I have an old house where some aluminum Branch wiring was used. On the oven, water heater and dryer. There is an 8 gauge aluminum wire for the dryer on 30 amp double pole breaker. I already bought and installed 10/2 solid copper Romex wire. Home Depot was sold out of 10/3. When I got home my receptacle and plug are both on a three-prong so it worked out. But should I have an extra hot anyways and switch out the receptacle also? My number one concern is fire safety with my family. Will I be okay?
The #1 threat to your family is the 3-wire connections to range and dryer.
This wiring method was allowed due to intense lobbying by the appliance industry. But what those connections do is BOOTLEG ground off the neutral wire. It was always illegal everywhere else, but this was delayed until 1996 for dryers and ranges due to their lobbying.
The problem with bootlegging ground off neutral is if the neutral wire gets loose anywhere, even just a socket pin, then it becomes a 100% certainty that the chassis of the appliance will be energized at 120V. Touch it and anything grounded (like the washer, or a sink, or another 3-prong appliance) and BLAMMO.
You must admit this is a "freshman" attempt at improving safety, which is under-supported by good research. You're on the right road though.
Oh... and next time, deal with a real electrical supply house. Home Depot is a terrible place to buy almost anything. Their selection is limited, their stocking is terrible, and their prices are ridiculous. (they once bothered to undercut other businesses, but now that you're convinced they're the best deal in town, they stopped undercutting and are just rooking you. CostCo is doing the same thing BTW.) As things were, since they were out of 10/3 it would've been wiser to go to 8/3 (you're always allowed to upsize).
Anyway, replace both the dryer's cord and the receptacle with NEMA 14-30 type, and also remove the bonding strap on the dryer, which is responsible for bootlegging ground. Very important, that!
The heavy aluminum wire is fine, but...
Obviously you've found some articles on the Internet that rips up aluminum wire. There's validity to those, as regards small 15-20A branch circuits such as to lights and receptacles, but it wasn't aluminum's fault. Aluminum lugs happily take any wire (that's why your panel uses them) but copper lugs do not like aluminum wire. In the 1960s in response to a copper shortage, they hastily approved for alumiunum use a bunch of outlets and switches previously designed for only copper. Those copper lugs refused to play well with the aluminum wire, and there were serious problems at the terminations. Also the installers were poorly educated on use of aluminum wire.
Mind you, heavy aluminum feeders have never been a problem.
Since then, every single thing about aluminum has been changed. A new wire alloy was made specifically for branch circuit wiring, called AA-8000. (the old AA-1350 alloy was straight up power-line aluminum, yes, the power lines are aluminum). The approvals were canceled and a new standard - CO-ALR (R for Revised) - now applies to switches and receps.
Now, your #8 feeders to dryer and water heater were wobblers: at #8 they are in the gray zone between the worrisome "#10-12 small branch circuit wiring" and "#6 and larger reliable heavy feeder". I would treat them as feeder; make sure they are terminated properly, then don't worry about it.
For the water heater, my recommendation is to double-check the connections to the Al wire at both ends - make sure they are on Al-Cu breakers (which were not affected by the CO-ALR standard change)... and on the other end, go into a modern approved terminal that is CO-ALR. If it's not, no big deal -- just pigtail it with copper, then use an approved aluminum splice. For mortals, that means an Alumiconn (#14-10), MAC Block (#14-#6), or Polaris splice (#4 and larger). As long as the connections are clean and torqued to spec, I wouldn't worry about it.
Use a torque wrench to tighten the screws. Very important. Most splice failures trace back to improper torque, and even electricians get torques right only 25% of the time (and that presumes +/-20% tolerance, which is pure luck, so basically nobody has a calibrated arm.)
Of course with the water heater, you now have that 10/2 cable you improperly used for the dryer. That has to come out. If you take it up carefully, you can reuse it for the water heater, as 10/2 is legal there (re-mark the white wire to be a hot wire; water heaters don't need neutral).
For the dryer and range, the deal-killer is the 3-wire connection. So we definitely will replace the dryer's cord and receptacle with a 4-prong NEMA 14-30 type, and rewire the range as appropriate. This includes removing the neutral-ground bootleg jumper from both range and dryer. What wire do we use? It's legal to retrofit a ground wire, so you could continue the old aluminum 3-wire in service (as I advise on the water heater), IF:
- The cable was a legal type at the time it was installed, meaning either a) an insulated white neutral, or b) SE cable (neutral webbed around the hots). AND
- The socket is CO-ALR rated, or, you pigtail with MAC Blocks.
However given that you already know the drill, and the cost of Cu 10/3 is not extreme, you might just replace it with that. Remove the 10/2 carefully and use it for the water heater.
You cannot retrofit a neutral or second hot wire, nor can you retrofit on stuff you just installed... so the 10/2 has to go.
Nope. You'll need to pull this out and replace with the correct cable (or wires in conduit.)
The correct cable does NOT "give you an extra hot" - the cable you had gave you two hots and a neutral and NO ground. The cable you have now installed gives you two hots, a neutral illegally running on the bare grounding conductor, and NO Ground. You can't add a ground to it (which you could have done for the old cable) because you can't run neutral on a bare or green wire, and you can't add a neutral wire separate from the cable (which you can do when retrofitting a ground to an old ungrounded cable.)
You need 10/3 cable (4 wires, ground is not counted in cable designations) or you need 3 wires in metallic conduit (acting as the ground), or 4 wires in non-metallic (or flexible metal) conduit, a 4 prong dryer plug, and a correctly wired to your dryer 4 prong dryer cord. "What you had" lost its grandfathered (54 year old...? I think Harper said 1966 for that code change) legality when you opted to replace it - the replacement needs to meet current standards/code.
As an aside - if fire safety is your main concern, 10/3 MC or AC cable (flexible metal armor) would be a definite upgrade from NM, without the need to learn to bend conduit, if you find that daunting.
Home Depot was sold out of 10/3. When I got home my receptacle and plug are both on a three-prong so it worked out.
It did not work out
The third prong on a dryer cable is neutral, not ground. Your dryer is wired incorrectly even by old NEC standards using the (bare) ground conductor as neutral. One could brainstorm a lot of reasons why this is a very bad idea, but it is kind of aside from the point.
If you are worried about fire safety get the right cable and install it to NEC specification.
I would personally not allow anyone to use the dryer until this was fixed.
Since you have removed the original cable I think you are required by code to install a cable with three insulated conductors plus ground.
If you already have 10/3 copper without ground installed, you MIGHT be allowed to establish a separate ground, but either way you must change the receptacle to accept a 4-prong dryer plug, then get a new cord and connect it properly to the dryer.