240v outlet not delivering 240 volts

Question

To spare you all the long version of my two week nightmare: bought a house built in 1976. Hooked up dryer, switched to 3 prong plug. Dryer ran fine, started to smell like burning plastic until it stopped running altogether. Dryer is fine, power cable apparently gave out. New power cable, dryer comes on, but no heat. It turns out the problem is really somewhere in the electrical.

I have a cheap voltmeter that only gives four readings 120, 240, 277, and over 400.

This morning I measured each leg at the receptacle for 120v to ground. Together, both hots only measured 120v, which makes no sense to anybody I've asked. At the dryer, each hot to neutral read the same 120v, but together give no reading.

Looking at the breaker each hot to neutral is 120v, and together the voltmeter says 277v. I noticed the breaker was a 40 amp which probably contributed to this mess. I replaced it with a 30 amp and the readings stayed the same. All of my double pole breakers give the reading of 277v. I also replaced the tired-looking receptacle that was probably original to the house on the hopes that maybe it was the cause to the problem. All readings were the same.

Now that I'm home from work, I have different readings at the dryer and the outlet. One hot says 120v to ground and the other gives no readings at all. Both hots together are also 0. Nothing has changed between this and my earlier reading. I was very careful switching the breaker out because I don't want to die and don't want to cause another problem somewhere else.

What's going on? Who am I? What dark force is keeping me from doing laundry?

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I'm willing to guess that my five dollar probe isn't known for its accuracy. On the off chance my house is getting 277v, what would that mean for my appliances and whether or not my house is going to burn down?

I tested everything again this morning, and both legs read 120 to ground, and I know that one leg wasn't doing that eight hours before. Clearly the line from box to receptacle is doing something it shouldn't. Luckily both dryer and breaker box are in my garage and I can follow the cable up from the box, across the unfinished joists, and into the drywall behind the dryer. I don't have to cave in several walls around the house to get to anything. Is this something an amateur can fix with the right materials and the help of other amateurs that know what 240v feels like?

Answer 1

Well, first of all...you probably didn't have an actual 277volts. What you had is a cheap meter. I have seen all kinds of whacky voltage readings from the $5 harbor freight meters I have laying around.

The only place one sees something other than 120 or 240 volts in a "normal" residential setting is the very rare "3 phase power". The vast majority of homes do not have any 3 phase power available. It has to be run to the house specifically as an unusual setup. When this exists in a home it would add "208V" to the list of possible voltages. Again, very rare and probably not at your house.

The only place you would see a real 277V is in a big factory. It is normally used for HUGE machines such as big welders and bigger shop equipment than you have probably seen before. Normal DIY shop equipment runs on 120V. Big shop equipment runs on 240V. HUGE shop equipment requires 3 phase connection with the 208V "wye 3 phase" mentioned above. It is extremely rare in a house. The 277V delta 3 phase would never be seen in a house, and only rarely in any commercial building you have been in. It is typical only in large factories.

Now as for what's probably wrong...you probably have a loose connection or a broken wire on one side of your 220 connection. This would give you 0v between the two hots, but still 120 from 1 hot to neutral.

As for how to fix it? Hire an electrician. Could you fix it yourself? maybe. Could you burn your house down? maybe. Could you sleep at night after messing with it yourself? only just maybe. Hire a professional for anything that is a combination of dangerous and slightly outside your comfort zone.

Answer 2

I would treat the 277V reading as equivalent to 240V in your case, as your tester is likely just a bit out of calibration (single-family dwellings are served by 240/120 split phase or occasionally 208Y/120 three phase, not 480Y/277 three phase in any case!).

As to your problem: You clearly have a bad connection or intermittent fault somewhere in the wiring for your dryer. I would turn the breaker off and examine the cable for that circuit to see if it is chafed against the edge of a knockout, pierced by a stray nail, or making bad contact with the receptacle; if you don't feel comfortable with that, turn the breaker off and call a local electrician.

Answer 3

Instead of Testing the Hots of the outlet, test the screws on the back where you connected the wires. There can be a connection issue with the meter probe lead and the inside of the socket. If you are sure you have 240(277, get a new meter and a non-contact voltage tester like https://www.amazon.com/dp/B001UAHZAM/) then its between the Breaker and the outlet. The Non-contact voltage tester is great as you can stick it in the hot hole of the outlet and it beeps if there is Power.

Not sure if the line is dedicated, but I've seen where the two Hots of a 240v circuit were wired to the same Main Hot-leg of the breaker panel.
Every other breaker in the panel is on a different hot leg, so adjacent breakers should measure 240. If some how they are both on the same Hot Leg, and you measure across them, you get 0v. But each one to ground is 120. If that happens they are both the same hot leg.