Refrigeration Rack with 10K SCCR and actual Available Fault current of 39KAIC

[petersonra]

Definitely, no amount of series-rated breaker combo will be applicable here as the sum of the motor load currents exceeds 1% (0.01 X 10,000 =100 A)of the lowest breaker interrupting rating.
There are only two ways one has to go: 1) try to interpose impedance between the 39 kA source and the 10 kA SCCR equipment or 2) have the panel re-designed to withstand a 39 kA available fault.

It is not really a series rating one is going after by adding current limiting fuses in front of a control panel. It is what ul calls a high short circuit current rating. It just means that you can take advantage of some combination of devices that allows a device with a relatively low sure circuit current rating to have a higher short circuit current rating. Often it involves current limiting fuses but it doesn't not have to be current limiting fuses. For instance it's not unusual to be able to put A specific motor protection circuit breaker in front of a specific contactor and the combination of the two assumes a higher short-circuit current rating than the contactor by itself.

UL 508A does not appear to recognize so-called series rating at all.

 

[topgone]

It is not really a series rating one is going after by adding current limiting fuses in front of a control panel. It is what ul calls a high short circuit current rating. It just means that you can take advantage of some combination of devices that allows a device with a relatively low sure circuit current rating to have a higher short circuit current rating. Often it involves current limiting fuses but it doesn't not have to be current limiting fuses. For instance it's not unusual to be able to put A specific motor protection circuit breaker in front of a specific contactor and the combination of the two assumes a higher short-circuit current rating than the contactor by itself.

UL 508A does not appear to recognize so-called series rating at all.

If the breakers are in series, there is no need to coordinate either of the breakers--> the loads lose power when either breaker trips, so you can employ series-rated breakers! The use of series-rated combinations is also a way out when loads are added to a panel and cause the fault current available at a certain point go beyond the existing protection breaker interrupting capacities! It's just that motor contribution to the fault will throw you off the desired results of the tested pair of protection breakers! IMO, series-rated combo can work with non-motor load panels.

 

[kwired]

One more time the electrician is expected to jump hoops and scramble to accommodate other trades who negligently or never consider implications of what they do on the electrical and it seems to default onto the electrician to make their improper installation work. The HVAC installer should have taken this issue into consideration before ordering the parts, and if they didn't know how the electrician should have been consulted. It sounds as if the panel was only ordered at the point where someone became aware of the issue, and the HVAC company should have fixed the order. Maybe if these other trades start paying for their screwups instead of passing off to the electrician to "just make it work", they might begin to consider the electrical parts when doing their jobs. (The "you move the panel" after they install other mechanical in the dedicated space already established by your installation mentality.)
Sometimes it feels as if electricians are the Rodney Dangerfield of the trades.

This is supposed to be where engineers earn their pay, but owners and/or GC's rather bypass them cause they are too expensive.

 

[JoeStillman]

Be careful - sometimes adding sufficient impedance upstream of a poorly rated control panel can ruin your ability to supply adequate voltage. Equipment that large should NEVER come with an SCCR that low!

I had a job once where the minimum-upstream-ohms for a 5KAIC control panel exceeded the maximum ohms for sufficient operating voltage. The chiller manufacturer re-built and re-rated the control panel on site for no charge to the customer because I told them they needed to recall all of the chillers of that model they had sold.