Questions tagged [mains]

Mains electricity, typically a higher voltage AC waveform used to deliver electrical power to households. In North America 120V, 60Hz, in most European countries 230V, 50Hz. What most people will plug appliances into.

Mains electricity, typically a higher voltage AC waveform used to deliver electrical power to households. In North America 120V, 60Hz, in most European countries 230V, 50Hz. What most people will plug appliances into.

Because it is so ubiquitous, many electrical devices are designed to plug directly into wall outlets, even if internally they convert that power to a more convenient voltage -- often , , or .

In turn, for efficiency reasons or compatibility with the above devices or both, many electrical systems deliver electrical power at standard mains voltage and more-or-less standard frequencies and waveforms, converting from power distribution systems or from "12 V" power.

A few systems use the same wires that carry mains electrical power to also carry data.

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What are these boxes mounted inline on each of the 3 phase wires of a high voltage power line in Miami?

They were only on this run and not any of the lines in the area. And what is the function of the flat u-shaped guards in front of each?
bigjosh
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Why is main's neutral tied to earth?

My dad is an Electrician and I myself am an Electronics Design Engineer, and to this day he still hasn't been able to give me a good reason for this. Consider the two following pictures/situations - both the same case, but with neutral not tied to…
DSWG
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Is the neutral wire considered safe?

If the neutral wire carries current, why do many people believe that it's safe? I've heard "You can touch the neutral wire/bar in the breaker box and not get shocked. Only the hot can hurt you." If the circuit is complete and current is flowing,…
Stephen Melvin
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Creepage distance for PCBs handling line voltage AC?

What is the required creepage (e.g. trace-to-trace) distance for PCBs handling 240VAC rms? What about 120VAC? This is for UL and CE certification. The standards for PCB Creepage (e.g. the distance across the surface of a PCB between high-voltage…
Connor Wolf
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If we could start our electrical grid from scratch with today's technology, which would be the most efficient choice? AC or DC?

Lately, I’ve been reading about the many advantages of HVDC transmission systems for long distance transmission, undersea links, and others. The historical reason of why AC was picked over DC was mostly due to the invention of the transformer, which…
Jota
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What killed these X2 caps?

A few years ago, I designed an MCU-controlled dimmer driving a 150W mains halogen lamp. This is in Western Europe; 50Hz 230VAC. It uses X2-rated capacitors as capacitive droppers for the power supply, and another X2-rated capacitor for interference…
marcelm
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How do electricians know where the line is down?

I had a power outage and I thought about the utility poles near the street. How do electricians know which power line is down considering that there are many miles of them? For example, if there's a car that crashed into the pole and brought the…
netrox
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Where exactly does the power company cut my power when I fail to pay my electric bill?

I only have a somewhat vague understanding how the electrical grid works. I know the basics of energy production, and that the electricity comes to our homes using power lines resting upon those big supports we see everywhere. I would imagine the…
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Why are relays still used in electric ovens?

I bought a new electric fan oven recently. It has a digital thermostat and control system. Yet much to my surprise, I can hear a relay clicking on and off inside it to control the power to its heating element. The oven is rated at 4kW (230V). I…
nigel222
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Why is three-phase offset by 120 degrees?

For three phase electricity the wave is offset by 120 degrees(2\$\pi/3\$ Rad). Why aren't the phases closer together? Is it because it will affect the frequency of the phases? How was this 120 degrees chosen?
Dean
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Is it OK to solder a power cord?

A few people have advised me to never solder a power cord directly to a PCB, but they couldn't explain why not. Why can/can't I solder it directly?
pebbles
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How do large electrical grids stay in phase?

I am a math student with some background in physics so apologies if the question is naive - but I'm trying to understand how large electrical grids like the Eastern Interconnection maintain locally a consistent phase, when it seems like the grid…
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Why do travel transformers have a setting for either 50W or 1600W?

I've noticed this "feature" on a number of travel-oriented voltage converters - they either are meant to be used for small 50W loads, OR for larger loads up to 1600W. But you can't run a small load on the higher setting. Here's an example of one…
StayOnTarget
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Why does turning on my desk lamp crash my board?

Whenever I turn on my desk lamp, my board crashes. Sometimes I get garbage out of the serial port, sometimes it resets. I tried adding some extra bypass capacitors on my breadboard, but that made no difference. (My desk lamp uses a 20W, 12V halogen…
Toby Jaffey
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How could using an ungrounded appliance with a grounded extension cord be a fire hazard?

I came across a tweet recently: Don’t even THINK about using a 2-prong plug in a 3-hole slot! Use only the required number of slots in an outlet or power strip. Below was a picture of a burned-out grounded extension cord. I'm hesitant to argue…
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