Thread: service entry cable sizing

House had a 225 amp SqD breaker with

[aluminum] 4/0 awg 600v rhh or rhw service

The breaker itself indicated the following: #4-300mcm cu/al.

I believe 4/0 can carry 200 amp max?

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Correct. #4/0 AWG aluminum is rated for 200 amps.

The rating on the breaker is for the approved conductor sizes allowed in the terminals.

I'm sure you got the multiple tapped neutrals. For all those empty terminals, why on earth did they put 2 and 3 in the same terminal? Then the grounds too.

aren't they allowed 2 per terminal? three i know is wrong.

Originally Posted by Jerome W. Young

aren't they allowed 2 per terminal? three i know is wrong.

Only one per terminal for neutrals. Typically two per terminal for the grounds -- IF they are the same gauge and material and meet size requirements. Read the paper instructions in the panel to let you know what this mfr allows.

Originally Posted by Kevin Barre

Only one per terminal for neutrals. Typically two per terminal for the grounds -- IF they are the same gauge and material and meet size requirements. Read the paper instructions in the panel to let you know what this mfr allows.

Plus, neutrals and grounds not allowed in same terminal. In same terminal bar, yes (if service equipment) ... in same terminal, no.

Originally Posted by Jerry Peck

Correct. #4 AWG aluminum is rated for 200 amps.

The rating on the breaker is for the approved conductor sizes allowed in the terminals.

I'm sure you got the multiple tapped neutrals. For all those empty terminals, why on earth did they put 2 and 3 in the same terminal? Then the grounds too.

Apparently Jerry, you've never seen a lazy sub contractor's effort ... :-)

Originally Posted by Jerry Peck

Correct. #4 AWG aluminum is rated for 200 amps.

The rating on the breaker is for the approved conductor sizes allowed in the terminals.

I'm sure you got the multiple tapped neutrals. For all those empty terminals, why on earth did they put 2 and 3 in the same terminal? Then the grounds too.

Do you mean 4/0 aluminum?

Rhw can only handle 190A
Rhh can only handle 205A

If it is rated for both then the higher of the two applies.

Originally Posted by Jeff Remas

Do you mean 4/0 aluminum?

Yes, thanks, I went back and corrected it.

Originally Posted by Jeff Remas

Rhw can only handle 190A
Rhh can only handle 205A

Jeff,

See: (underlining is mine)
- Table 310.15(B)(6) Conductor Types and Sizes for 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. Conductor Types RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2
- - 4/0 aluminum - 200 amp (reading through the table from right under Aluminum to the left under Rating)

Yes, I understand that but the cable is already rated at 205 so the 200A allowable ampacity for 4/0 aluminum in single family residences is not relevant since they used a higher rated conductor.

Originally Posted by Jeff Remas

so the 200A allowable ampacity for 4/0 aluminum in single family residences is not relevant since they used a higher rated conductor.

That is still relevant as those are the allowable ratings for those conductors in dwelling unit service and feeder use.

According to the California code, based on the NEC, 4/0 copper can handle 250 amps, while 4/0 aluminum or copper-clad aluminum will conduct 200 amps safely.