It is a fact that our ACOPOS P3 systems are suitable for power systems that can provide a maximum short-circuit current (SCCR) of 5 kAeff at 480 Veff and that are protected with class gG / class J fuses or circuit breakers compliant with IEC/EN 60947-2 / UL 489 requirements.
This given SCCR rating is less compared to e.g. the SCCR rating of our ACOPOSmulti system which comes with a 65kA SCCR.
With an additional fuse / circuit breaker in series to the anyways needed fuse / circuit breaker for ACOPOS P3 the SCCR rating in general can be increased.
Below I will try to summarize my findings and information from support cases I had.
Measures to improve the SCCR rating according the standard:
The standard UL 508A, Third Edition for Industrial Control Panels provides possibilites in Supplement SB to improve the SCCR rating of an electrical cabinet:
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SB4.3.1 considers the use of a power transformer with an isolated secondary winding
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SB4.3.2/SB4.3.3 - Feeder Components that limit the short circuit current available to improve the SCCR rating by using:
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- a Listed Circuit Breaker marked “current limiting” as described in clause SB4.3.2 or a Class CC, G, CF, J, L, RK1, RK5 or T fuse as described in clause SB4.3.3 in the feeder circuit.
Here it is suggest that the customer checks the option of Supplement SB of UL 508A, Third Edition to improve the SCCR rating.
Check according a table included in the standard (especially considering the North America market)
Apart from the points above I also received following screenshot from the mentioned UL 508A standard which belongs to fuses:
According the standard the above shown table, which gives information about the worst case situation, must be followed rather than the peak let-through current charts (current limitation curve) from the technical datasheets. UL does not recognize the peak let-through current charts from fuse manufactures. So from the standard we can derive that fuses with a current rating of 20A (not higher) are suitable for securing the SCCR rating of 5kA which is needed for our ACOPOS P3 system. The fuses would have to be of the mentioned fuse classes as well. Higher current ratings than 20A are not suitable, since then already a SCCR value of e.g. 7kA would be the case after this fuse which is not allowed.
Another point which must be considered when selecting the fuse is, that the fuse must be suitable for installation in the feeder circuit. This normally is indicated in the technical data of the fuse:
Additionally to these criteria then a check in the peak let-through current charts in the circuit breaker / fuse datasheets can be made to find out if the current limitation actually is enough:
In the example case from above it got checked if an SCCR reduction from e.g. 35kA below 5kA is possible. As it can be seen according the red drawn lines, a limitation below the needed 5kA SCCR (needed for ACOPOS P3) is not possible with that circuit breaker.
But the fusing in the machine for the ACOPOS P3 system in general could look like that:
Hope that gives you an idea about how that topic can be tackled and what things must be considered. But in the end we as B&R are not the ones which are selecting the fuse and/or circuit breaker for the customer. In the end here the knowhow much more is at the machine-builder / customer side and at their electricians.
Best regards
Philipp