conduit capacity

[Steve12]

I am remodelling a lab at our manufacturing facility and we have wires strung everywhere. What we are doing is installing standard electrical galvanized conduit with junction boxes and was wondering what size of conduit is required by code to fit (24) standard 18 gauge insulated wires? I'm thinking 3/4" may be enough but may have to go to 1" diameter conduit.

Out of the (24) wires, only 4 -6 of the wires will be energized at the same time by 120 volts every 30 - 40 minutes for 5 seconds. There are 24 in the conduit due to different tests that run at different times and for future expansion.

Thanks,
Steve
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That's the problem, I don't have access to a NEC manual right now.
The wire type is 18 AWG E25635 AWM Style 1015 or AWM Style 1230.

Im having to edit the post because the REPLY function is not working correctly.

 

[haskindm]

See annex c in the NEC for conduit fill, if the type wire that you are using is listed. If not you will use table 4 based on the area of your conductors and a 40% conduit fill.

 

[Steve12]

That's the problem. I don't have an NEC manual right now. The wire type is standard AWG Style 1015 or AWG Style 1230 18 gage wire.

 

[charlie b]

There are two considerations here. One is a determination of the required conduit size. That will depend on the type of wire (i.e., insulation material) and the type of conduit (e.g., PVC or EMT or some other). You can get the minimum size conduit from NEC Annex C. Actually, it is tabulated in terms of the maximum number of conductors in a given size conduit. Please note that the intended use (i.e., what is energized when with what current level) has no influence on this determination. This is all about getting wires pulled through the conduit without anything binding along the way. You might consider upsizing beyond the minimum, in order to make the process of pulling wires easier for the electrician.

The second consideration is ampacity. With more than three current-carrying conductors in a conduit, the ampacity of each conductor must be reduced. See Table 310.15(B)(2)(a). Please note that if you wish to take credit for not all conductors carrying current at the same time, you must install some type of interlock or control mechanism, or otherwise convince the local authority that there really is no way for all of the wires to ever carry current at the same time.

 

[charlie b]

I?m having to edit the post because the REPLY function is not working correctly.

The REPLY function did work, and all of your replies did get posted. However, for every new member, all posts will be held up for some amount of time, until a Moderator can read them and confirm that it is a real question or comment (i.e., not someone trying to sell cellular phones or non-prescription drugs). Thus, your replies did not become ?visible? to you or to any other member, until I ?approved? them. Then I immediately deleted the duplicates, and left you with a single thread.

Welcome to the Forum.

 

[charlie b]

The wire type is standard AWG Style 1015 or AWG Style 1230 18 gage wire.

I do not understand those "style" designations. I know what AWG 18 means, but what is "1015" and "1230"? What you need to know, in order to look up the conduit fill information in Annex C, is the insulation type. Examples are THW, THHN, THWN, and TW. Also, you need to know the type of conduit, as I mention above.