240V AC questions ...

[Bootstrap]

I'm installing a new cooktop to replace and old one, and I'm confused about something that I bet someone here can help with. I'm no electrician, I bet someone here is. If the real answer is that I am in over my head and should call a licensed electrician, that would be good to know too.

When I use the multimeter to measure voltage, the voltage across red and white is about 120 and the voltage across black and white is about 120. Fine, that's what I expected. But the voltage across red and black is reading 1. I was expecting it to read something like 240. What's up with that?

Also, for 240, the cooktop recommends a 40 amp circuit breaker. We have a 30 amp circuit breaker on the circuit now. I assume that needs replacing.

[ragpicker]

I'm installing a new cooktop to replace and old one, and I'm confused about something that I bet someone here can help with. I'm no electrician, I bet someone here is. If the real answer is that I am in over my head and should call a licensed electrician, that would be good to know too.

When I use the multimeter to measure voltage, the voltage across red and white is about 120 and the voltage across black and white is about 120. Fine, that's what I expected. But the voltage across red and black is reading 1. I was expecting it to read something like 240. What's up with that?

Also, for 240, the cooktop recommends a 40 amp circuit breaker. We have a 30 amp circuit breaker on the circuit now. I assume that needs replacing.

Let’s start with the breaker. You can’t just upgrade the breaker because that could lead to a dangerous situation. The breaker has to be sized to the wire. Or rather, the wire has to be size to the breaker and both are sized to the load. Can you get me the wire size and approximate length?

Also, can you FB message or post here the rating plate from the appliance?

Was the old cook top operational?

[Bootstrap]

Yes, the old cooktop was operational.

I'm not sure how to measure the length of the wire, it goes through the wall, down to the basement, and into the circuit breaker. Maybe 50 feet? Definitely less than 100 feet. I have photos of the rating plate for both the old cooktop and the new one, I can send them to you via FB.

But ... should I just let a pro do this one? From what you write, I'm suspecting this is something I could easily get wrong, and I'm seeing suggestions online that say replacing a circuit breaker is best left to the pros. Or are they just pros trying to scare me?

[Neto]

I cannot help with the part RagPicker already communicated with you about, but 220 VAC here in the States is (as your tests showed) 110-120 on each of the hot leads, plus the ground.
Interesting fact: Brazil has different voltages in different areas of the country. Some parts are 220, and others are 110. But the supply in an area where normal voltage is 220 is not 220, as it is here. It is 440. So the 220 voltage in those areas is a two wire system. If you want 110, you have to use a transformer. (And the outlets are exactly the same. 110 appliances do not run very long on 220....) At the 2nd place we lived in while in language school the owner had both 220 & 110 in each outlet. You had to remember which was which, or else. A lot of smaller appliances (like hair dryers & fans) had a switch to select the correct voltage.

[Bootstrap]

Ragpicker is helping me on Facebook. I now know that I need to call an electrician.

FWIW, in Germany, I learned that you can melt a screwdriver with 240V current. That caught me by surprise. And the fact that I learned that makes me a lot more cautious with electricity now.

[ohio jones]

When I use the multimeter to measure voltage, the voltage across red and white is about 120 and the voltage across black and white is about 120. Fine, that's what I expected. But the voltage across red and black is reading 1. I was expecting it to read something like 240. What's up with that?

Let me explain this in political terms so you can understand it.

The white wire is a conservative Anabaptist non-voter. The red and black wires are political partisans. You measure the difference between each of them and the non-voter, and yep, there's a big difference. But you don't know yet which side they are on. The red one is probably a Democrat, but the black one is ambiguous; there are some black Republicans, after all. So you measure the difference between those two, and there is only a small difference. One might favor Sanders, and the other one Biden, but they are on the same team. The cooktop is running in the Democratic primary and needs at least two votes to stay in the race. So now you can hook it up and feel the burn.

[ohio jones]

Also, for 240, the cooktop recommends a 40 amp circuit breaker. We have a 30 amp circuit breaker on the circuit now. I assume that needs replacing.

Now that we've addressed the voltage situation, let's move on to the general election, um, I mean, the amperage.

Our two friends are on their way to the precinct to cast their votes. Being environmentally woke, they decide to carpool on a single-seat bicycle. Halfway there, the tire blows out. They could replace it with a larger tire, but that wouldn't really fix the overloading situation. The safer thing to do would be to take a Prius instead.

[Neto]

Also, for 240, the cooktop recommends a 40 amp circuit breaker. We have a 30 amp circuit breaker on the circuit now. I assume that needs replacing.

Now that we've addressed the voltage situation, let's move on to the general election, um, I mean, the amperage.

Our two friends are on their way to the precinct to cast their votes. Being environmentally woke, they decide to carpool on a single-seat bicycle. Halfway there, the tire blows out. They could replace it with a larger tire, but that wouldn't really fix the overloading situation. The safer thing to do would be to take a Prius instead.

If you are REALLY woke, you walk. (Just think of all the pollution spewed irresponsibly into the air during the bicycle manufacturing process. And the tires & tubes?! Oh, and the grease used for lubricant. That supports oil exploitation. Please stop me now, before I start in on the Prius.)

[Fidelio]

I would get a licensed electrician to hook it up. It may be pretty simple to just connect the appropriate 240 volt outlet. The stove should be set up to receive both 120 leads separately and integrate them appropriately. But if each lead (black and red) has 120 volts you are fine. I don't think you can test across those two leads and get a meaningful reading.

I once had the two leads like that and touched the bare ends together and there was a loud pow, flash of light, and power outage. Downstairs in the laundry room the circuit box had two blown 35A cartridge fuses. Crazy, but this is what happens if you don't know what to do. Better to not do anything.

[ken_sylvania]

I would get a licensed electrician to hook it up. It may be pretty simple to just connect the appropriate 240 volt outlet. The stove should be set up to receive both 120 leads separately and integrate them appropriately. But if each lead (black and red) has 120 volts you are fine. I don't think you can test across those two leads and get a meaningful reading.

I once had the two leads like that and touched the bare ends together and there was a loud pow, flash of light, and power outage. Downstairs in the laundry room the circuit box had two blown 35A cartridge fuses. Crazy, but this is what happens if you don't know what to do. Better to not do anything.

If things are wired properly the voltage between black and red should read 220-240. If voltage between them measures 0 or 1 that would suggest they are running off the same leg of the 240V supply (likely also means it wasn't hooked up by a licensed electrician). And yep, if you touch the two leads of a 240V supply together you will get light, heat, and noise, often followed by a stunning absence of all three!