Is it allowable to connect some (a group) of three phase fan motors with Dahlander wiring inside in parallel? The whole group will be used for low and high speed according to request. Equal load on each motor. Maybe someone has such an experience? Common fuses for the whole group, not individual (know it is bad). The same power all of them.
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\$\begingroup\$ The company I work in does this routinely. We connect up to 4 3 phase ventilators in parallel, driving them from a single frequency controller and load reactor. Each motor has to be protected by it's own protective circuit breaker. \$\endgroup\$– BartCommented Nov 12, 2020 at 14:15
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1\$\begingroup\$ Dahlander wiring. I learned something today. :-) \$\endgroup\$– winnyCommented Nov 12, 2020 at 14:24
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Yes. Multiple motors have been connected to essentially "help each other" to drive a load in many ways for many decades. One common variation is to have both a supply and a return fan in a heating, ventilation and air conditioning (HVAC) system. You need to be careful in designing the mechanical system so that one motor is not taking all of the load or even "over driving" the other(s). Load sharing, multiple-motor systems have even been used is situations in which the loads are mechanically coupled together like two motors coupled to the same shaft, multiple motors with driving sprockets on the same chain or driving more than one pinion gear on the same ring gear. In some cases special motor control systems are used. With induction motors, the inherent slip of the motors helps with load sharing.
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\$\begingroup\$ Main thing in this is that in this connection the windings midpoints MUST remain interconnected between different motors -could it cause problems? \$\endgroup\$ Commented Nov 12, 2020 at 15:38
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\$\begingroup\$ That does not sound like proper implementation of a Dahlander motor controller. I can not picture how that would be possible. \$\endgroup\$– user80875Commented Nov 12, 2020 at 16:16
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\$\begingroup\$ It would be unnecessarily complex todo this with a single Dahlander (2 speed 1 winding) motor starter for multiple motors. Impossible? No, but worth the extreme effort in wiring it and the risk of losing ALL motors from making one mistake? Not in my book. And the fusing would be required to be separate for each individual motor, making a real mess if one fuse blows somewhere. FAR FAR simpler to just use a VFD and have separate overload protection for each motor. Add together the motor FLA values (in high speed), add 10% and use that to size the VFD. Put a load reactor on the VFD as well. \$\endgroup\$– JRaefCommented Nov 18, 2020 at 19:54
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\$\begingroup\$ @ JRaef It didn't occur to me that this could be a case of two motors with one motor starter. However I have heard enough stories to believe that every wrong thing that sort of works will be done by someone. \$\endgroup\$– user80875Commented Nov 18, 2020 at 21:05