5 tim the rated current should used.3 tim its rated current for a
sustained period./h
D
D
D
D
5 Locked motor
In the case
of motors with
thermally critical rotor
6 Overload phase failure
7 Over-/undervoltage supply mains
D
D
8 Variation frequency supply mains D
9 Increased ambient temperature D
10 External heating
of the motor
(e. Since general rules exist, will gladly give you further advice spe
cial cases such heavy starting.: bearing heating)
D D
11 Obstruction otor cooling D
Efficiency protection device: not effective
■ partly effective
• fully effective
Note fuses
Fuses not protect motor against overload.
S
2CDC 1GS 014 CG2G3
ABB STOTZ-KONTAKT GmbH
.Motor protection
Selection the protection device
Motor protection General aspects
Selection adequate motor protection great importance with regard the operational reliability and service life motor. The specifications relation short-circuit protection for contactors and overload relays
must noted when selecting the rating fuses circuit-breakers. order protect motors against short-circuits, advisable use fuses
aM conjunction with the thermal overload relay.
Protection against: overload
• phase failure imbalance
• phase loss
E fficiency rotection device
current-dependent:
Fuses
O verload relays ith
p rotection device
in case phase failure
P rotection device,
tem perature-dependent:
Therm istor
m achine protection
CUSTORAPID-
Reasons for unwanted overloading
of the motor winding
1 Current overloading
2 Rated duty types S1-S8
to IEC 34-I
3 Operation when starting,
braking, reversing
4 Operation starting rates
OOperating cycles ops. fuse must withstand 1. They serve only short-circuit protection switchgear and cables.g.
The following shows summary which facilitates the correct choice.
For direct starting, fuses around 1. This would entail thermal overload the motor.5 2.
The effectiveness the available motor protection devices depends the range application
