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


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.

Also, in Article " Electrical Rules and Calculations for Air-Conditioning Systems – Part Three ", I explained identification and Marking of Disconnecting Means for Air-Conditioning Systems.

Today, I will explain in where to locate Disconnecting Means used for Air Conditioning Systems.




Location of Disconnecting Means with respect to Controller, Motor and Driven Machinery Location




As we stated in Article  " Electrical Rules and Calculations for Air-Conditioning Systems – Part Two " that the definition of the term In Sight From (Within Sight From, Within Sight) was as follows:

Where one equipment is specified to be “in sight from,” “within sight from,” or “within sight of,” and so forth, another equipment, the specified equipment is to be visible and not more than 15 m (50 ft) distant from the other. (see Fig.1 & Fig.2)


Fig.1: Disconnect insight from an equipment


Fig.2: Disconnect out of site from motor





First: for Motors and Motor-operated Equipments



1- NEC Code “In Sight From” Rules

There are several Rules in the NEC Code for a disconnecting means to be in sight from the equipment that it controls.




Rule#1

NEC 430.102(A) requires an individual disconnecting means to be provided for each controller and shall be in sight from the controller location. This means that the controller must be visible and not more than 50 ft (15 m) from the disconnecting means.

Fig.3: The disconnecting means within sight of the controller location






Rule#2

NEC 430.102(B) requires that Disconnect must be in sight of motor location and driven machinery. If the disconnect as required in 430.102(A) is in sight of the controller, the motor location, and driven machinery, then that disconnect meets the requirements of both 430.102(A) and 430.102(B). (see Fig.4)

Fig.4: The disconnecting means within sight of the motor, controller and driven machinery locations

If, because of the nature of the installation, the disconnect is in sight of the controller, but not in sight of the motor location and the driven machinery, then, generally, another disconnect must be installed. (see Fig.5)

Fig.5: The disconnecting means within sight of the controller location but not in sight of motor and driven machinery locations


Note:

When providing more than one disconnecting means, At least one of them shall be readily accessible as per NEC 430.107.






Rule#3

NEC 430.102(A) Exception No. 2 requires that A single disconnecting means may be located adjacent to (or in sight from) a group of coordinated controllers, where the controllers are mounted on a multi-motor continuous process machine. (see Fig.6)


Fig.6: Disconnect means for multiple motors on a single machine


Note:

NEC Code uses the terms motor location and controller location instead of motor and controller because in many instances, the motor or controller is inside an enclosure and is out of sight until an access panel is removed. If the terms motor and controller were to be used, then it would be mandatory to install the disconnect inside of the enclosure. This is not always practical. The Commercial Building's roof-top air-conditioning units are examples.





Rule#4

  • NEC 430.113 for Motor and motor-operated equipment with More Than One power Source shall be provided with disconnecting means from each source of electric energy immediately adjacent to the equipment served.
  • Where multiple disconnecting means are provided, a permanent warning sign shall be provided on or adjacent to each disconnecting means to warn the user that other power sources are present.
  • Motor and motor-operated equipment that require multiple separate sources of power to operate properly like:
  1. Motor space heater,
  2. Motor with a speed switch,
  3. Synchronous motors commonly use dc power for excitation purposes. (see Fig.7)


Fig.7: Synchronous motors with 3-phase power supply and dc power supply for excitation.



Exceptions to Rule#4:

Exception No. 1: Where a motor receives electric energy from more than one source, the disconnecting means for the main power supply to the motor shall not be required to be immediately adjacent to the motor, provided the controller disconnecting means is capable of being locked in the open position.

Exception No. 2: A separate disconnecting means shall not be required for a Class 2 remote-control circuit conforming with Article 725, rated not more than 30 volts, and isolated and ungrounded.





2- Exceptions NEC Code “In Sight From” Rules

Three exceptions permit disconnecting means to be located elsewhereand not in sight of a motor.




430.102(A) Exception No. 1

For motors over 600 volts, the controller disconnecting means may be out of sight of the controller, provided the controller has a warning label indicating the location and identification of the disconnecting means, which must be capable of being locked in the open position.






430.102(A) Exception No. 3


Fig.8: valve actuator motor (VAM) assemblies


The disconnecting means shall not be required to be in sight from valve actuator motor (VAM) assemblies containing the controller (see Fig.8) where such a location introduces additional or increased hazards to persons or property and the following conditions are met:

  1. The valve actuator motor assembly is marked with a warning label giving the location of the disconnecting means.
  2. The provision for locking or adding a lock to the disconnecting means shall be installed on or at the switch or circuit breaker used as the disconnecting means and shall remain in place with or without the lock installed.





430.102(B) exception

the disconnecting means may only be out of sight of the motor, if the disconnecting means complying with 430.102(A) is individually capable of being locked in the open position and meets the following cases:

Case#1:

  • If locating the disconnecting means close to the motor location and driven machinery is impracticable due to the type of machinery, the type of facility, lack of space for locating large equipment such as disconnecting means rated over 600 volts, or any increased hazard to persons or property, the disconnecting means is permitted to be located remotely.(see Fig.9)


Fig.9: disconnecting means out of site for Motors rated in excess of 100 hp


  • Some examples of increased or additional hazards to persons or property include, but are not limited to the following:
  1. Motors rated in excess of 100 hp,
  2. Multi-motor equipment,
  3. Submersible motors,
  4. Motors associated with adjustable speed drives,
  5. Motors located in hazardous (classified) locations.


Case#2:
  • In industrial installations, if all of the following conditions are verified:

  1. Industrial installations have written safety procedures.
  2. The conditions of maintenance and supervision ensure only qualified persons service the equipment.


Notes:
  • The provision for locking or attaching a lock to the disconnecting means must be part of the disconnect and a permanent component of the switch or circuit breaker. (see Fig.10)

Fig.10: Locking Hardware as a part of a circuit breaker 

  • The provision for locking (or adding a lock to) the disconnecting means is on the switch or circuit breaker and remains in place whether or not the lock is installed i.e. the lock is not readily removable or transferable type. (see Fig.10
  • Disconnect switches or circuit breakers that are located only behind the locked door of a panelboard or within locked rooms do not comply with the requirements of 430.102.




Second: for Air Conditioning Equipment




1- NEC Code “In Sight From” Rule




NEC 440.14

  • The Disconnecting means shall be located within sight from and readily accessible from the air-conditioning or refrigerating equipment.
  • The disconnecting means shall be permitted to be installed on or within the air-conditioning or refrigerating equipment, but it can't be located in access panels or where it will obscure the equipment nameplate.
  • This requirement is amendatory even if there is also a remote disconnect capable of being locked in the “open” position under the provision of the exception to 430.102(B).


Note:
The main purpose of above rule is providing protection for service personnel working on equipment located in attics, on roofs, or outside in a remote location where it is difficult to gain access to a remote lockable disconnect




2- Exceptions NEC Code “In Sight From” Rule



440.14 Exception 1
There is no need to place a disconnecting means within sight from the equipment, if all of the following conditions are verified:
  1. The disconnecting means is capable of being individually locked in the open position.
  2. The equipment is essential to an industrial process in a facility that has written safety procedures.
  3. The conditions of maintenance and supervision ensure only qualified persons service the equipment.
  4. The provision for locking (or adding a lock to) the disconnecting means is on the switch or circuit breaker and remains in place whether or not the lock is installed i.e. the lock is not readily removable or transferable type.(see Fig.10


Note:
440.14 Ex 1 is for special conditions such as very large process refrigeration equipment and is rarely applicable for the following reasons:
  1. This equipment is very large ones, so rated disconnects may not be available,
  2. This equipment may be in hazardous locations, and locating disconnecting means within sight of the motor may introduce additional hazards.






3- Exceptions NEC Code “Readily Accessible” Rule




440.14 Exception 2

  • An accessible attachment plug and receptacle can serve as the disconnecting means for cord-connected equipment as per 440.13. The receptacle for the attachment plug doesn't have to be readily accessible.
  • Examples of cord-connected equipment included in 440.13:

  1. Room air conditioners,(see Fig.11
  2. Household refrigerators,
  3. Freezers,
  4. Beverage dispersers,
  5. Drinking water coolers.


Fig.11:  an attachment plug and receptacle as a disconnecting means for Room air conditioners


  • As per 440.63 for Room air conditioners, an attachment plug and receptacle or cord connector shall be permitted to serve as the disconnecting means for a single- phase room air conditioner rated 250 volts or less if:(see Fig.11

  1. the manual controls on the room air conditioner are readily accessible and located within 1.8 m (6 ft) of the floor, or
  2. An approved manually operable disconnecting means is installed in a readily accessible location within sight from the room air conditioner. You can’t, for example, run the cord through a sheet of plywood and plug it in on the other side.


  • And as per 440.64 , A flexible cord that supplies a room air conditioner can’t be longer than:

  1. 3.0 m (10 ft) for 120V units,
  2. 1.8 m (6 ft) for 208V or 240V units.




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


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