multiple grounds
- Thread starter Mike01
- Start date
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ryan_618
Senior Member
- Location
- Salt Lake City, Utah
I don't think there is any advantage to having an individual EGC for each circuit, as oppsoed to sharing one for all circuits.
rcarroll
Senior Member
- Location
- Fort Collins, Colorado
IMO, the only disadvantage would be the cost of wire.
bphgravity
Senior Member
- Location
- Florida
If the single EGC is disconnected, you lose the effective fault path for several circuits. At the same time, there is only one connection to wory about making good and if the shared EGC is sized based on a larger branch circuit, the impedance of the fault path is reduced.
It's purely a deisgn consideration
It's purely a deisgn consideration
One-More thing
One-More thing
What about when people talk about noise when using shared ground conductors, on a computer network or other sensetive electronics? does the term noisy or dirty ground come into play that much or is it more dependant on the type of facility? Just curious to hear everyone elses' opinions. One additional item what would happien if you experienced multiple ground faults at the same time? If the ground conductor is sized for the largest OCPD and of 8 branches they are all 20A does this mean all I nead is a #12 ground from the panel ground to the ground bar assembly? What about multiple faults?
One-More thing
What about when people talk about noise when using shared ground conductors, on a computer network or other sensetive electronics? does the term noisy or dirty ground come into play that much or is it more dependant on the type of facility? Just curious to hear everyone elses' opinions. One additional item what would happien if you experienced multiple ground faults at the same time? If the ground conductor is sized for the largest OCPD and of 8 branches they are all 20A does this mean all I nead is a #12 ground from the panel ground to the ground bar assembly? What about multiple faults?
Last edited:
peter d
Senior Member
- Location
- New England
Mike01 said:
I think this issue has more to do with improper N-G connections (after the service disconnect) than anything else. Anything more than a few volts between ground and neutral indicates a problem.
got_nailed
Member
With most of the computer stuff I have worked it is an issue of ground to neutral. A lot of warranties will be void if you there is voltage on the ground.
Dedicated sub panels are the best for computers. But trying to keep everything else not plugged into the computer outlets is a pain in the as. We have red outlets for the generator, gray the computers, and white for everything else.
Most of the work I do is low voltage relay systems that are computer controlled. And the one thing I have had the most issues with is when there is voltage on the ground wires. All of the machines were built in Japan for the auto industry. A lot of it is 480 (i think) and then the computers that run them are 110. For the last few years the have been blowing computers and now that were tracing down all of the voltage leaks on the ground wires we have cut the problems to about 5% of what they were.
Dedicated sub panels are the best for computers. But trying to keep everything else not plugged into the computer outlets is a pain in the as. We have red outlets for the generator, gray the computers, and white for everything else.
Most of the work I do is low voltage relay systems that are computer controlled. And the one thing I have had the most issues with is when there is voltage on the ground wires. All of the machines were built in Japan for the auto industry. A lot of it is 480 (i think) and then the computers that run them are 110. For the last few years the have been blowing computers and now that were tracing down all of the voltage leaks on the ground wires we have cut the problems to about 5% of what they were.
- Location
- Illinois
- Occupation
- retired electrician
If there is any current flow on the grounded conductor (neutral) there will be voltage between the grounded and grounding conductors.
Don
got_nailed
Member
In typical wiring where there is a 2 or 3 circuit in a box. All of the grounds and neutrals are tied together. If there is a leak to ground on one circuit to ground it can follow other circuit ground back to the box.
If you test the circuit for equipment with the cb?s off and there is voltage between the neutrals and grounds. It can mostly be fixed by dedicated circuits.
Our problem was like this but different.
They moved a lot of stuff around so that every assembly line has it?s own high voltage and low voltage cb panels. As the plant grew they would add new panels and transformers and would have a rat?s nest of wires. One line could be feed by up to 8 different panels. This is what led to a lot of our problems with having voltage on our grounding / bonding system. Now when we have an issue it mostly affects one line instead of a huge chunk of the plant.
If you test the circuit for equipment with the cb?s off and there is voltage between the neutrals and grounds. It can mostly be fixed by dedicated circuits.
Our problem was like this but different.
They moved a lot of stuff around so that every assembly line has it?s own high voltage and low voltage cb panels. As the plant grew they would add new panels and transformers and would have a rat?s nest of wires. One line could be feed by up to 8 different panels. This is what led to a lot of our problems with having voltage on our grounding / bonding system. Now when we have an issue it mostly affects one line instead of a huge chunk of the plant.
Twoskinsoneman
Senior Member
- Location
- West Virginia, USA NEC: 2020
- Occupation
- Facility Senior Electrician
don_resqcapt19 said:
Could you please explain his statement?
- Location
- Massachusetts
Twoskinsoneman said:
Current on the grounded conductor results in voltage drop on the grounded conductor.
This voltage drop will result in a difference of potential between the grounded and grounding conductors.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Originally Posted by got_nailed
I believe got nailed didn't intend to say all the neutrals get tied to all the grounds but rather all the neutrals get tied together and all the grounds get tied together.
I would like to comment on the the neutrals tied together. If you tie all the neutrals of different circuits together in a jb after the load, you will be creating unwanted EMF. IMO this is not a good scenario.
I also don't think you would want a neutral from one circuit picking up the load from another circuit unless you are talking about a MWBC or at least, a load from another phase. If they are the same phase you may overload the neutral.
dereckbc said:
I believe got nailed didn't intend to say all the neutrals get tied to all the grounds but rather all the neutrals get tied together and all the grounds get tied together.
I would like to comment on the the neutrals tied together. If you tie all the neutrals of different circuits together in a jb after the load, you will be creating unwanted EMF. IMO this is not a good scenario.
I also don't think you would want a neutral from one circuit picking up the load from another circuit unless you are talking about a MWBC or at least, a load from another phase. If they are the same phase you may overload the neutral.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Splicing the neutrals together creates parallel neutrals which would be a violation. Parallel conductors have strict limitations starting with being #1/0 as a minimum size.
- Location
- Massachusetts
Connecting all the neutrals together from more than one circuit is an NEC violation.
250.24(A)(5) and 310.4
250.24(A)(5) and 310.4
got_nailed
Member
Neutrals get tied together and all the grounds get tied together (not under the same wire nut) from different circuits.
I know it is a NEC violation. But look at the older homes, the ones built in the last 20 years. Most will have in a least one spot where there is a set of light switches (3 or 4) and will have them fed by 2 circuits. Every time I have seen this the neutrals were tied together.
If I?m thinking right isn?t this the big reason that it?s a pain to install ark fault in to these homes.
I do know there was a 50 plus post a few months back about different circuits sharing neutrals.
I know it is a NEC violation. But look at the older homes, the ones built in the last 20 years. Most will have in a least one spot where there is a set of light switches (3 or 4) and will have them fed by 2 circuits. Every time I have seen this the neutrals were tied together.
If I?m thinking right isn?t this the big reason that it?s a pain to install ark fault in to these homes.
I do know there was a 50 plus post a few months back about different circuits sharing neutrals.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Around here most of the homes are what I would consider old.. Anywhere from 100-20 years. Except for a DIY basement a few years ago, I've never seen the neutrals all tied together in a JB.
jaylectricity
Senior Member
- Location
- Massachusetts
- Occupation
- licensed journeyman electrician
dereckbc said:
I know that all of the grounds should be tied together, but I thought you would keep your neutrals separate to avoid having to disconnect a circuit that you weren't working on.
cripple
Senior Member
- Location
- Santa Fe, New Mexico
multiple grounds
The main propose of the isolated ground system is to reduce the potential difference (electrical noise) between the circuit grounded (neutral) conductor and equipment grounding conductor. This potential is in realty the voltage drop on the neutral, which is proportional to the current flowing on the neutral conductor. To reduce the voltage drop (E=I * R), current being constant the only thing to do is to lower the impedance of the grounded (neutral) conductor. To lowering the impedance of neutral two things can be done:
1. Increase the size of the conductor,
2. Shorten the length of the conductor form the main bonding jumper (service) or system bonding jumper (separately derived system).
The other thing to keep in mind is since the equipment grounding conductor (dirty ground) is required to be connected to all non?current-carrying metal parts, which is creating ground loops. The isolated grounding conductor is breaking the ground loop, since it is insolated form all non?current-carrying metal parts, except for the grounding terminal on the receptacle to which the sensitive electronic equipment is connect.
The main propose of the isolated ground system is to reduce the potential difference (electrical noise) between the circuit grounded (neutral) conductor and equipment grounding conductor. This potential is in realty the voltage drop on the neutral, which is proportional to the current flowing on the neutral conductor. To reduce the voltage drop (E=I * R), current being constant the only thing to do is to lower the impedance of the grounded (neutral) conductor. To lowering the impedance of neutral two things can be done:
1. Increase the size of the conductor,
2. Shorten the length of the conductor form the main bonding jumper (service) or system bonding jumper (separately derived system).
The other thing to keep in mind is since the equipment grounding conductor (dirty ground) is required to be connected to all non?current-carrying metal parts, which is creating ground loops. The isolated grounding conductor is breaking the ground loop, since it is insolated form all non?current-carrying metal parts, except for the grounding terminal on the receptacle to which the sensitive electronic equipment is connect.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
jaylectricity said:
The only shock I've received whilst wiring in the last couple of decades has been due to a retard who thought that saving a conductor by "borrowing" a neutral from another circuit was a Good Idea...
[/rant]
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