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I will be installing a new electric dryer and plan on updating the 3-prong connection I currently have with a 4-prong connection. Consequently, I will be running new 10/3Romex for the 30 amp circuit. From the panel itself I plan on on using 10 guage THHN to run inside PVC 40 for a 36 inch run outside the panel up into the soffit. From there, I will install a junction box to transition from THHN to 10-3 Romex, then off to the new 4-prong dryer receptacle. Just wanted to make sure transitioning in this manner would meet code.

More impoprtantly, the dryer receptacle is located approx 40 feet from the outside panel box. On this long of a run should I use larger wire, such as 8/3 Romex instead of 10/3? Or will 10/3 be sufficient? And if using 8/3 instead, would I still use the typical dryer cord that comes with the washer?

Thanks for anyone's help.
 

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40 feet is not a long run. 10/3 will be fine.
As long as the junction box remains accessible and has a cover you will be fine.
 

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Thanks for the quick feedback, appreciate it. I sort of figured that kind of transition is probably very common, just wanted to be sure.
 

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The panel is on the outside of the house. Normal NM-b cable is not rated for outside use.
 

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Didn't realize the main panel is outside. Thhn is not approved in wet location. Use THHW. J box must be accessable.
 

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If you are shopping at a big box, ask for THHN. The help is liable to tell you they don’t carry THWN.
I agree with you on this. Had this experience until I figured it out myself. The guy said they only carry THHN rolls of wire and handed it to me to show me. Yup, only said THHN on the outter packaging. But then I looked closely on the insulation on the wire and it did in deed say THHN/THWN - taught that guy something new that day. I won't mention the big box store name though.
 
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