I'm trying to power a door bell transformer with a 3-prong 120V dryer appliance cord. The doorbell transformer has black, white and green wires for the input, and screw terminals on the back for the 16/24 VAC output.

The Home depot dryer cord I bought is 16ga with 3 wires molded together: one is green which I confirmed goes to the round ground pin on the plug with VOM, but the other two are both gray. The plug isn't polarized; both plug blades are the same width.

Does it matter which gray wire goes to the black and white wires on the transformer input? I'm thinking it might since I don't have any AC output. Or maybe the HD transformer is tits up?

Time to ask for help instead of more fucking around...

Thanks
aileron

This message has been edited. Last edited by: aileron,

If it's what I'm picturing and the input wires are color coded then I'd say it does matter how it's wired. I would use my meter's continuity function to find the hot wire in my 'dryer cable' and mark it on both ends in some way. When looking at the plug it will be left side even though they are the same size.

Then splice that wire with the black wire on your transformer and since you know which is ground you can wire the rest of it.

quote:

Originally posted by BlackTalonJHP:
If it's what I'm picturing and the input wires are color coded then I'd say it does matter how it's wired. I would use my meter's continuity function to find the hot wire in my 'dryer cable' and mark it on both ends in some way. When looking at the plug it will be left side even though they are the same size.

Then splice that wire with the black wire on your transformer and since you know which is ground you can wire the rest of it.

I think you're telling me it does matter, but I'm too ignorant to understand what you wrote. If i'm looking at the wall receptacle, the left slot is wider than the right. You're saying whatever wire is connected to the left cord plug should go to the black wire on the transformer?

I think I did the opposite - could it have blown up the transformer? The breaker did not pop, and I still have 120 VAC between the wide and narrow slots in he receptacle.

I nearly flunked my EE class - luckily I had a lab partner who was a real EE; he told me to not touch *anything* and just take notes - that was about 50 years ago.

When I use my Fluke VOM it doesn't seem to matter if I put the red probe or the black probe in the left slot - I get 118 volts either way. ??

On 3 prong wire cord the 2 outside wires are line and the center wire is the neutral. However, that's 240 volts if you probe the 2 outside wires with a volt meter and that would definitely blow up a 120 volt transformer. I would assume a door bell transformer would be 120 volts??? If so, 1 line and the neutral would give you 120 volts, however, if there's an issue it wouldn't trip the dryer breaker if it's attached to a dryer plug on the wall. WHY on earth are you using a dryer cord for a doorbell transformer? Please call a licensed electrician because you're way over your head here.

Jimmy >> WTF are you talking about 240V for? I said it was 120VAC

quote:

Originally posted by jimmy123x:
On 3 prong wire cord the 2 outside wires are line and the center wire is the neutral. However, that's 240 volts if you probe the 2 outside wires with a volt meter and that would definitely blow up a 120 volt transformer. I would assume a door bell transformer would be 120 volts??? If so, 1 line and the neutral would give you 120 volts, however, if there's an issue it wouldn't trip the dryer breaker if it's attached to a dryer plug on the wall. WHY on earth are you using a dryer cord for a doorbell transformer? Please call a licensed electrician because you're way over your head here.

Ah, Nope. Yes, there are three prong 240v drier plugs, but they are much heavier and all three legs are blades, both thicker and taller than what aileron is talking about.

A 120 plug like he has (looking at the blades facing away from you as you were going to plug it in the wall) the hot (black) on the left, the neutral (white) on the right, and the ground (green, rounded “blade”) below. The hot blade may or may not be taller than the neutral blade. It doesn’t matter on a three prong plug as it can only go in one way, but two prong plugs sometimes use a taller hot blade so the polarity can’t be reversed by plugging the plug in upside down.

ETA: Aileron, do you have a continuity setting on your meter? If so, use that to determine which of the two grey wires is connected to the blade that will go into the slot on the left side of the outlet. Connect that one to the black wire and you should be good to go as long as the transformer is okay. I dunno if miswiring the polarity would hurt the transformer. My guess would be that it probably wouldn’t, but it might not work that way. That’s just a guess though. I’d wire it with the correct polarity and see what you have.

Like slosig said, you need to test the cord with a continuity tester to see which one is the 120v hot wire and which is the neutral. You can also do this with an ohmmeter. Do this with the cord unplugged, obviously. Typically the cords are made to coincide with the wall outlet, but that isn’t always the case.

On your wall outlet, the smaller of the two vertical slots (one on the right) is your 120v hot and the longer one (on the left) is your neutral.

Once you find out which is the hot on the cord, tap it to the black on the transformer and then the neutral from the cord to the white and the green to the last conductor (should be the one in the center of the cord). Do all of these connections with the cord unplugged. If the transformer is new more than likely it isn’t bad.

On a DB transformer polarity doesn't matter. That is why there is no white wire.

Now that is out of the way. From what you are describing, there is no legal way to do that.

DB transformers are meant to attach to a 1/2" knock out on an electrical box or panel.

Edit, just reread your post. Odd that transformer has color coded wires, because it doesn't matter. The cord wires line up to the corresponding prorngs. If looking at a wall outlet, left (bigger slot) is neutral, right (smaller slot) is hot, round one is ground.

Edit #2. You need something like this instead.

I looked up that label after seeing the prongs.
That is a 90 degree 120v, 15a appliance plug, not a 240v clothes dryer plug.
No idea why it says dryer plug except it was probably from China and the person mismarking the label didn’t know any better.
I’d hate to see the results of someone using this for a clothes dryer. Maybe a hair dryer?

OP, this is what a 3 prong dryer cord looks like and the cause for the confusion.
https://www.lowes.com/pd/eastm...ALw_wcB&gclsrc=aw.ds

^^^. The cord is only 16 gauge wire and 120v so yeah, calling it a dryer cord is a ridiculous. Hair dryer, yes. Clothes dryer only in you want to burn your house down.

Black Talon, slosig, powersurge, skins and 220: thank you so much for helping me. I had a 50:50 chance of wiring it correctly - and just like Vegas, I lost.

Monkey: Exactly!! There's a reason my flight callsign is Sparky.

I'm away from home where I have a Variac for such things. I received some prototype products from work for evaluation that require 16-24 VAC; this is a garage bench rig, not to be installed permanently in a house.

When wired as you gents suggest it now produces 16 or 24 VAC depending on the secondary taps. Who knew; I always thought AC didn't care which wire went where wire; apparently it is more like DC that you need to know +/- (sort of)

Jimmy: Here's something for you - Ancora Imparo. I built an airplane in my garage from plans; 3 of them actually. I wired them myself and have flown them IFR/VFR in 3 continents, over oceans, day and night. I'm an A&P with IA. I may not know what I'm doing, but I'm sure as hell not way over my head. Unlike you, I'm still learning.

The doorbell transformer is similar to this, only with multiple secondary taps for different voltages

^^^^. Everyone should still be learning until the day they throw dirt in your face. Know-it-all’s are dangerous and will get you hurt or killed. I’ve seen it. There’s a saying that goes, “Not tested. Not sure”. Also, “Not tested, not dead.” As in you can’t be sure something is off or wired a certain way unless it’s tested. Manufacturing and/or field errors happen.

I’ve been in the trades for 30 years and I’m still learning.

quote:

this is a garage bench rig, not to be installed permanently in a house.

OK, good.

quote:

Originally posted by 220-9er:
I’d hate to see the results of someone using this for a clothes dryer. Maybe a hair dryer?

That would work fine on our clothes dryer, as it uses 120v to turn the motor and gas (re-jetted to propane in our specific case) for the heat. It would even work on our stove which is also gas/electric (seems everything has a computer in it these days).

I agree that the should have labeled it a “120v 90 degree appliance plug” though to have avoided confusion.

quote:

Jimmy: Here's something for you - Ancora Imparo. I built an airplane in my garage from plans; 3 of them actually. I wired them myself and have flown them IFR/VFR in 3 continents, over oceans, day and night. I'm an A&P with IA. I may not know what I'm doing, but I'm sure as hell not way over my head. Unlike you, I'm still learning.

Okay, that is funny, but to be fair, when you say “Dryer cord” most people think 220v dryer cord. The washer cord is almost always 120v, I’ve never seen a 240v washer cord, but the dryer cord (or the stove cord) on a 240v unit is different, Now, you did say “120v dryer cord”, but I can’t say my eyes/brain have never skipped over a detail and left me in the weeds...

Thanks for the laugh.

This may be of some use to you:

Ribbed Leads
Wires that have a ridge along the length of a cord are found on flat cords and represent the neutral wire. The neutral wire will be connected to a larger, or polarized, prong if there is one on the plug.

https://www.ehow.com/facts_763...lead-power-cord.html

quote:

Originally posted by aileron:
Jimmy >> WTF are you talking about 240V for? I said it was 120VAC

Doing what Jimmy does best - trying to get people here hurt or killed from his soapbox level of ignorance.

"You smell smoke, sorry 'bout that". - Reddy Kilowatt.

It's probably a "Dryer Replacement Cord" for a gas dryer, which normally doesn't use a 230VAC feed, just 115VAC for the motor and no need to power heating elements.