paralleled grounded conductors

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kwired

kwired

Electron manager
Location
NE Nebraska
cheaptape said:
I am having problems understanding how I am to calculate
paralleled grounded conductors. Can some one give me and example
or two to clear this up for me.
Click to expand...
Can you give us an example of the application? They are no different than ungrounded conductors in most ways, find the conductor ampacity needed and divide by number of parallel components to come up with minimum size of each component. Remember that you can not use conductor smaller than 1/0 AWG as part of a parallel conductor set.
 
qcroanoke

qcroanoke

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Sorta retired........
kwired said:
Can you give us an example of the application? They are no different than ungrounded conductors in most ways, find the conductor ampacity needed and divide by number of parallel components to come up with minimum size of each component. Remember that you can not use conductor smaller than 1/0 AWG as part of a parallel conductor set.
Click to expand...

I know the OP said Grounded conductor. I wonder if they meant grounding conductor.
I say this because you can parallel smaller than 1/0 for the grounding conductor. 250.122.F
 
infinity

infinity

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Sounds like the correct response will be based on first receiving clarification from cheaptape.
 
C

cheaptape

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Location
Salina Kansas U.S.A.
It was grounded conductors

It was grounded conductors

my question is on paralleled grounded conductors.

I have 3 ph 4/0 feeders in parallel and need to calculate the ungrounded conductors for
each set of conductors
 
kwired

kwired

Electron manager
Location
NE Nebraska
cheaptape said:
my question is on paralleled grounded conductors.

I have 3 ph 4/0 feeders in parallel and need to calculate the ungrounded conductors for
each set of conductors
Click to expand...


First thing is to calculate ampacity needed for the neutral regardless if single or parallel conductor.

Second thing is to know that the grounded conductor can not be smaller than values in table 250.66 for service conductors, or no smaller than values in table 250.122 for feeders or branch circuits - again regardless of whether single or parallel conductors.

If parallel conductors then adding ampacity of each individual conductor is done to come up with a total for the parallel set (ampacity adjustments do apply if necessary). Again no matter what size is determined necessary you can not parallel conductors smaller than 1/0 AWG.

All that said, since your ungrounded conductors are 4/0, you may reduce the neutral if you determine the load is not capable of reaching the same level as it could on the ungrounded conductors, but no case will you be able to reduce the neutral to less than 1/0 if you are paralleling it.
 
C

cheaptape

Member
Location
Salina Kansas U.S.A.
some how i got confused

some how i got confused

I was thinking I was to find the size #2 from 250.66 and thin get the circular mils and x that by 2 and go with the 2/0
#2
66360 cir mils
x 2
=132720 cir mils and that would make it

2/0 133100

is this wrong
 
kwired

kwired

Electron manager
Location
NE Nebraska
cheaptape said:
I was thinking I was to find the size #2 from 250.66 and thin get the circular mils and x that by 2 and go with the 2/0
#2
66360 cir mils
x 2
=132720 cir mils and that would make it

2/0 133100

is this wrong
Click to expand...

Assuming you have 2 sets of 3/0 ungrounded conductors - 250.66 says you need a minimum of 2 AWG. You would divide that by two to come up with minimum size of parallel conductor, but since it is smaller than 1/0 you still must use at least 1/0 if you are going to parallel it.

If you were to run the parallel conductors all in one raceway (but you have to consider ampacity adjustment and possibly need to increase the 3/0 ungrounded conductors if doing that) then you could get by with a single 2AWG in that same raceway if the load were not there to require a larger conductor.
 
kwired

kwired

Electron manager
Location
NE Nebraska
cheaptape said:
do I multiply using ampacity or circular mils win calculating parallel grounded conductors
Click to expand...

Just like you did when you determined the ungrounded conductor sizes.

Say you need a 400 amp conductor, but want to use parallel conductors, then you need two 200 amp conductors to make the 400 amp set. If you want to make a 1200 amp conductor out of three parallel components they would each need to be 400 amps each to get a 1200 amp set.

If you put the parallel conductors all in the same raceway you have to derate for number of current carrying conductors in the raceway though, so four 3/0 conductors is able to be used for single phase 200 amps if in separate raceways because each conductor has an ampacity of 200, but if you ran all four in same raceway then they need a 80% correction factor applied because you will have more than three current carrying conductors in the raceway. But fortunately the deration would apply to the 90 deg C insulation value so as long as calculated load is not more than 360 amps two 3/0 can still be protected with a 400 amp overcurrent device, but if you want full 400 amp ability you need larger conductors.
 
C

cheaptape

Member
Location
Salina Kansas U.S.A.
HELLO can any body explain paralleled grounded conductors

HELLO can any body explain paralleled grounded conductors

the Nebraska chief electrical inspector told me it was calculated with cir mils
 
kwired

kwired

Electron manager
Location
NE Nebraska
cheaptape said:
the Nebraska chief electrical inspector told me it was calculated with cir mils
Click to expand...
Maybe I didn't understand your question. Were you asking about how to use table 250.66 or how to determine ampacity of a paralleled set of conductors?

If you are trying to determine what size conductor 250.66 requires based on your parallel 4/0 conductors, then yes you need to find the circular mil area of 4/0 (which can be found in chapter 9 table 8) and multiply by number of conductors to come up with an "equivalent" circular mil conductor for the parallel set to use as a base when using 250.66.
 
J

JDBrown

Senior Member
Location
California
Occupation
Electrical Engineer
cheaptape said:
HELLO can any body explain paralleled grounded conductors

the Nebraska chief electrical inspector told me it was calculated with cir mils
Click to expand...
It appears that "what we have here is a failure to communicate."

Are we talking about the groundED (white) conductor, or the groundING (green) conductor?
 
J

JDBrown

Senior Member
Location
California
Occupation
Electrical Engineer
infinity said:
He said grounded conductors in 4 separate posts. :)
Click to expand...
True, but he also keeps coming back to circular mils and Table 250.66. I know that's how you calculate the minimum grounded conductor size, but based on the OP's reaction to some of the other answers I feel like we may not be understanding what he's asking. I'm just trying to make sure that what he's saying and what I'm hearing are, in fact, the same thing.
 
kwired

kwired

Electron manager
Location
NE Nebraska
JDBrown said:
It appears that "what we have here is a failure to communicate."

Are we talking about the groundED (white) conductor, or the groundING (green) conductor?
Click to expand...

infinity said:
He said grounded conductors in 4 separate posts. :)
Click to expand...

JDBrown said:
True, but he also keeps coming back to circular mils and Table 250.66. I know that's how you calculate the minimum grounded conductor size, but based on the OP's reaction to some of the other answers I feel like we may not be understanding what he's asking. I'm just trying to make sure that what he's saying and what I'm hearing are, in fact, the same thing.
Click to expand...

He has also indicated that this is likely the grounded service conductor - if so there is no equipment grounding conductor in his application. And 250.66 would be the correct table for absolute minimum size for a grounded service conductor. For absolute minimum size of a grounded conductor of a feeder or branch circuit it must be no smaller than what is in table 250.122. It must also comply with 250.122 if it is a grounding conductor, but must be minimum 250.122 sized in each raceway of a parallel set, and not split up to have a 250.122 total CSA like you do with the ungrounded conductors.
 
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