Hello, I've been iteratively re-designing the controls for our conveyor system used for educational purposes and have another question, this time regarding the use of RCDs (residual current devices or GFIs) with VFDs. We want to build a motor control center with 5x VFDs (Siemens G120s) to drive 5x 0.37kW (0.5hp) 3-phase motors. This system will be plugged into a 3-phase 230/400V classroom wall outlet, which has an upstream 62A (30mA trip) RCD in the main wall cabinet (somewhat out of our immediate control).
The G120 manual says that current may flow through the earth conductors when using VFD's and can cause nuisance tripping. Therefore, they recommend a single 300mA trip RCD before each VFD for protection (no more than one VFD per RCD). In the main conveyor cabinet that we are building to distribute power to the MCC (and other cabinets), we would ideally like to put a 25A 30mA RCD in the main line right out of the wall plug and coordinate it with the main wall 62A RCD so it trips first (this would essentially mean two 30mA RCDs in series for convenience if tripped).
I have read a lot about people having issues tripping RCDs when running VFDs. I'm hoping someone more experienced with this can give some input as to whether or not they think it will be an issue trying to run all 5 of these low power motors off of the VFDs through a single 30mA RCD. If this is going to be an issue, what would you do as an alternative? Any input would be much appreciated.
The G120 manual says that current may flow through the earth conductors when using VFD's and can cause nuisance tripping. Therefore, they recommend a single 300mA trip RCD before each VFD for protection (no more than one VFD per RCD). In the main conveyor cabinet that we are building to distribute power to the MCC (and other cabinets), we would ideally like to put a 25A 30mA RCD in the main line right out of the wall plug and coordinate it with the main wall 62A RCD so it trips first (this would essentially mean two 30mA RCDs in series for convenience if tripped).
I have read a lot about people having issues tripping RCDs when running VFDs. I'm hoping someone more experienced with this can give some input as to whether or not they think it will be an issue trying to run all 5 of these low power motors off of the VFDs through a single 30mA RCD. If this is going to be an issue, what would you do as an alternative? Any input would be much appreciated.