Advice on heater and subpanel

[ned3000]

I'm installing a makeup air system with a 20kW 240v duct heater (83 amps) and wanted to get some input on wiring. There's no temperature rating for the heater, so I'm not sure which column on the amp chart to use. From my understanding, it's considered a 'continuous load' Was thinking about setting it up as two separate circuits, as I believe it would be easier to manage the smaller wire gauge required for that. In either case (1 or 2 circuits) I'm having some trouble determining the correct ground wire gauge.

Also, there aren't enough spaces in the existing 150A subpanel, so I was planning to add an additional subpanel chained from the first one directly from the feed (also 150A). Looks like that should be 1/0 wire. Also not totally clear on the ground wire size for that.

 

[don_resqcapt19]

In general. for most equipment on the market, the wire size is based on the 75°C rating. The EGC is based on the rating of the upstream OCPD. If that is 150 amps, then the minimum EGC size is 6 AWG copper.