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VFDs internal to AC units requiring fused protection

VFDs internal to AC units requiring fused protection

VFDs internal to AC units requiring fused protection

A contractor sent an RFI (referring to 430.31) indicating that VFDs that are coming with AC units must have fused protection.
I am providing just feeders as requested by mechanical engineer, to single point of connection, connecting to VFD which has an integral disconnect.

it seems as if the contractor is saying that we need to provide a separate disconnect (fused disconnect possibly) to protect the VFD and the AC Unit.

Can someone shed some light on it and let me know if I do need an additional disconnect?  

Thanks in advance.

RE: VFDs internal to AC units requiring fused protection

The user's manual says what is needed. A general answer would be  yes - you need separate protection for each VFD. But that protection is usually built into the panel feeding the VFD device.
I assume you are talking about so-called integral motors. If not, wait for someone other to chime in.

Gunnar Englund
Half full - Half empty? I don't mind. It's what in it that counts.

RE: VFDs internal to AC units requiring fused protection

In many cases the UL listing is based on protection by an upstream current-limiting fuse, not a circuit breaker.  We routinely put local fused disconnects at HVAC package systems for this reason.

Basically, if the manufacturer's instructions require a fused disconnect, it needs to be put in unless you can get an exemption from the manufacturer.  I think the issue is probably the fuse and not the disconnect.  The NEC will govern the need for a local (within sight) disconnect).  

RE: VFDs internal to AC units requiring fused protection

Thankyou Skogsgurra and dpc for your replies.
Got a little busy at work so I didn't make it back to thank you both earlier.

In regards to the issue, I am working with a contractor that is looking to sqeeze money out any way he can.
In his second RFI he actually answered his own question.
NEC 430.32.A.1 talks about overload protection but that overload protection is already provided either internal to the small motors or through the motor-starter or VFD.
In this case we are working with a monster AC unit from York, asked to provide only one point of connection. Internal to the AC unit they have a disconnect that feeds two motors.
Per section 440.14 disconnecting means shall be allowed to be located on or within the AC unit as long as it is capable of being locked from the outside of the unit, which is what this unit was provided with.

Thanks again  

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