4 #1THHN conducts in what size EMT C

[Eng]

What size conduit is required for 4#1AWG THHN conductors that are installed in a EMT conduit?

Per Table C.1 we can fit 4#1AWG THHN in 1-1/4? EMT C.

Per Chapter 9, Table 5 is listing the area of #1THHN is 0.1562 * 4 = 0.6248. Per Chapter 9, Table 4 the maximum allowable area in a 1-1/4?C utilizing the 40% fill rule for over 2 conductors is 0.598. This only allows us to install 3#1AWG THHN conductors in a 1-1/4? Conduit.

Which is correct?


Thanks

 

[Dennis Alwon]

There are many errors IMO in Annex C. IMO, you must use Chapter 9 Table 5

 

[Eng]

How do you know that one is more correct than the other?

 

[Mouser]

Annex C

Annex C

This informative annex is not a part of the requirements of this NFPA document but is included for informational purposes only. Tables 4&5 are in Chapter 9 which is code.

 

[Dennis Alwon]

This informative annex is not a part of the requirements of this NFPA document but is included for informational purposes only. Tables 4&5 are in Chapter 9 which is code.

This is correct. I am not sure why they include it as I have found other discrepancies in the table. When I brought it up to some cmp members they were surprised but just shrugged.

Anyway read the text right below the title in Annex C. In fact the title starts with Informational Annex C

 

[Eng]

This is correct. I am not sure why they include it as I have found other discrepancies in the table. When I brought it up to some cmp members they were surprised but just shrugged.

Anyway read the text right below the title in Annex C. In fact the title starts with Informational Annex C

Interesting, I'm sure the example that I gave is just one of many. If the CMP's are not willing to correct the discrepancies, then the entire Annex should be deleted.

 

[iwire]

I agree with the others as far as the tables not being part of the code, you must use Chapter 9.

Now beyond that, as a guy with some experience, don't even think of using 1.25", use at least 1.5" and if the run has a large number of bends, conduit fittings etc. I might even use 2"

 

[Dennis Alwon]

Interesting, I'm sure the example that I gave is just one of many. If the CMP's are not willing to correct the discrepancies, then the entire Annex should be deleted.

I agree and have said that many time. If it is not part of the code and the info is incorrect then why have it there.

 

[Eng]

---

I agree with the others as far as the tables not being part of the code, you must use Chapter 9.

Now beyond that, as a guy with some experience, don't even think of using 1.25", use at least 1.5" and if the run has a large number of bends, conduit fittings etc. I might even use 2"

Easy to say, except when dealing with existing conduits.

 

[copper chopper]

so does that mean you cant fit 4 - 500kcmill and a 250 kcmill ground in 3 inch scd-40 pvc?

 

[Dennis Alwon]

so does that mean you cant fit 4 - 500kcmill and a 250 kcmill ground in 3 inch scd-40 pvc?

You need more info. You go to Table 4 in Chapter 9 and look up the dimensions of 3" PVC with over 2 wires and you get 2.907. Now go to Table 5 and look up the dimensions of the wire sizes you gave but you need the insulation type. Add them up and if it is less then 2.907 then you are good to go.

 

[Eng]

An FYI.

Chapter 9: Notes to tables (1) refers us to see annex C for the maximum number of conductors and fixture wires, all of the same size permitted in trade sizes of the applicable conduit.

 

[Dennis Alwon]

An FYI.

Chapter 9: Notes to tables (1) refers us to see annex C for the maximum number of conductors and fixture wires, all of the same size permitted in trade sizes of the applicable conduit.

Yes another place where the NEC is at fault. Why have a table when it is not accurate. And how would you use this table if all the conductors are not the same size? The heading in Annex C is clear- it is an informational table and is accurate most of the time- i am not sure the cmp is aware of some of the errors.

 

[Dennis Alwon]

Here is another example where Annex C is off.

Per Table C.1 we can install 4 #12 THHW in 1/2" conduit

Per Chapter 9, Table 5 #12 THHW is .0181 sq. in.
Per Chapter 9, Table 4 the maximum allowable area in a 1/2" emt utilizing the 40% rule is .122 sq. in. Thus .122/.0181 = 6.7 This tables allows 6 wires

 

[hurk27]

Here is another example where Annex C is off.

Per Table C.1 we can install 4 #12 THHW in 1/2" conduit

Per Chapter 9, Table 5 #12 THHW is .0181 sq. in.
Per Chapter 9, Table 4 the maximum allowable area in a 1/2" emt utilizing the 40% rule is .122 sq. in. Thus .122/.0181 = 6.7 This tables allows 6 wires

I agree and don't know why the discrepancies for THHW which is not a common wire any more as it has a thicker insulation like TW, when you get to the more compact THHN/THWN conductors your down to 0.0133?" which gives you 9.77 or 9 wires at 40% which both tables agree, so it might be that because THHW is so uncommon that no one has ever looked at it?

So it is very important to know what type of insulation (conductor type) including if you are using compact conductors or not, and apply the correct raceway (I.E EMT verses RMC) as they have different dimensions that can throw you off.

Here is a little on the OP, #1 THHN/THWN regular cross stranded is 0.1562?"*4=0.6248?" which would require 1?" EMT at 0.814?" @40% but compact THHN/THWN is only 0.1352?" *4 = 0.5408?" which would be allowed in a 1?" EMT @ 0.598?"

But when you compare different type of conduit's you can see how fast you can get into trouble :

1?"-------Total Area-----40%fill
EMT---------2.036?"------0.814?"
IMC ---------2.225?"------0.890?"
RMC---------2.071?"------0.829?"
PVC----------1.711?"-----0.684?"

I have always questioned as to why EMT has less inside area then RMC?
And you can see that PVC has the worst inside diameter.

 

[iwire]

I have always questioned as to why EMT has less inside area then RMC?
And you can see that PVC has the worst inside diameter.

:huh:

The outside diameters remain constant, the wall thickness changes so the internal diameter must change.

 

[copper chopper]

great the answer to my question is NO.

 

[hurk27]

:huh:

The outside diameters remain constant, the wall thickness changes so the internal diameter must change.

And I have always thought that to be true, but if you look at the above, the EMT has the least area, with the thicker wall of RMC you would think it would have the least area inside.

 

[iwire]

And I have always thought that to be true, but if you look at the above, the EMT has the least area, with the thicker wall of RMC you would think it would have the least area inside.

What you say is true for 2" and smaller, in those sizes the OD of EMT is different than RMC. (Think of EMT vs RMC clips)


Once you get to 2.5" and above the ID of EMT is greater than RMC.

 

[roger]

How do you know that one is more correct than the other?

Might note 7 to Chapter 9 come into play for your question.

(7) When calculating the maximum number of conductors permitted in a conduit or tubing, all of the same size (total cross-sectional area including insulation), the next higher whole number shall be used to determine the maximum number of conductors permitted when the calculation results in a decimal of 0.8 or larger.

Roger