The current you may draw is capped by the lowest-rated part of the path — almost always a 60 °C or 75 °C terminal, not the cable. But you still derate from the cable\’s own 90 °C column, which is what makes the better insulation worth buying.
Heat flows into the lug as well as along the wire, so a 75 °C termination sets the temperature the whole junction may reach whatever the cable can survive. The order matters: derate the 90 °C figure for heat and grouping first, then cap the result at the terminal column. Do it the other way and you punish the cable twice, and 90 °C cable looks pointless when it is precisely what rescues a hot, crowded run.
Only where the terminals really are the weak point. Equipment listed for 90 °C throughout lets you use the 90 °C column outright — and the cap is on the continuous current, not on the insulation\’s ability to survive a fault.
Estimate with the rule, then check it against the calculator that models it properly.
Open Wire Gauge & Voltage Drop Calculator →The current you may draw is capped by the lowest-rated part of the path — almost always a 60 °C or 75 °C terminal, not the cable. But you still derate from the cable\’s own 90 °C column, which is what makes the better insulation worth buying. Heat flows into the lug as well as along the wire, so a 75 °C termination sets the temperature the whole junction may reach whatever the cable can survive.