Panel wire size

Old 07-28-03, 10:52 AM
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Panel wire size

Do anybody have a table or chart of sizing cable + ground + conduit for different size of panel: 100A, 200A, 225A.... and so on? Just a quick hint for me to know what size of AWG and ground to use depending on what size of panel I use.

Thank you so much,

Old 07-28-03, 11:19 AM
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Not to be a wise guy, but many books at the library, including the National Electric Code have these tables.
Old 07-28-03, 11:21 AM
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For 15 amps, 20 amps, and 30 amps, things are easy. We use 14-gauge copper for 15 amps, 12-guage copper for 20 amps, and 10-gauge copper for 30 amps.

But above 30 amps, the exact type of wire, temperature rating of the terminations, type of load, and method of installation are factors. In many cases, voltage drop is a consideration for subpanels too, which depends on distance and the types of loads. These things are normally designed on a case-by-case basis.

The size of equipment grounding conductor is easier to figure. There is such a simple table in the NEC. I'll post it tonight if nobody beats me to it. It's not based on the rating of the panel, but on the size of the overcurrent protection on the ungrounded conductors.
Old 07-28-03, 01:36 PM
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Hi Ron,
I guess I wasn't clear when I asked the question. My question is about the feeder cable for the panel (200A, 225A,... so on), not the breakers which are 15A, 20A, 30A...
A quick table to figure out the feeder size for the panel and ground is what I am looking for.
For example, a 400A, 208/120v 3p 4w, panel need 3#500Kcmil, #500kcmil N, #2 G, 3"C.

Sorry if I wasn't clear in my question.

Thank you Ron and John, please give me a link or post such table to help me quickly find out how many, and the feeder size, N, ground, and Conduit.

Old 07-28-03, 08:21 PM
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Table 310.15(B)(6)
--->for 120/240 1phase dwelling services

cu al amps
4 2 100
2 1/0 125
1 2/0 150
2/0 4/0 200
3/0 250 225
4/0 300 250

Otherwise Table 310.16 applies
(the standard table)
for 90 degree rated wire (thhw, xhhw, etc.)
CU amps(90) (75) AL 90 AL 75
3 110 100
2 130 115 100
1 150 130 115 100
1/0 170 150 135 120
2/0 195 175 150 135
3/0 225 200 175 155
4/0 260 230 205 180
250 290 255 230 205
300 320 285 255 230

The table is much large, more can be provide with details provided from you for exactly which figures you want.
this is for cable and conduit, there is another chart for single-insulated free-air conductores, and many other classifications of cables/conduit, such as triplexs, and quadplex for arial/underground installations for service.

Distance also plays a role, as do about 5 other factors.

cond temp rating, abient temp, dielectric loss, resistance of cond., skineffect resistance, thermal resistance

Old 07-30-03, 08:11 AM
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Thanks a lot GreenJacket


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