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Motor and Motor Circuit Protection

• Agenda• Motor Circuit Characteristics

• Protection from Overcurrents

• Motor Circuit Requirements

• Sizing OCPD’s

• Back-up Overload Protection

• Type 2 Protection

• How does a motor operate?• Starting

• Normally

• What do we protect against?• Overload

• Short-Circuit

0.0110 100 10001

Current in Amperes

Motor Inrush Curve

Inrush Current

Normal Operating Current

300 % Overload

0.0110 100 10001

Current in Amperes

Short Circuit

0.0110 100 10001

Current in Amperes

Motor Circuit Requirements(NEC®)

• 430.101- 430.113 (Part IX)• Disconnecting means

• 430.52• Branch-Circuit Short-Circuit Protection

• 430.32• Overload Protection

To Supply

MotorBranch

Motor Overload

• NEC® 430.102• Location(Of Disconnecting Means)

• (A) In sight from Controller

• Branch-Circuit Short-Circuit Disconnect

• (B) In sight from Motor

• Branch-Circuit Short-Circuit Disconnect

• Manual Motor Controller “Suitable as Motor Disconnect”

• Exceptions provided if (A) is lockable in open position.

Barrier, wall or isle with an obstruction

Lockable Disconnecting Means

1999 NEC® Code

Controller

In sight motor disconnecting means required per 430.102(B)

Barrier, wall or isle with an obstruction

In sight (of controller) disconnecting means ahead of controller required per 430.102(A)

Requirement since 2002 NEC® Code

Controller

• NEC® 430.52• Branch-Circuit Short-Circuit Protection

• (B) Must handle starting current

• (C) Rating or Setting• (1) Table 430.52

• Exception 1: Next Higher size is permitted if the values from table 430.52 do not correspond to a standard size

• Table 430.52 Maximum Rating*

Non time-delay Fuse1

Dual-Element (Time-Delay) Fuse

Instantaneous Trip Breaker

Inverse Time

Breaker

300% 175% 800% 250%

1Non-Time-Delay also applies to Class CC fuses

*Single-phase motors, AC polyphase motors other than wound-rotor, squirrel cage-other than Design B energy-efficient

Motor and Motor Circuit Protection• NEC® 430.52(C)(1) Exception 2:

• If Motor Unable to Start, then size according to following, or next smaller size

400%300%225%400%

Inverse Time

Breaker<100A

Inverse Time

Breaker>100A

Dual-Element (Time-Delay) Fuse

Non time-delay Fuse1

601-6000A Fuse

1Non-Time-Delay also applies to Class CC fuses

• NEC® 430.32 (Overload Protection)• (a) More than 1 Horsepower.

• (1) A separate overload device that is responsive to motor current. This device shall be selected to trip or rated at no more than the following percent of the motor nameplate full-load current rating.

Motors with a marked service factor 1.15 or greater - 125%

Motors with a marked temperature rise 40 °C or less - 125%

All other motors - 115%

MOTOR CIRCUIT DEVICES

• What OCPD(s) can be used in a motor circuit?• Fuse

• Circuit Breaker

• MCP

• Overload relay

0.0110 100 10001

Current in Amperes

Motor Inrush Curve

0.0110 100 10001

Current in Amperes

MCP at minimum setting

Motor Inrush Curve

0.0110 100 10001

Current in Amperes

MCP at minimum setting

0.0110 100 10001

Current in Amperes

MCP at maximum setting

0.0110 100 10001

Current in Amperes

Motor Inrush Curve

300 % Overload

0.0110 100 10001

Current in Amperes

0.0110 100 10001

Current in Amperes

Motor Damage Curve

0.0110 100 10001

Current in Amperes

300 % Overload

Motor Damage Curve

0.0110 100 10001

Current in Amperes

300 % Overload

0.0110 100 10001

Current in Amperes

15A Circuit Breaker

0.0110 100 10001

Current in Amperes

Motor Inrush Curve

15A Circuit Breaker

0.0110 100 10001

Current in Amperes

300 % Overload

Motor Damage Curve

15A Circuit Breaker

NON-2 Amp

0.0110 100 10001

Current in Amperes

0.0110 100 10001

Current in Amperes

Motor Inrush Curve

NON-2 Amp

0.0110 100 10001

NON-5 Amp

0.0110 100 10001

Current in Amperes

Motor Inrush Curve

NON-5 Amp

0.0110 100 10001

Current in Amperes

300 % Overload

Motor Damage Curve

NON-5 Amp

0.0110 100 10001

Current in Amperes

Overload Relay

0.0110 100 10001

Current in Amperes

Motor Inrush Curve

Overload Relay

0.0110 100 10001

Current in Amperes

300 % Overload

Motor Damage Curve

Overload Relay

0.0110 100 10001

Current in Amperes

300 % Overload

MCP at maximum settingMotor Damage Curve

Overload Relay

0.0110 100 10001

Current in Amperes

300 % Overload

Motor Damage Curve

15A Circuit Breaker

Overload Relay

0.0110 100 10001

Current in Amperes

300 % Overload

Motor Damage Curve

NON-5 Amp

0.0110 100 10001

Current in Amperes

FRN-R-1-6/10

0.0110 100 10001

Current in Amperes

Motor Inrush Curve

FRN-R-1-6/10

0.0110 100 10001

Current in Amperes

300 % Overload

Motor Damage Curve

FRN-R-1-6/10

• Optimal Branch Circuit Protection (Back-up Overload Protection):

• 125% or up of FLA - FRN/FRS

• 130% or up of FLA- LPN/LPS

• 150% or up of FLA- LPJ

• 200% or up of FLA- LP-CC

0.0110 100 10001

Current in Amperes

FRN-R-1-8/10

0.0110 100 10001

Current in Amperes

Motor Damage Curve

FRN-R-1-8/10

Overload Relay

0.0110 100 10001

Current in Amperes

300 % Overload

Motor Damage Curve

FRN-R-1-8/10

Overload Relay

Single-Phasing

• Single phasing is the opening of one phase of a three phase circuit.

Primary Single Phasing

• Primary wire broken by:• Storm - Wind - Ice - Sleet - Hail - Lightning

• Vehicle or Plane Striking Pole

• Falling Tree Limbs

• Construction Mishaps

• Primary wire burned out from short-circuit created by animals(i.e. squirrel to ground)

• Defective contacts on primary breaker - failure to make up on all 3 poles.

• Failure of 3 shot automatic reclosers to make up on all 3 poles.

• Open pole on 3Ø auto. voltage tap changer• Open winding in one phase of transformer• Primary fuse open

Normal Condition

208V 1/3 HP Motor 40 C

F.L.A. = 1.4 Amperes

Single Phase Condition

1.61 A

3.22 A

1.61 A208V 1/3 HP Motor 40 C

(230%)

(115%)

Assume one phase lost on the primary side of transformer.

(115%)

Secondary Single Phasing

• Damaged Motor Starter Contact - One Pole Open• Burned open overload relay (heater)• Damaged switch or circuit breaker on the main,

feeder, or branch circuit.• Open fuse or open pole in breaker on main,

feeder, or branch circuit.• Open cable or bus on secondary of transformer

terminals

• Open cable caused by overheated lug on secondary side-connection to service head.

• Open connection in wiring such as in motor junction box (caused by vibration) or any pull box

• Open winding in motor• Open winding in one phase of transformer

winding

Normal Condition

208V 1/3 HP Motor 40 C

Single Phase Condition

2.4 A208V 1/3 HP Motor 40 C

(173%)

Contacts on one phase are worn out resulting in an open circuit

0.0110 100 10001

Current in Amperes

Motor Damage Curve

FRN-R-1-6/10

0.0110 100 10001

Current in Amperes

Overload Relay

Motor Damage Curve

FRN-R-1-8/10

What about short circuit protection for a motor circuit?

• Short Circuit Condition

Current Source M

If the overcurrent protective devices are sized according to the maximums in NEC® 430.52, will the motor circuit components be protected from damage?

TYPE 1 PROTECTION vs. TYPE 2 PROTECTION

TYPE 1 vs. TYPE 2 PROTECTION

• What is Type 1 and Type 2 Protection?• IEC 947-4-1 Standard

• Type 1 Protection(Damage)

• UL 508 Listing

• Type 2 Protection(No Damage)

• Type 2 Tables from Manufacturer

• Type 1 Protection:• “Requires that, under short-circuit conditions,

the contactor or starter shall cause no danger to persons or installation and may not be suitable for further service without repair and replacement of parts.”

• Similar to UL 508 requirements

• Type 2 Protection:• “Requires that, under short-circuit conditions, the

contactor or starter shall cause no danger to persons or installation and shall be suitable for further use. The risk of contact welding is recognized, in which case the manufacturer shall indicate the measure to be taken as regards the maintenance of the equipment.”

Type 2 Protection Tables

• Does NEC® require Type 2 protection?

• NEC® section 110.10: Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics. The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit-protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit……Listed equipment applied in accordance with their listing shall be considered to meet the requirements of this section.

TYPE 2 PROTECTION

• Why Is Total Protection Important?• Maximum Safety To Personnel And Equipment

• Minimum Cost To Stay In Service

• Maximum Productivity From The Equipment

• Overload Protection• Overload Relay

• Fuses for Backup

• Short Circuit Protection• Fuse, Circuit Breaker, MCP

• Type 2 Protection(No Damage)

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