • Don't use a protective device that exceeds the manufacturer's values [440.22(C)].
  • If the equipment nameplate specifies "Maximum Fuse Size," use a one-time or dual-element fuse. If the nameplate specifies "HACR Circuit Breaker," use an HACR-rated circuit breaker [110.3(B)].
  • The rating of the branch-circuit short-circuit and ground fault protective device shall not be required to be less than 15 amperes [440.22(A) exception].
  • Equipment that starts and operates on a 15- or 20- ampere 120-volt, or 15-ampere 208- or 240-volt single-phase branch circuit, shall be permitted to be protected by the 15- or 20-ampere over‐ current device protecting the branch circuit, [440.22(B) exception#1].
  • The nameplate marking of cord-and-plug-connected equipment rated not greater than 250 volts, single-phase, such as household refrigerators and freezers, drinking water coolers, and beverage dispensers, shall be used in determining the branch circuit requirements, and each unit shall be considered as a single motor unless the nameplate is marked otherwise [440.22(B) exception#2].




Summary Of Sizing Steps For Branch-Circuit Short-Circuit and Ground-Fault Protection Devices For Combination Loads

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Case# A: Where a hermetic refrigerant motor-compressor is the largest load
Step#1

OPCD AR = 175% of  the largest motor-compressor rated-load current or branch-circuit selection current, which‐ ever is greater + the sum of the rated-load current or branch-circuit selection current, whichever is greater, of the other motor compressor(s)  +  the ratings of the other loads.

Step#2
Compare the time current curves for both the motor and the circuit breaker:
If there is intersection, go to step#3,

If not, the OCPD AR is adequate (end of sizing calculations).

Step#3

the Maximum Over-Current Protection (MOP) = 225% of  the largest motor-compressor rated-load current or branch-circuit selection current, which‐ ever is greater + the sum of the rated-load current or branch-circuit selection current, whichever is greater, of the other motor compressor(s)  +  the ratings of the other loads.

Case# B: Where a hermetic refrigerant motor-compressor is not the largest
Step#1
OPCD AR = the rated-load current or branch circuit selection current, whichever is greater, rating(s) for the motor-compressor(s) + the rated-load current For other motor loads not exceeding 800A + the rated-load current for other loads

 

Step#2
Compare the time current curves for both the motor and the circuit breaker:
If there is intersection, go to step#3,

If not, the OCPD AR is adequate (end of sizing calculations).

Step#3

the Maximum Over-Current Protection (MOP) = 225% of  the largest Load rated current or branch-circuit selection current , whichever is greater + the sum of the rated-load current or branch-circuit selection current, whichever is greater, of the motor compressor(s)  +  the ratings of the other loads.

 

Notes:
  • AR: Ampere Rating,
  • OCPD: Over-Current Protective Device,
  • MOP: Maximum Over-Current Protection,
  • MCA: Minimum Circuit Amps,
  • If the MOP value is not an even multiple of 5, and if the MOP value is not a standard value, the MOP is rounded down to the nearest standard size.
  • If the MOP is less than the MCA, the MOP is made equal to the MCA and then rounded up to the nearest standard fuse size, the MOP shall not be less than the MCA.
  • If the MOP is less than 15, it shall be rounded up to 15 amps. This is the minimum size of fuse or circuit breaker permitted by [NEC 440.22(A) exception].
  • The short-circuit and ground-fault protection device for motor-compressor must be capable of carrying the starting current of the motor.
  • The inrush current for motors is calculated from table NEC 430.251(B) @ the operational voltage.
  • For Design B energy-efficient motors, the peak transient current equal 1700 percent of full-load motor current as per NEC 430.52 exception (2).
  • You must provide separate overload protection for the motor [440.52(A)] and over-current protection for the conductors [440.52(B)].
  • Don't use a protective device that exceeds the manufacturer's values [440.22(C)].
  • If the equipment nameplate specifies "Maximum Fuse Size," use a one-time or dual-element fuse. If the nameplate specifies "HACR Circuit Breaker," use an HACR-rated circuit breaker [110.3(B)].
  • The rating of the branch-circuit short-circuit and ground fault protective device shall not be required to be less than 15 amperes [440.22(A) exception].
  • Equipment that starts and operates on a 15- or 20- ampere 120-volt, or 15-ampere 208- or 240-volt single-phase branch circuit, shall be permitted to be protected by the 15- or 20-ampere over‐ current device protecting the branch circuit, [440.22(B) exception#1].
  • The nameplate marking of cord-and-plug-connected equipment rated not greater than 250 volts, single-phase, such as household refrigerators and freezers, drinking water coolers, and beverage dispensers, shall be used in determining the branch circuit requirements, and each unit shall be considered as a single motor unless the nameplate is marked otherwise [440.22(B) exception#2].





Third: Sizing Branch Circuit Conductors




Summary Of Sizing Steps For Branch-Circuit Conductors
 For Single Hermetic Motor Only


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Step#1

If the equipment is marked with minimum circuit ampacity (MCA), use this value to size the branch circuit conductors. If not, go to Step#2.

Step#2

Size the branch circuit conductors ampacity ≥ 125% of the motor compressor rated-load current or the branch circuit selection current, whichever is greater

Special Case
For a Wye-Start, Delta-Run Connected Motor-Compressor:
The branch-circuit conductors ampacity between the controller and the motor-compressor = 72 % of either the motor-compressor rated-load current or the branch-circuit selection current, whichever is greater.
Notes:
  • Size these branch-circuit conductors no smaller than the minimum circuit ampacity on the equipment nameplate if existing.
  • The motor branch-circuit over-current protective devices are permitted to be sized much higher than the rated ampacity of the motor branch circuit conductors and overload protection must be used to protect motor branch-circuit conductors from overloads.
  • The size of conductors for electric motor-driven air-conditioning and refrigerating equipment (including hermetic motor compressors) shall be selected from Table 310.15(B)(16) through Table 310.15(B)(19) or calculated in accordance with 310.15 as applicable [NEC 440.6].
  • All of the derating factors in 310.15 apply to this ampacity and so do the termination limitations of 110.14.
  • For a hermetic refrigerant motor-compressor, the rated-load current marked on the nameplate of the equipment in which the motor compressor is employed shall be used in determining the rating or ampacity of the branch circuit conductors. Where no rated-load current is shown on the equipment nameplate, the rated-load current shown on the compressor nameplate shall be used. [NEC 440.6(A)]
  •  Where so marked, the branch-circuit selection current shall be used instead of the rated-load current to determine the rating or ampacity of the branch-circuit conductors. [NEC 440.6(A) Exception.1]
  • The nameplate marking of cord-and-plug-connected equipment rated not greater than 250 volts, single-phase, such as household refrigerators and freezers, drinking water coolers, and beverage dispensers, shall be used in determining the branch-circuit requirements, and each unit shall be considered as a single motor unless the nameplate is marked otherwise. [NEC 440.6(A) Exception.2]




Summary Of Sizing Steps For Branch-Circuit Conductors
 For Combination Loads


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Step#1
If the equipment is marked with minimum circuit ampacity (MCA), use this value to size the branch circuit conductors. If not, go to Step#2.
Step#2
Size Branch circuit conductor ampacity = 125% of the largest motor-compressor rated-load current or branch-circuit selection current, which‐ ever is greater + the sum of the rated-load current of the other motor + the ratings of the other loads.
Notes:
  • Size these branch-circuit conductors no smaller than the minimum circuit ampacity on the equipment nameplate if existing.
  • The motor branch-circuit over-current protective devices are permitted to be sized much higher than the rated ampacity of the motor branch circuit conductors and overload protection must be used to protect motor branch-circuit conductors from overloads.
  • The size of conductors for electric motor-driven air-conditioning and refrigerating equipment (including hermetic motor compressors) shall be selected from Table 310.15(B)(16) through Table 310.15(B)(19) or calculated in accordance with 310.15 as applicable [NEC 440.6].
  • All of the derating factors in 310.15 apply to this ampacity and so do the termination limitations of 110.14.
  • For a hermetic refrigerant motor-compressor, the rated-load current marked on the nameplate of the equipment in which the motor compressor is employed shall be used in determining the rating or ampacity of the branch circuit conductors. Where no rated-load current is shown on the equipment nameplate, the rated-load current shown on the compressor nameplate shall be used. [NEC 440.6(A)]
  •  Where so marked, the branch-circuit selection current shall be used instead of the rated-load current to determine the rating or ampacity of the branch-circuit conductors. [NEC 440.6(A) Exception.1]
  • For multi-motor equipment employing a shaded-pole or permanent split-capacitor-type fan or blower motor, the full-load current for such motor marked on the nameplate of the equipment in which the fan or blower motor is employed shall be used instead of the horsepower rating to determine the ampacity or rating of the branch-circuit conductors, This marking on the equipment nameplate shall not be less than the current marked on the fan or blower motor nameplate. [NEC 440.6(B)]
  • The amapacity of the conductor may never be lower than the “Minimum Circuit Ampacity” marked on the nameplate of combination equipment as required by 440.4(B).





Fourth: Sizing Controllers 




Summary Of Sizing Steps For Controller Serving Motor Compressor only


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Step#1
The controller must have a continuous duty FLC ≥ the nameplate rated current or branch circuit selection current (whichever is larger),
Step#2
And also,
The controller must have a LRC ≥ the locked rotor current of the compressor .
Notes:
  • FLC: full-load current
  • LRC: locked rotor current
  • A controller shall be marked with the full-load and locked-rotor current (or horsepower) rating (NEC 440.5).
  • If the selected controller is marked in only horsepower. We are directed to use the motor compressors nameplate FLC and locked rotor current and search in Tables 430.248-250 for FLC and 430.251(A) or (B) for LRC for the equivalent horsepower. The result that gives us the higher equivalent horsepower is the one we will use to size the controller. 




Summary Of Sizing Steps For Controller Serving More Than One Load


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Step#1
The ampere rating of the Controller ≥ 115% of the sum of all of the individual loads at rated load conditions
Step#2
Calculate the greater value A or B of equivalent horsepower rating for the selected disconnecting means in Step#1.
A
Use NEC Tables 430.248, 430.249 or 430.250 using the sum of all of the individual loads at rated load conditions, where:

The sum of all of the individual loads at rated load conditions = motor-compressor rated-load current(s) or branch-circuit selection current(s), whichever is greater + fan /blower motors rated-load current(s) + full load currents of other motors + the rating in amperes of other loads
B
Use NEC Tables 430.251(A) and 430.251(B) using the sum of all of the individual loads locked-rotor currents, where:

The sum of all of the individual loads locked-rotor currents = motor-compressor locked-rotor current + fan /blower motors locked-rotor current(s) + locked-rotor currents of other motors + the rating in amperes of other loads.
Step#3
Select Controller with HP rating ≥ the equivalent horsepower rating from step#1. If not, repeat step#1 with higher value of AR.
Notes:
  • FLC: full-load current.
  • LRC: locked rotor current.
  • AR: Ampere Rating.
  • In A or B, if the current value falls between two horsepower ratings in a table, round up to the larger HP.
  • A controller shall be marked with the full-load and locked-rotor current (or horsepower) rating (NEC 440.5).





Fifth: Branch Circuit Overload Protection




Summary Of Sizing Steps for Branch Circuit Overload Protection
 for Air Conditioning and Refrigeration Equipment

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Option#1
When using A separate overload relay, The relay must be selected to trip at no more than 140% of the motor-compressor rated-load current.
Option#2
When using a Thermal Protector, it must not permit a continuous current in excess of 156 percent of the marked rated-load current or branch-circuit selection current.
Option#3
When using A fuse or inverse time circuit breaker, The device must be rated for no more than 125% of the motor compressor rated load current.
Option#4
When the manufacturer uses a special protective system, it must not permit a continuous current in excess of 156 percent of the marked rated-load current or branch circuit selection current.
Notes:
  • The manufacturers of hermetic systems supply the correct protection, conductor sizing, and other information on the equipment nameplate. Use this information when wiring an air conditioner or other hermetic motor equipment.
  • All Motor-Compressors and Equipment on 15- or 20-Ampere Branch Circuits will follow the same rules as per 440.52(A). Noting that the rating of the attachment plug and receptacle or cord connector (for Cord- and Attachment-Plug-Connected Motor Compressors and Equipment) shall not exceed 20 amperes at 125 volts or
    15 amperes at 250 volts.
  • The NEC allows this type of overload protection and requires no further protection if the nameplate of the equipment is marked “Thermally Protected.”
  • Most AC equipment has nameplate marked with the maximum allowable over-current device. In accordance with 110.3 this marking must be followed exactly and the markings must be taken literally as follows:

  1. If the marking is “Maximum Fuse Size”, then only fuses may be used.
  2. If the marking is “Maximum HCAR Circuit Breaker Size”, then only HCAR breakers may be used.
  3. If the marking is “Maximum Fuse Size or HCAR Circuit Breaker Size”, then only fuses or HCAR breakers may be used.
  4. If the marking is “Maximum Fuse or Inverse Time Circuit Breaker Size”, then only fuses or Inverse Time Circuit Breaker may be used.





Sixth: Provisions for Room Air Conditioners





Summary of Sizing Steps for Provisions for Room Air Conditioners


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Sizing Branch-Circuit Short-Circuit and Ground-Fault Protection
Equipment that starts and operates on a 15- or 20- ampere 120-volt, or 15-ampere 208- or 240-volt single-phase branch circuit, shall be permitted to be protected by the 15- or 20-ampere over‐ current device protecting the branch circuit, [440.22(B) exception#1].
The nameplate marking of cord-and-plug-connected equipment rated not greater than 250 volts, single-phase, such as household refrigerators and freezers, drinking water coolers, and beverage dispensers, shall be used in determining the branch circuit requirements, and each unit shall be considered as a single motor unless the nameplate is marked otherwise [440.22(B) exception#2].
Sizing Branch Circuit Conductors
If a room air conditioner is the only load on the circuit, the circuit must be rated for 125% of the marked rating of the air conditioner.
If the room air conditioner is to be supplied from a standard receptacle circuit and other loads may be supplied from the circuit, the branch circuit must be rated at least 200% of the air conditioners marked rating.
Sizing Disconnecting Means
an attachment plug and receptacle can be used as the sole disconnecting means as long as one of two conditions is met:

The manual controls for the AC unit are readily accessible and located no more than 1.8 m (6 feet) of the floor.
An approved manually operable switch is installed in a readily accessible location that is in sight of the AC unit.
Protection Device For the Cord
As per NEC 440.65, the manufacturer must install one of the following protection devices:
  1. Leakage-current detector-interruptor (LCDI),
  2. Arc-fault circuit interrupter (AFCI),
  3. Heat detecting circuit interrupter (HDCI).

The protection device shall be an integral part of the attachment plug or be located in the power supply cord within 300 mm (12 in.) of the attachment plug. 
Notes:
  • These below rules will be applied only for the AC units rated less than 40A, 250V and must be single phase.  
  • If AC the unit is rated 3-phase or rated over 250 volts shall be directly connected to a wiring method recognized in NEC Chapter 3 and the below rules will not be applied.


In the next article, we will solve some examples for sizing calculations of Air Conditioning and Refrigeration Equipment as Per NEC Article 440. So, please keep following.
The previous and related articles are listed in below table:

Subject Of Previous Article
Article
Summary of heating and cooling systems,
Parts Consuming Power in HVAC Systems,
Types of motors used in HVAC Systems,
Types of pumps used in HVAC/refrigeration,
Parts consuming power as per used unit/system,
Motor Nameplate for Air Conditioner Motor Applications.

The Common Types Of Motors Used In HVAC Industry
First: the Common Types of Motors Used in HVAC Industry to drive Compressors

1- Single-Phase Hermetic Motors:

1.1 Split Phase (SP),
1.2 Capacitor-Start, Induction-Run (CSIR),
1.3 Capacitor-Start, Capacitor-Run (CSCR),
1.4 Permanent Split Capacitor (PSC),
2- Poly-Phase Hermetic Motors.
Second: the Common Types of Motors Used in HVAC Industry to drive Fans
1- Shaded-Pole Motors
HVAC System Units And Ratings
Energy Conversions In Air Conditioning / Refrigeration Systems
HVAC Equipment Power Rating Calculations – Part Two

Difference between Service, Feeder and Branch circuit load calculation
First: The HVAC System Contribution in Service/Feeder Load Calculations
First: NEC Standard Method
Second: NEC Optional Calculation Method
First: For Single Dwelling Units
Second: Multifamily Dwelling
Third: Two Family Dwelling (That are Supplied By a Single Feeder)
Forth: Existing Dwelling Unit

NEC Code & the Hermetic Refrigerant Motor-Compressors
Sizing Calculations for Air Conditioning and Refrigeration Equipment as Per Article 440:
First: Sizing Calculations for Disconnecting Means:
Case# 1: The load type is a single hermetic motor only as per 440.12(A),
Case# 2: The load type is a Combination loads as per 440.12(B).
HVAC Equipment Power Rating Calculations – Part Four


The Minimum Circuit Ampacity (MCA)
Maximum Over-Current Protection (MOP) or (MOCP)
Second: Sizing calculation for Branch-Circuit Short-Circuit and Ground-Fault Protection Devices
Case# 1: The load type is a single hermetic motor only as per 440.22(A),
Case# 2: The load type is a Combination loads as per 440.22(B).
Case# 2A: Where a hermetic refrigerant motor-compressor is the largest load,
Case# 2B: Where a hermetic refrigerant motor-compressor is not the largest.

Third: Sizing Branch Circuit Conductors Case# 1: The load type is a single hermetic motor only as per 440.32,
Special Case: For a Wye-Start, Delta-Run Connected Motor-Compressor
Case# 2: The load type is a Combination loads as per 440.33.

Fourth: Sizing Controllers
Case# 1: Controller Serving Motor Compressor only as per 440.41(A),
Case# 2: Controller Serving More Than One Load as per 440.41(B).
HVAC Equipment Power Rating Calculations – Part Six
Fifth: Branch Circuit Overload Protection
The methods for providing overload protection for the motor-compressors are listed as follows:
1-A separate overload relay,
2-A thermally protected motor-compressor,
3-A fuse or inverse time circuit breaker,
4-A special protective system.

Sixth: Provisions for Room Air Conditioners
1- Sizing Branch-Circuit Short-Circuit and Ground-Fault Protection
2- Sizing Branch Circuit Conductors
3- Sizing Disconnecting Means
4- Protection Device for the Cord





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