Size wire for VFD

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PowerdT

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I am not confident with this wire size. I need some help here please to understand
The system goes from main breaker —> local disconnect switch —->VFD —-> motor

The motor nameplate is 460V, 40HP, 3P. S.f 1.15, FLA, 45A

Table 430.250 gives us 40HP- FLC is 52A

Overload protection - VFD ACH580-01 matching the motor HP and voltage

430.22 - 125% of FLC = 65A——-> 3#4AWG

430.52 branch overcurrent protection
175% of FLC = 91A ~ 90A

Question is motor branch overcurrent protection size per motor is 90A fuse.

The VFD manufacturer protection is required 80A fuse maximum. Do I go with 80A?

main breaker(80A) --3#4 and 1#8G to local disconnect switch (80A fuse) —->VFD to motor 3#4 shield cable

Am I missing something?
 
ptonsparky said:
You need to size the wire to the VFD at 125% of it's rating. Wire from the VFD to the motor would be 125% of the NEC ampacity for that motor.
Use max or less rating for the VFD. 80 Amp fuse.
You are not required to use the Max fuse or CB. It can be smaller.
Click to expand...
VFD is 40HP is 52A FLC so 52A*125%=65A per 310.15(b)16 under 75C - I chose #4AWG.

My understanding is the VFD controls/protect the motor. If the VFD upstream is sized 80A fuse per the manufacture recommendation. Am I going to see nuisance trip? Since I got 90A ocpd per 430.52 for the motor per nec calculation.
 
The 430 stuff mostly only apply s to the wiring between the motor and the VFD.
The input wiring to the VFDis based on 125% of the maximum input of the VFD per its nameplate. The input side protection is sized per the VFD manufacturer.

Most of article 430 is based on the characteristics and behaviors of common induction motors while starting, such as currents that can be up to 600% FLC for up to 30 sec. However common VFDs rarely have more than 115% current even during starting.
 
Upstream Disconnect switch (80A) to VFD(40HP,480V) using 3#4+1#8G.
Then, from
jim dungar said:
The 430 stuff mostly only apply s to the wiring between the motor and the VFD.
The input wiring to the VFDis based on 125% of the maximum input of the VFD per its nameplate. The input side protection is sized per the VFD manufacturer.

Most of article 430 is based on the characteristics and behaviors of common induction motors while starting, such as currents that can be up to 600% FLC for up to 30 sec. However common VFDs rarely have more than 115% current even during starting.
Click to expand...
So your saying it’s normal installation if I size Upstream Disconnect switch (80A) to VFD(40HP,480V) using 3#4+1#8G.
Then, from VFD to Motor(40HP,480V) using 3#4 shielded VFD cable + 1#8G.
 
It doesn’t say input rating- it gives by HP or FLC 52A, I attached the nameplate
 

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Etanuye said:
It doesn’t say input rating- it gives by HP or FLC 52A, I attached the nameplate
Click to expand...
You are correct the input rating is 52A, according to the ABB instruction manual.
The required protection is a maximum 80A class T fuse.

Is this a standalone drive or part of an HVAC package?
 
If your terminals are 75C rated (which they probably are) you should be able to use 6 AWG for both input and output. You are right at the limit though if rating were 1 amp higher you would need to go with 4 AWG.
 
Don’t worry about that 79A peak output rating for 2 seconds, it’s irrelevant.

Pay attention to the line side fuse details though, using anything other than an 80A Class T fuse (like a Bussman JJS) will void the UL listing of it.

So the input conductors are to be sized at 125% of 52A minimum, the output conductors are to be sized for a 40Hp motor per the NEC tables. Don’t overthink it.
 
Jraef said:
Don’t worry about that 79A peak output rating for 2 seconds, it’s irrelevant.

Pay attention to the line side fuse details though, using anything other than an 80A Class T fuse (like a Bussman JJS) will void the UL listing of it.

So the input conductors are to be sized at 125% of 52A minimum, the output conductors are to be sized for a 40Hp motor per the NEC tables. Don’t overthink it.
Click to expand...
My understanding with VFD protects the thermal overload for the motor.
Am I required to have ocpd between the VFD and motor? Or is it optional this case
 
Etanuye said:
My understanding with VFD protects the thermal overload for the motor.
Am I required to have ocpd between the VFD and motor? Or is it optional this case
Click to expand...
Programmed correctly, the VFD will do everything thing but hand you the toilet paper. IDK about ABB, but many of the drives offer very basic setup parameters to get you started. Read the fine manual.
 
“Hand you the toilet paper” that’s funnny
ptonsparky said:
Programmed correctly, the VFD will do everything thing but hand you the toilet paper. IDK about ABB, but many of the drives offer very basic setup parameters to get you started. Read the fine manual.
Click to expand...
 
Etanuye said:
My understanding with VFD protects the thermal overload for the motor.
Am I required to have ocpd between the VFD and motor? Or is it optional this case
Click to expand...
Yes, the VFD does all of the motor protection**.

NEVER put fuses on the output of a VFD.

**So long as there is only one motor on the output of the VFD. Having multiple motors on one VFD requires some special treatment, the details are too long to get into if there is no need here.
 
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