Type-tested combinations

The standard short-circuit current rating (SCCR) is the minimum value that component manufacturers must demonstrate compliance with in order to obtain certification through product testing standards. This standard SCCR value allows the component to be adequately protected by a general fuse or circuit breaker. In case you are unable to find specific SCCR values in the documentation provided by the component manufacturer, you can refer to the UL 508A overview table SB4.1, which provides a comprehensive list of standard SCCRs. This table can be used as a reference to ensure proper protection and compliance, and also to determine the overall SCCR value of a control panel.

As you can see in the table, the standard SCCR is based on the minimum short-circuit value of the product testing standards, the maximum overall-SCCR value of the panel is limited in a range of 5 up to 10 kA in most practical cases when using these standard SCCR values, which often won’t cover the needs of the market.

To achieve higher short-circuit current rating values for the control panel, electrical designers have the option to utilize tested combinations known as high SCCR combinations.

The high SCCR combinations undergo individual short circuit tests where each component is tested with specified protection devices until their physical limits are reached. The results of these tests are documented and published in a Certificate of Compliance (CoC). By using these high SCCR values instead of standard SCCR values, designers can determine the overall SCCR of their panels to ensure higher levels of protection.

As an example, let's consider the standard short-circuit current ratings (SCCR) for different components. According to the UL 508A table SB4.1, a circuit breaker typically has a standard SCCR of 5 kA, while a 60 hp magnetic motor controller has a standard SCCR of 10 kA. Similarly, a fuse and fuse holder also have a standard SCCR of 10 kA.

However, as you can see in the table, Siemens offers a specific magnetic motor controller model for the same example, the SIRIUS 3RT2045-… 60 hp, which has a high SCCR value. This motor controller can be protected by a fuse with a maximum rating of 300 A, providing a high SCCR of up to 100 kA for 600V applications.

Alternatively, if you choose to protect this magnetic motor controller with a SIRIUS 3RV2742 circuit breaker with a maximum rating of 70 A, the high SCCR combination value would be 65 kA for 480Y/277V. Moreover, if you opt for a SENTRON 3VA5 circuit breaker with a maximum rating of 125 A, the combination test would yield a high SCCR of 100 kA for 480V applications.

So when using high SCCR values, then the lower standard SCCR values in the CoC can be ignored, therefore you can achieve an overall higher SCCR value for your control panel.

To access the specific high SCCR combination values for the Siemens magnetic motor controller mentioned, you can refer to the Certificate of Compliance (CoC) provided on Siemens Support Portal.

Learn more about Siemens CoC for magnetic motor controllers