Connect electric cable with 4 wires to 3-prong 30 Amp 125-Volt/250-Volt outlet?

Question

I purchased a 3-prong outlet for my dryer. The cable coming out of the breaker box has 4 wires (white, red, black, bare).

I was looking at a youtube tutorial, and it says to connect the white wire to the terminal of the outlet marked white, and the red and black to the other two terminals. The outlet has 3 terminals.

Then he says to leave the ground wire just behind the outlet. In other words, it's hanging not doing anything. But he cautions that it shouldn't be able to touch the outlet. Is this correct?

How is this grounded? My outlet box is metal, not plastic like in the video.

Some additional info related to the comments: I bought this GE washer/dryer combo about 8 years ago from Sears. The dryer came with the 3-wire prong. The installers did not change the cable in the dryer. The 3-wire prong was installed because the dryer came with a 3-wire prong.

Also, another question related to the comments: the dryer came with the 3-wire prong. This means that the dryer only has 3 cables as well. Assuming I change the cord to a 4-wire prong, where am I supposed to connect the neutral inside the dryer?

Answer 1

This is an obsolete, dangerous, configuration, which gets perpetuated as follows:

• Original 3-wire receptacle without ground (e.g., 1960s or earlier)
• Code changed to require new circuits to use 4-wire receptacles, but grandfathered existing 3-wire receptacles
• New dryer (because most people don't have a 50+ year-old dryer) is delivered and installers, since they are not electricians, install a 3-wire cord/plug to match the existing receptacle
• Dryer is moved to a different house and/or sold to someone to use in a different house
• Since the dryer already has a 3-wire cord/plug, new owner installs a 3-wire receptacle even though they have been obsolete for decades, and sometimes even if they already have a 4-wire receptacle - even though replacing the cord/plug is easier than replacing the receptacle

Any dryer made in the last few decades can be easily connected with a 3-wire (without ground) or 4-wire (with ground) cord/plug. To resolve this problem:

• Reinstall the 4-wire receptacle (if there was one before) or install a new one (NEMA 14-30)
• Since you have a metal box, the bare ground wire connects to the box. Some receptacles will ground automatically to the metal box, but if the instructions do not say "self-grounding" or give any other indication that they ground automatically to the metal box, add a bare wire from the receptacle ground screw to the metal box.
• Return the 3-wire receptacle or, if it is not returnable or you don't want to bother returning it, toss it in the trash. But don't put it out as a giveaway, because nobody else should be using it either (except perhaps in the very limited situation of replacing a broken 10-30 where there is no practical ground path, but that is actually quite rare).
• Replace the 3-wire cord/plug on the dryer with a 4-wire cord/plug.
• Remove the neutral/ground bond (typically one wire/screw) from the dryer. To verify, check continuity from the prongs on the plug to make sure ground is not connected to neutral.

Answer 2

Don't change the dryer socket. Change the dryer cord. They are designed to be easy to change and the dryer instructions (google the model number) or the labeling will show what to do with the ground strap.

It is illegal to install that socket and has been since 1965 for everything but dryers (1996 for those). That socket does not have a ground, and that's obviously dangerous.

Answer 3

The dryer came with the 3-wire prong

If that's true, whoever sold it to you was criminally negligent. Three-wire dryer connections have been obsolete and wrong for many, many years. These days (and for many years), everyone should be using four-wire dryer connections for everything. There is a narrow, narrow backwards-compatibility "grandfathering" exception, but I don't believe it applies to you, and even if it does apply it is (IMO) such a bad idea that you should not be using it anyway.

Then he says to leave the ground wire just behind the outlet. In other words, it's hanging not doing anything. Is this correct?

It is blatantly incorrect for your case.

The fundamental rule in safe, modern electrical systems is that every piece of metal that does not carry current should be grounded. You said you have a metal box, so: the ground wire must be, at least, connected to the box. But also: the metal frame of the dryer must be grounded, too, and this is precisely why you need a proper four-prong grounded outlet and a grounded, four-wire cord.

the dryer came with the 3-wire prong. This means that the dryer only has 3 cables as well. Assuming I change the cord to a 4-wire prong, where am I supposed to connect the neutral inside the dryer?

The dryer instructions explain this. The dryer has four connections internally, so connecting a four-wire cable is perfectly straightforward. There's a kludge (likely involving a temporary jumper) for connecting a three-wire cable. You do not want to use this kludge. Manassehkatz's answer has more on this, as does this other question.

What I don't seem to understand is why Home Depot sells these 3-prong outlets and the 3-wire dryer cords.

Two reasons:

1. For the narrow, narrow backwards-compatibility "grandfathering" exception I mentioned.

2. So that stupid people can do stupid and dangerous things.

As I said, I believe the grandfathering exception does not apply to you (and in my opinion you should not make use of it even if it does apply). And, needless to say, I think we both agree you don't want to be one of the stupid people in #2!

Answer 4

As others have said, you should replace the cord from a 3-prong to a 4-prong. Using a 4-prong receptacle is required for new installations and is safer. If you've got the 4 wires coming into the box, use them all.

Assuming I change the cord to a 4-wire prong, where am I supposed to connect the neutral inside the dryer?

Look up your dryer's installation manual; instructions to connect 3-wire and 4-wire cords should be there. For example, here's an instruction manual from a 2005ish Sears dryer model that shows how to connect a 4-wire plug:

Note that this is from a dryer that is almost 10 years older than yours. Yours may have 4 slightly different connection points, but you'll have to check it yourself and see what the manual recommends. Either way, dryers have had support for 4-prong cords since well before you bought this one.

Answer 5

There was this comment under another answer

If they're illegal, then why does Home Depot sell these outlets? And why does Home Depot also sell the 3-wire dryer cord?

I have a house built in 1975. They ran aluminum 6-gauge three-line cable to the receptacle. If the receptacle breaks, I need some way to replace it in a way that does not imply it is grounded. This is why you can still buy NEMA 10-30R receptacles and plugs. It's also why no new electric dryers come with the plug attached. The cost of replacing that cable would be pretty steep.

As mentioned by the other answers, if you have 4-line cable you really should be using a 14-30 outlet and plug, which affords you ground so you reduce the chances of electrical shock.