Elevator VFD Conductor Sizing

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infinity

infinity

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How would you determine the minimum conductor size for this VFD for an elevator motor? Seems simple to me 85 amps. Is there a different formula for elevator drives?

input current * 125%
67.31 amps * 125% = 84 amps

Someone is saying otherwise.

20180216_085323.jpg
 
infinity said:
How would you determine the minimum conductor size for this VFD for an elevator motor? Seems simple to me 85 amps. Is there a different formula for elevator drives?

input current * 125%
67.31 amps * 125% = 84 amps

Someone is saying otherwise.
Click to expand...

First thought is that 430.122(A) seems to agree with you.

Maybe something is different about elevators, I did not look.
 
infinity said:
Yes, the question is for sizing the conductors based on the input current to the drive, do you use the 67.31 amps or do you need to factor in the 125% as required by 430.22(A)?
Click to expand...

Well that made my eyes cross and wonder WTH.

430.122(A) sounds better. Input current of the drive is my answer and that would be based on the 67.31 amps. Not the output of 75.
 
ptonsparky said:
Well that made my eyes cross and wonder WTH.

430.122(A) sounds better. Input current of the drive is my answer and that would be based on the 67.31 amps. Not the output of 75.
Click to expand...

In this case the output current is likely irrelevant because if I remember correctly the motor operates at 400 volts. I'm only concerned with the input conductors to the VFD, the elevator constructors will install the conduit and conductors to the motor itself. My drawing shows #6 THHN conductors which I believe is incorrect.
 
I don't believe an elevator is continuous duty so wouldn't 620.13

620.13(B) Conductors Supplying a Single Motor Controller.
Conductors supplying a single motor controller shall have an
ampacity not less than the motor controller nameplate current
rating, plus all other connected loads. Motor controller nameplate
current ratings shall be permitted to be derived based on
the rms value of the motor current using an intermittent duty
cycle and other control system loads, if present.
Click to expand...
 
Mgraw said:
Does it matter if the elevator is continuous duty, or is the relevant question is the motor rated as continuous duty?
Click to expand...

Let me state I am not an expert on elevators but going from what I see and what I know about the NEC is that the conductors for the VFD in an elevator would be based on art. 620 which overrides any other articles.

The only info I see in 620 that mentions continuous is that an escalator motor must be rated continuous duty. An elevator motor is not continuous but it still can be rated continuous duty- I don't think that is the same
 
Dennis Alwon said:
Let me state I am not an expert on elevators but going from what I see and what I know about the NEC is that the conductors for the VFD in an elevator would be based on art. 620 which overrides any other articles.

The only info I see in 620 that mentions continuous is that an escalator motor must be rated continuous duty. An elevator motor is not continuous but it still can be rated continuous duty- I don't think that is the same
Click to expand...

Doesn't 620.13 send us to 430.22E to size conductors? Table 430.22E gives us 4 possible motor ratings within intermittent duty.
 
The way I 'm reading it 620.13(B) is for the motor controller (VFD) so as Dennis has pointed out that would be the applicable section for the conductors feeding the drive. The conductors between the drive and the motor are not relevant in determining the size of the conductors to the elevator controller.
 
infinity said:
The way I 'm reading it 620.13(B) is for the motor controller (VFD) so as Dennis has pointed out that would be the applicable section for the conductors feeding the drive. The conductors between the drive and the motor are not relevant in determining the size of the conductors to the elevator controller.
Click to expand...


As odd as that sounds that is how I see it also.
 
620.13(B) does state the nameplate be based on intermittent duty so I assume elevators use intermittent duty motors. What happens if you use a continuous duty motor? IDK but one would think it would be the same.
 
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