Annex c

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marinesgt0411

marinesgt0411

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conduit and tubing fill tables

got in an arguement the other day about how many wires are allowed in a conduit

I say annex c tables tell you how many of what size of what kind of wires are allowed in which type of conduit. with no derating

the other guy says you have to derate the wires for longer runs and can not pull the max allowed in the conduit.

if you already have determined the size needed for Voltage drop,amp of circuit and all other considerations that the number listed in the tables is what you can pull into the conduits.

am I missing something somewhere?
 
Re: Annex c

Annex C is for conduit fill, 310.15(B)(2)(a) is for ampacity adjustment.

If you have more than 3 current carrying conductors in the raceway, figure on using the table for ampacity adjustment.

Ex:
In Annex C - Table C1 EMT

12AWG Type THHN, in 4 inch - permits 443 conductors ;) . Lets see ya pull that :eek:

More realistically: 500s in 4 inch EMT - permits 8 conductors - (lets say 6 are CCC) ampacity adjustment of 80%.
 
Re: Annex c

I guess my question is if annex c says I can put 9 #12's (THHN)in a 1/2" conduit 4 hots 4 nuetrals and a groud why can I not do so?
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Well, you can. But remember that each type of conduit has it's own fill capacities. So 9 conductors in 1/2" trade size of one type of conduit may not be permitted in another.
 
Re: Annex c

Originally posted by marinesgt0411:
I guess my question is if annex c says I can put 9 #12's (THHN)in a 1/2" conduit 4 hots 4 nuetrals and a groud why can I not do so?
Click to expand...
As Pierre said you are mixing two issues.

1)How many will fit

2)What the ampacity of the conductors will be.

Table C1 tells me I can put sixteen 10 AWG THHNs in 1" EMT.

So I go ahead and do that.

10 AWG THHN is rated 40 amps per Table 310.16, it happens my sixteen 10 AWGs supply 8 two wire circuits, that means I have 16 current carrying conductors in that 1"

That means I go to Table 310.15(B)(2)(a) and I find with 16 current carrying conductors I must de-rate the 10 AWGs by 50%

40 amp x .5 = 20 amps.

So I can fit sixteen 10 AWGs in 1" EMT but I will only be able to use a 20 amp breaker with them.

The reason for this is heat, the more conductors in a single raceway the more heat we have to deal with.

In general 3/4" EMT is the largest practical pipe for 15 and 20 amp circuits or you end up running larger conductors due to de-rating.

I can install 443 12 AWGs in a 4" EMT, but I will need to use a 10 amp breaker with them. :p
 
Re: Annex c

Also, the annexes are not part of the code, (with an exception IMO) so annex C is better looked at as a quick reference to the amount of conductors (rounding considered) a conduit or tube can contain at the percent of fill. This doesn't relieve any code requirement for derating ampacity of current carrying conductors.

Roger
 
Re: Annex c

I tryed to point that out in my origanal post
if you already have determined the size needed for Voltage drop,amp of circuit and all other considerations that the number listed in the tables is what you can pull into the conduits.
Click to expand...
by the way how do you use the quote function? it does not look correct

I understand I need to derate for more then three current carring conductors and ambiant temperatures and I need to increase wire size for voltage drop but once that has been determined I can fill the conduit to what it says in annex c. is my point and his is that you can only fill the conduit to 80 percent of what is in the tables. my arguenent is if that were true the tables would say so
 
Re: Annex c

If you want to quote from another post, click on this
quote_ubb6.gif
icon in the others post.

To pick out a segment you can do as you did in your post by using the
ubb_quote.gif
button, you can also use your keypad and type putting your text in between the quotes.

Roger
 
Re: Annex c

There is a FAQ on the topic of using the "Reply with Quote" feature. Look at the top thread in any of the Topic Areas.
 
Re: Annex c

Originally posted by marinesgt0411:


I understand I need to derate for more then three current carring conductors and ambiant temperatures and I need to increase wire size for voltage drop but once that has been determined I can fill the conduit to what it says in annex c. is my point and his is that you can only fill the conduit to 80 percent of what is in the tables. my arguenent is if that were true the tables would say so
Click to expand...
You are correct
He is wrong

If it says 9 #12 THHN will fit in 1/2" EMT, then it does not matter if it's 10'; 100'; or 1000'. It meets code minimum.
 
Re: Annex c

I can fill the conduit to what it says in annex c. is my point and his is that you can only fill the conduit to 80 percent of what is in the tables. my arguenent is if that were true the tables would say so
Click to expand...
Here is the answer:

Annex C

ac1.jpg


Table 1 Chapter 9

t9.jpg
 
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