Over current protection location/need....

Status
Not open for further replies.
R

rtbullfighter

Member
Good morning everyone. I would like to start by saying thank you to all that try and help me with this question.

I work for a company that builds a "control panel" that runs a 3? motor and does some other small details. We are using a VFD to run the motor,and right now we install fuses into our equipment just before the VFD. I was wondering, since the VFD protects the motor within the parameters that we set, and there is a breaker installed at the source, is there a need for the fuses or can we get rid of them in the build.

Thanks again.
 
What are the requirements of the VFD? I think many do require fuses on the input. Can't say I always see them installed that way, but if you want to follow instructions....
 
Talked to the manufacture and they said that as long as the Breaker was sized correctly the fuses were acting as a redundant protective device. My other concern was some of the distances that we see at some of the installations sites, up to 1500'. Does the breaker still provide accurate protection to be able to remove the fuses.
 
The problem with distance is impedance of conductor during a fault. Fuse or breaker will still operate same for overloads but for short circuits or ground faults will actually draw less fault current but possibly for longer duration before overcurrent device operates. Really depends on trip characteristics of the overcurrent device.

Another reality is if the short circuit or ground fault is in the drive, it is likely toast, and will need repair or replacement no matter what is protecting it.
 
rtbullfighter said:
Talked to the manufacture and they said that as long as the Breaker was sized correctly the fuses were acting as a redundant protective device. My other concern was some of the distances that we see at some of the installations sites, up to 1500'. Does the breaker still provide accurate protection to be able to remove the fuses.
Click to expand...
Too vague of qestion to give definitive answer. That said is actually an indication that it may not.

IMO, unless you control the supply circuit installation requirements, to remove the fuses from the design, make sure you provide a resilient nameplate with electrical data stated in Article 430, including MCA (minimum circuit ampacity) and MOCP (maximum overcurrent protection).
 
Thank you for the prompt and great feed back. Kwired, that is what I was thinking. Smart $, The company provides all of the proper MCA and MOCP to the customers during the purchase process so that they can make sure they have the correct power requirements. I guess I was looking to make sure that when we discuss the option of taking them out again, my thinking wasn't way off base and have some ground to stand on. Personally I think taking them out would not benefit us (as a company) as leaving them in would.


Thank you very much for your time.
 
Status
Not open for further replies.
Top