hhsting
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How would one size the vfd output cables between the vfd and the motor? Which NEC 2017 Article and section apply here?
VFD output cable size
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hhsting
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What protects the output cables? Overcurrent protection wise
From overload? The drive.
hhsting
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ptonsparky
Tom
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- EC - retired
The drive protects the cable and or the motor from overcurrent/overload. Think of it as the overload block on a standard ATL starter. Only way better. That does not mean that you cannot screw up by setting the parameters incorrectly. No different than using the overload twice what they should be.
hhsting
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I dont understand how drive protects from overcurrent protection? Their is no overcurrent protection in vfd and if their is one provided does that not protect the drive not the output conductors?
petersonra
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The drive knows how much current is being fed to the motor. Most drives you can see this in the display. It's a fairly simple mathematical calculation to do the I squared t calculations that the heaters do mechanically in a typical thermal overload.
Krusscher
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Like Pton said, think of the drive like a variable overload block where you can set the amps from lets say 10-20 amps. Even if you are protecting a motor that has a FLA of 10 amps and you run 14AWG you could still crank that thing up to 20 and then your wire wouldn't be protected. Same thing with a drive but you don't have a physical overload block it is all in the drive. You still set the over current protection for that motor/wires. You still have to fuse your drive for the correct short and ground fault protection.
hhsting
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So lets say you have fuse in the vfd integral does that protect the output conductors or not?
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Krusscher
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Fuse in the VFD? What is the make/model of this VFD?
ptonsparky
Tom
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- EC - retired
It does, but that is not what it's for. I believe it is to protect against rapid disassembly.
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Just like a standard motor starter the drive will provide the OVERLOAD protection.
hhsting
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Ok what is the short circuit or ground fault protection for output conductor?
ptonsparky
Tom
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- EC - retired
The drive.
Not needed. Here is an article of VFD output circuits.
www.linkedin.com
Why is there no short circuit protection for VFD (Variable-frequency Drive)?
Short-circuit protection is a function of the device connected between the power supply and the load, which can effectively disconnect the short-circuit point from the power supply when a short-circuit occurs on the load side. A device has a short-circuit protection function, so it must have a certa
www.linkedin.com
Krusscher
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- Washington State
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The fuses/breaker before the drive. check 430.130
Krusscher
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Or the drive itself if rated for it
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- Illinois
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- retired electrician
Most drives have had listed motor overload protection built in for a couple of decades now.
hhsting
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- Junior plan reviewer
What protects the output conductors from short circuit and ground fault?
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