Monitoring Danfoss VFD in "Bypass"


Hi!  Recently a customer asked about a way to tell remotely if a Danfoss VFD was in bypass-  there are probably several ways to do this but here are a couple methods:

1.  Wire the EMCS point to X56 5/6

On 3-contactor bypass drives (ask us WHY we recommend and sell 3-contactor bypass), Danfoss gives you a customer connection board in the bypass section that allows you to monitor the bypass contactor directly.  You have to hunt for the board a bit, on different sizes drives it is in different places but they usually look similar:  a couple rows of small green terminal blocks.  Find the X56 terminal block that has 12 terminals, a contact between 5/6 indicates that the drive is on bypass (see picture and dwg).

This works if your intent is to show that the drive is on bypass.  If you want to show that the drive is "not ready" for ANY reason (major alarms, power failure, disconnect off, fuses blow, OR selector switch in bypass) then try method #2.



bypass connections.jpg

2. Wire the EMCS point to Relay 2 NO (4/5). 

Program Relay 2 parameter 5-40 to [160] "no alarm".  The relay will go high and have a contact closure between 4/5 if everything is OK with the drive.  Contact would be open if power failure, bypass, or alarm.


Program Relay 2 5-40 to [3] "Drive Ready/remote control"  Does the same as above but contacts open if the drive is placed into "manual" control from the keypad.  Might be useful if you are concerned that operators won't return the drive to auto mode-- might be a nuisance alarm if they do manual control a lot.

*Final Notes:  Unfortunately the bypass status can't really be a bacnet point, because the point of a bypass is to take over if there is a critical failure in the drive (and it wouldn't be talking bacnet at that point).  There are "electronic" bypasses that continue to talk while in bypass BUT we like the simplicity of a 3-contactor old school bypass when you need it -- don't add complexity to your backup emergency option.