Electrical Rules and Calculations for Air-Conditioning Systems – Part Three


In Article Electrical Rules and Calculations for Air-Conditioning Systems – Part One ", which was the first Article in our new Course HVAC-2: Electrical Rules and Calculations for Air-Conditioning Systems, I explained the following points:
  • Introduction for Air-Conditioning Systems Types
  • Introduction for Types of Motors/Compressors used in Air-Conditioning Systems

And in Article " Electrical Wiring Diagrams for Air Conditioning Systems – Part One ", I explained the following points:

  • Importance of Electrical Wiring for Air Conditioning Systems,
  • How to get the Electrical Wiring for Air Conditioning systems?,
  • Types of Electrical Wiring Diagrams For Air Conditioning Systems,
  • How to read Electrical Wiring Diagrams?

Also, I explained the electrical wiring diagrams for Typical Air conditioning equipments in the following Articles:

And in Article " Electrical Rules and Calculations for Air-Conditioning Systems – Part Two ", I explained Types of Disconnecting Means for Air-Conditioning Systems

Today, I will explain in detail identification and Marking of Disconnecting Means used for Air Conditioning Systems.





1- Classification of Electrical Distribution Systems
 according to Interrupting Ratings of their OCPD Combinations





All the disconnecting means (or generally all the overcurrent protective devices OCPD) in a building’s electrical distribution system are arranged, with respect to their short circuit ratings /interrupting ratings, in two combinations as follows:

  1. Fully rated system,
  2. Series rated system.


Each system from the above can consist of all fuses, all circuit breakers, or a combination of fuses and circuit breakers.



  

1.1 Differences between Fully Rated And Series Rated Systems

Fully Rated System
Series Rated System
Interrupting rating of overcurrent protective devices OCPD is equal to or greater than (typically 10% greater) the available fault level at the bus where the OCPD are installed.

i.e.:
interrupting rating of downstream and upstream OCPD ≥ fault level  where OCPD are installed.

Interrupting rating of overcurrent protective devices OCPD is above the interrupting rating of the load side (protected) circuit breaker, but not above the interrupting rating of the line-side (protecting) device.

i.e.:
interrupting rating Rating of downstream OCPD < fault level  where OCPD are installed < interrupting rating of main upstream OCPD.
Interrupting rating of downstream OCPD fault level where OCPD are installed.
It allows installing of downstream OCPD with interrupting rating < fault level  where OCPD are installed.
Fully rated systems can consist of all fuses, all circuit breakers, or a combination of fuses and circuit breakers.
A series rated combination can consist of fuses protecting circuit breakers, or circuit breakers protecting circuit breakers.
Fully rated systems are recommended and can be used everywhere, as long as individual interrupting ratings are in compliance with 110.9.
series rated combinations have limited applications (the only proper application of series rated combinations is for branch circuit, lighting panels)
Series rated combinations can’t applied in health care systems, or emergency circuits like fire pumps and elevators.
Series rated combinations have extra NEC requirements that must be met.
fully rated combinations can be selectively coordinated.
Series rated combinations inherently can’t be selectively coordinated.
Fully rated system is more expensive than series rated system.
Series rated combinations can lower the overall system cost.






1.2 Examples for Fully Rated And Series Rated Systems


1- Example for Fully Rated System:

As In Fig.1 , fully rated system has protection devices tested to withstand the fault current available at their respective applied location.

Fig.1: Example for Fully Rated System


2- Example for Series Rated System

In the event of a short circuit as in Fig.2, both downstream and upstream breakers will open simultaneously to clear the fault which results in unnecessarily blackout a portion of the electrical system.


Fig.2: Example for Series Rated System


Note:

Replacement of breakers and fuses of panelboards and switchboards in series rated systems must be done by using either:

Breakers and fuses part number listed on the panelboard /switchboard label, or
Tables of available fuse/circuit breaker series rated combinations published by panelboard and switchboard manufacturers (see Fig.3).


 Fig.3: Example for Series Rated Combinations Published by Panelboard and Switchboard Manufacturers






1.3 Difference between Series Rated System and Selective Coordinated System


Fig.4: Difference between Series Rated System and Selective Coordinated System


  • As shown in Fig.4, Series rated combinations can’t be selectively coordinated. In order to protect the load side circuit breaker, the line side (protecting) device must open in conjunction with the load side (protected) circuit breaker. This means that the entire panel can lose power because the device feeding the panel must open even under relatively low-level short-circuit conditions.
  • But in selective coordinated system, only the load side circuit breaker will open in a case of fault without opening the line side (protecting) device.







2- Identification and Marking of Disconnecting Means




Based on the above discussion, any disconnect means will be used either in a fully Rated Combination System or in a Series Rated Combination System as described in above.

First: Identification of Disconnecting Means used in a fully Rated Combination System

For Identification of Disconnecting Means used in a fully Rated Combination System, the rules NEC 240.60 and 240.83 are applied as shown in below.

As we stated above that a fully rated system consist of all fuses, all circuit breakers, or a combination of fuses and circuit breakers. For this reason, we will explain the identification/Marking of Fuses and Molded Case Circuit breakers that widely used as disconnecting means for Air conditioning systems.






1- Marking for Fuses

Fuses shall be plainly marked, either by printing on the fuse barrel or by a label attached to the barrel showing the following: (see Fig.5)

  • Ampere rating,
  • Voltage rating,
  • Interrupting rating where other than 10,000 amperes,
  • Current limiting where applicable,
  • The name or trademark of the manufacturer.


Fig.5: Fuse Marking






2- Marking for Molded Case Circuit breakers

Circuit breakers shall have marking showing the following:

A- General Marking
B- Position Indication
C- Interchangeable Trip Units
  • Type Designation,
  • Manufacturer’s Name,
  • Voltage Rating,
  • Ampere Rating,
  • Line and Load Identification.


  • On and Off (Open and Closed)
  • Trip and Reset,
  • Electrical Operation (On and Off),
  • Electrical Operation (Trip and Reset).


  • Manufacturer’s Name,
  • Ampere Rating,
  • Frame Designation,
  • Magnetic Settings.


D- Interrupting Ratings
E- Terminations
F- Adjustable Trip
  • Interrupting Ratings.


  • Cu-Al Wire,
  • Small Size Wire,
  • Tightening Torque,
  • Maximum Wire Size,
  • Multiple Conductor Connectors,
  • 60/75°C Wire,
  • Separately Shipped Connectors,
  • Cable Connection Only,
  • Bus Bar Sizes.


  • Instantaneous Trip,
  • Type A and Type B,
  • Adjustable Controls.


I- Special Markings
J - Fused Circuit Breakers
K- Circuit Breaker/Ground Fault Circuit Interrupter
  • Non-Conducting Enclosure,
  • Ventilated Enclosure,
  • 40°C,
  • Current Limiting,
  • Class CTL,
  • Delta,
  • 2-Pole — 3-Phase Rated,
  • 3-Pole — 1-Phase Rated,
  • 4-Pole — 3-Phase Rated,
  • Multi-Wire Circuit,
  • DC Rated 3-Pole,
  • 100 Percent Continuous Rated,
  • SWD,
  • Independent Trip,
  • Special Characteristics,
  • For Replacement Not CTL,
  • Special Purpose Not General,
  • HID,
  • Remotely Operated Circuit Breaker.


  • Line and Load Identification,
  • Identification of Fuses,
  • No Open Fuse Tripping,
  • General Markings.


  • “Test” Function,
  • “Class A” Marking,
  • Instructions,
  • Terminal Identification,
  • General Markings.


L- Circuit Breaker/Equipment Ground Fault Protection
M- Circuit Breaker Surge-Protective Device
N- High-Fault Protectors And Accessory High-Fault Modules
  • “Test” Function,
  • Trip Level Marking,
  • Instructions,
  • Terminal Identification,
  • Use Marking,
  • General Markings.


  • Types,
  • Voltage Protection Rating,
  • Maximum Continuous Operating Voltage Rating (MCOV),
  • Nominal Discharge Current (In) Rating,
  • Short-circuit Current Rating (SCCR),
  • General Markings.


  • Type Designation,
  • Manufacturer’s Name,
  • Terminations,
  • Circuit Breaker,
  • Interrupting Rating.


O- Accessories
P- Circuit Breaker Adapters
Q- Circuit Protectors
  • Ratings,
  • Shunt Trip,
  • Separately Shipped,
  • External Dropping Resistor.


  • Type Designation,
  • Manufacturer’s Name,
  • Terminations,
  • Circuit Breaker,
  • Instructions.


  • Manufacturer’s Name,
  • Voltage Rating,
  • Ampere Rating,
  • Reset Instructions.


R- Circuit Breakers For Use In Communications Equipment
S- Molded Case Circuit Breakers Also Listed As Combination Type Arc-Fault
Circuit Interrupters
T- Molded Case Circuit Breakers Also Listed As Branch/Feeder Type Arc
Fault Circuit Interrupters
  • Ambient Operating Temperature,
  • Wire Insulation Temperature Rating,
  • Same Polarity,
  • General Markings.


  • Device Identifier,
  • “TEST” Function,
  • Instructions,
  • General Markings.


  • Device Identifier,
  • “TEST” Function,
  • Instructions,
  • General Markings.


U- Classified Molded Case Circuit Breakers For Use In Specified Equipment
V- Molded Case Circuit Breakers For Use In Photvoltaic (Pv) Systems
W- Marking Location Codes
  • Classified Only and Compatibility List,
  • Classified and Listed Compatibility List,
  • Compatibility List,
  • Classification and Listing Mark,
  • General Markings.


  • Voltage Rating,
  • PV marking,
  • Multi-pole PV Circuit Breakers,
  • Temperature Rating,
  • Wire Range and Type,
  • General Markings.


  • A
  • B
  • C
  • D
  • E
  • F
  • G
  • H
  • I
  • J
  • K



Examples for important markings of Molded Case Circuit breakers:


Example#1As shown in Fig.6, the numbered marking will be as follows:


Fig.6

1. ON and OFF:
The ON and OFF (closed and open) positions of the handle must be marked (NEC 240.81). These positions may also be marked with the internationally recognized “I” and “O” symbols, although this is not a UL requirement. If these markings are not visible when a motor operator is installed over the circuit breaker markings, then they must appear on the motor operator. Motor operators may be found in applications where remote or automatic operation of a circuit breaker is required.

2. Ampere Rating (if 100 A or less):
The ampere rating may be located on the handle escutcheon or on the handle itself (NEC 240.83(B)). Circuit breakers that are rated more than 100 A may have their ampere rating marked in a position that is not visible with trims or covers in place.

3. HACR type:This marking indicates the circuit breaker is suitable for use with the group motor installations typically found in heating, air conditioning and refrigeration equipment. The NEC 2005 no longer has this marking requirement. The electrical industry determined that circuit breakers are considered suitable for use with such equipment without any further testing, therefore, the HACR marking is no longer required on air conditioning and refrigeration equipment or on circuit breakers for use in these applications. The requirement for this marking has also been removed from the UL 1995 product standard for HVAC equipment.


Example#2As shown in Fig.7, the numbered marking will be as follows:


Fig.7

1. Manufacturer’s Name:
This marking may be the manufacturer’s name, trademark or other recognized means to identifying the company that made the circuit breaker.

2. Type Designation:
All circuit breakers are marked with a type designation, which may be a catalog number prefix or a separate designation. Equipment labels, such as on panelboards, will list the circuit breaker types suitable for use. Note that the word “type” may or may not be used on the circuit breaker or equipment labels. It is important to review the markings on the equipment, such as a panelboard, to make sure the circuit breaker designations on the equipment match the marking on the circuit breaker.

3. Voltage Rating:
All circuit breakers must be marked with a voltage rating. If the rating is not marked “ac” or “dc,” then it is suitable for both. 120/240 V rated circuit breakers are suitable for use on single and three-phase 4-wire systems where the line-to-ground voltage does not exceed 120 V. Wye rated circuit breakers such as those rated 480Y/277 V, are suitable for use on three-phase 4-wire systems where the voltage to ground does not exceed 277 V. Special attention needs to be given to high leg or corner-grounded delta systems to insure that the circuit breaker has the appropriate rating. A review to see that the circuit breakers installed have a voltage rating suitable for the application is paramount for a code-compliant installation (NEC 240.83(E)).

4. SWD:
15- or 20-A circuit breakers rated 347 V or less may be marked “SWD,” meaning that they are suitable for switching fluorescent lighting loads on a regular basis (NEC 240.83(D)). These circuit breakers are evaluated for high endurance use, since they will be used similar to a light switch.

5. HID:
50 A or less circuit breakers rated 480 V or less may be marked “HID,” meaning they are suitable for switching high intensity discharge or fluorescent lighting loads on a regular basis. These circuit breakers may employ a different construction than a standard SWD circuit breaker in order to address the high inrush current resulting from the lower power factor created by the HID lighting (NEC 240.83(D)). These circuit breakers also undergo additional endurance evaluation to demonstrate their ability to perform the switching duty.

6. Trip and Reset:
Circuit breaker handles typically assume an intermediate position when tripped. This position must either be marked on the circuit breaker or on the equipment into which it is to be installed. If these markings are not visible when a motor operator is installed, then a “tripped” marking may appear on the motor operator.


Example#3As shown in Fig.8, the numbered marking will be as follows:


Fig.8


1. Line and Load Designation:
Circuit breakers marked with “line” and “load” designations are not suitable for reverse connection. Circuit breakers with interchangeable trip units must be marked “line” and “load” unless there is no risk of shock when changing the trip unit.

2. Interrupting Ratings:
All circuit breakers with an interrupting rating more than 5000 A must be marked with an interrupting rating (NEC 240.83(C)). Interrupting ratings are stated in RMS symmetrical amperes. If the short-circuit current rating of the equipment in which the circuit breaker is installed is less than the interrupting rating of the circuit breaker, then the lesser rating applies. Circuit breakers should be reviewed after installation to ensure they have an interrupting rating suitable for the application. This marking may be found in any location except the back of circuit breakers that are 1-½ inches wide per pole or less due to the size constraint.

3. Ampere rating (if more than 100 A):
 The ampere rating of a circuit breaker larger than 100 A may be found in a location that is visible after the cover or trim is removed. This marking requirement also applies to interchangeable trip units (NEC 240.83(A)).

4. 40°C:This marking indicates the maximum ambient temperature in which the circuit breaker can be applied at its marked ampere rating without re-rating the ampacity of the circuit breaker. This marking is required for thermal- magnetic circuit breakers and is optional for electronic trip circuit breakers unless they are only suitable for a 25°C ambient, in which case they must be marked 25°C. When the ambient temperature rises above 40°C, the designer may need to consult the manufacturer to obtain rerating information.

5. Terminations (Cu-Al wire):
Circuit breakers must be marked with the type material (Cu-Al) and size of wire for which their terminals are suitable for use. If suitable for use with only copper or only aluminum, then the word “only” must be used. The abbreviations “CU” and “AL” are generally found on circuit breakers as permitted by the product standard. If only solid 10–14 AWG wire can be used, then that information must be noted. The number of wires per terminal will also be noted if more than one wire per terminal is permitted (NEC 110.14(A)).

6. Tightening Torque:
The nominal torque for all field-wiring terminals must be marked. If the width of the circuit breaker is 1-½ inches per pole or less, then this marking may be found in any location except on the back.

7. Wire Temperature Ratings:
Circuit breakers rated 125 A or less may be marked as suitable for use with 60°C, 60/75°C or 75°C only wire. Circuit breakers rated more than 125 A are rated for use with 75°C wire; the marking is optional. It is always permissible to use wire with a higher temperature rating, but it must be sized in accordance with the temperature marking on the circuit breaker and NEC Table 310.16. If the width of the circuit breaker is 1-½ inches per pole or less, then this marking may be in any location except on the back (NEC 110.14(C)1).

8. Separately Shipped Connectors:If connectors are not factory installed on a circuit breaker, then it must be marked with the proper connectors or terminal kits required in any location except the back.


Example#4As shown in Fig.9, the numbered marking will be as follows:


Fig.9


1. “1 – 3” Marking:
A 2-pole circuit breaker used to protect a 3-phase load on a corner-grounded delta system must be rated and marked for such an installation. Circuit breakers marked “1-phase – 3-phase” or “1 – 3 “are suitable for use on 3-phase corner-grounded delta or single-phase circuits (NEC 240.85).

100% Rated Marking:
100 percent continuous rated – Circuit breakers are typically intended for use at not more than 80% of rated current where the load is considered continuous, or will continue for 3 hours or more (NEC 210.20). However, some circuit breakers are rated for continuous use at 100% of their current rating. These circuit breakers must be so marked in any location except on the back. Enclosure information such as a specific type or specific volume must also be marked. A requirement for the use of 90°C insulated wire sized to the 75°C column in NEC Table 310.16 and specific ventilation requirements may also be marked on the circuit breaker or equipment (NEC 210.20(A) and 215.3).






Notes for Marking of Fuses and Circuit breakers

  • Fuses or circuit breakers used for supplementary overcurrent protection of fluorescent fixtures, semiconductor rectifiers, motor-operated appliances, and so on, need not be marked for Interrupting Current IC.
  • Circuit Breakers with interrupting rating 5000 amperes will not have Interrupting rating marking.
  • Fuses with interrupting rating 10,000 amperes will not have Interrupting rating marking.







Second: Identification Disconnecting Means used in a Series Rated Combination System

For Identification of Disconnecting Means used in a Series Rated Combination System, the rules NEC 240.86 and 110.22 are applied as shown in below.

The arrangement of protective components in a series rated system is determined by two methods as follows:

  1. A licensed professional engineer and in this case the system is called Engineered Series Combination Systems and It can be applied For Existing installations only.
  2.  The system manufacturer and in this case the system is called Tested Series Combination System and It can be applied For Existing and new installations.


The marking of a series rated system will differ according to the two above method used for arrangement of protective components as follows:

1- Marking for Engineered Series Combination Systems:

Equipment enclosures for circuit breakers or fuses shall be legibly marked in the field as directed by the engineer and the marking shall be readily visible.

2- Marking for Tested Series Combination Systems: (see Fig.10)


Fig.10: Marking for Tested Series Combination Systems



  • The enclosures of circuit breakers or fuses must be legibly marked by the equipment manufacturer and the marking shall be readily visible.
  • When the equipment is installed in the field, the equipment must have an additional label to indicate that the equipment has been applied with a series combination rating.


Example for series rated system marking:

A- In case of Engineered Series Combination Systems, The marking can be as follows:

CAUTION — ENGINEERED SERIES COMBINATION SYSTEM RATED ………. AMPERES. IDENTIFIED REPLACEMENT COMPONENTS REQUIRED.


B- In case of Tested Series Combination Systems, the field marking can be as follows:

CAUTION — SERIES COMBINATION SYSTEM RATED ………. AMPERES. IDENTIFIED REPLACEMENT COMPONENTS REQUIRED.






General Notes For Disconnecting Means Markings

  • The markings shall specifically identify the purpose of each piece of equipment unless located and arranged so the purpose is evident (see Fig.11). For example, the marking should not simply indicate “disconnect means” but rather “disconnect means, water pump” or not simply “disconnect means” but rather “disconnect means, front lobby.”

Fig.11: Purpose/Location Specified Marking

  • The marking shall be of sufficient durability to withstand the environment involved.
  • The markings shall not fade or wear off.




In the next Article, I will explain in detail How to Locate and Size of Disconnecting Means used for Air Conditioning Systems. So, please keep following.



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