OVR40150SP datasheet(39/62 Pages) ABB

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Residual

Curr

ent

Devices

Low Voltage Products & Systems

16.37

ABB Inc. • 888-385-1221 • www.abb.us/lowvoltage

1SXU000023C0202 Rev. A

Application guide

Residual current devices

Introduction

Residual current devices (RCD) have always played an important role in

circuit protection by detecting leakage to ground for equipment in many

installations. RCD’s are used in unison with a circuit protective device in

industrial applications in the United States. The following guide will give

an insight to the construction, mechanical operation, and applications of

RCD’s.

RCD Definitions

Important definitions:

Earth leakage current

Current that flows between line to line or line to earth.

Residual current

The sum of the values of the electric currents in all live conductors

Fault current

Current that flows between line to line or line to earth.

Earth fault

When a conductive path is accidentally induced between a line and the

earth

RCD Definition

RCD’s provide ground fault protection to equipment by monitoring the

leakage of current to ground. An RCD will trip when a ground fault is

detected in excess of the trip rating of the device. An RCD is designed

to disconnect a circuit whenever it detects that the electrical current is

unbalanced between the phase conductor and the neutral conductor. An

imbalance may be caused by phase leaking to ground.

Difference between type A and AC

Types of RCD’s

Type AC

Must be used for protection against AC earth leakage current.

Type A

Must be used for protection against AC and pulsating DC (rectified

AC) earth leakage current. The type A RCD must be installed in any

circuit where the main supply is likely to be rectified. Some examples of

applications where this would apply are motor speed controllers (drives)

and power tools.

Current

transformer

Test wire

Test button

Position indicator

Operator handle

Sense circuitry

Solenoid

Solenoid pin

Terminals

ABB Residual Current Device

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