I have an application for running multiple circuits in flexible steel conduit. I know about fill limits (thank you, online calculators) and the idea of de-rating ampacity of bundled conductors, but I haven't yet found information that specifies any ground wire requirements for multiple circuits in a conduit. I know that the steel of the conduit has grounding capabilities, but I also know that modern flexible steel cable designated as AC has an aluminum bonding wire added for safety reasons, and I want to add a ground wire to gain those safety advantages. I also want to have a ground wire of sufficient size to satisfy requirements for non-conductive conduits. (In case that will work to my advantage in an inspection)
I also have a de-rating question. I see some AC cable ratings that seem to match the 90-degree C ratings of the THHN wires inside. For instance, a 10/2 AC (steel jacket with aluminum bonding wire) shows a maximum ampacity of 40 amps. I assume it has a 30 amp rating for a lower temperature. So my question is, am I allowed to use a higher-temperature wire ampacity, and derate from there? The idea is that I can take advantage of the high-temperature ampacity to derate from, and get to a load rating equal to or better than what is customary for the wire gauge. This isn't about running on the edge of safe practices so much as trying to get circuit capacities to match up with the breakers.
I also have a de-rating question. I see some AC cable ratings that seem to match the 90-degree C ratings of the THHN wires inside. For instance, a 10/2 AC (steel jacket with aluminum bonding wire) shows a maximum ampacity of 40 amps. I assume it has a 30 amp rating for a lower temperature. So my question is, am I allowed to use a higher-temperature wire ampacity, and derate from there? The idea is that I can take advantage of the high-temperature ampacity to derate from, and get to a load rating equal to or better than what is customary for the wire gauge. This isn't about running on the edge of safe practices so much as trying to get circuit capacities to match up with the breakers.