Home electrical

[chim]

Here's a pretty good explanation:

 

[Runner]

Here's a pretty good explanation:

Excellent video!

 

[DarkBlack]

Excellent video!

Except for 12:58-13:40. The conclusion isn’t correct for the scenario setup

 

[MossRoad]

Doing service upgrades early on as an apprentice, the regular method of operation was to disconnect the overhead utility conductors while they were live. Then re-connect them at the end of the day when the larger panel install was completed.

Fortunately the company required fiberglass ladders be placed on dry 3/4" plywood panels. They required us to have an extra pair of boots that had never been used on a construction site so there was no risk of anything stuck to the bottom of the boots that would make the soles conductive.
Then we used a systematic approach for every job to disconnect the correct conductors first while leaving the grounded conductor to be disconnected last. No one was ever shocked in all the service upgades we did. Reconnect was grounded conductor first.
We were never allowed to do a service upgrade in the rain.

Now the utilities require a kill (term used here to open the circuit) at thier transformer before performing any work. OSHA rules kicked in.

When we bought our current house, we wanted the meter moved from the back of the house to the side of the house and a proper riser off of the meter through the eaves and roof. Then a new service disconnect added under the meter, and a new panel in the house. The guy we hired installed the new equipment, then moved the wires from the old riser to the new riser hot. He said as long and he as on a fiberglass riser with gloves and boots, he'd be fine, and grabbed one of the legs to show me.

A few weeks after it was done, I get a call from the electric company wanting to know who cut the seal on the meter and moved the service on the house. They seemed a big miffed. I told them it was a guy I found in the Penny Saver and that was that. They installed a new seal and left.

 

[caver]

220, 221 whatever it takes

 

[MossRoad]

 

[WinterDeere]

220, 221 whatever it takes

Right up there with "I'll be back", or "You talkin' to me?", in terms of memorable movie one-liners.

Here's one lots of you will be watching this month, and on-topic, considering how much of the film is dedicated to electrical problems: "If I woke up with my head sewn to the carpet, I wouldn't be more surprised than I am right now."

 

[RayIN]

I work with high voltage, and so there are some numbers we always keep in our heads. Those of us who drink coffee all day, and then a cocktail after work, usually have very dry skin. If I grab an ohmmeter between my two hands right now, it's going to measure several hundred k-ohms. Those who properly hydrate will be much lower, in the 10's of k-ohms. If you wet your hands, you'll get down closer to 1 k-ohm, in fact 3 k-ohm seems to stick in my head from my own testing.

We probably all remember Ohm's law from high school physics class: V = i*R, which is easily rearranged as i = V/R. In this case, since we're talking AC mains power, everything is RMS voltages and currents.

If you touch anything energized, it doesn't matter whether you're a "better" or "worse" conductor to ground, as you're a parallel path to a constant voltage supply. Current will flow through you according to this i = V/R, with you being the R, say maybe 30 k-ohm. Get your hands wet, and the current that will flow though you goes up 10x, due to 3 k-ohm.

Now, you've probably heard people repeat "voltage doesn't kill, current kills". That's really kind of stupid, as you can all see you can't have one without the other. V = i*R always holds, V being voltage, and i being current. What they really mean by this is that damage to you is dictated by the amount of current flowing through you, and the amount of voltage required to create that current varies enormously by person and temperature, as there's such a huge variation in skin resistance.

The threshold for sensation is around 1-2 mA, which for someone with wet hands at 3 k-ohm, will occur around V = 1.5m*3k = 4.5 volts. For those properly-hydrated individuals not dipping their hands in water, that's going to be somewhere in the 10's of volts (e.g. 50 volts), depending on your particular skin resistance.

Going above that, there's something called the "can't let go response", which occurs around 15 mA at 60 Hz, or V = 15m*3k = 45 volts, for a really sweaty electrician. This is very dangerous, as it is exactly what it sounds like, your muscles contract and cause you to involuntarily grab the conductor, with no ability to let go. I imagine some of the professionally-trained electricians here will tell you they were taught to use the back of their hand the first time they touch a circuit, for this reason... I'm not an electrician.

Side note, residential breaker panels in our older homes of the northeastern states are often in the basement utility room, right next to a screaming-hot oil-fired boiler, so the poor electrician is always sweating while working in the panel.

These are the rough numbers to keep in your head:

Threshold of sensation: 1 mA
Maximum "harmless" current: 5 mA
"No leg go" response: 10 - 20 mA
Onset of pain: 50 mA
Ventricular fibrillation: 100 - 300 mA (varies by individual)
Burning skin: 300 mA

Note that the "no let go" response is basically a forced contraction of your muscles, so it can also cause you to stop breathing, if the current happens to be passing thru your chest from one arm to another or from an arm to a leg.

When talking about residential electrical scenarios, I suspect the only time being a "better" conductor than something else matters, is when you have something like a loose connection causing current to a circuit to be interrupted. In those cases, grabbing the wrong thing will finally allow current to flow in the circuit... through you. But the current is still limited by old i = V/R, with R being the sum of you + the rest of the circuit.

You've likely seen this a long time ago. It's out of an old Navy training manual, and graphically explains the formula. It's not mine so use as you wish.

 

[WinterDeere]

I like that, Ray! I've always used the plumbing analogy:

Pressure = voltage
Flow rate = current
Restriction = resistance

But in explaining it to someone else recently, I started thinking that a dam is actually a better analogy than plumbing, especially when trying to explain why a neutral wire at a load has nearly zero voltage to ground. Once water spills over the spillway or thru the sluice gate into the drainage basin, there's no potential (height) left in the water.

I guess the guy pinched in the middle of your cartoon should be labeled Coulomb, for charge. "Amp" is the measure of how many of those guys get through the pipe, over time.

 

[MossRoad]

Right up there with "I'll be back", or "You talkin' to me?", in terms of memorable movie one-liners.

Here's one lots of you will be watching this month, and on-topic, considering how much of the film is dedicated to electrical problems: "If I woke up with my head sewn to the carpet, I wouldn't be more surprised than I am right now."

That's pretty low mister. If I had a rubber hose I would beat you