250.122(B) Again

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George Stolz

George Stolz

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Hospital Master Electrician
Lets suppose I have a 200A feeder, and decide to use two parallel 1/0 CU to supply it for voltage drop and to comply with 310.10(H).

When calculating the upsize in my 200A feeder, do I use a 3/0 CU as my starting point or two parallel 3 AWG?

:happyyes:
 
I guess I have always use the 3/0 as the starting point especially since you cannot parallel #3. A good question though
 
I see it also as the reverse of 250.66. If you use parallel then you figure the grounding electrode conductor based on the equivalent size. I know it is not the same but that is how I have done it.
 
Since #1/0 is the minimum size conductor that you can parallel 250.122(B) does not apply since you haven't gone up from the minimum required.
 
I'd use 3/0 as my starting point and the equivalent of two 1/0 in cmils (which amounts to one 4/0)... so one AWG size up (#6 to #4).
 
George Stolz said:
Lets suppose I have a 200A feeder, and decide to use two parallel 1/0 CU to supply it for voltage drop and to comply with 310.10(H).

When calculating the upsize in my 200A feeder, do I use a 3/0 CU as my starting point or two parallel 3 AWG?

:happyyes:
Click to expand...

I take it is not a residential feeder to supply the entire load?
 
infinity said:
Since #1/0 is the minimum size conductor that you can parallel 250.122(B) does not apply since you haven't gone up from the minimum required.
Click to expand...

ActionDave said:
This makes as much sense as 250.122(B) so I'll go with it.
Click to expand...

:D

Not to derail George's thread but the same argument would hold true here. In either case (60? C or 75? C) the EGC would be the same size based on 50 amps and T250.122.

6_15_34_3_2.gif
 
infinity said:
Since #1/0 is the minimum size conductor that you can parallel 250.122(B) does not apply since you haven't gone up from the minimum required.
Click to expand...

Now that is a seasoned response. :lol:

Just curious how others would handle it, I debated it alone for a bit and figured it would make for good conversation. :)
 
George Stolz said:
Lets suppose I have a 200A feeder, and decide to use two parallel 1/0 CU to supply it for voltage drop and to comply with 310.10(H).

When calculating the upsize in my 200A feeder, do I use a 3/0 CU as my starting point or two parallel 3 AWG?

:happyyes:
Click to expand...

Been a long weekend (work wise) but where does the 3 AWG figure in here?
 
George Stolz said:
Now that is a seasoned response. :lol:

Just curious how others would handle it, I debated it alone for a bit and figured it would make for good conversation. :)
Click to expand...
The text of thread title's subsection says it all...

250.122 said:
(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.
Click to expand...

3/0 cmil = 167800
(2) 1/0 cmil = 211200

Closest single conductor in cmil is 4/0 at 211600.

Also being an AWG size, it is just a one AWG size increase, so #6 Cu to not less than #7 Cu, which is typically not available... so next size larger = 8 AWG Cu.

That's my take and I'm sticking to it (until someone offers up a better take ;)).
 
Smart $ said:
The text of thread title's subsection says it all...



3/0 cmil = 167800
(2) 1/0 cmil = 211200

Closest single conductor in cmil is 4/0 at 211600.

Also being an AWG size, it is just a one AWG size increase, so #6 Cu to not less than #7 Cu, which is typically not available... so next size larger = 8 AWG Cu.

That's my take and I'm sticking to it (until someone offers up a better take ;)).
Click to expand...
Ooops! Must have been brain dead last night when I posted that.

Should have been... #6 Cu to not less than #5 Cu, which is typically not available... so next size larger = 4 AWG Cu.
 
George Stolz said:
So, with the new text of the 2014, that seems to call for parallel 12s or 10s, doesn't it? :D
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I've yet to "preview" the 2014 edition, so I take your comment to mean will we be looking at some form of combined-EGC sizing for parallel conductors... ?
 
Smart $ said:
The text of thread title's subsection says it all...



3/0 cmil = 167800
(2) 1/0 cmil = 211200

Closest single conductor in cmil is 4/0 at 211600.

Also being an AWG size, it is just a one AWG size increase, so #6 Cu to not less than #7 Cu, which is typically not available... so next size larger = 8 AWG Cu.

That's my take and I'm sticking to it (until someone offers up a better take ;)).
Click to expand...



200 amp feeder EGC = 6# cu = 26240 cm, 3/0 cm = 167800, (2) 1/0 cm = 211200, 211200/167800= 1.26 proportional size increase, 26240* 1.26= 33062 cm, 4# cu would be the EGC in each parralelled run.
 
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mwm1752 said:
200 amp feeder EGC = 6# cu = 26240 cm, 3/0 cm = 167800, (2) 1/0 cm = 211200, 211200/167800= 1.26 proportional size increase, 26240* 1.26= 33062 cm, 4# cu would be the EGC in each parralelled run.
Click to expand...
You quoted post #14...

See post #15.
 
Not really -- looked like he used 250.66 as he went with total cm -- came up with same answer though -- just being specific
 
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