VFD SCCR

[C3PO]

I have a 10HP drive that has a sticker on the side that says "Short Circut Withstand 5000A 480V, when protected by fuse UL Class J 40A max"

I also have a 75HP drive that has a sticker that says "Short Circut Withstand 10000A 480V, when protected by fuse UL Class J 175A max"

My question is: what would be the SCCR if the drives are not protected by Class J fuses?

 

[jim dungar]

My question is: what would be the SCCR if the drives are not protected by Class J fuses?

It would have to come from the manufacturer, but I would not be surprised if there wasn't any.

 

[Jraef]

Basically you can easily get a "courtesy" rating of 5,000A if it doesn't otherwise have a rating from testing, which is interesting in light of the smaller one only having 5kA even with the fuses. It likely means they didn't really test it.

 

[kwired]

Let me ask an additional question. Lets say the available short circuit current is less than 5000 amps but the class J fuse is not used - same drive(s) as in OP situation, is that a problem?

 

[Jraef]

Let me ask an additional question. Lets say the available short circuit current is less than 5000 amps but the class J fuse is not used - same drive(s) as in OP situation, is that a problem?

Probably not. But SCCR relates to industrial control panels as defined in Article 409 of the NEC since the 2005 edition. If you are putting the drive in an ICP, the SCCR rating affects the overall rating of the panel in that the overall panel rating cannot be higher than the lowest rated component if untested. The rule is, it cannot be connected to a system capable of delivering MORE than the panel's SCCR rating. So if everything else in that panels is rated 5kA or above (and it will be), then no problem.

 

[kwired]

Probably not. But SCCR relates to industrial control panels as defined in Article 409 of the NEC since the 2005 edition. If you are putting the drive in an ICP, the SCCR rating affects the overall rating of the panel in that the overall panel rating cannot be higher than the lowest rated component if untested. The rule is, it cannot be connected to a system capable of delivering MORE than the panel's SCCR rating. So if everything else in that panels is rated 5kA or above (and it will be), then no problem.

Most of what you said I already was aware of. I guess my question is when as the OP says it is marked "Short Circut Withstand 5000A 480V, when protected by fuse UL Class J" what difference does it make if it is a class J fuse or not as it is supposed to be rated 5000 A anyway? I can understand being rated more than 5000 amps with a condition that a specific fuse is used.

 

[C3PO]

Both of these drives are being fed directly from breakers in an I Line panel. The drives are just mounted to the wall with a conduit kit on them. I am trying to figue out what the avaible fault current is at the panel but I would be very surprised if it is as low as 10K.

The is an arc flash label on the panel that says it is a HRC 4; 29 cal/cm^2 flash hazard at 18 inches; 158 inch flash boundry

 

[petersonra]

For a UL listed ICP, if the device does not have a specific rating, the "courtesy rating" another poster spoke of can be taken from a table in the UL chart.

You can't use this chart if it is not a UL listed panel, so they are giving you a means by which you can determine the SC withstand rating if you are just installing it not in a UL listed ICP.

 

[Jraef]

For a UL listed ICP, if the device does not have a specific rating, the "courtesy rating" another poster spoke of can be taken from a table in the UL chart.

You can't use this chart if it is not a UL listed panel, so they are giving you a means by which you can determine the SC withstand rating if you are just installing it not in a UL listed ICP.

Ah, you caught that subtle issue in the original post that I missed.

The first part of the post said " Short Circuit Withstand 5000A at 480V", and then later referred to "SCCR", so you're right, they are separate issues.

So kwired, you picked up on the same thing I did, why bother saying you need the fuses for 5kA SCCR if you can essentially have that anyway? The answer was what Bob picked up on, Withstand, not SCCR. Withstand would be for stand-alone, SCCR only relates to ICPs.

 

[C3PO]

So if this I Line's fault current is >10KA, what options do I have to compliantly install the drives, put in an isolation transformer or something?

 

[petersonra]

So if this I Line's fault current is >10KA, what options do I have to compliantly install the drives, put in an isolation transformer or something?

Find out what the fault current is first.

figure out how much more resistance/impedance you need between the source and the drive to get the fault current below 10kA.

it might be as simple as some extra wire. maybe some line reactors. run the numbers first. it may not be as big of a deal as it first seems like.