I’m a Habitat volunteer with experience in all phases of home construction. We are currently building 5 homes. 4 of the homes have power going directly to the main breaker box….no problems here. The problem is the 5th house. Because of how it sits on the lot, the power comes in to the back of the house were the meter head and a disconnect switch are located. They then run SER cable to the front of the house and main breaker panel which is located in the garage. This is fine so far. During a recent lunch break which was provided in this garage, I noticed that the grounds and neutrals were bonded in this panel and in a nice way asked if this was correct. They looked at me like I was crazy. The job was directed by a professional electrician and it had passed inspection. I argued with the head of construction that this was actually a sub panel and we walked to the outside cutoff switch where I opened the box and showed him that the ground and neutral were also bonded there. He now agrees that it is probably an error but would be too costly to fix (SER cable is probably cut off too short to go to ground bar).
Should I press the correction? What are the potential problems if it is not corrected?
You get out of life what you put into it……minus taxes.
Marv
Replies
You are not a professional. It is not your house.
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My judgment as an engineer is that it is good enough. (Being code compliant is a different concern, but as an engineer I am not bound by prescriptive codes.)
First off, some of this is up to local utility rules, not code. It's not clear exactly where one lets off and the other begins.
Beyond that, while this is a technical violation of code, it doesn't, so far as I can think of (with my EE degree and a smattering of practical experience) represent any sort of significant safety hazard.
However, I'm a bit unclear on the particulars: How many wires run between the two boxes, and where are the grounding electrode (ground rod) connections?
How many wires run between the two boxes, and where are the grounding electrode (ground rod) connections?
The SER cable has 4 wires I believe. two hot, one neutral and one ground. Ground rod is tied into the outside cut off breaker.
You get out of life what you put into it......minus taxes.
Marv
I believe the problem arises if there is a short in a neutral wire of an appliance. Then the grounding system of the house may be energized.
You get out of life what you put into it......minus taxes.
Marv
edited for spelling
Edited 6/1/2007 11:20 am by Marv
If you have four wires, then it seems to me all you have to do is seperate the ground bar and the neutral bar. If the SEC is to short, add an extension using those split clamps.
"If the SEC is to short, add an extension using those split clamps."From 2005 NEC 250.64:(C) Continuous Grounding electrode conductor(s) shall be installed in one continuous length without a splice or joint except as permitted in (1) through (4):(1) Splicing shall be permitted only by irreversible compression-type connectors listed as grounding and bonding equipment or by the exothermic welding process.
Edited 6/5/2007 6:53 pm ET by CaseyR
Dang. Where do I find these irreversible compression-type connectors? What do they look like? I got to splice in a lead to the ground rod, where some $@&#$ scum stole it. And I ain't got an exothermic welder.
The irreversible compression connectors are a form of crimp connector that takes a very expensive tool and die. The exothermic welding , typically known as cadweld, is a much less expensive investment.
Ed
Casey, the section you quote is specifically in reference to the system grounding electrode conductor, i.e. the conductor that connects the service entrance to the grounding electrode(s), be they a set of rods, or water-pipe, a well-casing or whatever.
The ground wire in the SER is part of the equipment grounding system, an entirely different animal that can be spliced when needed and whose purpose is to keep the non-current-carrying parts of everything electrical downstream of the mainswitch bonded to the grounded (neutral) conductor, which is also bonded to the service ground.
It's a very important distinction between the two.
Ed
Edited 6/6/2007 7:03 pm ET by edlee
Edited 6/6/2007 7:10 pm ET by edlee
Simplest and most "proper" way to correct this is to leave the bond in the first box and remove it in the second. But it's safe as is. Bad neutral connection could cause the ground wire in the cable to overheat (assuming it's a size smaller, which is the norm), but only in very extreme conditions.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
There's a failure mode that'll leave one of the two boxes hot. I don't remember the details - Bill Hartmann will know...
Brooks
Only for certain wiring configurations could a single failure cause this. Need to know more about the grounding config to say for sure.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
I was thinking it took a dual failure. Everything's getting fuzzy in my dotage...Hmmm. A failure of the ground at the meter, and a failure of the sub-box's neutral assembly and an un-balanced load will leave the sub-box and all-down-stream components and their grounds hot. And a simple neutral failure would have the ground carrying the neutral's load without it being obvious you had a problem...
I wouldn't want my house to be wired like that...Brooks
I agree that it's wrong though likely reasonably safe.
I don't see why the grounding conductor couldn't be detached in the sub-panel, spliced and then tied in to a new grounding bussbar. Is there a bond between the neutral buss and the sheet-metal panel? That should be removed if a grounding bussbar is added.
Ask the electrician what is the point of running 4-wire if two of the conductors are bonded to each other at both ends? (there is no point)
Ed
The ground wire in the second panel should have been brought in and terminated at the ground bus, the neutral terminated on the neutral bus, with a jumper between. Simply removing the jumper would make it compliant.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
DanH: The ground wire in the second panel should have been brought in and terminated at the ground bus, the neutral terminated on the neutral bus, with a jumper between. Simply removing the jumper would make it compliant
Huh? The OP said that the grounds and neutrals are bonded. That could mean a bunch of different things in terms of the actual mechanical installation. The usual is to install the branch-circuit neutrals and equipment grounds on the same bussbar.
Your "should have been" is total speculation and in my experience, likely wrong. Residential-grade main breaker and MLO panels tend to come with a set of bussbars isolated from the can and with a bonding screw. The equipment-grounding bussbar is , in my experience, an accessory that needs to be purchased separately.
Ed
"Your "should have been" is total speculation and in my experience, likely wrong. Residential-grade main breaker and MLO panels tend to come with a set of bussbars isolated from the can and with a bonding screw. The equipment-grounding bussbar is , in my experience, an accessory that needs to be purchased separately."Some panels have two bus bars. One bonded to the case and the other one not. Then there is a strap/jumper between them. Remove the strap and you have a ground bus and isolated neutral bus.But having to buy a ground bus bar kit is no big deal. About $10 or less..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Bill H: Some panels have two bus bars. One bonded to the case and the other one not. Then there is a strap/jumper between them. Remove the strap and you have a ground bus and isolated neutral bus.
Hey whatever Bill. It's hard to cover every potentiality in an online chat forum.
Ed
Thanks everyone for the discussion. This panel has all the bars tied permanently together. The green screw can be removed separating it from he case and ground bars added. I'll try to talk them into this.You get out of life what you put into it......minus taxes.
Marv
Depending on local practice they might have to also move some of the neutral and ground wires to get them to land on the right busses..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
If it's wired as you describe, it's clearly a violation of the code. You have the bare wire and the insulated neutral wire acting as parallel conductors. This is definitely verboten.
The panel should be wired as a subpanel. Is there enough slack in the SER anywhere to gain some cable in to the box?
On the positive side, there are probably a few million boxes in the US where some home grown electrician has done the same thing without any bad consequences.
Edited 6/1/2007 8:09 pm ET by BoJangles
One more thing...When you refer to the "cutoff" switch, are you referring to a circuit breaker??
If not, then running the SER unprotected across the house to the other box is also a violation.
As the local inspector explained it to me, the issue is that, if the neutral conductor fails in that SER, the current will be carried by the ground wire. In most cables, the ground wire is smaller than the neutral conductor, which produces an unsafe condition. The solution is to separate the two so that, if the neutral conductor fails, things quit working.
But on a service entrance it's highly unlikely that you'll have severely unbalanced current on the 240V legs (all big loads are 240V), so neutral current will be well below ratings.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
"But on a service entrance it's highly unlikely that you'll have severely unbalanced current on the 240V legs (all big loads are 240V), so neutral current will be well below ratings."But the small unbalanced loads will have neutral current, which is now imposed on the ground wire. Half the neutral current in the neutral conductor, the other half in the ground conductor.The object is to eliminate ground current.Frank DuVal
Speaking of Bill H, anyone else notice he is MIA?Parolee # 40835
Been busy and when I saw the thread, most things had been covered..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I was hoping that you were just busy, and not flooded or Tornado'd.Parolee # 40835
Yeah. He would've been over this like white on rice. Vacation, maybe?George PattersonGeorge Patterson
I thought for sure he'd show up in this thread.
> The object is to eliminate ground current.I understand that. But it doesn't, by itself, create a hazard.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
I agree that it's unlikely, but I don't think the code people deal with likelihoods. Seems to me that they try to outlaw possibilities.What does it take to comply, anyway? You remove a green screw and attach all the white lines to one buss and all the bare lines to another. Why not do it?George Patterson
I agree -- it should be reasonably easy to bring it all into compliance if there is a 4-wire cable between the two panels and the second panel is a more or less standard breaker panel with bonding screw and provisions (at least) for a separate ground bar.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
"if the neutral conductor fails in that SER, the current will be carried by the ground wire."But, even if the neutral wire is working fine, the current divides between the two paths, and the ground wire carries half of the neutral current all the time. Not good!This is why you cannot parallel the neutral and ground conductors.Frank DuVal
That's only partially correct. It will split the current, but not in half. Since the neutral conductor is larger, it has less resistance. The current will divide itself in inverse proportion to the resistance on the conductors.
George: As the local inspector explained it to me, the issue is that, if the neutral conductor fails in that SER, the current will be carried by the ground wire. In most cables, the ground wire is smaller than the neutral conductor, which produces an unsafe condition. The solution is to separate the two so that, if the neutral conductor fails, things quit working.
George, if the neutral fails then you actually start getting some crazy stuff happening because the entire system goes from 120/240 to straight 240v. It's called "loose neutral" and if you ever want to get the utility company to your house fast, you call them up and tell them you think you have a loose neutral coming into the house.
Ed
You're talking about the neutral failing on the service line. I'm talking about the neutral conductor in that SEC between the input breaker and the load panel failing. If that fails, the current is carried by the ground wire, and there will be no sign of a problem unless the load builds up to the point that the ground wire overloads.George Patterson
I'm talking about the neutral conductor in that SEC between the input breaker and the load panel failing. If that fails, the current is carried by the ground wire, and there will be no sign of a problem unless the load builds up to the point that the ground wire overloads.
Only if the two wires are bonded in the sub-panel, which is not allowed, as everyone keeps saying.
Ed
But that is exactly the case here.George Patterson
This is dangerous and needs to be corrected. You have a ground loop, or parallel neutral circuit.
Imagine the current in this single phase 20 amp circuit:
A current of 20 amps flows from the service entrance (single breaker disconnect) to the second panel (the distribution panel) on a hot wire. The same 20 amps flows from the second panel to the 20 amp load.
The returning current of 20 amps flows along the neutral wire from the load to the second panel. So far so good. Now, that 20 amps of neutral current has two paths back to the service entrance since the neutral and ground wires are connected together at both panels.
So now the neutral wire between the second and first panel is only carrying 10 amps, and the ground wire is carrying 10 amps! The 20 amps is divided between the two conductors available.
This current can be measured with a clamp on ammeter. Have your electrician measure it if he doesn't see a problem with this parallel circuit.
I don't know about you, but I do not want current flowing in my ground wires. You can use E=IR to determine how far above ground potential your grounded equipment is now resting. Now recalculate with fault current and see how far above ground your equipment can be in extreme situations.
I have measured 50 amps of ground current in industrial applications where the neutral was grounded at a second point. Lots of weird control problems.
Keep your current carrying conductors separate from your equipment grounding conductors and your equipment will thank you. And so will your people.
Frank DuVal
The situation does cause some slight elevation of ground potential, but nothing "dangerous", unless this is a hospital.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
"I don't know about you, but I do not want current flowing in my ground wires. You can use E=IR to determine how far above ground potential your grounded equipment is now resting. Now recalculate with fault current and see how far above ground your equipment can be in extreme situations."You want to rethink that one?What would be the potential difference if you have a ground fault and it all flows through the SMALLER EGC?In case like this I don't see much of a safety issue. All you have meter and disconnect that is at a different poltential than the house wiring/equipment. And in many cases there won't be anything near by the meter with referenced to the house wiring.Now, for example if you had two "sub-panels" wired like this off the disconnect that where be much different and serious problem.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
BillH: In case like this I don't see much of a safety issue. All you have meter and disconnect that is at a different poltential than the house wiring/equipment. And in many cases there won't be anything near by the meter with referenced to the house wiring.
Now, for example if you had two "sub-panels" wired like this off the disconnect that where be much different and serious problem.
I agree with this, I think Bill addresses the crux of this specific OP's situation. We're going directly from service disconnect to distribution panel in an insulated, sheathed cable with no stops in between. It's in effect a 3-wire installation, running from the subpanel back to the bonded point of the system grounding electrode conductor.
Ed
"In case like this I don't see much of a safety issue. All you have meter and disconnect that is at a different potential than the house wiring/equipment. And in many cases there won't be anything near by the meter with referenced to the house wiring."Granted the E=IR voltage rise on the equipment grounding conductor will typically be low, there will be a large ground current flowing between the two panels, which will raise the EGC potential for all downstream outlets. So, when you plug your outdoor equipment into an outdoor outlet, the equipment case will be at a potential above the earth you are standing on. Maybe not enough to notice, but what if the ground is wet? What if I have a pacemaker and no shirt on? I wouldn't want to experiment with this as I have seen how much ground current can flow when the neutral and EGC are in parallel. Microprocessors hate it when there is noise on the ground.Frank DuVal
there will be a large ground current flowing between the two panels, which will raise the EGC potential for all downstream outlets.
Frank, would you explain this to me in more detail?
How is that different than when there is current flowing on the grounded conductor of the service entrance and you have your equipment grounding conductor(s) and your grounded conductor bonded at the main switch?
According to what I understand you saying, wouldn't that put the same potential on those same downstream outlets?
Ed
When you bond the grounded conductor (neutral) to the equipment grounding conductors (bare wire) to ground rods, water pipes, building metal, etc at the service entrance, you are trying to eliminate any potential above earth of the equipment grounding conductors and giving a fault path for shorts to ground.If there is no ground current, then there should be no rise in potential above earth of the equipment grounding conductors anywhere in the circuit.If one connects the neutral conductor to the equipment grounding conductors at two locations, the neutral and ground circuits between these two locations are now a parallel circuit, and the neutral current will now divide between the two paths it sees. The grounding conductor will now carry half of the neutral circuit current.So if you only connect the neutral to ground at one point on the system, everything is fine and no ground current flows, except at the time of a fault to ground.Draw the schematic and it will be obvious what is going on. It did not occur to me what was happening until I used a clamp on ammeter on a ground conductor while troubleshooting equipment problems. Then the light bulb went off.In the case of this thread, if the second panel was where the ground bonding took place, then everything EXCEPT the meter and service entrance breaker box would be at ground potential, and all equipment and people would be happy. But of course that is not allowed by code either....Frank DuVal
OK, so then, see if I understand what you are saying:
Suppose you have a meter socket, then maybe 50' of SE cable run to a disconnect, which will be the service disconnect.
Suppose the grounding and bonding of the system occurs at this main disconnect, i.e. GEC and "neutral".
Will the non-current-carrying metal of the meter socket be at a potential above earth?
Ed
Yes, the meter case will be above earth potential.In the case of a typical 200 amp service entrance, 4/0 aluminum wire is used. 4/0 aluminum has a resistance of .0804 ohms per 1000 feet.
A 50 foot run, .0804 / 1000 * 50 = .00402 ohms.If the neutral current was 50 amps, the potential rise would be
.00402 * 50 = .201 volts.At the maximum 200 amp neutral current, which would be not likely to happen, the potential rise would be .00402 * 200 = .804 volts. Still under one volt. So this is why the others said there was no safety issue, as the voltage is very low. Now in this case you have, no ground current is flowing, so I have no issue either. However, you do have 50 feet of unfused SE cable, so I do not think it will pass code.Frank DuVal
Frank,Not to divert this discussion, but I have a question.I see 4/0 typically used from meter to masthead. But some much smaller gauge used from the top of the masthead to the street.Do you have any idea what guage that feed wire is ?In my own application, (200 amp RV service panel), Which is typical of every new setup I have seen in the past ten years or so... 4/0 was demanded by the electric company, from meter to masthead. But then they ran what looks like 4 from there to the street.I see that for any street run to masthead, up to nearly a hundred feet. For any panel size up to 200 amps.
Fight fire with water.
Edited 6/4/2007 5:41 am by Luka
I do not know the drop size the power company uses. I do know they have their own rules, and do not use the NEC. Maybe their rules take into account the cooling effect of air.Around these parts a 200 amp meter base seems the smallest the power company stocks. So even a milking shed gets a 200 amp service panel and meter base with owner supplied 4/0 SE cable between them. But, the power company installs the SE cable from the meter to the masthead.Frank DuVal
Thank you Frank, and Ed.=0)I remember something said by the electric company employee, about the fact that it was air cooled... That's probably it.Still makes everything that WE are required to do, seem like dreadful overkill.Don't get me wrong. I tend to overkill even above what is required. I just think they should hold up their end of the line a bit better as well. I can't help seeing that #2 line as being a bottlenect in front of my service panel. I think at least 1/0 would be a good compromise...
Fight fire with water.
The limiting factor is insulation and tempature that the insulation can withstand.The NEC assume that most wiring is in walls or insulation where cooling is limited. And above that it requires derating is you have bundled cables together or multiple wires in conduit.But in free air you have much better cooling.For example there is a type TFE insulated niekl coated copper that is rated at 250*C and #2 381 amps.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
The limiting factor is insulation and tempature that the insulation can withstand.
What about voltage drop? Do the power companies typically consider that, or don't they care- or is it usually not a big issue?
Don
I started to add VD, but that was a different than what was being discussed here.My guess is that in most "standard" subdivision drops the run are relatively short and known. So VD is not an issue.But have somthing like a 200-300 ft drive way and the discussion of who pays for the run and if you have a primary service (ie, run high voltage to the house and a transformer) or the POCO has the transformer on the pole at the road and secondary voltages are run up the driveway becom a BIG ISSUE..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
"What about voltage drop? Do the power companies typically consider that, or don't they care- or is it usually not a big issue?"
Remember they are running a much higher voltage on their side of the transformer, so voltage drop isn't as big a problem. It varies on location, but around here I believe 13,800 volts is a common value on the primary side of the transformer in residential areas.
Voltage drop is often taken care of by adjusting the output voltage - different taps. Not the best solution, but it usually works.
The NEC does have an ampacity table for conductors in "free air", and the differences are large. For example (using same insulation and temp ratings), regular #2 AWG Cu conductors (not service feeders) are rated for 130 amps in conduit or cable, but in "free air" are rated for 190 amps, almost 50% higher. This is from my 1999 NEC, but I doubt the relationship has changed.
As has been stated, the NEC doesn't apply to utilities.
once I was able to get 87 A on some #12 TW everything was working fine till somebody stepped on one of the wires..then it was the 4th of July....ah to be young again..:)
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., wer ist jetzt der Idiot ?
once I was able to get 87 A on some #12 TW
everything was working fine till somebody stepped on one of the wires..then it was the 4th of July....ah to be young again..:)
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Yee-hahhhhhhhh!!!!!!!!!
the good ole days, huh?.
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., wer ist jetzt der Idiot ?
Around here, Northeast Utilities likes #2 Al for all the 100a-200a overhead services. As Frank said, they follow their own rules and the wires in free air can carry considerably higher currents.
And it seems to work.
Underground utility feeds are a different story..........they tend to run big stuff regardless of the service size.
Ed
Aside re: service drop wire gauges.
I live in a late 70's house, 125A, split buss panel was here when we moved in in the early 90's, underground service - 2/0 aluminum, direct burial. Oil heat; gas stove, dryer and hot water heater; 2 AC units (1= main house + 1 = studio)
About 1993 we were going to add a 600 sqft addition to house a studio. Decided to upgrade service to 200A, and pull a 100A subpanel to service the studio.
My electrician buddy said he would install the new meter pan, arrange for the power to be shut off, install the new SEP, handle inspections, etc. Power company showed up at about 0800 to disconnect at an underground box.
We dutifully ran 4/0 AL from the meter to the SEP - power company left their 2/0 AL in place and told us to reconnect to new meter pan.
We questioned their feed size - reply: "Company policy says we only replace an underground service run if it burns down." As an aside, he added that most people don't really need 200A of service - they just need a lot of breakers.
After 14 problem-free years of service, I would say he and the company policy was right, at least in my case.
Jim
Never underestimate the value of a sharp pencil or good light.
Thank you Frank, I find that I do understand what you are saying about the OP situation.
Now in this case ........ you do have 50 feet of unfused SE cable, so I do not think it will pass code.
I'm not gonna get into this!
Ed