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Old 02-06-2012, 10:07 PM   #1
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Meter to LC, is this a Raceway?


Hi, I'm trying to understand my application as it applies to the 1-Ph 3-wire feeder wire from the meter to the load center so I can choose/determine the proper wire temperature rating for load purposes.

The two boxes are separated by a ~2" offset fitting, so if I measure from the meter lugs to the Main lugs, the total length of L1 or L2 will be about 6-ft. So when I run this wire, is the effective enclosure considered a raceway or are the conductors considered "in free air". I suspect its a raceway but I need clarification.

I'm looking at NEC-2008 Table 310.16; is this the correct table for my application?

I may need to get some 90 Deg-C wire (i.e. THW-2 or THWN-2) instead of 75 deg-C wire like THWN.

Thanks for your expert help.

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Old 02-06-2012, 10:13 PM   #2
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Meter to LC, is this a Raceway?


Are you trying to size the conductors to feed your panel?

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Old 02-06-2012, 10:15 PM   #3
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Meter to LC, is this a Raceway?


Yes, exactly. Its a 200A panel.
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Old 02-06-2012, 10:18 PM   #4
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Meter to LC, is this a Raceway?


2/0 copper or 4/0 aluminum.

Table 310.15(B)(7) 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
Conductor (AWG or kcmil)
Service or Feeder
Rating (Amperes) Copper
Aluminum or
Copper-Clad
Aluminum
100 4 2
110 3 1
125 2 1/0
150 1 2/0
175 1/0 3/0
200 2/0 4/0
225 3/0 250
250 4/0 300
300 250 350
350 350 500
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Old 02-06-2012, 10:36 PM   #5
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Meter to LC, is this a Raceway?


Thanks Jim. But, does that table trump the next table "Allowable Ampacities... for no more than 3 conductors in a raceway"?

Why I ask is if I use my referenced table, and assuming I use CU 2/0 wire, the allowable ampacity is 145A/175A/195A depending on wire temp rating as opposed to your table reference which says the allowable is 200A for 2/0 wire (but fails to mention wire temperature rating!). Thus, I'm at odds with the data, seems contradicting. What am I missing?
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Old 02-06-2012, 11:22 PM   #6
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Meter to LC, is this a Raceway?


Quote:
Originally Posted by Johnd85053 View Post
Thanks Jim. But, does that table trump the next table "Allowable Ampacities... for no more than 3 conductors in a raceway"?

Why I ask is if I use my referenced table, and assuming I use CU 2/0 wire, the allowable ampacity is 145A/175A/195A depending on wire temp rating as opposed to your table reference which says the allowable is 200A for 2/0 wire (but fails to mention wire temperature rating!). Thus, I'm at odds with the data, seems contradicting. What am I missing?
Two reasons: Service entrance conductors are treated differently than other wiring, and also the conductor temperature ratings are often not very important because the termination ratings are usually lower. You can't use 90C wire at the 90C ampacity if you have 60C terminations.
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Old 02-07-2012, 04:03 AM   #7
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Meter to LC, is this a Raceway?


You are also allowed to round up for service cables.
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Old 02-07-2012, 05:22 AM   #8
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Meter to LC, is this a Raceway?


Quote:
Originally Posted by Johnd85053 View Post
Hi, I'm trying to understand my application as it applies to the 1-Ph 3-wire feeder wire from the meter to the load center so I can choose/determine the proper wire temperature rating for load purposes.

The two boxes are separated by a ~2" offset fitting, so if I measure from the meter lugs to the Main lugs, the total length of L1 or L2 will be about 6-ft. So when I run this wire, is the effective enclosure considered a raceway or are the conductors considered "in free air". I suspect its a raceway but I need clarification.

I'm looking at NEC-2008 Table 310.16; is this the correct table for my application?

I may need to get some 90 Deg-C wire (i.e. THW-2 or THWN-2) instead of 75 deg-C wire like THWN.

Thanks for your expert help.
Is this a single phase service to a dwelling unit?
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Old 02-07-2012, 11:31 PM   #9
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Meter to LC, is this a Raceway?


Yes, this is 1-Ph to a dwelling.

mpoulton, thanks for your response, it got me thinking. I see your answer is explained by 110.14(C) which I had to re-read a few times until I really understood the issue regarding wire temperature rating and how you can manipulate the ampacities by choosing the right equipment. Checking all my equipment datasheets I find 75C is the limit at all my terminations; I couldn't use 90C wiring if I wanted to (legally). Very interesting. Again, thanks for the info.
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Old 02-08-2012, 12:26 AM   #10
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Meter to LC, is this a Raceway?


Quote:
Originally Posted by Johnd85053
Yes, this is 1-Ph to a dwelling.

mpoulton, thanks for your response, it got me thinking. I see your answer is explained by 110.14(C) which I had to re-read a few times until I really understood the issue regarding wire temperature rating and how you can manipulate the ampacities by choosing the right equipment. Checking all my equipment datasheets I find 75C is the limit at all my terminations; I couldn't use 90C wiring if I wanted to (legally). Very interesting. Again, thanks for the info.
You could use 90c wiring, you just treat it as 75c for figuring the ampacity. However when derating you will have an advantage of starting at the 90c ampacity.

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