JayMcJay
Active member
Which conductors burned to which conductors?
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Electricians jump in.
- Thread starter 71PA_Highboy
- Start date
Chevy_man
Leftjizz
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Floating neutral. If the neutral is broken the voltage can vary between 0 and 240v on either phase.
What baffles me is I've seen it on 5 different service calls in the last 15 years, and every time it's on the power company side and I have to explain it to the lineman to get them to even investigate it.
Hot to messenger. Only 3 wires going to the shack.
JayMcJay
Active member
So that’d get you 120v to ground, not 240v, right?
Your neutral burned to one of the hots. Each carry 120v. Or is there a way to actually get 240 from the neutral to ground?
Your neutral burned to one of the hots. Each carry 120v. Or is there a way to actually get 240 from the neutral to ground?
TanTJJim
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Glad this conversation was brought up, one thing that I "get" now that I struggled with understanding before was "why" ground and neutrals are or aren't bonded.
Please correct me if I'm wrong, but here's my understanding.
Why you bond ground to neutral:
Obvious reason, you want a path for current to go if there's a fault where there's a potential on exposed metal (i.e. the farmer who electrocutes his livestock on accident).
Not so obvious reason, "neutral" isn't held to a specific potential coming off of the transformer on the pole (i.e., it's floating). Bonding it to ground at the first point of disconnect ensures it's potential is held at that of earth ground (which ideally should be zero volts). The reason why you only do this at the first point of disconnect is explained next
Why you don't bond ground to neutral (at a sub panel):
Neutral does not mean zero volts (or zero potential). Neutral is a really bad word that really means return path for current, but that's too many words so we just call it "neutral". Because of this, your "neutral" will have a potential (voltage) on it when current is flowing through it. More current = more voltage. More distance = more voltage. More resistance = more voltage. Right at the bonding point, this voltage will ideally be zero volts, but the further you go from this point the higher the voltage will be based on those things.
Point being, you can't prevent some voltage being present on neutral. And when you have a sub panel that's some distance from the first disconnect, you're going to have "some" voltage on it. What that "some" is depends on the reasons above, but the value matters less than knowing that something will be there.
So here's why the sub panel ground and neutral shouldn't be bonded at the sub panel in any instance. We know there's going to be "some" voltage on the neutral, if we then go ahead and bond ground to neutral at the sub panel, we've created a path for current to go where it's not supposed to go. (Which in this case is through ground and not neutral)
All of your line current should always return through neutral, but bonding ground to neutral at a sub panel ensures that some current will go to ground which at best results in weird things happening as others have mentioned and at worst, can create enough electrical current in the ground, which you walk on, to cause a hazard.
How much of a hazard is certainly a question. One that I'm not going to answer and is sure to be debated, but the whole point being, current code is designed to ensure normal operation has all current returning through neutral while still providing the safety of a path to ground if a fault occurs. I mean, that's the whole purpose of code, right?
Please correct me if I'm wrong, but here's my understanding.
Why you bond ground to neutral:
Obvious reason, you want a path for current to go if there's a fault where there's a potential on exposed metal (i.e. the farmer who electrocutes his livestock on accident).
Not so obvious reason, "neutral" isn't held to a specific potential coming off of the transformer on the pole (i.e., it's floating). Bonding it to ground at the first point of disconnect ensures it's potential is held at that of earth ground (which ideally should be zero volts). The reason why you only do this at the first point of disconnect is explained next
Why you don't bond ground to neutral (at a sub panel):
Neutral does not mean zero volts (or zero potential). Neutral is a really bad word that really means return path for current, but that's too many words so we just call it "neutral". Because of this, your "neutral" will have a potential (voltage) on it when current is flowing through it. More current = more voltage. More distance = more voltage. More resistance = more voltage. Right at the bonding point, this voltage will ideally be zero volts, but the further you go from this point the higher the voltage will be based on those things.
Point being, you can't prevent some voltage being present on neutral. And when you have a sub panel that's some distance from the first disconnect, you're going to have "some" voltage on it. What that "some" is depends on the reasons above, but the value matters less than knowing that something will be there.
So here's why the sub panel ground and neutral shouldn't be bonded at the sub panel in any instance. We know there's going to be "some" voltage on the neutral, if we then go ahead and bond ground to neutral at the sub panel, we've created a path for current to go where it's not supposed to go. (Which in this case is through ground and not neutral)
All of your line current should always return through neutral, but bonding ground to neutral at a sub panel ensures that some current will go to ground which at best results in weird things happening as others have mentioned and at worst, can create enough electrical current in the ground, which you walk on, to cause a hazard.
How much of a hazard is certainly a question. One that I'm not going to answer and is sure to be debated, but the whole point being, current code is designed to ensure normal operation has all current returning through neutral while still providing the safety of a path to ground if a fault occurs. I mean, that's the whole purpose of code, right?
MurderYota
Throbbing member
I Just did this. Only 60 feet though. Neutral and ground not bonded. Two ground rods. 8' deep 10' apart. Neutral and ground bonded at main panel.So I have a friend looking to put in a sub panel.
So my questions are: Does the sub panel need a ground rod?
Does the sub panel get the neutral and ground tied together.
Does the ground and neutral get tied together at the main panel?
In VA if it matters.
Chevy_man
Leftjizz
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I feel like the answers are out there, you need to buy a book or two...
To make it even more fun there's conventional current flow theory, and reverse current flow theory.
And then it's all theory. So smart asses like myself can tell employees and customers "theoretically, this could be happening, so let's measure here, there, and then over there and compare theory with reality."
Chevy_man
Leftjizz
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Can I really break your brain and tell you that the wires on the poles don't include a neutral.
To get single phase power for a home, they pull power off 1 phase. The secondary side of the xfmr has a center tap on the coil that is grounded with 4-8 ground rods, and grounding this creates the neutral. So then you have split that single phase into 2 sides with a neutral in the center.
3 phase can be done with 2 or 3 phases available. You need a second xfmr with only 2 phases and you can only create an open delta, which has a high leg of 240v to ground. The other 2 legs will only be 120v to ground.
And a wye will have 120v on each phase, but 208v between phases.
It makes a lot more sense if you can see it all in polar coordinates with angles attached. I'm far too lazy to think back to 15 years ago in school though.
No - 240v.
The one hot 'took over' the neutral/ground at the well shack when it burned together. The resulting short-circuit of #10, ground rods, and dirt couldnt pull enough fault current to trip the breaker.
Thus, anything 'neutral', 'bonded' or 'grounded' at the shack was 240v potential difference to the remaining hot.
This is an example of why we dont do 3-wire distribution anymore. Does it work? Well ya. How shitty can it be be when it goes wrong? Well...
TanTJJim
Red Skull Member
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I hate to disappoint but no brain breaking will occur today (on this subject at least)
The fact that you just mentioned is actually what brought me to the realization of all the nonsense I posted above.
I've known for quite some time that transformers on the pole (speaking primarily residential here) are center tapped and there's only 2 wires coming in from the grid, but as we all know (or should), knowing does not necessarily mean understanding. I think that I now understand a little better.
The delta wye stuff is still a little over my head, I have a little bit of understanding of 3 phase power but would need to spend some brain power digesting what you mentioned to really grasp more of it. Fortunately I don't ever have to dabble in the 3 phase world so what little I know is more for personal curiosity than anything. Power generation and distribution is a pretty fascinating system the more I learn about it.
billdacat
No road...no problem.
This whole grounding thingy always causes a huge shit-storm of controversy... I opened up a big ass can of worms when I questioned the wisdom of bonding Ham radio ground to the utility. Whew....it is still going on two months later.
But, I will toss in someting that I learned a few months ago when I installed a service entrance and sub pannel on the ranch.
We were 40' to the pad transformer; ran 4-0 4-0 2-0 UHD. Two ground rods connected with #4 copper and bonded at the service entrance neutral.
I got a chance to have a look-see at the transformer while the POCO was landing the UHD. I noticed a ground rod under the transformer that was also bonded to neutral... My take-away from seeing this; the POCO is using the ground and neutral as a return current path. (2-0 neutral/ground conductor).
But, I will toss in someting that I learned a few months ago when I installed a service entrance and sub pannel on the ranch.
We were 40' to the pad transformer; ran 4-0 4-0 2-0 UHD. Two ground rods connected with #4 copper and bonded at the service entrance neutral.
I got a chance to have a look-see at the transformer while the POCO was landing the UHD. I noticed a ground rod under the transformer that was also bonded to neutral... My take-away from seeing this; the POCO is using the ground and neutral as a return current path. (2-0 neutral/ground conductor).
Animalmother
Flexed cracker
This whole grounding thingy always causes a huge shit-storm of controversy... I opened up a big ass can of worms when I questioned the wisdom of bonding Ham radio ground to the utility. Whew....it is still going on two months later.
But, I will toss in someting that I learned a few months ago when I installed a service entrance and sub pannel on the ranch.
We were 40' to the pad transformer; ran 4-0 4-0 2-0 UHD. Two ground rods connected with #4 copper and bonded at the service entrance neutral.
I got a chance to have a look-see at the transformer while the POCO was landing the UHD. I noticed a ground rod under the transformer that was also bonded to neutral... My take-away from seeing this; the POCO is using the ground and neutral as a return current path. (2-0 neutral/ground conductor).
There is no mechanical connection between primary and secondary windings on a transformer. If you have a delta primary its 3 phases and a ground with no neutral. A wye secondary will have 3 phases and xo which is bonded to ground, which establishes neutral, usually bonded to the transformer case, with all the other ground wires and the grounding electrode conductor to the available grounding electrodes.
billdacat
No road...no problem.
That I understand.....The primary doesn't have or need a ground....What is really interesting to me is the shared ground and neutral between neighbors.
Got me thinking why we use 2-0 UHD for the neutral, and 4-0 for the hots.
plym49.2
Sasquatch49.2
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None of you knuckleheads know what the heck you're talking about.
OP, here's what you do:
- Install a pole pig at each end.
- Now you have 7400 volts for your 350 foot transmission line.
- Which means that for 60 amps you can run lamp cord.
You're welcome.
OP, here's what you do:
- Install a pole pig at each end.
- Now you have 7400 volts for your 350 foot transmission line.
- Which means that for 60 amps you can run lamp cord.
You're welcome.
Chevy_man
Leftjizz
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That I understand.....The primary doesn't have or need a ground....What is really interesting to me is the shared ground and neutral between neighbors.
Got me thinking why we use 2-0 UHD for the neutral, and 4-0 for the hots.
Because the phases cancel each other out for neutral load.
If you have 60A on A, and 75A on B, you have 15A on the neutral...
71PA_Highboy
An Unknown but Engorged Member
This is the sub panel I was going to use:
www.se.com
Thoughts?
And it is going inside a currently existing shed, but they are talking about replacing it with a larger pole barn so I dontt want to undersize the feed....
HOM816L125PC - Load center, Homeline, 1 phase, 8 spaces, 16 circuits, 125A convertible main lugs, PoN, NEMA1, combo cover | Schneider Electric USA
Schneider Electric USA. HOM816L125PC - Load center, Homeline, 1 phase, 8 spaces, 16 circuits, 125A convertible main lugs, PoN, NEMA1, combo cover.
Thoughts?
And it is going inside a currently existing shed, but they are talking about replacing it with a larger pole barn so I dontt want to undersize the feed....
I prefer main breaker style, QO (not homeline), and more spaces.This is the sub panel I was going to use:
HOM816L125PC - Load center, Homeline, 1 phase, 8 spaces, 16 circuits, 125A convertible main lugs, PoN, NEMA1, combo cover | Schneider Electric USA
Schneider Electric USA. HOM816L125PC - Load center, Homeline, 1 phase, 8 spaces, 16 circuits, 125A convertible main lugs, PoN, NEMA1, combo cover.
Thoughts?
And it is going inside a currently existing shed, but they are talking about replacing it with a larger pole barn so I dontt want to undersize the feed....
71PA_Highboy
An Unknown but Engorged Member
I typically do as well.. But in reality panels are cheap and these folks can't make up their mind... so no matter what I do I will end up swapping it out in a couple of years.
They have too much money and not enough sense or understanding of what they want.
They have too much money and not enough sense or understanding of what they want.
71PA_Highboy
An Unknown but Engorged Member
Ok,
Slightly confused here.
If I am using a ground rod at the sub panel, and I have tied the ground and neutral at the main panel, what do I do with the extended ground in the sub panel since I am not supposed to tie them together (with the ground rod as well) at the sub panel.
Someone want to draw a diagram that can clear this up for me?
Slightly confused here.
If I am using a ground rod at the sub panel, and I have tied the ground and neutral at the main panel, what do I do with the extended ground in the sub panel since I am not supposed to tie them together (with the ground rod as well) at the sub panel.
Someone want to draw a diagram that can clear this up for me?
Simply DO NOT connect the neutrals together with any ground or bond at subpanel.
Chevy_man
Leftjizz
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Put the ground on the ground buss, put the neutral on the neutral buss, and remove the bonding jumper/screw from the neutral buss.
If you bought the one without a ground, get a kit...
PK27GTA - Load center accessory, QO/Homeline, ground bar kit, 27 terminals | Schneider Electric USA
Schneider Electric USA. PK27GTA - Load center accessory, QO/Homeline, ground bar kit, 27 terminals.
Yota Up
Dull man
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Glad I'm smart enough to know I'm stupid when it comes to electrical and hire out rather than do my own.
Well, anything above wiring up a generator hookup to panel or other minor stuff.
I'm reading the above and trying to wrap my head around it and gotta admit I'm still pretty lost.
Anyone recommend a decent youtube vid that explains it all?
Well, anything above wiring up a generator hookup to panel or other minor stuff.
I'm reading the above and trying to wrap my head around it and gotta admit I'm still pretty lost.
Anyone recommend a decent youtube vid that explains it all?
Land the feeder bonding wire and ground rod wire on the bar circled in green. Homeline MLO panel for reference.
71PA_Highboy
An Unknown but Engorged Member
Thank you,
JayMcJay
Active member
Whelp, based on this description of why to not have the grounds and neutrals tied together on a sub panel I went down to my basement sub panel and had a look at it. Ended up doing a bit of re-work on it last night. Now all of my grounds are on that side-bar bus jobbie with the fault ground coming in from the main, and my neutrals are all on the neutral bars under the breakers where they belong.
Oh, by the way, I'm in the midst of finishing my basement and my electrical work was just inspected AND APPROVED last week!
I guess the inspector didn't actually look that hard?
Yarz
Lurker
MurderYota
Throbbing member
Put your grounds on a separate buss and put all of your new grounds on it as well. Neutrals get their own buss.
71PA_Highboy
An Unknown but Engorged Member
I get it now... Thanks for verifying I was finally understanding.
sdmuleman
Red Skull Member
The requirement for a ground wire in this situation is just plain bloody stupid. This is only needed if there's other conductors between the areas served by the 2 panels. For instance, if you have an iron water piping connected to ground at the main panel and leading to the other building near an outlet, and the subpanel only has a local ground. In the event of a fault, the ground rod at the sub panel would dissipate the fault current, but you could have a difference in ground potential between the 2, which means if some touched the pipe and subpanel grounded conductor they could be shocked.
This is however only a hazzard if there's a conductor connected to ground only at one end. If there's nothing conductive connecting the buildings, or if anything that is is tied to ground at both ends, then there is no hazard.
Functionally, a subpanel without a ground tie is the same as 2 different building with independent mains feeds - both have hot/hot/neutral coming in and a ground conductor at the main panel. No difference if you run hot/hot/neutral from a main panel, and have a separate ground & ground/neutral tie as subpanel.
This is one of the examples of why I really dislike the NEC - it's one size fits all made for the least common denominator, and requires what can be significant extra cost for absolutely zero actual benefit.
This is however only a hazzard if there's a conductor connected to ground only at one end. If there's nothing conductive connecting the buildings, or if anything that is is tied to ground at both ends, then there is no hazard.
Functionally, a subpanel without a ground tie is the same as 2 different building with independent mains feeds - both have hot/hot/neutral coming in and a ground conductor at the main panel. No difference if you run hot/hot/neutral from a main panel, and have a separate ground & ground/neutral tie as subpanel.
This is one of the examples of why I really dislike the NEC - it's one size fits all made for the least common denominator, and requires what can be significant extra cost for absolutely zero actual benefit.