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	Subject - Max number of wires in conduit? johnny Though I'm not an electrician, I'm fairly handy with wiring and circuits. I'm doing some volunteer work for my kid's school and installing a dryer circuit so they can... well, dry. ;o) They want to park the dryer next to the hot water heater (for space reasons) and there is 1" metal conduit running from the panel to it (approx. 30ft from the panel). Inside the conduit are 4 wires, two for the 30a hotwater and two for the 20a outlet. My question is... is it OK to put in two more wires for the dryer (of correct AWG, of course), or is there a number or amperage limit to a given size conduit? Thanks! JimmyDee The problem we run into here is the wires have to be derated because there are more than 3 wires in the pipe. You will have to actually have to add 3 wires because the dryer needs a neutral. I think you are approaching a gray area here but there should be enough room for the job. I would recommend running a new 1/2 EMT and pull your #10 wire to do the job. Jim David Hyatt Jim is correct, conduit fill dosen't really play a factor as much as ampacity. What is connected to the 20 amp outlet? Anytime you have more than three current carring conductors in a raceway have to derate ampacity. If the exsisting wires are THHN this helps because of their higher ampacity. Make sure you pull THHN as well. Right now I you have 4wires and will be adding three for a total of seven. Code requires a 70% derate. A 5KW dryer will pull approx. 21amps. #10awg THHN has an ampacity of 40 amps @ 70%=28amps. You should be fine adding these wires. johnny Right, 3 wires... I knew I needed neutral (separate from ground, which I assume is provided by the conduit) but just spaced it. As for running new EMT? I'm lazy and in-experienced with that, so would like to use existing... OK, so de-rating is based on ampacity... that's what I assumed, thank you for the confirmation. I'll check if the current wires are THHN. The 20a circuit looks to be #12awg and I'm guessing (will have to look) that the water heater is #10awg. Nothing currently plugged into the 20a circuit, but occasionally a battery charger (let's assume a 10a car charger). So... as a proposal... - replace the 20 amp ckt with 15 amp breaker and outlet (to derate... or is #12awg sufficient in this scenario?) - pull 3 more THHN #10awg wires (red, black, white) and install 30a breaker I assume #10awg is fine for the water heater since it has standard 4KW elements... Thanks for your help! -Johnny JimmyDee 7 wires = 70% @ adjustment of the ampacity. You can use the higher ampacity in the amp chart for correction purposes. #12, 25 amps .07 x 25 = 17.5 amps. 15 amp breaker will protect but not sure if OK or not. #10, 35 amps, .70 x 35 = 24.5 amps, 4000 watts / 240 volts = 16.6 amps. Looks like #10 wire will work for this. I would say that 3-#8 would be OK for the dryer and will fit in conduit as well. If they were all #8 wire it would go in a 1" inch EMT with one to spare. Jim JimmyDee 7 wires = 70% @ adjustment of the ampacity. You can use the higher ampacity in the amp chart for correction purposes. #12, 25 amps .07 x 25 = 17.5 amps. 15 amp breaker will protect but not sure if OK or not. #10, 35 amps, .70 x 35 = 24.5 amps, 4000 watts / 240 volts = 16.6 amps. Looks like #10 wire will work for this. 3- #10 THHW/THWN wires .70 x 40 = 28 amps. 125% of 21 amps for a continuous load = 26.25 amps. If you can get by the inspector, I would be tempted to do this. OR I would say that 3-#8 (THW) would be OK for the dryer and will fit in conduit as well. If they were all #8 wire it would go in a 1" inch EMT with one to spare. Jim tony thrower If your electrical system is single phase your derating factor will only be 80%. NEC art. 310.15 B 4 says you need not count the neutral for the dryer since it will only carry the unbalanced current. johnny Sweet! 80%? It's 3ph at the panel, but only 1ph for all ckts in the EMT, so I should be able to use the 80% number, yes? Why wouldn't a 15a breaker be ok? My assumption has always been if the downstream is rated higher than the breaker, you're ok. I would replace the outlet with a 15a just to keep people from plugging in 20a devices. Is this a bad assumption? I'll look at THW over THHN and make the decision... I assume #8 THW has a higher capacity than #10 THHN? Might replace the #10 that's there with #8 to be safe (for the water heater). Also, I probably could've looked all this stuff up myself, but... does anyone know a good link for this? I couldn't find one and that's why I posted. And thank you, one and all, for your input. You *all* rock! Thx, -J tony thrower Sorry You must use 70%. 310.15B 4b says in a 3-wire circuit consisting of two phase wires and the neutral of a 4-wire three phase , wye connected system, a common conductor(neutral) carries approximately the same current as the line-to-neutral load currents of the other conductors and shall be counted.