This section applies to AC an DC motors, 600 V or less, 186 watts (1/4 HP) and larger.
3.8.1 General Requirements. Every motor and motor circuit shall have:
1. Means of disconnecting all ungrounded conductors.
2. Circuit protection , not exceeding conductor ampacity, in each ungrounded conductor.
3. Circuit arrangements so that a fault will cause circuit protection devices to open all ungrounded conductors.
4. Conductors rated for at least 125 % of motor full load amperage (FLA).
5. Thermal overload protection.
3.8.2 Overload Protection Devices. Overload protection devices shall comply with the following:
1. One of the following protective devices is required for all motors:
a. A manual motor starter with thermal overload protection.
b. A magnetic motor starter with manual reset thermal overload protection.
c. A manual reset thermal protective device integral with the motor.
d. An automatic reset thermal protective device integral with the motor.
2. The resetting of the thermal overload device shall not restart the motor unless there are no exposed moving parts, e.g., enclosed refrigeration compressors and close coupled pumps.
3.8.3 Portable Motors. Portable motors equipped with attachment plugs do not require thermal overload protection as they are considered to be protected by the receptacle branch circuit protection device.
3.8.4 Single-Phase AC Motors. Single-phase AC motors shall have thermal overload protection meeting the following requirements:
1. 120 V motors - Protection installed in the ungrounded conductor. See FIG. 6.
2. 208 V motors - Protection installed in both ungrounded conductors. See FIG 7.
EXCEPTION: 208 V motors with manual starters may have the thermal sensor in only one ungrounded conductor, however the starter must disconnect both ungrounded conductors.
3.8.5 Three-Phase AC Motors. Three-phase motor requirements are:
1. All motors equal to or greater than 559 watts (3/4 HP) should be three-phase.
2. Thermal overload protection hall be installed in all ungrounded conductors.
3.8.6 DC Motors.
1. DC motors should have thermal protection integral with the motor controller.
2. Shunt and compound wound motors shall be equipped with field loss protection to prevent excessive motor speed when this condition exists.
3.8.7 Labels. The following labels are required:
1. Thermal protection- Motors with integral thermal protection shall be marked "Thermally Protected" or "TP."
2. Direction Arrow- Where rotation is critical, a direction arrow shall be installed.
3.8.8 Mounting. Motors Shall be mounted so that they:
1. Are accessible for lubrication, maintenance, and replacement.
2. Have sufficient air circulation to maintain temperature below 90% of rating.
3.8.9 Grounding. Motors shall be grounded as specified in Section 5.
3.8.10 Guarding. All motor driven couplings, belts, and chains shall be suitably guarded. See Sec. 10.
3.8.11 Under Voltage Protection. Undervoltage protection shall be provided for all motors which may initiate hazardous equipment motion upon return of power after an under voltage condition.
3.8.12 Motor Selection. Table 8 is to be used as a guideline to aid in balancing phase loads when selecting electric motors. Specific amperage requirements for motors can be determined by the manufacturer’s specifications or by tables in the NEC.
Figure 5. 120 V, 1 Phase, Portable Motor Protection
Figure 6. 120 V, 1 Phase, Motor Protection
Figure 7. 208 V, 1 Phase, Motor Protection
Figure 8. 208/480 V, 3 Phase,
Motor Protection
|
Motor Size |
Rec. Volts & Phase |
Typical Amperage |
|
1/6 to 3/4 HP |
120V, 1 Ph 208V, 1 Ph |
4.4 to 13.8 A 2.4 to 7.6 A |
|
3/4 to 5 HP |
208V, 3 Ph |
3.1 to 16.7 A |
|
5 HP and up |
480V, 3 Ph |
7.6 A and up |
Table 8. Motor Selection Guidlines
Table 9 is provided for information only to show typical magnetic device inrush and sealed current.
3.9.1 Relays. Relays are typically used for logic and switching in control circuits.
1. Coil shall be 120 V or less.
2. Contacts shall be 120 V or less.
3. Contacts shall not switch more than their rated "break" amperage.
3.9.2 Contactors. Contactors are typically used for switching in power circuits.
1. Coil shall be 120 V or less.
2. Contacts shall not switch more than their rated "break" amperage.
3. Contactor shall be appropriately selected for inductive or resistive switching applications.
3.9.3 Motor Starters. Motor starters are typically used for switching motor loads.
1. Coil shall be 120 V or less.
2. Contacts shall not switch more than their rated "break" amperage.
3. Motor starters shall have thermal overloads sized for motor full load amperage (FLA).
3.9.4 Solenoids. Solenoids are typically used for converting electrical signals to mechanical motion.
1. Solenoids with coil inrush of less than 240 VA may be connected in control circuits but should be separately fused.
2. Solenoids with coil inrush of 240 VA or more shall be in power circuits, controlled by a contactor and individually protected for overcurrent.
Note: The facilities disconnecting means does negate this requirement.
3.10.1 Single Source of Power. Equipment shall not have more than one source of power.
EXCEPTION: When frequencies in addition to 60 Hz are required and all the requirements of 8.1.7 are complied with.
3.10.2 Disconnect Rating. The supply disconnect overcurrent protection shall be rated at not more than 150 %, and not less than 115 % of the total normal operating full load current of the equipment.
3.10.3 Disconnect Connection. Supply conductor connections to the disconnecting means shall comply with the following:
1. The supply conductors shall be connected directly to the disconnecting means in the main electrical enclosure with no connection to terminal blocks or other devices.
2. There shall be no exposed live parts when the disconnecting means is in the open position.
3. All ungrounded conductors of the supply circuit shall be disconnected simultaneously.
4. Grounded conductors (neutral) shall not be disconnected.
EXCEPTION: The grounded conductor (neutral) may be disconnected for valid safety and design requirements, providing that it is disconnected simultaneously with the ungrounded conductors.
5. Grounding conductors (earth) shall not be disconnected.
3.10.4 Disconnect Mounting. The disconnecting device shall not be mounted on hinged or removable access covers or doors.
3.10.5 Disconnect Handle. The disconnect handle:
1. Shall not be more than 6.5 feet or less than 1.5 feet above the operating floor line.
2. Shall clearly indicate the ON and OFF positions.
3. Shall be accessible from the front of the enclosure.
4. Shall be readily accessible by the equipment operator when it is used as the emergency off (EMO) switch.
5. Shall not disengage from the disconnect device when the enclosure door is opened.
6. Mechanism of hardwired equipment shall be lockable in the OFF position.
7.Mechanism should be mechanically or electrically interlocked with the enclosure door.
3.10.6 System Disconnecting Means. When disconnects are mounted in separate enclosures (each supplying power to one unit of a system), the following provisions shall be made:
1. The disconnecting device in each of the separate system units shall de-energize all hazardous potentials and energy levels within that unit.
2. A main disconnecting device shall be furnished to de-energized the entire system.
EXCEPTION: See 8.4.3.
3.10.7 Disconnect Type. The type of disconnecting means required is based on the equipment power requirements.
3.10.7.1 Small Equipment. Single phases equipment operating at 120 V or less with up to 2 kVA main protection requires one of the following disconnecting means.
1. Switch and Fuse. See figure 9.
2. Circuit breaker with a minimum of 5000 Amperes Interrupt Capacity (A.I.C.)
See fig 10.
EXCEPTION: The power attachment plug may be used as the disconnecting means for self contained (free standing ) units under 0.25 kVA if they have the following:
a. A POWER ON indicator light
on the unit.
b. Adequate overcurrent protection
within the unit.
3.10.7.2 Large Equipment. Multiphase equipment and equipment operating at 120 V with 2 kVA or more main protection require a circuit breaker with a minimum of 10,000 A.I.C. for disconnecting means. See Fig. 10 & 11.
Notes:
1. Fuse must be sized to protect the load, the switch, and the conductors.2. See item 4 under 3.10.3.
Figure 9. 120 Volt, 1 Phase Main Switch
and Fuse
Notes:
1. Circuit breaker must be sized to protect the load and the conductors.2. See item 4 under 3.10.3.
Figure 10. 120 Volt, 1 Phase Main Circuit
Breaker
Notes: 1. Circuit breaker must be sized to protect the load and the conductors.
2. See item 4 under 3.10.3.
Figure 11. 208/480 Volt, Multiphase Main Circuit Breaker
- They can be reset without exposure to energized terminals and, therefore, can be reset safely by nontechnical personnel.
- They provide more assurance the ratings can not be inadvertently changed , as when fuses are used.
- Multipole units (such as used on three phase circuits) can be obtained, which open all conductors simultaneously when an overload occurs on any conductor.
Fuse Breaker Protector
3.11.1 General Requirements. General requirements for circuit protection are:
1. Ampacity - Circuit protection devices shall not exceed the ampacity rating of the conductors they protect. See Table 10.
2. Location in the circuit - Circuit protection devices shall be located at the point in the circuit where an ungrounded conductor connects to its supply source or to a larger conductor.
EXCEPTION 1: Where all of the following conditions are complied with. The conductor:
a. Is not over 25 ft. long.
b. Ampacity rating is at least one-third that of the conductor from which it is supplied.
c. Terminates at a single circuit protection device.
d. Is protected from physical damage.
Note: The conductor shall not connect to any component or device prior to termination at the protection device.
EXCEPTION 2: Where all of the following conditions are complied with. The conductor:
a. Is not over 10 ft. long.
b. Ampacity rating is not less than the maximum continuous load current of the circuit.
c. Ampacity rating is not less than the rating of the device supplied or the rating of the overcurrent protective device at the conductor termination.
EXCEPTION 3: Where the circuit protection device protecting the larger conductor also protects the smaller conductor in accordance with Table 10.
3. Parallel devices - Circuit protection devices shall not be connected in parallel to attain required amperage.
4. Thermal devices - Thermal devices are not designed for short circuit protection and shall not be used for conductor protection.
5. Grounded conductors - Circuit protection devices shall not be connected in series with grounded or grounding conductors.
6. Accessibility - Circuit protection devices shall be readily accessible by service personnel.
7. Enclosures - Circuit protection devices shall be enclosed.
8. Labeling - The amperage rating of circuit protection devices shall be indicated in a manner that is clear, durable, and visible after installation.
9. Resets - Automatically resetting circuit protection devices are not acceptable.
10. Mounting - Circuit protection devices shall not be mounted on hinged or removable access panels.
11. Connection - Circuit protection devices shall be connected to the load side of the supply circuit disconnection means.
3.11.2 Clip Type Fuse Holders and Fuses. Clip type fuse holders and fuses shall meet the following requirements:
1. Use - As branch circuit protection.
2. Rating - Fuse holders shall be rated for the ampacity and voltage of the fuse and shall be a minimum of:
-250 V for 120/208 V circuits.
-600 V for 277/480 V circuits.
3. Enclosures - Fuses shall be installed within a NEMA type enclosure that has a positive de-energization capability before opening.
3.11.3 Inline Fuse Holders and Fuses. Inline fuse holders and fuses are unacceptable for installation in equipment.
3.11.4 Panel Mounted Fuse Holders and Fuses. Panel mounted fuse holders and fuses shall meet the following requirements.
1. Shock proof fuse holders should be used.
2. Use - 120 V, 15 A or less, single-phase circuits (less than 2 kVA).
3. Rating - Minimum of 125 V.
4. Wiring - Fuse holders that have exposed metal when the cap is removed (non shock proof fuse holders) shall have the line conductor connected to the side terminal.
5. Disconnect - Provision shall be made for de-energization of the fuse during replacement.
6. Mounting - Fuse holder shall have a "D" punched hole or equivalent, so that it will not rotate while the fuse is being removed.
3.11.5 Circuit Breakers. Circuit breakers and circuit protectors are not designed and / or listed for the same function. Circuit breakers shall meet the following requirements:
1. Use - Short circuit and / or overcurrent protection in any circuit.
2. Method of operation - Shall be manually operable and must clear a fault even if the handle mechanisms were held closed.
3. ON and OFF indication - Shall clearly indicate ON (closed) and OFF (open) positions.
4. Mounting Position - Shall be mounted on a vertical surface with the handle up for the "ON" position.
EXCEPTION: If horizontally mounted in a commercial distribution panel, the handle may be toward the center for the "ON" position.
5. Disconnect - Shall open all ungrounded conductors if a fault occurs in any phase.
6. Installation - The supply conductors shall be connected to the line side of the breaker.
3.11.6 Circuit Protectors (Circuit Interruptors) Circuit protectors are recognized as component appliance controls and are not interchangeable with circuit breakers because they may not provide short circuit protection. Circuit protectors shall meet the following requirements.
1. Use - Supplementary (branch circuit protection) overcurrent protection in nonindustrial applications, e.g., data processing equipment
2. Method of operation - Shall be manually operable and must clear a fault even if the handle mechanisms were held closed.
3. ON and OFF indication - Shall clearly indicate ON (closed) and OFF (open) positions.
4. Mounting Position - Shall be mounted on a vertical surface with the handle up for the "ON" position.
5. Disconnect - Shall open all ungrounded conductors if a fault occurs in any phase.
6. Installation - The supply conductors shall be connected to the line side of the breaker.
3.12.1 General Requirements
1. This section applies to stand alone heating units and heating units contained within equipment such as furnaces, ovens, and tanks.
2. All material use with the unit and associated equipment shall be suitable for the chemical, thermal, and / or physical environment. See 9.1.
3. Heating elements shall be protected from physical damage.
4. Hot surfaces shall be physically shielded, isolated, or insulated to protect against personnel contact.
5. Hot surfaces shall be properly labeled as such.
3.12.2 Circuits.
1. Heating units contained within equipment shall be powered form the load side of the equipment supply circuit disconnecting means. See 3.10 and 8.4.
2. Heating units contained within equipment shall be controlled by the equipment control circuits.
3.12.3 Controls.
1. Appropriate safety controls shall be installed to shut down the heating units independently of the normal machine controls. See 7.5.3 and 8.1.1.
2. Immersion heater applications may require redundant level and temperature controls.
This section applies to stand alone power supplies and power supplies contained within equipment.
3.13.1 Circuits.
1. Power supplies contained within equipment shall be powered from the load side of the equipment supply circuit disconnecting means. See 3.10 and 8.4
2. Power supplies contained within equipment shall be controlled by the equipment control circuits.
3.13.2 Protection. Power supply outputs may be protected by overcurrent and / or voltage variation circuits provided that the safety of these circuits is equivalent to that obtained by circuit breakers, circuit protectors, fuses, or thermal devices.
3.13.3 Marking. Each power supply shall have a nameplate indicating manufacturer, rating, input voltage and output voltage(s).
3.13.4 Guarding. Power supplies shall be securely fastened and protected from physical damage. All exposed hazardous potentials shall be guarded by shields or enclosures.
3.13.5 Ventilation. Ventilation shall be adequate to dissipate the transformer full load heat losses without creating an excess ambient temperature.
3.13.6 Isolation. Power supplies shall provide complete electrical isolation between input and output circuits. They shall be designed to minimize faults that could cause unexpected hazardous potentials to be present on circuits or components.
3.13.7 Discharge. Power supplies shall meet the discharge requirements specified for capacitors in 3.5.
3.13.8 Enclosure. Power supplies having outputs greater than 600V DC and capable of supplying over 5 mA through a 500 Ohm test load, shall be enclosed in a rigid compartment equipped with interlocks and a shorting bar.
3.13.9 Ferroresonant Regulators.
1. Shall have potentials of not more than
550 V at the line voltage.
2. Resonant circuits up to 275 V can be connected to other circuits if grounded and the maximum voltage to ground is less than 150 V.
3. Resonant circuits greater than 275 V shall not be connected to any other circuits.
3.13.10 Grounding.
3.13.10.1 Conductive Metal. Exposed, noncurrent-carrying metal guards, cases, etc., shall be effectively bonded to the equipment grounding conductor as specified in Sec. 5.
3.13.10.2 Output (secondary) Grounding. DC common shall be connected to an isolated bus (isolated from ground). When referencing to ground is required, one circuit grounding conductor shall be used to connect the isolated DC common bus to ground.
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