(1) VFD for (2) Motors

You should probably explain to the customer that they will need to have a backup for the VFD in case of a failure or risk having their system down for an extended period. It makes more sense to have the second VFD connected and ready to go than sitting on a shelf in the maintenance spares.

Rson said:

I think what happened is that we quoted the customer and they had sticker shock, and now we are trying to find ways to cheapen our product.

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Then, the absolute cheapest way.... and I helped do it once, just swap the leads when you need to switch over, we did not have room for a second and the drive never failed it was always the pump seals or the motor bearings so we installed a second motor/pump and ran the leads to the cabinet, put some lugs on the bottom and had two sets of jumpers going from drive to either set of lugs, they were large and when you needed to switch over to the other system you would pull out one set of jumpers and install the other set.

Since the wire were a 0 or 00 it held the shape so it was easy to remove and re-install and only took a few minutes to swap over.

geniusintraining said:

Then, the absolute cheapest way.... and I helped do it once, just swap the leads when you need to switch over, we did not have room for a second and the drive never failed it was always the pump seals or the motor bearings so we installed a second motor/pump and ran the leads to the cabinet, put some lugs on the bottom and had two sets of jumpers going from drive to either set of lugs, they were large and when you needed to switch over to the other system you would pull out one set of jumpers and install the other set.

Since the wire were a 0 or 00 it held the shape so it was easy to remove and re-install and only took a few minutes to swap over.

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it's either that or just use two fuse blocks, and keep one set of fuses remove with a note about why lol.

Now we're getting beef processing facility cheap.

cidchase said:

Install two disconnects. Interlock them (hard-wire or inputs) via auxiliary contacts so your single MS cannot pull in unless either one is on and the other off. Hard wire is safer. We do this whenever we have backup drop-lifter motors.

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This is what we decided on. We are planning to have a power distribution block for the wiring from the VFD so they can send it to each disconnect (which the customer is going to provide). Then the disconnects will be interlocked so that the VFD can't run if both are on.

Thanks for all the replies, they were all helpful!

If as you say you need and have a redundant fan running on a VFD and you want to be able to switch fan motor for service or on a fan failure then I would say you missed the boat on that one. You more likely to have a failure on the vfd then the motor it’s self. While either could fail at any time for any number of reasons a power spike would take out the vfd well before the motor. The most vulnerable component of the system is the vfd. Depending on the size of the fan motor a replacement motor would be much more readily available then a vfd. If you need is that critical then I would recommend that you have a complete redundant system for fan. Both a vfd and a motor already connected up ready to go. Set them up as lead lag alternating system where both will be run on a regular bases a failure on one will automatically start the other and sound an alarm.

GaryS said:

If as you say you need and have a redundant fan running on a VFD and you want to be able to switch fan motor for service or on a fan failure then I would say you missed the boat on that one. You more likely to have a failure on the vfd then the motor it’s self.

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We have many similar setups, and they have nothing to do with failures, but with maintenance. If they know the fan will have to be serviced like every half a year, or just cleaned or something every few months, then this setup is good.
We usually have this with pumps that get sent to service regularly and it takes a week or two to get it back. So while one is at the service, the other runs..
So, even if there is a bigger chance of failure in the VFD than in the motor, the fan or a pump being "out of order" is not only much higher, but certain.

GaryS said:

You more likely to have a failure on the vfd then the motor it’s self. While either could fail at any time for any number of reasons a power spike would take out the vfd well before the motor.

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I think Rson has came up with a way they are going but... Gary I respect your opinion but disagree, maybe it was just the processes I have been involved with but the motor/pump fails 5 times more likely then the drive failing. I guess to m_turk's point you can call it maintenance but regardless if its a seal, bearing, gland or winding I have had to work on the other end (mechanical) a LOT more than the drive side.

Thanks again for the feedback and concerns. The redundancy was specified by the customer, and the recommendation to use a single VFD was also from the customer. I understand that sometimes we have to try and save the customer from themselves, but in the end I can only build what they are willing to pay for.

Rson said:

Thanks again for the feedback and concerns. The redundancy was specified by the customer, and the recommendation to use a single VFD was also from the customer. I understand that sometimes we have to try and save the customer from themselves, but in the end I can only build what they are willing to pay for.

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"The customer is always right even when he is wrong."