MCC breaker feeding disco in an enclosure

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dpslusser

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Hey guys!

I have (hopefully) a quick question.

I have an MCC in a factory on the first floor. It will be feeding a new electrical control/VFD enclosure on the second floor. The MCC will have a 1200 amp breaker to feed the enclosure. I've been told that the enclosure, due to it being upstairs, will need a breaker as well. I don't see why this would be the case. Why should a feeder need back to back breakers. I would rather put a disconnect in the cabinet.

Thanks
 
Who is telling you that you need a main breaker in the upstairs panel.
not a seperate building then no main breaker. MLO panel
 
dpslusser said:
Hey guys!

I have (hopefully) a quick question.

I have an MCC in a factory on the first floor. It will be feeding a new electrical control/VFD enclosure on the second floor. The MCC will have a 1200 amp breaker to feed the enclosure. I've been told that the enclosure, due to it being upstairs, will need a breaker as well. I don't see why this would be the case. Why should a feeder need back to back breakers. I would rather put a disconnect in the cabinet.

Thanks
Click to expand...

A disco may not even be necessary, unless it will be used as disconnecting means for the (in sight) equipment connected to the new enclosure. The panel builder can simply write "Circuit protection provided upstream" (to comply with UL508A) on the as-builts provided with the VFD panel. Although a 1200 amp feeder breaker may indicate a rather large motor which may mean 18 pulse.

Agree with MLO panel unless someone can point out a reason this wouldn't be acceptable.
 
It is weird how this factory is laid out. The MCC room is on the 1st floor on one side of the plant. The Control/VFD cabinet (that im referencing above) is on the 2nd floor towards the middle of the plant. And the equipment that is it control is back on the 1st floor on the opposite side of the plant.

So they will be running paralleled phases out of the MCC w/1000amp breaker to the Control/VFD panel upstairs. But the equipment is on the other side of the plant. They use shunt trips every where in this plant to trip each equipments respective breaker as a last resort after the Local Estops are pressed.

I would like a way to kill the power at the Control/VFD panel, so I will go with the disconnect. No breaker.
 
I would say 430.102 would require a disconnect at the drive (unless it has one built-in) and a disconnect at the motor unless you meet the exception.
 
In many cases with VFDs, especially large ones, the UL listing of the drive (in particular the SCCR rating) will require very specific fuses regardless of whether there is an up stream breaker or not. If you have fuses on the box, you need a disconnect switch in the box, or a very organized procedure for allowing safe access to them, including being an industrial facility with engineering supervision (words to that effect that I can't recall) and lots of signage. I always tell people it's just better to include the disconnect switch and not worry about someone doing it wrong.
 
Jraef said:
In many cases with VFDs, especially large ones, the UL listing of the drive (in particular the SCCR rating) will require very specific fuses regardless of whether there is an up stream breaker or not. If you have fuses on the box, you need a disconnect switch in the box, or a very organized procedure for allowing safe access to them, including being an industrial facility with engineering supervision (words to that effect that I can't recall) and lots of signage. I always tell people it's just better to include the disconnect switch and not worry about someone doing it wrong.
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My Control/VFD cabinet is chucked full of all different flavors. The customer spec'd Vacon VFDs and they uses some funky gL/gG european fuses.
 
vfd disco

vfd disco

since the mcc is in another location the needs to be protected by an ocpd but then to service the equipment fed by the vfd then you have to disconnect from the line side of vfd and not leave the vfd without a load.ie feed disco first at sight equipment is then vfd from the disco ....MCC to DISCO to VFD to equipment.the only reason for another ocpd would be to protect the wire not the vfd or the unit being fed.
 
dpslusser said:
My Control/VFD cabinet is chucked full of all different flavors. The customer spec'd Vacon VFDs and they uses some funky gL/gG european fuses.
Click to expand...
Ooh, be careful, those European fuses can be really hard to find in a hurry. Either buy some spares and keep them on the shelf, or check with Vacon in the US to see if there is a more common form of fuse thats more readily avaiable here that can replace those, then be ready with those plus a new fuse holder for the first time anything happens. I had to buy two 630A gL fuses one time in a hurry and they had to be flown in from Germany, cost me over $2k (I bought 6 just to be safe, but most of the money was in shipping and customs expediting charges).
 
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