Protection Against Thermal Overload - Siemens SENTRON Instructions Manual

The rated switching capacity of RCBOs is considerably higher than that for residual
current operated circuit breakers as the MCB component, which is specially
provided for short-circuit protection, performs short-circuit clearing. Should this
switching capacity not be adequate, a back-up protection shall also be provided
here in accordance with the manufacturer's information.
5.5

Protection against thermal overload

Protection against thermal overloading of an RCCB shall primarily be provided by
careful planning of the load circuits downstream of the RCCB taking the manufac-
turer's information into consideration.
A note in DIN VDE 0100-530 states that it is permissible to use the expected ope-
rational current as a rating selection criterion to prevent overloading of residual
current operated circuit breakers as long as the instructions of the manufacturer
regarding the rated current and type of overcurrent protective device are used to
form the basis for the estimation.
The following points must be noted in order to avoid overloading the residual
current operated circuit breaker:
• The rated current of the RCCB is the maximum permissible uninterrupted load
current and must not be permanently exceeded.
• The back-up fuse value indicated on the rating plate (63 A to 125 A) only
provides back-up protection for the RCCB (see section 5.4).
The considerations regarding thermal loading no longer apply if RCBOs are used as
the MCB part provides overload protection through its thermal release.
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