Aluminum Wire

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sparky37

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When you use #3/0 AWG wire, what wire size ground do you need? Wondering because a hotel is using aluminum wire to power panels on floors to main panel which has copper in it.
 
sparky37 said:
When you use #3/0 AWG wire, what wire size ground do you need? Wondering because a hotel is using aluminum wire to power panels on floors to main panel which has copper in it.
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If the 3/0 wire is aluminum, it has an ampacity of 155 at 75 degrees C. Table 250.122 says it needs #6 copper or #4 aluminum grounded conductor.

If the 3/0 wire is copper, it has an ampacity of 200 at 75 degrees C. Same result.

The breaker size is what you are actually supposed to be using to determine the ground size but you didn't give that. If the 3/0 wire is oversized on a 100 amp breaker, you can go down a size on the EGC.

If these are the main feeders you are talking about, the allowed ampacity will be higher and the EGC will be required to be bigger.
 
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Coppersmith said:
The breaker size is what you are actually supposed to be using to determine the ground size but you didn't give that. If the 3/0 wire is oversized on a 100 amp breaker, you can go down a size on the EGC.
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I think mean go up a size on the EGC. If the feeder is increased in size, ex. voltage drop, so must the EGC.
 
Depends on other factors. As mentioned 3/0 ampacity is 155. Such conductor could be installed on a 175 amp overcurrent device, but still can't have more then 155 amps of load connected to it. Go to mentioned T250.122 and find size of EGC needed based on 175 amp device.

Also mentioned though was upsized conductor (maybe for voltage drop reasons). If this 3/0 were on a 100 amp breaker you may need to increase necessary EGC by same ratio as increase in ungrounded conductor (100:155)
 
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