The controller disconnect can serve as the disconnecting means for the motor control circuit conductors (430.74) and the motor [430.102(B) Ex.]. The disconnecting means for the motor controller and the motor must
open all ungrounded supply conductors simultaneously
[430.103].
Where the motor controller also serves as a disconnecting means it shall open all?
Terms in this set (37) A motor controller shall open all
conductors to the motor where not used as a disconnecting means
. Motor control circuits shall be arranged so they will be disconnected from all sources of supply when the disconnecting means is in the open position.
When a motor disconnecting means is also a motor circuit switch the switch must be rated in _____?
QUESTION: “How is the motor disconnecting means sized?” ANSWER: Section 430-110(a) requires the disconnecting means for motor circuits rated
600 volts or less
to have an ampere rating of at least 115 percent of the motor full load current (FLC).
Where does the NEC refer specifically to disconnecting means for a motor?
Section 430.102(B)(1) requires a disconnecting means for each motor, and it must be
located in sight from the motor location and the driven machinery location
. “Within Sight” is visible and not more than 50 ft from each other [Art. 100].
Where the motor short-circuit and ground-fault protection devices determined by Table 430.52 do not correspond to the standard sizes or ratings a higher rating that does not exceed the next higher standard ampere rating shall be permitted?
The first exception
under 430.52(C)(1)
states, where the values for branch-circuit short-circuit and ground-fault protective devices determined by Table 430.52 do not correspond to the standard sizes or ratings of fuses, nonadjustable circuit breakers, thermal protective devices, or possible settings of adjustable …
Does a motor controller need to open all conductors to the motor?
The motor controller is
required to open only as many conductors of the circuit as necessary to start and stop the motor
(430.84). For example, one conductor must open to control a two-wire, single-phase motor; two conductors must open to control a three-wire, 3-phase motor.
How do you calculate motor load?
Por = Nameplate rated horsepower Load = Output power as a % of rated power Pi = Three-phase power in
kW η = 0.7457 x hp x Load Pi
Page 8 8 By definition, a motor of a given rated horsepower is expected to deliver that quantity of power in a mechanical form at the motor shaft.
Where is the disconnect means for a motor required to be located?
The disconnecting means must be located
within sight of the multiple controllers and in sight from the machinery or apparatus
.
What size motor requires a disconnect?
When you install a disconnect switch for a single-motor application, it must meet the following two criteria:
Have an ampere rating at least 115% of the rated motor full load current
.
Have a horsepower rating the same or greater as
the rated motor horsepower (at applied voltage)
Do all motors need overload protection?
EVERY motor needs overload protection
of some type. Some small motors are impedance protected by design. Some motors can be overload protected by breakers or fuses.
Can a breaker be used as a disconnect?
Unlike a switch, a circuit breaker automatically does this and shuts off the power immediately, or darn close to immediately. In this way it works as an automatic service protection device. … An exception to this is a
disconnect switch
, which is used to connect or disconnect power to an entire control panel, or machine.
How high can I mount a disconnect?
Minimum mounting height is not mandated by the NEC. When in its highest position, the center of the operating handle of the switch or circuit breaker should
not be more than 6 ft 7 in.
What is a local disconnect?
Beyond fusing, local disconnects typically have auxiliary contacts to wire back to a VFD (Variable Frequency Drive) or PLC (Programmable Logic Controller) and are HorsePower Rated based upon the possibility that the switch will be used to break the direct motor power under load.
How do you protect an electric motor from overload current?
Overload relays
protect the motor, motor branch circuit, and motor branch circuit components from excessive heat from the overload condition. Overload relays are part of the motor starter (assembly of contactor plus overload relay). They protect the motor by monitoring the current flowing in the circuit.
What devices are going to use to prevent overcurrent?
Examples of overcurrent protection devices are many:
fuses, electromechanical circuit breakers, and solid state power switches
. They are utilized in every conceivable electrical system where there is the possibility of overcurrent damage.
How do you protect an engine from overload?
Motor overload protection
is necessary to protect the motor and to help ensure the motor performs as expected. Continuous duty motors are protected against overload by a separate overload device sized between 115% and 125% of the motor nameplate full-load current, FLA.
