ELECTRICAL CALCULATIONS

[JACK55]

DO YOU COUNT THE GROUND WIRE WHEN SIZING RACEWAY FOR A FEEDER/

I'M INSTALLING 4-#600 THWN AND 1#3 GROUND WIRE IN A 3-1/2 RIGID CONDUIT
I DID'NT COUNT THE #3 GROUND WIRE IN MY CALCULATIONS

 

[Little Bill]

DO YOU COUNT THE GROUND WIRE WHEN SIZING RACEWAY FOR A FEEDER/

I'M INSTALLING 4-#600 THWN AND 1#3 GROUND WIRE IN A 3-1/2 RIGID CONDUIT
I DID'NT COUNT THE #3 GROUND WIRE IN MY CALCULATIONS

All the conductors count when sizing a raceway.

Sounds like you need a 4" raceway (rigid)

 

[barclayd]

I see it as 'legal' in 3-1/2" (36% fill), but it will be a heck of a lot easier to pull in 4".
The 40% fill limitation relates only to heat - depending on the configuration of the conduit, pulling could be difficult.
db

 

[charlie b]

For a 3.5 inch RMC, the 40% limit gives you 4.004 square inches to work with. Per table 5, a 600 MCM THWN takes up .8676 square inches, so four of them would take up 3.47 square inches. You do need to account for the ground wire in the calculation of cross sectional areas. A #3 will take up 0.0973 square inches. That gives you a total of 3.567, and this is under the 4.004 limit. Overall it gives you 35.6% fill. So yes, you can do it. I cannot speak for the possible difficulty of pulling that much wire through that size conduit.

 

[charlie b]

The 40% fill limitation relates only to heat. . . .

I have to disagree with that. I believe that the basis of the 40% fill limit has everything to do with reducing the risk of damaging the conductors during the pulling process, and nothing to do with the operation of the conductors once they are in place.

 

[charlie b]

By the way, Jack, please do not type your posts with the ALL CAPS feature turned on. It makes the post more difficult to read, and is considered impolite (i.e., as though you were SHOUTING at us).

 

[kwired]

I have to disagree with that. I believe that the basis of the 40% fill limit has everything to do with reducing the risk of damaging the conductors during the pulling process, and nothing to do with the operation of the conductors once they are in place.

I agree. Also makes sense when you look at the fill requirements for when there is only one or two conductors.

 

[barclayd]

If this is a 50' straight run - no problem at all with 3-1/2"
If it is 300' with 4 90's - I recommend 4".

db

 

[JACK55]

Electrical Calculations

Electrical Calculations

Thanks everyone

 

[kingpb]

If this is a 50' straight run - no problem at all with 3-1/2"
If it is 300' with 4 90's - I recommend 4".

db

Without a pulling tension calc, or knowing jam ratio, how is it possible to recommend anything. :?

 

[kwired]

Without a pulling tension calc, or knowing jam ratio, how is it possible to recommend anything. :?

Pulling tension is not addressed in NEC other than pretty vague limitation of number of bends in a section of raceway.

Isn't jam ratio part of why Chapter 9 Table 1 exists?

 

[kingpb]

I would agree the NEC does not address this much, nor should it, as this is installation related issue and really doesn't pertain to safety, which is what the NEC is for.

Just becasue the NEC allows 360 deg worth of bends in a run doesn't mean it will work without exceeding pulling tension of cable.

 

[T.M.Haja Sahib]

I agree.

I do not feel like agreeing with

I believe that the basis of the 40% fill limit has nothing to do with the operation of the conductors once they are in place.

because, even though for a group of more than three conductors, a derating factor is applied, the additional derating for method of installation of cables i.e in conduit is also taken care by 40% fill limit, IMHO.