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Guide to choose electrical protections

Guide to choose electrical protections
Here are several types of electrical protections, as well as their different characteristics. See also the wiring diagram.
Type of
Protection
Function Symbol Selection criterion
Curve
sensitivity
Breaking capacity Nb of poles Nominal intensity
(In)
Disconnector
– Enables to disconnect (cut) a circuit manually.
– No protection.
Nominal intensity 1 to 4 Choose the disconnector depending on the circuit intensity downstream.
Fuse disconnector
– Enables to disconnect (cut) a circuit manually.
– Protection by fuse
Fuse activation speed:
GL :
AM :
1 to 4 Choose the fuses depending on the circuit intensity downstream.
(Thermal magnetic) circuit breaker
– Circuit disconnection downstream.
– Automatic activation for protecting installations:
– against overloads (overage In, see curve).
– against short-circuits.
See detail
Curve B: 3-5xIn
Curve C: 5-10xIn
Curve D: 10-20xIn
Choose the circuit breaker depending on the activation speed.
Maximum limit for short-circuit current (4.5, 6, 10… KA) 1 to 4 Choose the disconnector depending on the circuit intensity downstream, for overload protection
Residual current device
– Circuit disconnection downstream.
– Activation in case of insulation fault.
See detail
Differential sensitivity: 30 mA, 300 mA Maximum limit for short-circuit current (4.5, 6, 10… KA) 2 or 4 The disconnection speed is calculated for this intensity.
Residual current circuit breaker
– Circuit disconnection downstream.
– Automatic activation for protecting installations:
– against overloads. (overage In, see curve).
– against short-circuits.
– against insulation faults.
See detail
Curve B: 3-5xIn
Curve C: 5-10xIn
Curve D: 10-20xIn
Choose the circuit breaker depending on the activation speed.
Differential sensitivity: 30 mA, 300 mA
Maximum limit for short-circuit current (4.5, 6, 10… KA) 2 or 4 Choose the disconnector depending on the circuit intensity downstream, for overload protection.
Motor circuit breaker
– Circuit disconnection downstream.
– Adjustable thermal protection: in case of nominal current overage of the motor for some time (overload).
– Magnetic protection: overcurrent in the motor.
– Activation in case of phase unbalance.
See detail
Magnetic protection: Curve D: 10-20xIn 3 (can also be used for a single-phase motor) Nominal intensity adjustment range (ex from 6 to 10 A) for thermal protection
Thermal relay

Must be mounted on a contactor
– Adjustable thermal protection: in case of nominal current overage of the motor for some time (overload).
– Magnetic protection: overcurrent in the motor.
The contact must be inserted in the contactor command line.
See detail
Magnetic protection: Curve D: 10-20xIn 3 (can also be used for a single-phase motor) Nominal intensity adjustment range (ex from 6 to 10 A) for thermal protection
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