I bought a new electric dryer, I have a 4 wire cord that I like to use from an older dryer that was never used. I even have a 4 prong outlet that I got on sale. But I have a 3 wire outlet currently installed and inside there are only 3 wires, 2 reds and a white....thicker wires than I am used to.

The guy at the store told me I have to remove the "bonding strip" for it to be safe.

What is the purpose of the ground on this 4 wire cord and this bonding strip? Is there any voltage on this wire and in what type of fault would there be?

And how do you wire up a new 4 wire outlet, including remval of this bond strip, the strip length for the wires and how tight should the screws be?

 

The guy at the store is confused and ill informed. You can not install a 4-wire receptacle on your wiring unless it is in continuous metal conduit from the receptacle box to the breaker box. If it is not metal conduit you need to either replace the cable with four wire cable or use a 3 prong receptacle and leave the bonding strap in place on the dryer.What size breaker?Not with your current wiring.It provides a ground that is independent of the neutral. You have a combined neutral ground (unless metal conduit) so you can't use an isolated ground wire.The bonding strap is use on 3-wire circuits such as you have and should be left in place.

 

to add... I have metal box and pipe between the fuse panel and the outlet. Its on a 30 amp circuit.

Original questions remain, perhaps they are easyier to answer with that information.

 

When you have rigid (not spiral) metal conduit all the way from the metal outlet box for the receptacle to the panel with the 3 conductors inside then that may be the equipment grounding conductor. The "ground" contact of the new 4 prong receptacle is connected to the box (using a short #10 bare or green wire). Rgw The ground contact screw may be an inch away on the frame (yoke) of the receptacle unit. Note that this short wire may not share a screw with something else attached to the box such as a box clamp.

The 30 amp breaker requires at least 10 gauge wires for that branch circuit.

It is impossible to describe how tight to make the screws using fewer than 25 words unless numbers are used, and numbers are not useful unless you have a screwdriver with a torque dial readout. I say tighten them with reasonable force but not with all our might and main for fear of stripping the threads.

 

Upon further inspection, there is a bare wire in the box with the 3 large wires. What do I do with this bare wire in regards to my new outlet and cord?

 

Look for a label or stamping on the receptacle showing the recommended torque for the screws in inch-pounds.

 

The bare wire* is pigtailed to the box and receptacle. The cord is not relevant to connections in the box except the wiring in the box determines the type of cord used.

*Assumes bare wire is a ground wire connected at the breaker box.

 

what exactly is the difference between a 4 wire or 3 wire dryer? From a safety standpoint I guess. Why is one considered better/safer than the other?

 

The neutral and ground are not connected together on a 4 wire dryer. If 3-wire ground and neutral are connected and that puts the neutral current on every grounded metal cased appliance you have. While a ground such as a metal faucet on a metal water pipe should be 0 volts relative to neutral sometimes it isn't. That means if you touch a ground such as a metal faucet while touching the metal casing of an appliances you could end up as a path for the neutral current. Example reach for refrigerator, or stove, or dishwasher while touching the sink and you get a shock maybe a tingle or or, to quote Fred Sanford, "The big one".

 

The purpose of the Grounding Conductor in the four-wire appliance cord is to avoid relying on the Grounded Circuit Conductor ( Neutral , White insulated Conductor) for setting the metallic frame of the dryer at " Ground Zero" potential, and as a path for a "Fault-Current" should the dryer frame be "energized" by contact with one of the two "live" Un-grounded Circuit Conductors.

A "Circuit Conductor" is a "current" Conductor that connects the internal wiring of the appliance to the "power-source". A "Grounding Conductor" connects the metallic surfaces of whatever is connected to the power-source to the "Main" Grounding Conductor at the Service location.

At one time the Neutral Conductor of a appliance circuit was both a Circuit Conductor and a Grounding Conductor , but now Current / Grounding Conductors are separate Conductors.

 

So is that is the only fault scenario where that ground is used on a dryer?

I assume that means if you were using a 3 wire, if you disconnected the neutral of the cord then the return would then be the ground wire or the metal pipes for that matter. Where as with the 4 wire, if you disconnect the neutral, the 120 portion of the dryer (lights, motor) just wouldn't work. But the heating element would?

How do you test metal pipes to see if there is voltage or current on them?

 

The Grounding Conductor as a possible "current" conductor emphasizes why it's important that at the connection-point where the Neutral Conductor connects to the internal wiring of the dryer, the Neutral Conductor not be "Bonded" to the metallic frame when using a 4-wire line-cord.

 

If there were current on the conduit the breaker should trip. The conduit should be grounded.