Using 10/3 wiring vs 2x 10/2

[JoshHellcat]

First off, thanks to everyone for the massive wealth of information on this site. I have been piecing together my electric brewery and had a question for you electricity experts.
I need to make a 25ft run from my dryer outlet to the spa panel I am using for gfci. The wire will all be mounted in place, most likely in conduit so It looks nice, with a plug on the end so I can unplug the dryer and and use that plug on brew day. I have a ton of left over 10/2 for another project. Can I run 2 strands of 10/2 and wire it like 10/3? Obviously I would mark the improperly colored strand to avoid confusion. Should I do anything with the 4th strand?
Thanks for the help.

 

[BrunDog]

Any wiring that is plugged in should technically be portable cord. Conduit is used to run single wires safely, but that is lost and off code when it exits the conduit to a plug/user service. So, yes, you can use 2 x 10/2 and it will work, though won't be code. You should never, however, use two smaller wires to carry the current of a single larger one. I don't think this is what you mean, but just in case. For example, don't use 2x10AWG wires to carry 50A in place of a single 6AWG wire. That is not safe, as one wire d/c will overload the other wire rather than an open circuit.

-BD

 

[JoshHellcat]

I didn't think about the open plug not being code. What if the conduit terminated into a box, then a flexible dryer cord going from the box to the outlet?
and yes, I would be using all 10ga lines independently to run a 30a max load. Thanks!

 

[Onkel_Udo]

I didn't think about the open plug not being code. What if the conduit terminated into a box, then a flexible dryer cord going from the box to the outlet?

Totally valid method but will likely still have some inspections challenges. Is there not a second knock-out in the dryer plug box that you can connect your conduit into? That way you can just hard wire everything and use the dryer or brewing receptacle/spa panel at will.

 

[Dert]

You cannot run Romex in conduit.

You could de-sheath it if the internal wires are THHN or similarly rated for the conduit, but I bet they are not.

 

[Onkel_Udo]

You cannot run Romex in conduit.

You could de-sheath it if the internal wires are THHN or similarly rated for the conduit, but I bet they are not.

This is untrue as NEC 334.15 Exposed Work covers protection from physical damage and calls out situations where it is acceptable. I believe 300.5 excludes it in wet conditions but I am too lazy to look that one up.

You usually drop your fill rate and have to find the tables for elliptical cable and in most situations you are de-rated from 90C to 60C which is about all of use are running anyway in residential.

Your LOCAL modifications to the NEC may exclude it.

De-sheathing 90% of the NM-B sold renders is non-code compliant because the individual conductors are not stamped, only the outer sheath.

 

[BrunDog]

Yes on the termination into a box, but Onkel makes the best point of terminating into the dryer outlet box if there is room and you can manage the drywall work.

You can run short lengths of romex into conduit for protection, say from ceiling to outlet. But behind walls etc it's a no-no as is unsheathing.

-BD