Over Current and Wire Size Calculations.

[zach_zachary1@yahoo.com]

I am installing two autoclaves in a lab. It takes 208v 3ph power and has a full load amp rating of 26 amps. It runs for less then 3 hours so it is a non continous load. Using 210.20 I specked a 30 amp breaker. According to 310.15(B)16 10 AWG wire is rated at 40 amps if I use THHN rated at 90 *C . I am going to have 6 conductors together because I installing two autoclaves. Using table 310.15(B)(3)(a) I down grade the amps on 10 AWG by 20%. 40 amps x 80% = 32 amps. I am going to use 1" RMC aluminium. Using Chapter 9 table 1, I can fill the conduit to 40%. I will be pulling 8 wires. 6 conductors and 2 grounds. According to my calculations I will only fill the conduit to 21%.

Does this look good to everyone?

Thanks!

 

[david luchini]

I am installing two autoclaves in a lab. It takes 208v 3ph power and has a full load amp rating of 26 amps. It runs for less then 3 hours so it is a non continous load. Using 210.20 I specked a 30 amp breaker. According to 310.15(B)16 10 AWG wire is rated at 40 amps if I use THHN rated at 90 *C . I am going to have 6 conductors together because I installing two autoclaves. Using table 310.15(B)(3)(a) I down grade the amps on 10 AWG by 20%. 40 amps x 80% = 32 amps. I am going to use 1" RMC aluminium. Using Chapter 9 table 1, I can fill the conduit to 40%. I will be pulling 8 wires. 6 conductors and 2 grounds. According to my calculations I will only fill the conduit to 21%.

Does this look good to everyone?

Thanks!

Looks fine. You could use #10 THWN (75C) if you wanted and it would still be fine. 35*0.8 = 28.

I get 19% fill, rather than 21%...#10 THHN = 0.0211 in²,1" RMC = 0.887 in²... (8*0.0211 / 0.887) = 19%.

 

[JoeStillman]

Why two ground wires?

 

[zach_zachary1@yahoo.com]

I am pulling everything through one 1" conduit to a 4 11/16 junction. Then I will use ? flex steel conduit to wire in two seperate receptacles. I guess I could just pull one ground and splice it in the junction box.

 

[JoeStillman]

I am pulling everything through one 1" conduit to a 4 11/16 junction. Then I will use ? flex steel conduit to wire in two seperate receptacles. I guess I could just pull one ground and splice it in the junction box.

That's what I would do.

 

[Dennis Alwon]

I am pulling everything through one 1" conduit to a 4 11/16 junction. Then I will use ? flex steel conduit to wire in two seperate receptacles. I guess I could just pull one ground and splice it in the junction box.

Or use the conduit as a equipment grounding conductor.

 

[petersonra]

why the aluminum rmc?

 

[zach_zachary1@yahoo.com]

I am adding a branch circuit to an existing panel board. All other branch circuits use aluminium RMC.

 

[lielec11]

Why be cheap and share a ground? Buy out the separate grounds and let the contractor make the decision in the field.

 

[ActionDave]

Why be cheap and share a ground? Buy out the separate grounds and let the contractor make the decision in the field.

Why use two wires to do the exact same thing one would do?

 

[ActionDave]

Or use the conduit as a equipment grounding conductor.

That's what I would do.

 

[JoeStillman]

Laboratorys usually require good power quality and maximum safety. I would use one ground wire spliced in the 1st 1900 box instead of the conduit. The rigid aluminum threaded conduit will be an excellent grounding conductor by itself, but the weak link is wherever it connects to a sheet metal box. Ground bushings will help, by why bother with them when you can just pull a copper ground wire?