![]() ![]() I believe in the NEC book motors are an exception to our standard rules for ampacity. This assumes that proper motor protection set for the FLA is in place. ![]() Basically double the FLA for the breaker to run a motor. I am a electrical engineer and worked in the field for 30+ years Wrong, you must size wire for the breaker size Pretty sure they FLA on plate says 36ish amps Edited by APF 22:01 Maybe you guys are looking at 120 single phase instead of 240 I have some 15HP fans that an 80 amp carries just fine Single phase 240 will carry a 7.5 HP motor on 50 amps for sure There may be reason to increase the wire size though, based on length of run, or number of wires in the conduit for example. It would meet and pass an inspection with NO problem. It's what's called for in my motor chart. The #8 on a 80A breaker, when used to run a motor, is perfectly fine and legal. The breaker is sized appropriately for the inrush current, which is often around 6X higher then the FLA. When working with motors, you're in essence sizing the wires to the FLA (Full Load Amps ) of the motor. The reason for the breaker size is the starting current Edited by Lind1980 21:55 Posted 21:46 (#5172451 - in reply to #5171853) Subject: RE: Grain bin wiringħ.5 hp, 80 A single phase, circuit breaker but circuit breaker requires, #4 wire, thhn wire, 1 inch conduitġ0 hp, 90 A single phase, circuit breaker but circuit breaker requires ,# 3wire, thhn wire,1.25 inch conduitĪs per neca code, disconnects are required if farther than 50 foot from panel or out of line of sight Wonder what the starter is protected to ? Posted 20:30 (#5172265 - in reply to #5172209) Subject: RE: Grain bin wiringĬhecking the amps draw when having different amount of grain I've used that same Square D slide rule for years and I've never had a problem by following it. I don't think a 50 amp on 10 hp single phase fan would work that great, really don't know but i have a gut feeling that could trip it. Local electrician who does it every day uses the same chart. While i'm not saying your wrong, 7.5 with 80 seems little big, we have air compressor running on 60 for few years now, just going off my eaton/square D breaker slide rule. Single phase 10 hp rated 42 amps running with 6 ga 50 amp breaker 10 hp shows 60 amp breaker and still 8 gauge wire. Breaker shouldn't be used as a switch although many do. Posted 19:59 (#5172189 - in reply to #5172177) Subject: RE: Grain bin wiringĪssuming this is 230 volt 3 phase, The 7.5hp should have 45 amp breaker and 8 gauge THHN wire, you should have a disconnect no question. Stranded wire is much nicer to deal with. And it's going to require larger conduit. I'm not 100% using Romex is legal in that situation. I don't have 10 hp single phase on my slider chart, your probably 3 phase anyway. Single phase 7.5 shows 80 amp breaker and 8 gauge wire. 3/4" should be just fine but 1" will be better, i'd probably use rigid steel pipe conduit Posted 19:55 (#5172177 - in reply to #5171853) Subject: RE: Grain bin wiringĪssuming this is 230 volt 3 phase, The 7.5hp should have 45 amp breaker and 8 gauge THHN wire, you should have a disconnect no question. I would definatlly put a disconnect right next to the door. What size conduit will 6 and 8 fit in? Looking at NM-B since it's cheaper than running single strands Fan has starter switches so will direct wire Probably needs 6 gauge? Probably 20-30 feet from panel. Will 8 gauge hold it with a 40 amp breaker? Should I put a disconnect in or just use breaker in panel. Posted 17:54 (#5171853) Subject: Grain bin wiringħ.5 HP unload/sweep. Grain bin wiring Jump to page : 1 Now viewing page 1
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