Brochure
Table Of Contents
- Introduction
- Motor Failure and Protection
- Trip Class Designation
- Withstand Ratings
- Thermal Overload Relay
- Melting Alloy
- Non-Compensated Bimetallic
- Automatic Reset
- Ambient Temperature Compensated Bimetallic
- Thermal Overload Relay Trip Characteristics
- Solid State Overload Relay
- Additional Standard Features
- Optional Features
- Additional Standard Features
- Optional Features
- General
- Nameplate Versus NEC Full-load Current
- Service Factor
- Motor Branch Circuit Design
- Overload Relays
- Hand Reset Melting Alloy
- Accessories
- Isolated Auxiliary Contacts for Motor Logic Overload Relays
- DIN Adapter
- Lug-Lug/Lug-Extender Kits
- Remote Reset Module
- 4 – 20 ma DC Communication Module
- Contact Units for Melting Alloy Type Overload Relays
- Melting Alloy Overload Relay Jumper Strap Kits
- Bimetallic Overload Relays
- Motor Logic™ – Solid State Overload Relay
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© 1998 Square D All Rights Reserved
IEC components are typically application rated. This means the controller is sized very close to its
operational limit for a given application. IEC motors are also generally more application rated. For these
reasons, Class 10 trip is most common on IEC applications. Because NEMA products are applied with
more built-in excess capacity, the Class 20 trip is most common.
Figure 1 shows the three types of trip curves.
Protection to Motor Branch Circuits
To protect the motor branch circuit against short circuits, overload relay protection must be coordinated
with protection provided by the SCPD. The SCPD may be a fused switch or a circuit breaker. Figure 2
shows the critical point (I
c
) in this coordination.
Class 10
Class 20
Class 30
10000.0
1000.0
100.0
10.0
1.0
1.0 10.0
Multiples of FLA
Trip Times (s)
Figure 1 Typical Trip Curves
Motor Current
Overload Relay
Motor Damage
SCPD
10000.0
1000.0
100.0
10.0
1.0
1.0 10.0
Multiples of FLA
Trip Time (s)
100-125% NEMA
105-120% IEC
Run Current
Starting
Current
I
c
Figure 2 Typical Coordination Curves
Product Description