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Electrical Wiring

Upgrade 3 prong to 4-prong dryer receptacle question

16 years ago

We have purchased a new dryer that has a 4 prong cord. Our current receptacle is the older 3 prong. I have been told to purchase a nema 10-40 to replace my 10-30. I have black, red and white wires and what looks to be a bare copper wire (ground?)not connected to the receptacle but to the back of the box. Is this considered the 4th wire and shouldn't it be green? Can I install this new receptacle or do I need a new run from the panel? Thanks

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Comments (8)

normel
16 years ago
The ground may be green or bare. If you have all four wires at the receptacle, you can connect the new 4prong receptacle without having to run new wire.
radioguy4ever
16 years ago
smh12, the wiring you have is correct, but you will most likely have to change the receptacle itself to one that accepts a 4 prong cord. the wiring instructions with the new receptacle will show you what wires go where.
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While dryers and ranges have typically been 120/240 V loads there is a long standing exception allowing the use of 3-wire circuits. The exception still allows the use of the older 3-wire circuits and almost all ranges and dryers come with instructions for either installation. The change to the exception is that it is now strictly a 'grandfather' exception. All new circuits must be 4-wire, and if any changes are made to a 3-wire circuit it must be changed to 4-wire. Many ranges and dryers do not even come with a cord attached, but one is purchased to match the circuit in the house the unit will be installed in. The difference in the equipment is usually the removal of a bonding screw between the neutral terminal and the chassis. A 3-wire installation bonds the neutral to the chassis for safety, while a 4-wire uses the ground in the circuit to ground the chassis. The wire resistance is low enough that having a neutral grounded chassis for the small 120 V loads (motor and timer typically) does not produce enough voltage drop in the wiring to be detected by people (the chassis has a voltage equal to the voltage drop in the neutral leg present).
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Our house is from the same era. GFCI might not fit in the box if it is a steel box, they tend to be too small. A GFCI breaker would work or add another outlet for the GFCI at the beginning of the run, right where it comes from the main panel if that is possible. Probably no grounds unless the electric has been upgraded. You likely have 220 service. Check the overhead wires where they attach to the building and count the wires where the POCO connects to your wiring. There should be three, one neutral and two hot. Also, if you have an electric stove, water heater or dryer you have 220. If you are comfortable with electricity, take the cover off the main panel and count the main cable wires, usually at the top of the panel. Two hots and a neutral would be 220.
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@Ron Natalie, I'm trying to understand what you're so upset and shouting about. First of all, @barnaclebob didn't reply "four years late": I posted my question yesterday asking for his experience since his original post, and he answered it promptly the same day. Secondly, I don't understand why it's OK to bond ground to neutral at the chassis (for a 3-wire installation), but somehow more dangerous to do it 1 foot further away (at the outlet) for a 4-wire cord. Yes, of course it's better to separate ground and neutral, but code allows bridging them for existing 3-wire installations. In my case running a new 4-wire cable would be very difficult, so I'm considering this low-risk workaround, at least for the short term. If there's a real and imminent danger to doing this then it'd be great if you could let me know what it is - I certainly don't want to burn the house down - but please keep the sarcasm in your pocket.
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smh12
Original Author
16 years ago
Is it normal for a home built in 1995 to have a bare copper wire in the back of the box instead of a green wire?
radioguy4ever
16 years ago
smh, yes it is. the bare copper comes from inside the "romex" wiring of the home. most likely, when the dryer was installed it was a 3 prong, but the builder knew enough to make sure it could be "upgraded" later on ny running the 3 wire + ground setup.
smh12
Original Author
16 years ago
ok, new 4 prong receptacle is installed. Now I guess I need a new box/faceplate in/on the wall...the new 4 prong won't quite fit. Is there any certain kind I need? Is it better to use metal vs plastic? Can you tell I've never done this before...
bigbird_1
16 years ago
"ok, new 4 prong receptacle is installed. "
Did you wire the new receptacle without seeing if it will attach to the old box?

Use a square 4 11/16" box, designed specifically for dryer/stove receptacles. We mostly use metal boxes in Canada. Plastic boxes are much more expensive here.
The receptacle is the "faceplate" as you call it.
cobraguy
16 years ago
smh..are you saying the new 4 prong receptacle is installed in the box and the existing faceplate won't fit?
smh12
Original Author
16 years ago
cobraguy- I guess "installed" was the wrong word. The new receptacle is wired and hanging out of the current, too small, box (power off at main). I didn't even think about seeing if I needed a new box...it looked like it would fit the same as the old. I guess I was wrong. I now have a new square metal box to install and still need to get a faceplate for the outside.

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