What can you do to connect an old dryer with 3 wires to a new house 4 wire outlet?

Answer 1

Answer for USA, Canada and countries running a 60 Hz supply service.No matter whether they are connected though a 3-prong or a 4-prong outlet, all dryers should have ground wires.

With a 3-prong set-up, a 240V appliance uses both legs A and B (also known as the "red" and "black" hots) to connect to 240 volts for the main heating elements and/or motors, plus a ground.

The newer 4-prong set-up is the same plus a separate NEUTRAL. The neutral was added to be able to utilize 120 volts for the dryer's smaller components. (Time-of-day clock, programmer, dial illumination lights, etc.)

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The 4-wire outlet has a separate connection ifor the neutral wire but the old dryer's 3-prong plug does not, it only has a safety ground wire that is also used as the neutral for any 120V devices such as time-of-day clocks, programmers, lights, etc.

3-wire outlets are old and outdated.

Way back in the old days, when only 2-wire connections were used, they didn't ground equipment via the socket outlet. (Remember the old 2-wire 110V outlets on houses built before the 50s?) A few people got killed so they decided to add a safety grounding wire and connection using a 3-prong plug. It took them longer to catch on with heavy appliances, but eventually they did.

Nowadays there is a 4th pin that is used to connect a neutral wire separately to the grounding wire. Since many homes still have the older 3-wire outlet, it is allowed in older homes. New homes must use the new 4-wire outlet.

Changing your 4-wire cord to a 3-wire cord is similar to plugging a 3-wire 120V appliance into one of those 3-prong to 2-prong plug adapters: your appliance works but it may be unsafe to use without being properly grounded. Anyway it does not have the separate neutral which you get in a 4-prong outlet.

Don't listen to anyone who says to replace the new up-to-code outlet with an older outlet with only 3 connections. That is the same as replacing your 3-prong 120V outlets with old fashioned 2-prong outlets! Ignore anyone who tells you to do so, they think they know a lot more than they actually do. Buy a new cord. It is cheap and safer.

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The best advice anyone can give you is that you must purchase a new 4-wire appliance cord for your dryer - with a plug that matches your outlet - and connect this correctly to your dryer. The new 4-wire cord should come with full wiring instructions.

This may sound like a lot of work, but it has to be done in the right way for the installation to be safe.

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Although configuration of the plugs are not universal, NEMA has a huge listing of plugs and receptacles. Once you know which one you need, all you have to do is rewire it: the old dryer outlet in your last home didn't have have a separate safety ground (bare or green wire, which only carries current in a fault situation). The new outlet does.

So, to operate the dryer safely without risk of electrical hazard:

1) You MUST disconnect any existing copper wire or metal strap linking the dryer's neutral connection terminal to the frame of the dryer,

and then:

2) You MUST obtain a new 4-wire appliance cord and connect it correctly, including the safety ground wire - which either has green insulation or is bare copper - to the frame of the dryer.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.

Answer 2

If you're using 10/3, then you may as well use a 4-wiredryer receptacle, provided that your dryer is rated for 30 Amps. The NEC in America actually requires this now.