Code for disconnects

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Alwayslearningelec

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I have two motors. One HWP & one AC unit each have a VFD but then the point to it with a "pie/circle looking thing... a circle with 4 quandrants" that say 250/3/30/U.... which I know is the disconnect info. But I though if a motor had a VFD it would not have a disco. THanks.
 
Both the motor and the motor controller (starter or VFD) require disconnects within sight of each item. In some cases a controller disconnect installed out of sight from the motor can serve as the motor disconnect. See 430.102(A)&(B).
 
don_resqcapt19 said:
Both the motor and the motor controller (starter or VFD) require disconnects within sight of each item. In some cases a controller disconnect installed out of sight from the motor can serve as the motor disconnect. See 430.102(A)&(B).
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So if a motor has a starter or a vfd, two disconnects are required within sight. THat does not sound right.:?
 
You can create a problem by installing a disconnect downstream of a VFD. The inverter doesn't like to see an open circuit.

If the motor is not within sight of the drive and I have to have a disconnect, I use aux contacts to stop the drive.
 
VFD does not care if the output is an open circuit. The problem is turning on a load to a energized output. If output is at full voltage and frequency and you switch the load on, it is not going to like the resulting current the motor will be demanding.
 
kwired said:
VFD does not care if the output is an open circuit. The problem is turning on a load to a energized output. If output is at full voltage and frequency and you switch the load on, it is not going to like the resulting current the motor will be demanding.
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Opening the output circuit under load can also smoke the VFD.

Early break aux contacts on the downstream disconnects can eliminate this issue.
 
horsegoer said:
So if a motor has a starter or a vfd, two disconnects are required within sight. THat does not sound right.:?
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The starter or VFD requires a disconnect. The motor requires a disconnect. The disconnects must be within sight from the equipment to be disconnected. If the line side disconnect for the starter or VFD is within sight of both the starter or VFD, then a single disconnect can serve both purposes. For industrial occupancies, a lockable starter or VFD disconnect that is not within sight from the motor can be used as the motor disconnect, but there are restrictions.

Does a manual motor stater (motor controller) require a line side disconnect within sight of the controller?:)
 
horsegoer said:
I though if a motor had a VFD it would not have a disco. THanks.
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Most VFD's have an integrated disconnect. They use an separately fused wire to feed the computer portion so that there is no problem when power is cut. Using this method they can still soft stop the motors and prevent damage. I can't tell from your post, but check to see if the VFD does or does not have an integrated disco.
 
tsamples said:
Most VFD's have an integrated disconnect. They use an separately fused wire to feed the computer portion so that there is no problem when power is cut. Using this method they can still soft stop the motors and prevent damage. I can't tell from your post, but check to see if the VFD does or does not have an integrated disco.
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The ones that have integrated disconnect are no different than a combination motor starter. The disconnect simply disconnects the supply conductors from the drive and is located in the same enclosure as the drive. It is there for convenience. If it does not open the supply conductors from the source it is not a disconnect it is a control switch.
 
kwired said:
The ones that have integrated disconnect are no different than a combination motor starter. The disconnect simply disconnects the supply conductors from the drive and is located in the same enclosure as the drive. It is there for convenience. If it does not open the supply conductors from the source it is not a disconnect it is a control switch.
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Huh?:?:?:?:?
 
iwire said:
Huh?:?:?:?:?
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Supply conductors enter cabinet>>>>> land on disconnect>>>>> from disconnect they supply VFD.
The whole thing is factory assembled except the supply conductors and load conductors - maybe some control conductors for remote control stations, just like a combination starter.

If that 'disconnect' does not open all supply conductors and isolate the drive from the supply it is not a disconnect it is simply a control switch.
 
kwired said:
Supply conductors enter cabinet>>>>> land on disconnect>>>>> from disconnect they supply VFD.
The whole thing is factory assembled except the supply conductors and load conductors - maybe some control conductors for remote control stations, just like a combination starter.

If that 'disconnect' does not open all supply conductors and isolate the drive from the supply it is not a disconnect it is simply a control switch.
Click to expand...

I disagree entirely. what you are saying would mean we need a disconnect in front of a combination starter.
 
iwire said:
I disagree entirely. what you are saying would mean we need a disconnect in front of a combination starter.
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That is not what I am saying maybe I come across the wrong way.

Go back to tsamples post:

Most VFD's have an integrated disconnect. They use an separately fused wire to feed the computer portion so that there is no problem when power is cut. Using this method they can still soft stop the motors and prevent damage. I can't tell from your post, but check to see if the VFD does or does not have an integrated disco.
Click to expand...

I mentioned (or at least meant) that if the disconnect opens all the supply conductors it is a disconnect for the purpose of disconnecting the controller (VFD). If it does not open all supply conductors it is nothing more than a control switch.

I don't see how in his example you could turn off the disconnect and still soft stop the motor. Sure when you disconnect a drive from power it stays active until the capacitors on the DC bus are discharged - but that is with the motor stopped. If the motor is running those capacitors will not stay charged long at all. What he is describing can not be a disconnect.

I gave an alalogy to a combination motor starter.

An motor starter in an enclosure with an on off switch that only controls the coil of the magnetic contactor is the analogy to what is not a disconnect.
 
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