Wiring a Dishwasher
December 6, 2004 10:04 AM   Subscribe

Electricity: I'm wiring up a new dishwasher with the power cord from the old dishwasher. Just to make things interesting, the power cord has absolutely no indication of which side is positive and which side is negative. Is this because it's AC and it doesn't matter? I'm in the US on 110.
posted by yerfatma to Home & Garden (14 answers total) 1 user marked this as a favorite
Do the old terminals it was connected to have any indication of +/- ?

You might still be able to tell which way the cord was connected, based on the kink of the wire, but with a major appliance, I don't recommend you rely on that.
posted by scarabic at 10:10 AM on December 6, 2004

it doesn't matter (assuming you have just two wires; if you have three, it's important to know which is earth).
posted by andrew cooke at 10:11 AM on December 6, 2004

While there is very much a proper way to wire this up, practically speaking there's no useful difference.

Can you match colors?
posted by majick at 10:11 AM on December 6, 2004

Alternating current (AC), by definition, has no constant positive and negative. The two sides effectively switch positive and negative 120 times a second (that is, a full cycle, one side going positive to negative to positive, occurs 60 times per second, thus the frequency of common household AC in the US is 60 Hz).

Instead, AC comes into your house on a "hot" wire and a "neutral" wire. For some appliances it can be important to hook them up correctly; on others it doesn't matter. Unfortunately, that's the limit of my knowledge (no formal training; I've picked this much up from my father who is an electrical engineer and has done some household wiring). Whether it's likely to make a difference on your dishwasher, or how to tell which is which is beyond me.
posted by DevilsAdvocate at 10:37 AM on December 6, 2004

Most large appliances are designed to use a three-wire connection that has a hot, a neutral and a ground wire. Always make sure you wire the ground (usually green) wire correctly, an improperly wired ground is definitely a hazard. In a strictly operational sense an AC appliance will operate if you get the hot wire (usually black or red) and the neutral wire (usually white) reversed. However, reversing hot and neutral can have an impact on the safety of the appliance. If your home is wired correctly it should be safe to touch a live neutral wire when the appliance is off. However, touching a live hot wire will deliver a shock. Well designed appliances will be built to make it difficult to accidentally come into contact with the hot side of the circuit, even if the device has failed or is being misused. If you reverse the hot and neutral wires you might defeat such safety considerations, so I don't recommend you do it.
posted by RichardP at 10:48 AM on December 6, 2004

Silly silly people,

First off, are you sure it's not 220V?

With AC, there is no +/- because it alternates. One wire will be the "live" one, one will be neutral but necessary, closing the circut. Depending on the appliance, mixing these two up might not matter so much.

If it's grounded, there will be a third wire. Don't get this one mixed up. At best, you'd trip a breaker or blow a fuse; at worst, you'll also fry your dishwasher. The ground wire will be of a different gauge than the other two.

Don't go by colors alone. Easy way to get electrocuted.

On Preview, other people have this covered...
posted by blasdelf at 10:52 AM on December 6, 2004

buy a new appliance power cord that comes with detailed directions on how to attach it to the appliance. you can get them at almost any hardware/home improvement store (or where you bought your appliance).

to further it a bit, some new appliances may even require new power cord/outlet combo that older ones did not (my new dryer, for example)

for about $15 you save yourself the uncertainty and possible danger
posted by angry jonny at 11:17 AM on December 6, 2004

Response by poster: Sorry to forget: yes there's a ground and I've connected it to the ground screw. When I removed it from the old dishwasher I started to look at which was hooked up to what and then thought, "Why bother? There's obviosuly some color coding inside the cord." There is not. Pulling back the grey outer cord reveals twisted copper and nothing else.

I do have a power meter/ multitester (I had one last night too, but it turned out to be beyond useless, so I bought a new one today). I'm assuming I can undo the cord from the dishwasher, plug it into the wall and figure out hot and neutral that way too. Is that correct?
posted by yerfatma at 11:30 AM on December 6, 2004

Response by poster: Second sentence: "it" refers to the power cord and not the ground screw.
posted by yerfatma at 11:32 AM on December 6, 2004


If your multimeter has either a continuity setting or a resistance/ohms setting you should be able to determine which wire is hot and which is neutral without risking a shock from a live plug. Try this:
  • Put your multimeter in either a continuity or resistance setting.
  • Unplug the cord from the wall socket.
  • Disconnect the cord from the dishwasher.
  • Connect one probe to the wide spade of the plug. This should be neutral.
  • Test each of the two non-ground wires with the second probe to determine which is neutral. The other should be the hot wire.
  • To verify these results, connect the first probe to the narrow spade of the plug. This should be hot. Verify with the other probe that the second wire is indeed connected to hot.
If your multimeter lacks either a continuity setting or a resistance/ohms setting, you can still test the cord, but you will have to test while it is live. There is a chance you can shock yourself, so be careful. Never come into contact with any of the bare wires while the cord is live, and never allow the ends of the cord to come into contact with each other.

Here is how you would test if you only have an AC voltmeter:
  • Put your multimeter in an AC volt setting (> 120 VAC).
  • Unplug the cord from the wall socket.
  • Disconnect the cord from the dishwasher.
  • Make sure the cord ends are well separated.
  • Plug the cord into the wall socket.
  • Test the voltage differential between ground and each of the two other wires. Between ground and hot should be 120 VAC, between ground and neutral should be 0 VAC. You can also verify that between hot and neutral is 120 VAC.

posted by RichardP at 12:08 PM on December 6, 2004

Your meter can determine which is which using the meter. At the outlet, set the meter on AC, put one lead into the ground or on the ground screw and the other into one of the two sockets. One should read 0 or so and the other 125 or so. The one that reads 0 is the neutral. For a three prong outlet with the ground on the bottom the right hand slot should be hot and the left hand slot neutral. I take it that the wire you are talking about has a plug on one end and then two or three bare wires at the other end. Rather than plug this in and test the wire, it would probably be safer to verify the outlet is wired correctly and then use the resistance scale on the meter to see which wire corresponds to which plug blade and then mark the wires. The new dishwasher should have markings for ground, neutral and hot connections. All this said, I agree with angry johnny, you should probably get yourself a new cord.
posted by caddis at 12:21 PM on December 6, 2004

Now, this is what happens when you get a phone call on preview and then fail to preview it again before posting.
posted by caddis at 12:22 PM on December 6, 2004

If your meter doesn't do AC voltage, but has dwell, you can compare the readings from the wires (should be + 60 degrees dwell) to a known outlet.
posted by notsnot at 7:29 PM on December 6, 2004

Response by poster: In summary: went to Home Depot to get a new cord. All of the cords had female ends. Obviously I could have snipped those ends, but the plugs also had one horizontal and one vertical prong, which did not match the outlet. Both HD employees I spoke to said my current (ha!) situation wouldn't make a difference for AC (which matches my limited understanding: the power cycles between wires constantly), but if I was worried, hook the hot wire to the left-hand side of the plug. It all worked out fine.

notsnot, what's "dwell"?
posted by yerfatma at 4:30 AM on December 7, 2004

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