text: <s>[INST] Protection for external brake resistor Hi guys! We have problems with 755 drive's brake resistor: one terminal was grounded by loose metal clamp, resulting in IGBT blowup... My question is ¿What is the apropiate protection to drive? I don't find rockwell's recomendation to this. [/INST] For externally mounted braking resistors, the recommendation is to protect the drive from resistor temperature rise. This is done typically by a normally closed contact from an internal thermostat in the resistor. This signal is often used to open a contactor upstream the drive and remove the supply. However, the protection above will not be able to detect the failure of the internal breaking IGBT on a PowerFlex 755 drive. That type of IGBT failure may require fast DC bus branch short circuit protection. A possible way maybe the use of an external breaking chopper (or DBU - Dynamic Breaking Unit) and use an appropriate fast fuse to open the DC bus circuit and protect the IGBT inside the DBU. More information and general guidance about this is discussed on https://literature.rockwellautomation.com/idc/groups/literature/documents/um/akdbu-um001_-en-p.pdf Please, also note that for High Horse Power PowerFlex 755 (frame 8 and above) the only way to use an external braking resistor is with an additional breaking chopper (since those frames do not have the internal breaking IGBT). For frames 1 to 5, the breaking IGBT comes a standard and from frames 6 and 7 is optional. Thanks. \\n </s>