200 AMP feeders 1/0 copper

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pkelectrical

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According to table 310.15B16
1/0 Copper at 90 is rated 170 amp
310.15B7 says its ok to size the entrance conductors 83% of the feeder rating

So 170/.83 = 204.8 amps

So why 2/0 is required?
 
The terminals on the equipment are only rated 75C so you are limited to using the 75 C column

1/0 @ 75C is only rated 150 amps.
 
83% of 170 is 141.1A, but as noted above the 75*C limit still applies.
so the 150A @ 75*C is the appropriate limit under "normal" conditions
Found in 310.15(B) [2014 NEC]

3/0 is the first size in the 75*C column that meets the 200A required
 
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When they say allowed ampacity is 83% of the feeder rating, that means you do 150/.83 = 180.7 amp, not 150x.83
For that reason 1 awg copper is allowed for 150 Amp service. 130/.83 = 156 Amp.
With the 75 degree rating he is correct. I just though some meters had terminals rated for 90 degrees.
 
pkelectrical said:
I just though some meters had terminals rated for 90 degrees.
Click to expand...

As far as I know there is no electrical equipment rated less than 600 volts that has terminations rated more than 75c.

Remember that the lug could be rated 90 yet the equipment it is connected to only rated 75C.
 
The section says: shall be permitted to have an ampacity
not less than 83% of the service rating. So for example
200 x 83% = 167A. For one family dwellings.
This is how it has been interpreted in this area.
For 167A the required min. amperage in the column that
excedds 167A is 175A or a 2/0 wire.
The 200A installations that I have been a part of always
used 3/0 (but these were industrial installations)
 
JRW 70 said:
The section says: shall be permitted to have an ampacity
not less than 83% of the service rating. So for example
200 x 83% = 167A. For one family dwellings.
This is how it has been interpreted in this area.
For 167A the required min. amperage in the column that
excedds 167A is 175A or a 2/0 wire.
The 200A installations that I have been a part of always
used 3/0 (but these were industrial installations)
Click to expand...

What it is saying is for dwelling units that meet all the requirements of the section - you can use 83% of the ampacity for a service or feeder then you normally would. So a 200 amp protected conductor only need an ampacity of 166. @75C 2/0 is the first copper conductor over 166.

You are not going to find less then 600 volt equipment that has more then 75C terminals.
 
In the late 90 s we did some track houses and I would go measure each house for the 220 wire as well as service wire. I use to swear on a 200 amp service we used 2/0 amp might have used 1/0 for neutral but went to 2/0 cause its easier to cut and send 6' of one size. Many have said no way so I quit saying I think we did.
 
electricalist said:
In the late 90 s we did some track houses and I would go measure each house for the 220 wire as well as service wire. I use to swear on a 200 amp service we used 2/0 amp might have used 1/0 for neutral but went to 2/0 cause its easier to cut and send 6' of one size. Many have said no way so I quit saying I think we did.
Click to expand...
2/0 would have been compliant with 310.15(B)(7). For many years it was a table and it said 2/0 copper for 200 amps. 2014 the table was removed, you now use 83% which in most instances give you same size conductor as the old table did, but the old table did not need adjustments applied to it, the new method does. Should you run that conductor in a high ambient temp it will need derated where before 2014 it did not.
 
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