71–80 of 213 posts
I absolutely love reading about a topic from a super enthusiastic non-expert. I want to subscribe to a weekly series called "Reasonably Intelligent Person Obsesses Over Something"
[1] https://medium.com/graphicfacilitation/all-you-need-to-know-...
Regarding three-phase power: The electrical outlets in your home have two power-carrying prongs. The third prong is just for safety (it connects to the ground), and should never carry power unless something is going horribly wrong. In that case, the power should hopefully prefer to reach the ground through that third wire than through your human body. Anyhow, the voltage in those two power-carrying wires is constantl…
> the voltage in those two power-carrying wires is constantly switching directions I'm not buying this (in the USA). I've been in my breaker box. For a typical 110 volt outlet, the black (hot) wire is connected to the breaker, which is connected to one of the wires coming into the house from the street. The white (neutral) wire is connected to the same ground bracket that the bare (ground) wire is connected to. 240 v…
Regarding three-phase power: The electrical outlets in your home have two power-carrying prongs. The third prong is just for safety (it connects to the ground), and should never carry power unless something is going horribly wrong. In that case, the power should hopefully prefer to reach the ground through that third wire than through your human body. Anyhow, the voltage in those two power-carrying wires is constantl…
> the voltage in those two power-carrying wires is constantly switching directions I'm not buying this (in the USA). I've been in my breaker box. For a typical 110 volt outlet, the black (hot) wire is connected to the breaker, which is connected to one of the wires coming into the house from the street. The white (neutral) wire is connected to the same ground bracket that the bare (ground) wire is connected to. 240 v…
In a breaker box, one wire (white) gets tied to ground, and the other wire (black or red) goes between +170 (relative to ground) and -170 (relative to ground). The black and red wires are 180 degrees out of phase, so when the black wire is at +170, the red wire is at -170. This gives a 340V peak difference between the black and red wires, which averages to 240V. You get your normal 120V outlet power between the hot legs and ground/neutral, and you get your 240V dryer & water heater power between the two hot legs themselves.
So, in a normal outlet, we can safely say that one wire is "more positive" than another, and that this flip-flops through time. When we look at voltages relative to ground, though, one wire stays put at 0V while the other goes between +170 and -170. It's just a question of where you put your reference frame.
Regarding three-phase power: The electrical outlets in your home have two power-carrying prongs. The third prong is just for safety (it connects to the ground), and should never carry power unless something is going horribly wrong. In that case, the power should hopefully prefer to reach the ground through that third wire than through your human body. Anyhow, the voltage in those two power-carrying wires is constantl…
Now: For two phase in your home, why is one side considered "hot" and the other side considered "neutral", resulting in keyed plug blades?
The neutral side is connected to the ground. (Literally - they stick a metal pole in the ground.)
The 3rd wire, is also attached to the ground, and in the electrical box the two wires are attached together.
Anyway, that's why it's neutral - because it's attached to the ground, so it's at the same potential as you.
Earlier quoted context omitted.
The two hot wires are perfectly out of phase, so connecting to both of them gives you 240V outlets (used for large appliances like clothes dryers). Your standard 120V appliance outlets are only using a single phase and neutral. IIRC the smaller prong is hot and the larger prong is neutral.
Fun fact - the reason outlets in new construction are installed upside down (ground prong on top) is that the groudn prong can stop this from happening if something falls on it: https://i.redd.it/bm1gqw8hzppz.jpg Of course that's an ungrounded plug so they're in trouble either way, but you get the idea. Another option (which I've never seen in the US) is plugs where the first chunk of the line/neutral prongs are insu…
Someone put a lot of thought into the design. Ground at top to prevent accidents like you show. Ground pin is longer. Insulation covers enough of the pins that live and neutral disconnect before conductor is exposed from socket. Both will be fully disconnected before earth disconnects.
Earlier quoted context omitted.
> the voltage in those two power-carrying wires is constantly switching directions I'm not buying this (in the USA). I've been in my breaker box. For a typical 110 volt outlet, the black (hot) wire is connected to the breaker, which is connected to one of the wires coming into the house from the street. The white (neutral) wire is connected to the same ground bracket that the bare (ground) wire is connected to. 240 v…
Right, that is correct. To understand how that works, you have to realize that there is no such thing as an "absolute voltage", only the voltage difference between two wires. In a breaker box, one wire (white) gets tied to ground, and the other wire (black or red) goes between +170 (relative to ground) and -170 (relative to ground). The black and red wires are 180 degrees out of phase, so when the black wire is at +1…
Earlier quoted context omitted.
Correct, and more conventions in the US that are mostly true so don't bet your life on them: hot has black insulation, neutral white hot wire insulation will be smooth, neutral ribbed hot terminal screws will be brass, neutral silver (chrome)
Screw terminals in a house installation?!
I absolutely love reading about a topic from a super enthusiastic non-expert. I want to subscribe to a weekly series called "Reasonably Intelligent Person Obsesses Over Something"
I completely agree, and Tedium is probably what you're looking for: https://tedium.co
Earlier quoted context omitted.
> and not where it can have direct contact with people. Could you expand on that? My elementary school had a playground structure made of old utility poles. Other than getting pitch on our clothes, they didn't seem particularly hazardous.
They're treated with lots of preservatives. They're probably not all that dangerous in the short term (unless you eat some of the pitch), but it's annoying to deal with the potential long term safety. My scoutmaster worked for the power company, and I was going to ask him if we could have a couple of poles for my Eagle project, but after looking at what you had to do to reuse them I decided it was simply too much of…
Some of the older ones near me have already been vandalized by woodpeckers
Earlier quoted context omitted.
Three phase power is extraordinarily useful for electric motors. Mount three electromagnets radially and wire each up to a different phase, and you get a rotating magnetic field that spins on the axis. Electric generators produce three-phase power pretty naturally through the inverse process of spinning a magnet through the resistance provided by three groups of windings.
You can have a two phase power system[1], but two phase generators are less efficient and more expensive relative to three phase – for the exact same reason why power distribution is less efficient and more expensive relative to three phase. [1] two phases in quadrature, which is very different from split phase, which is not two phase at all.