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:
Today, I will explain in detail Different Types, Locations and Sizes of Disconnecting Means used for HVAC Systems.
Types of Disconnecting Means for Air-Conditioning Systems
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In this Article and next
Articles, you will learn the following:
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And before proceeding with the above points, let’s take a general overview for NEC Rules controlling motor loads of Air-Conditioning Systems.
2- Important Definitions
2.1 Disconnecting Means:
A device, or group of
devices, or other means by which the conductors of a circuit can be
disconnected from their source of supply.
2.2 In Sight From (Within
Sight From, Within Sight):
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.
2.3 Branch-Circuit Selection
Current (BCSC):
When a branch-circuit selection current is marked
on a nameplate, it must be used instead of the rated-load current to
determine the size/Ratings of the disconnecting means, the controller, the
motor branch circuit conductors, and the overcurrent protective devices for the branch-circuit conductors
and the motor. The value of branch-circuit selection current is always
greater than the marked rated-load current.
2.4 Rated-Load Current (RLC):
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3- Types of disconnecting means
Disconnecting means for air-conditioning and refrigerating
equipment are used mainly to disconnect the main load(s) in these equipment,
which is motor-compressors, from the power circuit. The specified types of disconnection means
for this purpose as per NEC 430.109 will be as follows:
1- A listed Motor Circuit Switch:
Ii must be a horsepower-rated switch
capable of interrupting the maximum overload current of a motor.
2- A listed Molded Case Circuit Breaker.
3- A listed Molded Case Switch (non-automatic circuit
interrupter):
It is a circuit-breaker like
device without the overcurrent element and automatic trip mechanism. It is
rated in amperes and is suitable for use as a motor circuit disconnect based
on its ampere rating, as is a circuit breaker.
4- Instantaneous Trip Circuit
Breaker that is part of a listed combination motor controller.
5- Listed Self-Protected Combination
Controller:
6- Manual Motor Controller:
7- System Isolation Equipment
SIE:
8- branch-circuit overcurrent
device:
It shall be permitted to
serve as the disconnecting means for Stationary Motors of 1⁄8 Horsepower or Less.
9- A general-use switch:
It can be used as a
disconnecting means in the following cases:
10- A general-use snap switch
suitable only for use on ac (not general-use ac–dc snap switches):
It can be used as a
disconnecting means for stationary motors rated at 2 hp or less and 300 volts
or less and with the condition that the motor full-load current rating is not
more than 80 percent of the ampere rating of the switch.
11- Isolating Switches:
For stationary motors rated
at more than 40 hp dc or 100 hp ac, the disconnecting means shall be
permitted to be a isolating switch where plainly marked “Do not operate under
load.”
12- A Horsepower-Rated
Attachment Plug and Receptacle :
For a cord-and plug- connected
motor, a horsepower-rated attachment plug and receptacle, flanged surface
inlet and cord connector, or attachment plug and cord connector having
ratings no less than the motor ratings shall be permitted to serve as the
disconnecting means.
Note:
Horsepower-rated attachment
plugs, flanged surface inlets, receptacles, or cord connectors shall not be
required for cord-and-plug-connected appliances in accordance with 422.33,
room air conditioners in accordance with 440.63, or portable motors rated 1⁄3
hp or less.
13- An Attachment Plug and
Receptacle:
Note:
Demand factors authorized elsewhere in this
Code shall be permitted to be applied to the rating of a receptacle or of a
separable connector.
14- The branch-circuit switch
or circuit breaker:
Note:
If an appliance of more than
1⁄8 hp is provided with a unit switch in below paragraph, the switch or
circuit breaker serving as the other disconnecting means shall be permitted
to be out of sight from the appliance.
15- A unit switch(es) with a
marked-off position that is a part of an appliance and disconnects all
ungrounded conductors where other means for disconnection are provided in the
occupancy:
These switches are permitted
as the disconnecting means where other means for disconnection are provided
in the following occupancies:
A- Multifamily Dwellings:
In multifamily dwellings, the
other disconnecting means shall be within the dwelling unit, or on the same
floor as the dwelling unit in which the appliance is installed, and shall be
permitted to control lamps and other appliances.
B- Two-Family Dwellings:
In two-family dwellings, the
other disconnecting means shall be permitted either inside or outside of the
dwelling unit in which the appliance is installed. In this case, an individual
switch or circuit breaker for the dwelling unit shall be permitted and shall
also be permitted to control lamps and other appliances.
C- One-Family Dwellings:
In one-family dwellings, the
service disconnecting means shall be permitted to be the other disconnecting
means.
D- Other Occupancies:
In other occupancies, the
branch circuit switch or circuit breaker, where readily accessible for
servicing of the appliance, shall be permitted as the other disconnecting
means.
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4- Configuration Of
Disconnection Means for Motor(S) in Multi-Wire Branch Circuit
As per NEC 210.4 (B) Each multi-wire branch
circuit shall be provided with a disconnecting means that will simultaneously
disconnect all ungrounded conductors at the point where the branch circuit
originates.
1- For a single-phase
multi-wire branch circuit supplying only one utilization equipment:
The disconnecting means could
be one of the following:
In Fig.16, in which
line-to-line loads are supplied from single-phase, identified handle ties or
multi-pole common trip circuit breakers are permitted.
2- For a 3-phase
installation:
The disconnecting means could
be one of the following:
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In the next Article, I will explain in detail identification, Locations and Sizes of Disconnecting Means used for HVAC Systems. So, please keep following.
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