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The 10/2 line as both the black and white wires hot. From what I can see that's "okay" but better to have a 10/3 line with white being the neutral. I'm not having any trouble with it and I'm not planning on upgrading my dryer at this time but may in the future.

Should I take this opportunity (with the wall busted open) to rerun a 10/3 line incase I need it in the future?

Or will the 10/2 line fit my needs and I'm overthinking this?

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  • Aside: "while the wall is open" <-- yes, take the opportunity to do whatever you reasonably can even if its not mandatory. That includes running ethernet cable, more power points, or even adding sound insulation on interior walls.
    – Criggie
    Commented Oct 26 at 4:10

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Dryers are entirely 120V machines except for the heating element (for parts commonality with gas dryers). The neutral wire handles real live no-kidding working current - 100% of the dryer's draw on "fluff/no heat" setting is on the neutral. Most of us look at the 3rd wire as a lazy hanger-on that does no work (except during a ground fault)... but not neutral on a dryer! It's a no-kidding for-real working conductor on a dryer.

Why do we insulate neutral (generally) if it's near 0 volts when everything is working properly? Because if neutral gets loose (a commonplace occurrence that should not make anything dangerous) it energizes the neutral on the field side of the break. Worse, 3-wire dryers "ground" to neutral, so dryer chassis gets energized too and that's why 3-wire dryer runs were outlawed in 1996.

The 10/2 line as both the black and white wires hot. From what I can see that's "okay"

No. It was never OK. It was illegal the day it was installed, even if prior to 1996. Even prior to 1965 when grounding was not generally required.

The GROUND in 10/2+ground NM cable was never designed to be a neutral. It lacks the necessary insulation and thermal design, and in older NM it is undersized.

Prior to 1996, 3-wire connections were allowed, but only with cable with a certified neutral (but not a ground). Specifically

  • "/3 no-ground" type NM/Romex cable, which largely went extinct after 1965 when everything but dryers and ranges needed grounding.
  • Service Entrance cable type SE-U with a bare mesh neutral (and extra thick insulation to support that). Service entrances don't have ground because they run between the overhead utility supply wire and the meter, and ground isn't established yet. However utilities stopped offering services smaller than 60-100 amps, so 30 amp SEU has no reason to exist.

If you're thinking "Wow, when this rule was written in 1965, NEC deliberately allowed only cable types they knew were going extinct". EXACTLY! The plan was to sunset the 3-prong dryer connections as supplies of legal cable dried up. Once the only cable available was 10/3+ground, everyone would switch to 4-prong dryer outlets.

Of course, as those legal cable types dried up, some went "hey I'll just use /2+ground!" A lot of inspectors shrugged. This idea became a meme, but it's still a code violation.

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  • Incidentally, I'm certain it's safer if you have a 3 prong dryer to plug it into a 3 prong outlet than it is to jury-rig a 3-4 conversion cable to plug it into a 4 prong outlet. But these days not running all four wires to the box is a bad idea.
    – Joshua
    Commented Oct 26 at 3:59
  • @Joshua In a contest of "bad vs bad", I'll take "good". Dryers (and ranges) are easily swapped between 3-prong and 4-prong by changing a $12 cable. The instructions (and often labeling) explain how to handle the ground jumper.
    – Harper - Reinstate Monica
    Commented Nov 5 at 4:02
  • I encountered one that wasn't. On disassembling it for disposal we found it only had three screwdown points and a four prong cable would have had to leave one screw connector dangling or creating a bootleg ground or neutral. Anyway, good riddance. It was starting to go and eating away at itself.
    – Joshua
    Commented Nov 5 at 4:10
  • It's normal for dryers to have 3 prominent terminals. The ground terminal is off on the side in this weird place. That is so if the cable is yanked out, hots and neutral break before ground does.
    – Harper - Reinstate Monica
    Commented Nov 5 at 4:14
  • If I knew I was going to be in this debate years later I would have gotten my ohmmeter out and checked what I thought I saw; the neutral screwdown bonded directly to the outer metal chassis.
    – Joshua
    Commented Nov 5 at 4:17
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Yes to replacing with a 10/3 cable(plus ground).

What you have now is two hots and a neutral with no separate ground.

Usually known as the old nema 10 type receptacle/plug which was ban in 96 for killing people when stuff went wrong.

It is grandfathered in(if done in code at the time it was installed), so you could keep on using it(need to rip up half the house to replace), but highly recommended to use the safer nema 14-30 receptacles/plugs.

Most dryers are just needing a simple screw to undo to separate the dryer ground from neutral connection to use the safer 10/3 circuit.

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  • 3
    “It is grandfathered” No. You don’t know that for sure. It might be, if it was done with the right type of wire at a time when code allowed it. There is plenty of work out in the wild that absolutely was not done according to code at the time.
    – nobody
    Commented Oct 24 at 14:04
  • @nobody You are right. I have edited the answer to make it a bit more clearer.
    – crip659
    Commented Oct 24 at 14:49
  • "During a renovation" makes it hard to know if it is grandfathered. If the renovation is significant, there may be no grandfathering allowed. If it is minor, it's unlikely a homeowner would be held to the standard of @nobody's comment above, even if it's technically accurate. If it was once allowed and is otherwise to code, you cannot usually tell what the exact sequence of events was and usually nobody tries. But ... "Yes" is the right answer. :)
    – jay613
    Commented Oct 24 at 18:36

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