#2 Aluminium 100amps?

[James Norman]

Had question today that caused confusion.... Type RHW-2 #2 Aluminum(mobile home feeder) has always been used for a 100 amp service. If that same wire is connected to a 75c terminal/lug do you derate it the 75 degree column...which makes it only carry 90 amps?

[Garry Blankenship]

Allowable ampacity depends on the insulation, # of conductors & location. #2 Al: 60o rated = 75 amps, 75o rated = 90 amps and 90o rated = 100amps. There is a special rating chart in the code for single phase dwelling services & feeders ~

100 amps = #4 cu or #2 al ( normally 85 amps & 90 amps )
200amps = 2/0cu or 4/0 al ( normally 175 amps & 180 amps )

The free air rating of the wires about 50% higher.

Sorry Jerry. Yes whatever rating is lower, ( the wire or the termination ), is it. In this case the special residential service ratings make it OK @ 100 amps.

[Robert Meier]

The NEC reference for Garry's post is 310.15(B)(6).


310.15(B)(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.