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I've bought an appliance power cord for my dishwasher, however, unlike this cable:

enter image description here

(my car was parked)

only the green (ground) cable is colored.

Does this mean that when I connect the cord to the appliance, the black and white wires are in fact interchangeable?

Is this because it is AC?

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1  
Make sure you're using a cord approved for this use. The conductors have to be the appropriate size for the load. –  Tester101 May 12 at 10:50
    
Honestly, ignore the old cable and use the either the wires you will connect the cord to or the screw terminals as your guide. If the old cable was wire capped to a set of wires, then you should see black, white & green inside the wiring box of the dishwasher. Wire to like colors. If there are terminals, then they should be marked. If you have questions about which wire goes where, take a picture of the terminal posts and post it. I'm sure someone will then tell you where black, white & green goes. –  diceless May 13 at 4:55
    
@diceless - If you read the question, the new cord has NO color coding except for the ground wire. –  Fiasco Labs May 14 at 0:24
    
@Fiasco, You're right, my bad. –  diceless May 14 at 16:26

1 Answer 1

up vote 4 down vote accepted

Look for another identifier besides color such as a stripe or rib on one of the two other wires. That will be the Neutral wire. Make sure it connects to the Wide blade on the plug.

Is this because it is AC? No, if it isn't so identified, you are dealing with a cheap knockoff pigtail that probably belongs in the waste bin. In the 120V single phase world, Neutral is effectively at ground potential, therefore if you touch it, you shouldn't get shocked. Hot while alternating isn't at ground potential and so the voltage is alternating between +120V and -120V (RMS, actual voltage peak ±170V), making you the conductor if you connect the hot wire to the dishwasher chassis and you touch it and ground. If the neutral connects to ground in the dishwasher, you've just connected up a dead short.

As this is for a dishwasher, neutral must connect to neutral and hot to hot, any mess-up here is going to be ugly. The only other method is to use an ohmmeter to trace which wire is attached to which blade. Normally narrow blade hot, wide blade neutral and ground pin to ground. If there is no difference in blade widths, then use the socket chart below to figure out which blade is Hot and Neutral from its position and attach the wire to the appropriate terminal in the appliance.

There is only one instance where the connections could be considered even remotely "interchangeable" and that is on a double insulated device where neutral is totally and completely isolated from ground.

NEMA socket listing with blade width and "polarity". Note that NEMA 5-15 and 5-20 can be installed with the ground prong up (coat hanger excluder mode) so right and left slot position is relative.

enter image description here

National Electrical Code 2014

Chapter 4 Equipment for General Use

Article 400 Flexible Cords and Cables

II. Construction Specifications

400.22 Grounded-Conductor Identification. One conductor of flexible cords that is intended to be used as a grounded circuit conductor shall have a continuous marker that readily distinguishes it from the other conductor or conductors. The identification shall consist of one of the methods indicated in 400.22(A) through (F).

(A) Colored Braid. A braid finished to show a white or gray color and the braid on the other conductor or conductors finished to show a readily distinguishable solid color or colors.

(B) Tracer in Braid. A tracer in a braid of any color contrasting with that of the braid and no tracer in the braid of the other conductor or conductors. No tracer shall be used in the braid of any conductor of a flexible cord that contains a conductor having a braid finished to show white or gray.

(C) Colored Insulation. A white or gray insulation on one conductor and insulation of a readily distinguishable color or colors on the other conductor or conductors for cords having no braids on the individual conductors. For jacketed cords furnished with appliances, one conductor having its insulation colored light blue, with the other conductors having their insulation of a readily distinguishable color other than white or gray.

(D) Colored Separator. A white or gray separator on one conductor and a separator of a readily distinguishable solid color on the other conductor or conductors of cords having insulation on the individual conductors integral with the jacket.

(E) Tinned Conductors. One conductor having the individual strands tinned and the other conductor or conductors having the individual strands untinned for cords having insulation on the individual conductors integral with the jacket.

(F) Surface Marking. One or more ridges, grooves, or white stripes located on the exterior of the cord so as to identify one conductor for cords having insulation on the individual conductors integral with the jacket.

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I did not downvote this because everything else is basically correct, except that the ribbed conductor is the neutral, the smooth is the hot. –  Speedy Petey May 12 at 0:58
    
Oh, crud, I knew that and flubbed it. Thanks for not downvoting, making the fix right now. –  Fiasco Labs May 12 at 1:05
    
Oh yeah, I keep forgetting. I could have just edited. Duh me. –  Speedy Petey May 12 at 1:15
    
@FiascoLabs I've edited in the relevant NEC section, feel free to remove it if you like. –  Tester101 May 12 at 11:03
    
Small correction: hot actually alternates from +170V to -170V. 120V is the RMS average. –  BlueRaja - Danny Pflughoeft May 12 at 11:05

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