conductor properties
- Thread starter Derick
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- Chapel Hill, NC
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- Retired Electrical Contractor
One of the most common uses of Table 8 is for parallel runs. Lets say you want to pull a parallel run of 1/0 wire that is equivalent to 500KCM. If you look at Table 8 under 1/0 and the cir. mil column you get 105600 cir. mil.
500 kcm is equivalent to 500,000 cir. mil. So with quick division it would take 5 runs of 1/0 to be equivalent to the 500kcm wire.
Suppose you wanted to know the value of 2 sets of 1/0. Again you get 105600 X 2= 211200 cir. mil. Look at Table 8 and you see that 4/0 is equal to 211600 cir. mil. Since this is slightly larger than the paralleled 1/0 conductors then the paralleled 1/0 are equivalent to a 4/0 conductor.
Hope this helps-- I have never used Table 9.
500 kcm is equivalent to 500,000 cir. mil. So with quick division it would take 5 runs of 1/0 to be equivalent to the 500kcm wire.
Suppose you wanted to know the value of 2 sets of 1/0. Again you get 105600 X 2= 211200 cir. mil. Look at Table 8 and you see that 4/0 is equal to 211600 cir. mil. Since this is slightly larger than the paralleled 1/0 conductors then the paralleled 1/0 are equivalent to a 4/0 conductor.
Hope this helps-- I have never used Table 9.
Cold Fusion
Senior Member
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Derick -
You didn't give us any clues as to where you need help. So I start this pretty simple - but I suspect you already know all of this.
The secrets are in the tables notes.
(discussion is limited to US units, copper conductors)
T8 gives the direct current resistance per 1000 feet and 75C.
So if you wanted to know the DC resistance (at 75C) of a #6 wire, 350 foot long circuit
R =((350 x 2)/1000) x 1.608
The "x 2" is because the circuit is 350 feet out and 350 feet back - total conductor length is 700feet
The "/1000" is because the table gives resistances in ohms/1000feet, not "ohms/foot". So dividing by 1000 gets the units right.
And 1.608 is the ohms per 1000 feet for #6
Table 8 also gives the formula for the resistance change with temperature. See note 2.
Note on DC resistance:
For resistive loads, power factor = 1, stuff like heaters, incandesant lights, the DC resistance is effectively the same as the 60hz AC resistance.
I appoligize if this is too simple. As I said, I suspect you already know this.
cf
You didn't give us any clues as to where you need help. So I start this pretty simple - but I suspect you already know all of this.
The secrets are in the tables notes.
(discussion is limited to US units, copper conductors)
T8 gives the direct current resistance per 1000 feet and 75C.
So if you wanted to know the DC resistance (at 75C) of a #6 wire, 350 foot long circuit
R =((350 x 2)/1000) x 1.608
The "x 2" is because the circuit is 350 feet out and 350 feet back - total conductor length is 700feet
The "/1000" is because the table gives resistances in ohms/1000feet, not "ohms/foot". So dividing by 1000 gets the units right.
And 1.608 is the ohms per 1000 feet for #6
Table 8 also gives the formula for the resistance change with temperature. See note 2.
Note on DC resistance:
For resistive loads, power factor = 1, stuff like heaters, incandesant lights, the DC resistance is effectively the same as the 60hz AC resistance.
I appoligize if this is too simple. As I said, I suspect you already know this.
cf
Hope this helps-- [/QUOTE]
Yes it did.By your example I see it can be used to find the size of the conduit if conductors of different sizes to be placed in the same raceway as well.
Have couple more questions in ref.to T8.
For example #8 wire.It shows two rows.I think upper row is for solid and lower row is for stranded.So,by going to Quanity column: shows 7.Does it means there are 7 strands of wire size 0.049 of inch each? (from Diameter column)
If this is true to find CM of 7 strands I should:from stranding column
(0.049 X 1000) X (0.049 X 1000) x 7 =16510 CM table 8 shows 16510 as well so let say I did it OK.
But what the Overall columns stands for:
If I take overall diameter/stranding diameter = not quantity
0.146 / 0.049 =(not 7) but =2.97......
What am I missing?
Thank you,and have great THANKSGIVING
Yes it did.By your example I see it can be used to find the size of the conduit if conductors of different sizes to be placed in the same raceway as well.
Have couple more questions in ref.to T8.
For example #8 wire.It shows two rows.I think upper row is for solid and lower row is for stranded.So,by going to Quanity column: shows 7.Does it means there are 7 strands of wire size 0.049 of inch each? (from Diameter column)
If this is true to find CM of 7 strands I should:from stranding column
(0.049 X 1000) X (0.049 X 1000) x 7 =16510 CM table 8 shows 16510 as well so let say I did it OK.
But what the Overall columns stands for:
If I take overall diameter/stranding diameter = not quantity
0.146 / 0.049 =(not 7) but =2.97......
What am I missing?
Thank you,and have great THANKSGIVING
Cold Fusion
Senior Member
- Location
- way north
T9 is similar, but a bit more complicated. It is laid out for 3 phase, 60hz, and takes into account power factor and different conduit materials.
Again the secrets are in the table notes. In particular read note 2.
You would use T9 for calculating voltage drop to a 3ph motor. You would use the "Effective Z column" for voltage drop at normal running current.
From here it gets a little more complicated:
If you were calculating the voltage drop for a fire pump circuit per 695.7 then you would use T9 to size the wire for a 15% VD at locked rotor current, the power factor is probably about zero. (I've never had to do this, so someone can jump in here and correct me on the locked rotor power factor)
To get the Effective Z at the low power factor, one would use the formula in note 2, and the values in the XL column and the resistance column.
cf
Again the secrets are in the table notes. In particular read note 2.
You would use T9 for calculating voltage drop to a 3ph motor. You would use the "Effective Z column" for voltage drop at normal running current.
From here it gets a little more complicated:
If you were calculating the voltage drop for a fire pump circuit per 695.7 then you would use T9 to size the wire for a 15% VD at locked rotor current, the power factor is probably about zero. (I've never had to do this, so someone can jump in here and correct me on the locked rotor power factor)
To get the Effective Z at the low power factor, one would use the formula in note 2, and the values in the XL column and the resistance column.
cf
Don't apologize,I realy apreciate any inputs and you gave me great example
to work on.Couple things looking at your formula you ment to X 0.491 instead of 1.608. 1.608 is for ohm/km and 0.491 will give us units in feet in K.
Another question I had:What is the meaning of Uncoated and coated.
Coated means insulated (THHN,TW......)? or just coated with clear insulation (don't know what it is ) like we see in motor winding,coils,transformers etc.
Thank you
Cold Fusion
Senior Member
- Location
- way north
Cold Fusion
Senior Member
- Location
- way north
Excellent job. You passed your test and caught the error:roll: (laughing at me)
T8 is all about bare wires. I THINK coated is the tinned wire one sees occasionally. I THINK with the tin coating, the copper diameter is a bit smaller so that the diameter with the tin coating is the same as the diameter with out the tin. Copper is lower resistance that the tin, so the tinned wires are a bit higher resistance.
And I am guessing cause I don't know this.
Anyone want to jump in here?
cf
Yes,thank you got it now
nuetral voltage
nuetral voltage
i have a question about nuetrals, i have a commerical building that the nuetral has the same amp readings as the hot when applicances are on. is that normal? a dedicated circuit was ran with nothing else on it and it has the same reading. i aplogize if i did not post this right or in the right forum.any help on both issues with be greatly appricated. thank you
nuetral voltage
i have a question about nuetrals, i have a commerical building that the nuetral has the same amp readings as the hot when applicances are on. is that normal? a dedicated circuit was ran with nothing else on it and it has the same reading. i aplogize if i did not post this right or in the right forum.any help on both issues with be greatly appricated. thank you
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Welcome to the forum. If I am reading your question right, you are asking about current flow in a circuit. Current flow in a simple series circuit is constant.
You can learn more about series and parallel circuits here:
http://www.allaboutcircuits.com/vol_2/chpt_1/4.html
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