VFD with bypass breaker sizing question

[hhsting]

I have vfd that has bypass. The vfd manufacturer says input breaker size is 15A and motor full load amps is 11A.

I am not sure how to size breaker since this has bypass. If i consider bypass then i take 11x2.50 has inverse time breaker which come out to 27.5A so next size would be 30A breaker.

Based on NEC 2017 Article 430.130(A)(B) Should their be 30A breaker or 15A breaker feeding the vfd with bypass?

 

[petersonra]

I have vfd that has bypass. The vfd manufacturer says input breaker size is 15A and motor full load amps is 11A.

I am not sure how to size breaker since this has bypass. If i consider bypass then i take 11x2.50 has inverse time breaker which come out to 27.5A so next size would be 30A breaker.

Based on NEC 2017 Article 430.130(A)(B) Should their be 30A breaker or 15A breaker feeding the vfd with bypass?

I would be putting a separate breaker on the VFD and the bypass contactor in this case.

 

[hhsting]

I would be putting a separate breaker on the VFD and the bypass contactor in this case.

Bypass is integral to vfd. Also doesnt NEC 2017 Article 430.130(B) allow for one circuit breaker to feed vfd with bypass? Just not sure what breaker size

 

[hhsting]

I would be putting a separate breaker on the VFD and the bypass contactor in this case.

Sorry forgot to write whole thing previous post: Bypass is integral to vfd. Also doesnt NEC 2017 Article 430.130(B) allow for one circuit breaker to feed vfd with bypass? See below

“…..Where a single branch-circuit short-circuit and ground-fault protective device is provided for circuits containing both power conversion equipment and a bypass circuit, the branch-circuit protective device type and its rating or setting shall be in accordance with those determined for the power conversion equipment and for the bypass circuit/device(s) equipment”



I am not sure what breaker size though. The part in accordance with those determined for the power conversion equipment and for the bypass circuit/device(s) equipment in NEC 2017 Article 430.130(b) is confusing for post #1?

 

[infinity]

I have vfd that has bypass. The vfd manufacturer says input breaker size is 15A and motor full load amps is 11A.

Since the bypass is integral to the VFD and the manufacturer said to use a 15 amp OCPD then you use a 15 amp OCPD.

 

[hhsting]

Since the bypass is integral to the VFD and the manufacturer said to use a 15 amp OCPD then you use a 15 amp OCPD.

15A is the input breaker size by manufacturer of vfd. What about when it switches to integral bypass? 15A no small


Sent from my iPhone using Tapatalk

 

[don_resqcapt19]

15A is the input breaker size by manufacturer of vfd. What about when it switches to integral bypass? 15A no small


Sent from my iPhone using Tapatalk

There is nothing that requires that the inverse time breaker for a motor circuit be sized at 250%...that is simple the maximum permitted size for the device.

 

[infinity]

There is nothing that requires that the inverse time breaker for a motor circuit be sized at 250%...that is simple the maximum permitted size for the device.

I agree, which is why I said to simply follow the manufacturer's recommendation. I think that when they designed the device with an integral bypass they knew what the size the OCPD would need to be for it to operate in either VFD or bypass mode.

 

[hhsting]

I agree, which is why I said to simply follow the manufacturer's recommendation. I think that when they designed the device with an integral bypass they knew what the size the OCPD would need to be for it to operate in either VFD or bypass mode.

When I rechecked it is actually 15A input Fuse size not breaker size by vfd manufacturer

How does one provide fuse in the panel?

 

[infinity]

When I rechecked it is actually 15A input Fuse size not breaker size by vfd manufacturer

How does one provide fuse in the panel?

You can use a fused disconnect switch.

 

[kwired]

Does this unit always start via the VFD and only goes into bypass when running at 100% speed?

The 15 amp fuse will be fine if that is the case. If it ever starts "across the line" then it may not hold though. But it seems that kind of defeats the purpose of even having the VFD in many instances and might as well went with a simple contactor for a controller.

 

[hhsting]

See attach wiring diagram. Integral bfd bypass actually bypass the 15A fused and the disconnect. So engineer has sized the breaker upstream feeding vfd for rules of NEC Article 430 for bypass mode while internal fuse protects when vfd mode.

Would this be in compliance with NEC 2017 Article 430.130(A)(1)(2)?

 

[steve66]

My only question is what provides the motor overload protection? Both in VFD mode and in bypass mode? Do the CT's monitor the load and shut off both 1M and 2M for an overload?

The breaker and fuses only provide short circuit protection.