It may be surprising to some, but the number of wires allowed in any given conduit is not “as many as can be jammed in there.” The National Electrical Code, AKA NEC or NFPA 70 gives specific guidance on the number of current-carrying conductors allowed in any specific size and type of conduit.<\/p>\n\n\n\n
This is due to the fact that current-carrying conductors generate heat. \u00a0Cables enclosed in a conduit need to dissipate that heat so that the insulation on the cable doesn’t melt, which would be a bad outcome.<\/p>\n\n\n\n
Conduit fill tables are found in Chapter 9 of the NEC. \u00a0There are several tables that give the number of conductors for each size and type of conduit. \u00a0Then there is the general rule of thumb that for more than two cables, the maximum conduit fill is 40%. \u00a0This comes in handy when several different size conductors are being run in the same conduit.<\/p>\n\n\n\n
An example of this is when several circuits are going across the room to the same general location, in this case, a row of transmitters and racks. Instead of running individual conduits for all those units, one or two conduits from the electrical panel are run to a square wireway, then the individual circuits are broken out and wired from wireway to the individual loads. In this case, the following equipment is being connected:<\/p>\n\n\n\n
Excluding grounding conductors, which will be addressed below, the total current carrying conductor count is thus:<\/p>\n\n\n\n
Ampacities based on NEC table 310.16, THHN insulation in dry locations, maximum temperature rating is 90\u00b0 C (194\u00b0 F) based on the ambient temperature of 30\u00b0 C (86\u00b0 F)<\/p>\n\n\n\n
Grounding conductors for each of those circuits, based on NEC Table 250.122 (all conductors are copper):<\/p>\n\n\n\n
The final conductor count is:<\/p>\n\n\n\n
The plan is to use two 1 and 1\/2-inch EMT conduits between the electrical service panel and the 4 x 4 square wireway. According to \u00a0NEC Chapter 9, Table 4, the 40% cross-sectional size of this conduit is 526 mm2. \u00a0It is easier to simply use metric measurements for this. \u00a0The cross-sectional wire areas are found in Chapter 9, Table 5. \u00a0Chart of various conductor sizes and areas:<\/p>\n\n\n\n Thus, in order to break this up into two 1 and 1\/2-inch conduits, the #2, #6, and #8 (main transmitter HV power supply, backup transmitter, and grounds) are run in one conduit, the remaining circuits in the other. \u00a0The idea is that the main transmitter and backup transmitter will not be running simultaneously for long periods of time. \u00a0Those cable areas total 369.48 mm2<\/sup>, well within the 40% limit of\u00a0526 mm2<\/sup>\u00a0for 1 and 1\/2 inch EMT. \u00a0 The rest of the circuit’s cable areas total 256.041 mm2<\/sup>. \u00a0That leaves room for additional circuits in the second conduit if future needs dictate. \u00a0The extra conduit area will make pulling the wires through easy.<\/p>\n\n\n\n From the square wireway to the HV power supply, 1 and 1\/4 inch conduit will carry the three #2 and one #8 ground. \u00a01 and 1\/4 inch EMT has a cross sectional area of 387 mm2<\/sup>, the conductors contained within will be 271 mm2<\/sup>. \u00a0Less room here, but still well within the 40% limit.<\/p>\n\n\n\n Pictures will be posted when the project is done.<\/p>\n","protected":false},"excerpt":{"rendered":" It may be surprising to some, but the number of wires allowed in any given conduit is not “as many as can be jammed in there.” The National Electrical Code, AKA NEC or NFPA 70 gives specific guidance on the number of current-carrying conductors allowed in any specific size and type of conduit. This is … Continue reading Conduit fill<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[235,234,96],"class_list":["post-4326","post","type-post","status-publish","format-standard","hentry","category-tech-stuff","tag-code","tag-nec","tag-wiring"],"_links":{"self":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/4326","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/comments?post=4326"}],"version-history":[{"count":12,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/4326\/revisions"}],"predecessor-version":[{"id":11666,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/4326\/revisions\/11666"}],"wp:attachment":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media?parent=4326"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/categories?post=4326"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/tags?post=4326"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Conductor<\/td> Area (mm2<\/sup>)<\/td> Total conductor<\/td> Total area (mm2<\/sup>)<\/td><\/tr> #2 THHN<\/td> 74.71<\/td> 3<\/td> 224.13<\/td><\/tr> #6 THHN<\/td> 32.71<\/td> 3<\/td> 98.13<\/td><\/tr> #8 THHN<\/td> 23.61<\/td> 2<\/td> 47.22<\/td><\/tr> #10 THHN<\/td> 13.61<\/td> 9<\/td> 122.49<\/td><\/tr> #12 THHN<\/td> 8.581<\/td> 9<\/td> 77.229<\/td><\/tr> #14 THHN<\/td> 6.258<\/td> 9<\/td> 56.322<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n