100 amp feed to panelboard

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Machiavelli999

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I need a sanity check. I am QAing a job and a feed to a 100 amp panelboard is 4#1 THHN, #8G in a 1.25" EMT.

Table C.1 in Appendix C claims you can put up to 4 #1 in a 1.25" EMT. I wanted to check if you can stick a #8G in there as well.

When I did the calculation, I struggle to see how you can even put 4#1 in the 1.25" EMT.

#1 THHN cable has an area of 0.1562 squared inches according to Chapter 9, Table 5. Multiply by 4 and you get 0.62 squared inches.

A 1.25" EMT has an area of 1.5 squared inches.

0.62/1.5 = 41.33% > 40% allowed fill!

What am I doing wrong here??
 
You need to look at note 7 to chapter nine tables. 1-1/4 " emt under the 40% fill column is .598 divided by the inches squared for each # 1 thhn (.1562) = 3.83. Note seven allows you to go to 4 conductors.
 
CONDUIT said:
You need to look at note 7 to chapter nine tables. 1-1/4 " emt under the 40% fill column is .598 divided by the inches squared for each # 1 thhn (.1562) = 3.83. Note seven allows you to go to 4 conductors.
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Good point however throw in the #8 egc and it is not compliant.

BTW(to the OP), you do know that an egc is not required unless it is speced
 
Note 7 does not help the present situation. It applies only when all conductors are the same size. We have four phase conductors the same size, and one EGC a different size. So I agree that a 1.25" EMT is not large enough for this set of conductors.

But I have another problem with this design. A #3 THHN has sufficient ampacity for a 100 amp load. This design uses a conductor that is two sizes larger than that. Do we not need to upsize the EGC, per NEC 250.122B?
 
charlie b said:
Note 7 does not help the present situation. It applies only when all conductors are the same size. We have four phase conductors the same size, and one EGC a different size. So I agree that a 1.25" EMT is not large enough for this set of conductors.
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I think Conduit was responding to the OP's question on the original install that did not have the egc.
 
Dennis Alwon said:
I think Conduit was responding to the OP's question on the original install that did not have the egc.
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I realize what Conduit was saying. But the OP was not talking about an install, but rather about a design, and the design does include the EGC.
 
@Dennis Alwon,

How is the EGC not required? It's a new panelboard. What will I bond the ground bus bar in the new board to? A new grounding electrode?

@charlie b,

Yea, I also thought it was oversized. However, 110.14(C)(1)(a) states that for

"circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following

(1) Conductors rated 60 deg C
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60 deg C ampacity of the conductor size used

So, from that I inferred that for circuits 100 amps or less I need to use the 60 degree C ampacity column to comply with code regardless of the insulation temperature rating.

But I have seen 100 amp circuits with #2 & #3 conductors in the past, so it seems unclear.
 
Machiavelli999 said:
@Dennis Alwon,

Yea, I also thought it was oversized. However, 110.14(C)(1)(a) states that for

"circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following

(1) Conductors rated 60 deg C
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60 deg C ampacity of the conductor size used

So, from that I inferred that for circuits 100 amps or less I need to use the 60 degree C ampacity column to comply with code regardless of the insulation temperature rating.

But I have seen 100 amp circuits with #2 & #3 conductors in the past, so it seems unclear.
Click to expand...

If the panel board terminations are known and they are 75C then you may use the 75C column for circuits under 100 amps. Look at (3)
 
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