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Table of abbreviations

Summary

Meaning of abbreviations used in this document

Abbreviation

Meaning

AC

AC voltage

ACT

ACTIVE (ready signal)

AL

ALARM (pre-alarm)

ASCII
[Modbus interface]

American Standard Code for Information Interchange

ATAM

Adjustable Thermal Adjustable Magnetic Trip Unit (adjustable thermal overload trip unit, adjustable magnetic trip unit with short-circuit protection)

ATFM

Adjustable Thermal Fixed Magnetic Trip Unit (adjustable thermal overload trip unit, permanently set magnetic trip unit with short-circuit protection)

ATSE

Automatic Transfer Switching Equipment

AUX

Auxiliary switch

C

Common

CB-S

Circuit Breaker Switch (standard auxiliary switch (NO contact))

CD

Compact Disk

COM‑DO

COM-Draw-out-Kit

DC

Direct voltage

DIN

Deutsches Institut für Normierung e. V. (German Institute for Standardization)

DISCON

DISCONNECT

DO

Draw out

EFB

External Function Box

ESD

Electrostatic sensitive devices

EMC

Electromagnetic compatibility

EN

European Standard

ETU

Electronic trip unit

FTAM

Fixed thermal adjustable magnetic trip unit (permanently set thermal overload trip unit, adjustable magnetic trip unit with short-circuit protection)

FTFM

Fixed thermal fixed magnetic trip unit (permanently set thermal overload trip unit, permanently set magnetic trip unit with short-circuit protection)

G

Ground fault (protection)

GF [tripping characteristic]

Ground fault

HH‑fuse

High-voltage fuses

I

Instantaneous (short-circuit protection)

I

Isolated

I‑ / O‑

Input / Output

IEC

International Electrotechnical Commission

INST [tripping characteristic]

INST [tripping characteristic]

INSTA

Final distribution area

IP

International Protection

IT

Injection Tester

IT

Isolated ground, French: "Isolé Terre"

L

Long-time delay (overload protection)

L

Overload protection

LBS

Load Break Switch (switch disconnector)

LCS

Leading changeover switch

LI

Overload protection (L) and instantaneous short-circuit protection (I)

LIG

Overload protection (L), instantaneous short-circuit protection (I) and ground-fault protection (G)

LIN

Overload protection (L), instantaneous short-circuit protection (I) and neutral-conductor protection (N)

LSI

Overload protection (L), short-time delayed short-circuit protection (S) and instantaneous short-circuit protection (I)

LSIN

Overload protection (L), short-time delayed short-circuit protection (S), instantaneous short-circuit protection (I) and neutral-conductor protection (N)

LSING

Overload protection (L), short-time delayed short-circuit protection (S), instantaneous short-circuit protection (I) and ground-fault protection (N)

LT [tripping characteristic]

Partial overload range of the characteristic curve of a switching device

MCCB

Molded case circuit breaker

MO

Motor operator

MRCD

Modular residual current device [without integrated trip device]

N

Neutral conductor

NC

Normally closed contact

NEMA

National Electrical Manufacturers Association

NFPA

National Fire Protection Association.

NO

Normally open contact

LV

Low voltage

LV fuse

Low-voltage fuse

PAC

Power Analysis & Control

PI

Plug-in (unit)

RCD

Residual Current Device

R

RESET

RCR

Residual Current Release

REC

Reclose (automatic reset)

RJ [connector]

Registered Jack

RMS

Root Mean Square

RS [interface]

Formerly: Radio Selector; now usually: Recommended Standard

RTU
[Modbus interface]

Remote Terminal Unit

SAS

Short circuit alarm switch

PLC

Programmable logic controller

ST

Shunt trip

STF

Shunt trip flexible

STL

Shunt trip left

T

Test

T [IT systems]

French: Terre (ground)

TC

Test device for molded case circuit breaker or MRCD, suitable for systems with grounded phase

TCP

Transmission Control Protocol

TD

Test Device

TM

Thermal Magnetic

TMTU

Thermal Magnetic Trip Unit

TRIP-IND

TRIP INDICATOR (trip alarm switch)

TRUE RMS

TRUE root-mean-square

TU

Trip Unit

UAR

Universal release

UL

Underwriters Laboratories Inc.

UR

Undervoltage release

USB

Universal Serial Bus

UPS

Uninterruptible power supply

UVR

Undervoltage release

UVR (LNO)

Undervoltage release with leading NO contacts

VDE

Verein Deutscher Ingenieure (Association of German Electrical Engineers)

VDI

Verein Deutscher Ingenieure (Association of German Engineers)

ZSI

Zone Selective Interlocking

ZSS

Zone Selective Interlocking

Meaning of symbols and abbreviations

Symbol/abbreviation

Meaning

Δt

Delay time

IΔn

Residual current; rated residual current; response current

I1

Inrush current

I"KG

Initial balanced short-circuit current

I2t

Let-through energy

IB

Take-over current

Ib

Pickup value blocking protection

Icm

Making capacity; rated short-circuit making capacity

Icn

Rated breaking capacity; rated short-circuit breaking capacity

Ics

Maximum short-circuit breaking capacity (partial selectivity); rated service short-circuit breaking capacity

Icu

Maximum short-circuit breaking capacity (full selectivity); rated ultimate short-circuit breaking capacity

Icw

Rated short-time withstand current; rated short-time current

Id

Prospective current; residual current; response residual current

ID

Let-through current

Ig

Ground-fault protection; ground-fault release; ground-fault current setting value

Ii

Instantaneous tripping current; instantaneous short-circuit protection; instantaneous magnetic protection; rated tripping current of instantaneous trip

Ik

Short-circuit current

IKD

Uninterrupted short-circuit current

IK MAX

Maximum short-circuit current

IKmaxline

Uninterrupted short-circuit current of system

In

Rated operational current

InG

Rated operational current (generator)

IP

Rated peak withstand current, impulse short-circuit current

Ir

Thermal protection; setting current; response value; current setting value of adjustable overload protection (pickup value overload protection)

Is

Limit current with selectivity; maximum short-circuit current for selectivity limit

Isc

Prospective current

Isd

Short-time delayed tripping current; response current of S protection; short-time delayed short-circuit release; short-time delayed short-circuit protection; delay time of S protection

Ith

Conventional free-air thermal current

IU

Rated uninterrupted current

RA

Contact resistance of exposed conductive part ground

t1

Time of inrush current

t2

Ramp up time

tA

Safety clearance

tb

Delay time (delay of blocking time)

td

Response time

tg

Delay time associated with the adjustable response current; trip time associated with ground-fault current setting value

ti

"Virtual" trip time of I protection; highest trip time associated with rated tripping current of instantaneous trip

Tp

Trip time; delay time; time-lag class

tr

Trip time associated with current setting value of adjustable overload protection

tsd

Trip time associated with short-time delayed tripping current; delay time of S protection

tS

Fuse operating time

tZSI

Delay time of all molded case circuit breakers which detect the short circuit but do not receive a blocking signal when ZSI is activated.

U

Voltage across main contacts of the molded case circuit breaker

Ue

Maximum voltage; rated operating voltage

UNn

System rated voltage