Thank you for noticing.
Does the unit have a motor contactor or electronic drive within to control the motor(s)? That is the control panel portion of it if it does.
If the upstream impedance is enough to keep the AFC below 5kA there is no need to "upgrade" any rating. The AFC is under 5kA.
Did you calculate the AFC at the HVAC unit? You later mentioned 5 ton units. @ 480 volts that unit could possibly be supplied with 14 AWG, impedance of that conductor likely puts the AFC at the unit well below 65kA and unless immediately adjacent to the main gear likely will still be under 5kA.
Right, but we tried calculating the size of reactors to put upstream to knock it down to 5k and found that the reactors would also cause too much voltage drop.
Which is why you rarely find reactors in the real world, except for some dedicated loads.
Air core reactors are used often at the transmission and distribution level by utilities, but yes, it is very uncommon for them to be used at the user level. I tried once, it was a major endeavor to try to get a quote, because I was not a utility. The suppliers were totally disinterested.
We see them upstream of VFD's a lot.
There was a vfd I used once that had to have line reactors to get above a certain sccr. Don't recall what brand off hand. Was a long while ago.
Those wouldn't be air core reactors, and reactors on VFDs are for different purposes than fault current reduction (notwithstanding Bob's posting about having encountered that). A drive mfr. can easily attain a 100kA listing just using current limiting fuses with most VFDs.
Which are dedicated loads. How often have you seen one reactor feed multiple VFDs?
I see it pretty regularly. No idea why but we have several customers that design things that way.
Branch circuits and feeder conductors have impedance as well. Just because one has 65kA rated main gear doesn't mean there is 65kA available everywhere in the facility. As you progress through feeders, possibly separately derived systems, and eventually through the final branch circuit you may have a lot less available at equipment supplied by conductors that are small when compared to the service capacity.
Voltage drop depends on the load current on a specific conductor and its length. You haven't posted the load of your install and if our initial calculations tell us you needed a reactor with an inductance of 66 uH, that would be a 3% VD for a load of 360A and a run of 120 feet, 2/0 conductor. The resulting short-circuit kA will be 4.8 kA. 465V at the load terminal is good, I think.
Kind of a small conductor for 360A @ 75C ampacity rating isn't it?
Ooops, sorry! Don't know why I was typing 2/0 there! Should be 500. But the fault currents are fine!
It would be good, if the starting voltage is 480V. But the utility is allowed to go as low as 90% of nominal.
It would be nice discussing this problem as I have faced this problem once. My solution was just installing a line reactor to drop the fault levels down below the equipment withstand capacity. But it looks to me the OP just left after throwing the problem in.
