Max amps for #4 TW in 1960

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Sierrasparky

Sierrasparky

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Electrician ,contractor
HI ,
I have a customer with an old resi service. What was the max main breaker size for #4 TW serving the entire house built around the late 50's to 60's.
Was it only 70 amps. ?
 
unfortunate as it is the service wires are old TW.
The current chart for resi service allows 100 for THW

The ampacity for TW #4 is only 70 as per chart 310.
 
480sparky said:
I don't think the 'resi cheat table' T310.15(B)(6) appeared until the 1978.
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I looked in the 1971 & 1975 NEC in the 1975 Notes to Tables 310-16 through 310-19 has note #3 for 3 wire 1? residential services,it did not show up in the '71 nor is it marked as a change in '75, note #3 refered AL & CU clad Al conductors in the '71 NEC & was relocated as note #4 in '75.
 
norcal said:
I looked in the 1971 & 1975 NEC in the 1975 Notes to Tables 310-16 through 310-19 has note #3 for 3 wire 1? residential services,it did not show up in the '71 nor is it marked as a change in '75, note #3 refered AL & CU clad Al conductors in the '71 NEC & was relocated as note #4 in '75.
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Yea, I went back and rechecked myself, and it wasn't a Table in the 70s, just a note.

That's why it's so hard to 'go back' and look stuff up. Every edition, things get changed, moved, renumbered, relocated (remember Art. 305 anyone?), shifted, rewritten, sliced, diced, split up, you name it.

Good old T310.16 has 10 previous addresses.
 
so I take it that #4 TW was never allowed greater than 70 amps even for Service conductors for a single family Dwelling.
 
Sierrasparky said:
so I take it that #4 TW was never allowed greater than 70 amps even for Service conductors for a single family Dwelling.
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Without checking every Code cycle, I can't say with 100% certainty that this would be a correct statement.

But TW is not listed either in Note 3 in the '75 or 310.15(B)(6) in the '08. My guess is it won't be in any of them inbetween.
 
Sierrasparky said:
What was the max main breaker size for #4 TW serving the entire house built around the late 50's to 60's.
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In the 1959 NEC, Allowable Current-Carrying Capacities were laid out in four tables, Table 310-12, 310-13, 310-14 and 310-15.

I'll assume the TW in the house you are asking about is copper. That limits one, under the 1959 NEC, to Table 310-12 copper "not more than three conductors in raceway or cable or direct burial." #4 TW ( 60?C wet or dry) is rated for 70 Amps. Period.

The only place the 1959 NEC even comes close to the modern 2008 NEC 310.15(B)(6) sizing is only in an * (asterisk) note on certain sizes of aluminum conductors of certain insulation types in the 1959 Table 310-14. Table 310-14 was aluminum "not more than three conductors in raceway or cable or direct burial." #2 THW was rated in the table at 90 Amps, with an asterisk and a note saying that a three wire, single phase service #2 could supply 100 Amps.

For comparison, that same table (310-14) states that #2 Al, not more than three conductors, TW was rated for 75 Amps.
 
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