also i will like to add this to this disscussion that if you use the disconnect switch [ non fused type ] i suggest that you add a "polit" switch or microswitch on the camshaft of the disconnection switch so it will send the signal to the VFD contoller to shut off the power to prevent spikeing voltage and sorta like lock out to prevent the VFD firing up with very high voltage with low HZ it can wreack hovac and also during running if disconnected it will spike as well
Merci , Marc
Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)
#74944 - 02/08/0701:55 AMRe: Disconnect on the secondary of a VFD
A disconnect is required on the line side of the VFD. Quite often, a fused disconnect is furnished as part of the VFD equipment. For small VFD's, the disconnect needs to provide the short circuit and fault current protection. The VFD feeder breaker will provide this over current protection.
A disconnect (safety) switch on the load side, for disconnecting the motor is not required as long as the VFD line side OCP device can be locked in the open position.
It is standard practice to provide a LOCKOUT STOP pushbutton at the motor, whether or not a motor disconnect switch is provided.
I also like to install a JOG or START/STOP control station at the motor in order to locally check rotation, etc.
#74945 - 02/08/0705:14 PMRe: Disconnect on the secondary of a VFD
How is a spike from the motor that was caused by the switch opening getting back to the motor through an open switch?
By arcing back across the contacts as they open? The voltage developed by rapidly dumping current through a motor winding can easily get up into the several kV range.
I've repaired several VFDs that got wiped out by this kind of abuse. In one incident, it was a simple safety disconnect switch at the motor that killed it. In the others (machine tool retrofit applications), it was the installation (by a well-meaning machinist) of the VFD upstream of a reversing contactor or drum switch, to try to keep as much of the original setup in use as possible. Those problems were solved by wiring the VFD right to the motor, and handling the reversing at a low level, with a logic input to the VFD.
#74947 - 02/08/0707:41 PMRe: Disconnect on the secondary of a VFD