Home electrical

[qualsite]

For 120v circuits, a split single phase, the center tap of the 240v transformer feeding your house is grounded at the power pole and at your main panel with rods actually going into the ground. You get 120v referenced to ground [or the center tap] from either 240v hot leg.
The ground is a good ground, but if you provide a quicker, better ground, some current will also flow to that ground to get back to that center tap on the main feed transformer. A GFI will monitor the current coming in from the hot leg to be used to power something, and compare the power going back on the neutral wire back to ground and the feed transformer neutral center tap. If the two don't match, the GFI will trip, cutting off the hot leg, assuming that part of the current is going back to ground through something else... like you. If you have a defective ground with high resistance, yes the neutral/ground will be energized compared to a better ground with lower resistance. This is why proper grounding and bonding is so important. The principles for 3-phase are similar, but we won't get into that for now, since that wasn't the question.

 

[Williy]

I can remember back in the mid 50's my uncle's farm
my cousin would pull the know off of the radio and had
a puddle of water on the floor in the kitchen who ever
would touch that medal for dial on the radio would get
one hell of a shock!

This must have been around 1952 we were detassling
corn and this one kid said every one could grab the
electric fence and the only one that would not get a
jolt was the guy on the end I told every guy to grab
hands and put him on the end and I grabed the wire
of the electric fence and you should have seen him jump
and yell

willy

 

[NibbanaFarm]

Probably not uncommon, in any major city, at the time. Philly was built at the confluence of the Schuylkill and Delaware rivers, just as most confluences are populated by old cities, water being the primary forms of transportation and power at one time.

I used to water ski in the Delaware river, from Bristol down to Philadelphia, and while I don't want to even think about what might have been in that water, it probably wasn't worse than the Jersey shore water where I did the rest of my skiing. Off-shore dumping was very common along the east-coast, and the water was very noticeably dirtier in the 1970's and 1980's, but much cleaner by the early 1990's.

Yea, I don't think any environmental regulations kicked in until the 1970's. The surface of rivers in industrial areas were known to catch fire. The dielectric oil back then used to contain PCB's. That's why all seafood today is contaminated with PCB's, mercury and dioxins.

 

[Snezzy]

I can remember back in the mid 50's my uncle's farm
my cousin would pull the know off of the radio and had
a puddle of water on the floor in the kitchen who ever
would touch that medal for dial on the radio would get
one hell of a shock!

This must have been around 1952 we were detassling
corn and this one kid said every one could grab the
electric fence and the only one that would not get a
jolt was the guy on the end I told every guy to grab
hands and put him on the end and I grabed the wire
of the electric fence and you should have seen him jump
and yell

willy

Here's a good explanation of why removing that knob (not "know" damn spell correction I bet) created a shocking situation. Those radios are damned dangerous.

Antique Radio Safety: Understanding the Dangers of a Hot Chassis

Also, not mentioned in that link, is one must never use any old plug-into-the-power-line radio in the bathroom. Not that anyone would, nowadays, but that was a correct warning for electrical safety in our younger days.

 

[chim]

Probably not uncommon, in any major city, at the time. Philly was built at the confluence of the Schuylkill and Delaware rivers, just as most confluences are populated by old cities, water being the primary forms of transportation and power at one time.

I used to water ski in the Delaware river, from Bristol down to Philadelphia, and while I don't want to even think about what might have been in that water, it probably wasn't worse than the Jersey shore water where I did the rest of my skiing. Off-shore dumping was very common along the east-coast, and the water was very noticeably dirtier in the 1970's and 1980's, but much cleaner by the early 1990's.

The company I worked for did some projects for a certain chemical company back in the 80's. When excavating, everyone had to wear full hazmat. According to one of the guys who worked there, at least once the earth caught fire when the backhoe disturbed it.

Then there's the Aberdeen Proving Ground.

 

[geteh]

It is my understanding (and also stated in the video) that the only reason the grounding conductors aren't energized is because the neutral bar and main connection is a "better" path to ground than going to the water pipe or rod.

I don't know (but I think) that if you were standing in a pool of water, barefooted on a concrete floor and touched the neutral bar, you could become the better path for current to flow.

Of course, if there is a fault condition (like the hot wire contacting the metal components of the outlet in the video) then the grounding conductor absolutely is carrying current.

The EE's and electricians will be along shortly to provide the correct answer.

Edit: Even though I just said that I don't trust that touching the neutral bar (while standing in a puddle) is safe, I’ve read some American Power and Gas reviews mentioning safety concerns in different contexts, so I’m especially cautious about electrical hazards., it is bonded to the main service panel, so it can't be any worse that touching the service panel.

The reason the ground wires are not energized, even though they share the same bus bar as the neutral wire, is that the neutral carries the return current under normal conditions, while the ground is only for safety. The ground is not meant to carry current unless there's a fault (like a short circuit), so it stays inactive in normal operation. The neutral and ground are only connected together at the main panel to complete the circuit, but beyond that, they are kept separate to prevent unintended current flow through the ground system.

 

[WinterDeere]

I don't know (but I think) that if you were standing in a pool of water, barefooted on a concrete floor and touched the neutral bar, you could become the better path for current to flow.

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.

 

[Runner]

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.

So, cutting to the chase, knowing what you know, would you, personally, have any reservations about touching the neutral bar in a live service panel?

Say for instance, you want to install a new circuit. You run the conductors into the panel (live), prep the conductors, attach the black wire to the circuit breaker, attach the neutral and grounding conductors to the neutral bar. Then, plug the breaker into the frame.

 

[WinterDeere]

So, cutting to the chase, knowing what you know, would you, personally, have any reservations about touching the neutral bar in a live service panel?

As long as the system is properly grounded, there is zero danger in touching the neutral. As you already noted, at least in the mains panel coming into the house, it's screwed right into the panel, so it's as safe as touching the door of the panel.

That said, especially when considering sub-panels, ground paths aren't always properly maintained. So it's never bad practice to treat it as if it were hot, any time you have the mains breaker energized.

In reality, even with a floating neutral and bad ground, the likelihood of seeing more than ~30 volts on that bus bar is very low. Getting even that high would require a 50% mismatch in loading between the two legs on that panel, and a floating neutral or missing ground. For most people, 30 volts is above the threshold of detection, but way below pain or "no let go" response, so relatively safe.

Say for instance, you want to install a new circuit. You run the conductors into the panel (live), prep the conductors, attach the black wire to the circuit breaker, attach the neutral and grounding conductors to the neutral bar. Then, plug the breaker into the frame.

Yep... and I do that all the time! Again, in my own house, where I know ground and neutral are both properly connected.

 

[grsthegreat]

So, cutting to the chase, knowing what you know, would you, personally, have any reservations about touching the neutral bar in a live service panel?

Say for instance, you want to install a new circuit. You run the conductors into the panel (live), prep the conductors, attach the black wire to the circuit breaker, attach the neutral and grounding conductors to the neutral bar. Then, plug the breaker into the frame.

As an electrician that survived over 30 years working in live industrial and commercial panels…..i would NOT touch any live panel part…period.. they make insulated tools for a reason. On certain gear, we hade flash guards and PPE on before we ever opened a panel.

On one job, while tightening a connection on a replacement breaker, a metal socket fell off the insulated socket wrench and made contact in panel. Huge flash and boom. No one got hurt, but never found any parts of that socket. This panel had to remain live during work as it was in a hospital. Very thankful for PPE and flash protection. And no circuit tripped….which i found strange. Alot of the very large panels we worked on for say a school had a main service GFCI protection to protect entire panel, but not so in a hospital. They dont want to shut down entire system for facilities like these.

I worked at a pharmaceutical manufacturer facility replacing breaker sections as part of normal maintenance. Everything live . Accidentally shutting down wrong circuit could destroy a million dollar run of product if it affected the environmental system of the clean rooms. This work became too stressful for my employer .. not to mention us grunts.

I took this respect for unbalanced or faulty returns to ground with me when i transferred to residential electrical. Mind you, a 200 amp panel is nothing compared to a 2000 amp panel, but 200 amp can kill you just as fast.