I just ran a 4 wire feed in PVC to a 100 amp subpanel in a separate building, no metallic paths attatching the two buildings. I ran two hots, a neutral, and a ground wire from a 200amp main panel in the first structure. My question is on the 100 amp subpanel, it came with a green screw (not installed) that the instructions said would need to be installed if it was necessary to bond the panel to the neutral. I know I didnt need this since I ran a 4 wire system...but my question is I thought if I ran a 3 wire system I would have to tie the ground buss to the neutral buss..the panel has what looks like it already has a tie bar from the ground buss to the neutral buss at the top? Should this be here? I looked at the 200 amp main and it also has a tie bar from the neutral buss to the ground buss. Is this correct? I thought there should be no mechanical connection between the ground or neutral buss but maybe I am missing something?
Does this panel have the nuetral and gnd buses bonded?
- Thread starter maiden70
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websparky
Senior Member
- Location
- Cleveland, Ohio
Re: Does this panel have the nuetral and gnd buses bonded?
maiden70,
You are correct, do not install the green screw.
The two busses you refere to are both neutral busses and connected together.
You will need to add a separate grounding terminal strip to land all of your EGC's and the grounding wire that you ran with the feeders from the other building.
You will also need to bond the water line and drive a ground rod, both of which will be landed on the strip.
Dave
maiden70,
You are correct, do not install the green screw.
The two busses you refere to are both neutral busses and connected together.
You will need to add a separate grounding terminal strip to land all of your EGC's and the grounding wire that you ran with the feeders from the other building.
You will also need to bond the water line and drive a ground rod, both of which will be landed on the strip.
Dave
Re: Does this panel have the nuetral and gnd buses bonded?
Dave,
Erased my first response, read some more and am getting more informed
. I now understand that the neutral to ground tie bar should be there on the original panel because that is the service disconnect. I also see that it has been stated that the tie bar between the neutral and ground on the sub panel should not be there, but does it matter that I have a main breaker in the sub panel and am using it as a main disconnect for that panel? Essentially the 100 amp feeder breaker in the 200 amp supply panel is protecting the feeder wires to the sub panel and the 100 amp breaker in the sub panel is the service disconnect for that panel...so should I remove the tie bar between the gnd and neutral busses on the sub panel or leave it?
[ June 28, 2003, 10:49 PM: Message edited by: maiden70 ]
Dave,
Erased my first response, read some more and am getting more informed
. I now understand that the neutral to ground tie bar should be there on the original panel because that is the service disconnect. I also see that it has been stated that the tie bar between the neutral and ground on the sub panel should not be there, but does it matter that I have a main breaker in the sub panel and am using it as a main disconnect for that panel? Essentially the 100 amp feeder breaker in the 200 amp supply panel is protecting the feeder wires to the sub panel and the 100 amp breaker in the sub panel is the service disconnect for that panel...so should I remove the tie bar between the gnd and neutral busses on the sub panel or leave it?[ June 28, 2003, 10:49 PM: Message edited by: maiden70 ]
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: Does this panel have the nuetral and gnd buses bonded?
OK,
Typically there are two verticle bars, one on the outside of each verticle row of breakers. These two bars are joined via a jumper bar across the top. This bar is never removed. These two bars are always neutral bars and are insulated from the enclosure.
When this panel is the first means of disconnect from the service, the green screw is installed through one of these bars, effectivly bonding the bars to the enclosure and the gounding electrode conductor is also landed on these two bars along with the equipement grounds and any bonding. There is only one service disconnect.
When this same panel is installed at a separate building, as in your example, there is a slight difference. The green screw is NOT installed and therefor the neutral bars are not bonded to the enclosure. Both bars are now only for neutrals. All of the grounding conductors must be separate from neutrals in this panel. This is where the extra bar is installed in and attached to the enclosure only. This grounding bar is where all of the equipement grounds go to and where the grounding electrode concuctor goes to, and where any other bonding or grounding takes place.
This second panel is not a service disconnect. It is a sub-panel or sub-service panel.
Hope this helps.
Dave
OK,
Typically there are two verticle bars, one on the outside of each verticle row of breakers. These two bars are joined via a jumper bar across the top. This bar is never removed. These two bars are always neutral bars and are insulated from the enclosure.
When this panel is the first means of disconnect from the service, the green screw is installed through one of these bars, effectivly bonding the bars to the enclosure and the gounding electrode conductor is also landed on these two bars along with the equipement grounds and any bonding. There is only one service disconnect.
When this same panel is installed at a separate building, as in your example, there is a slight difference. The green screw is NOT installed and therefor the neutral bars are not bonded to the enclosure. Both bars are now only for neutrals. All of the grounding conductors must be separate from neutrals in this panel. This is where the extra bar is installed in and attached to the enclosure only. This grounding bar is where all of the equipement grounds go to and where the grounding electrode concuctor goes to, and where any other bonding or grounding takes place.
This second panel is not a service disconnect. It is a sub-panel or sub-service panel.
Hope this helps.
Dave
Re: Does this panel have the nuetral and gnd buses bonded?
This will add some confusion, but here goes...Siemans panels have a bolt on tie link from the left to right bus. When it is necessary to separate the equipment ground conductors from the neutral conductor, the link is removed and replaced with a plastic retainer. The green screw is installed in the ground bus, to bond the can. The green screw is not a main bonding jumper as indicated in the handbook, it is a plain old bond(short).
This will add some confusion, but here goes...Siemans panels have a bolt on tie link from the left to right bus. When it is necessary to separate the equipment ground conductors from the neutral conductor, the link is removed and replaced with a plastic retainer. The green screw is installed in the ground bus, to bond the can. The green screw is not a main bonding jumper as indicated in the handbook, it is a plain old bond(short).
Re: Does this panel have the nuetral and gnd buses bonded?
thanks guys,
I understand now that with the sub panel I want the grounding and neutral busses separate even though the panel has a main breaker..is that correct? The only reason I question why I cant remove the tie bar and use one of the horizontal busses as a ground is because the label inside the panel notes one of the busses as the ground bus (if needed). If I remove the tie bar between the busses and bond the buss now considered the ground to the enclosure would that be good? Or are you saying that the two busses are tied together regardless if I remove this tie bar? This is a square D homeline 100 amp service.
thanks guys,
I understand now that with the sub panel I want the grounding and neutral busses separate even though the panel has a main breaker..is that correct? The only reason I question why I cant remove the tie bar and use one of the horizontal busses as a ground is because the label inside the panel notes one of the busses as the ground bus (if needed). If I remove the tie bar between the busses and bond the buss now considered the ground to the enclosure would that be good? Or are you saying that the two busses are tied together regardless if I remove this tie bar? This is a square D homeline 100 amp service.
Re: Does this panel have the nuetral and gnd buses bonded?
Are you really a 70 year old maiden?
On panels with a factory installed main, and marked "for service only", the tie link is not removable. Those marked "suitable for service equipment" may have a removable link to make them
for dual application.
MLO panels will usually have a removable tie link.
This tie link is the main bonding jumper. The exception No.1 of 250.28 implies that the green screw is the main bonding jumper.
On a NM wiring method job, the green screw is only a green screw. It bonds the enclosure to the neutral and ground electrode conductors. It does not meet the definition of a main bonding jumper.
Are you really a 70 year old maiden?
On panels with a factory installed main, and marked "for service only", the tie link is not removable. Those marked "suitable for service equipment" may have a removable link to make them
for dual application.
MLO panels will usually have a removable tie link.
This tie link is the main bonding jumper. The exception No.1 of 250.28 implies that the green screw is the main bonding jumper.
On a NM wiring method job, the green screw is only a green screw. It bonds the enclosure to the neutral and ground electrode conductors. It does not meet the definition of a main bonding jumper.
Re: Does this panel have the nuetral and gnd buses bonded?
LOL I would explain the maiden70 thing but who wants stories anyway..checked this panel and the tie bar isnt removable. I bought a grounding condutor buss and installed it in the panel, and then tied my ground wire from the rod and the ground wire from the main panel to it. Dave was right with his first response, it just threw me because this panel was "recommended" to me for my install..no mention was made of needing another bus. Thanks for all the help, should be good to go now.
LOL I would explain the maiden70 thing but who wants stories anyway..checked this panel and the tie bar isnt removable. I bought a grounding condutor buss and installed it in the panel, and then tied my ground wire from the rod and the ground wire from the main panel to it. Dave was right with his first response, it just threw me because this panel was "recommended" to me for my install..no mention was made of needing another bus. Thanks for all the help, should be good to go now.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: Does this panel have the nuetral and gnd buses bonded?
The important thing to understand here is that the only place the neutral and ground are connected together is at the service disconnect right after the meter. This can be a main breaker panel containing other branch circuit breakers or a separate breaker or fusible disconnect located away from the branch circuit panel. The service neutral, load neutral and grounds such as the equipment ground(s) , cold water, grounding electrodes and the housing itself are tied together by a common bus.
Any panel after this point is a sub panel and will have separate equipment ground and neutral bars.
Panels can be used for both purposes and manufacturers are always designing different ways to achieve this. With some panels you use a bonding screw to bond the neutral to ground and then install a separate ground bus if needed. Others have a jumper that you remove to separate the two buses on either side of the panel. You install a bonding screw to make one an equipment ground. Whatever. Point is that if you understand the concept you can just look at the panel and see what needs to be done to configure it for either a main panel or a sub panel.
The important thing to understand here is that the only place the neutral and ground are connected together is at the service disconnect right after the meter. This can be a main breaker panel containing other branch circuit breakers or a separate breaker or fusible disconnect located away from the branch circuit panel. The service neutral, load neutral and grounds such as the equipment ground(s) , cold water, grounding electrodes and the housing itself are tied together by a common bus.
Any panel after this point is a sub panel and will have separate equipment ground and neutral bars.
Panels can be used for both purposes and manufacturers are always designing different ways to achieve this. With some panels you use a bonding screw to bond the neutral to ground and then install a separate ground bus if needed. Others have a jumper that you remove to separate the two buses on either side of the panel. You install a bonding screw to make one an equipment ground. Whatever. Point is that if you understand the concept you can just look at the panel and see what needs to be done to configure it for either a main panel or a sub panel.
- Location
- Illinois
- Occupation
- retired electrician
Re: Does this panel have the nuetral and gnd buses bonded?
hbiss,
While you are correct that most panels can be used a either service or sub-panels, there are some that are marked "suitable only for use as service equipment". In these panels the grounded bus is permentaently bonded to the enclosure and cannot be used as a sub-panel.
Don
hbiss,
While you are correct that most panels can be used a either service or sub-panels, there are some that are marked "suitable only for use as service equipment". In these panels the grounded bus is permentaently bonded to the enclosure and cannot be used as a sub-panel.
Don
Re: Does this panel have the nuetral and gnd buses bonded?
I understand these previous posts re; not bonding neutrals & grounds @ subpanels .. but can someone PLEASE give me a clear and reasonably easy to digest reason why this has to be done. I'm still confused. I know it relates to possbly putting current on grounding sources .. cold water lines etc. but obviously I'm still not clear on this and I get asked ALL the time as a real estate inspector when I find continuity on these ?????
I understand these previous posts re; not bonding neutrals & grounds @ subpanels .. but can someone PLEASE give me a clear and reasonably easy to digest reason why this has to be done. I'm still confused. I know it relates to possbly putting current on grounding sources .. cold water lines etc. but obviously I'm still not clear on this and I get asked ALL the time as a real estate inspector when I find continuity on these ?????
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
- Occupation
- ESI, PI, RBO
Re: Does this panel have the nuetral and gnd buses bonded?
You will always get continuity because they are electrically the same at the main panel.
Mike P.
You will always get continuity because they are electrically the same at the main panel.
Mike P.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Does this panel have the nuetral and gnd buses bonded?
Eagle
The main reason for the main bonding jumper is for fault path. The grounding always has to be bonded to the neutral of the service. this provides a return path for a ground fault. if this was not done the current would try to go through the earth to get back to the source (transformer) the resistance of the earth at 25 ohm's would not conduct 5 amps this would not allow for the opening of a over current protector (breaker or fuse) this would also allow for all the grounding to become hot (120 volts to ground) this would put a shock hazarded at every thing that is connected to the grounding sys. including the ground rod remember the ground rod is there only for the protection from lightning strikes and incase of a contact from a source of higher voltage. not for the tripping of breakers and fuses! The reason for the separation of the grounding and neutrals at a remote sub-panel is to keep the voltage potential on the grounding at 0 volts if the neutral is bonded to the grounds at a remote panel the voltage drop on the neutral will be present between the grounds and earth. Without the bond there will be no voltage on the grounds without current on the grounding there is no voltage drop. the reason that the NEC allows for the bonding of the grounds and neutral at a remote building only when there is no other metal paths between the two buildings is that that the voltage drop of the neutral will be always less than the voltage drop of the earth so with a grounding electrode installed there will be no potential for shock hazard. If there was any metal paths then this path could have the main service grounding potential without the voltage drop that the earth would provide so the voltage drop of the neutral would have a voltage potential between it and this metal path.
hope this helps.
[ July 03, 2003, 02:47 AM: Message edited by: hurk27 ]
Eagle
The main reason for the main bonding jumper is for fault path. The grounding always has to be bonded to the neutral of the service. this provides a return path for a ground fault. if this was not done the current would try to go through the earth to get back to the source (transformer) the resistance of the earth at 25 ohm's would not conduct 5 amps this would not allow for the opening of a over current protector (breaker or fuse) this would also allow for all the grounding to become hot (120 volts to ground) this would put a shock hazarded at every thing that is connected to the grounding sys. including the ground rod remember the ground rod is there only for the protection from lightning strikes and incase of a contact from a source of higher voltage. not for the tripping of breakers and fuses! The reason for the separation of the grounding and neutrals at a remote sub-panel is to keep the voltage potential on the grounding at 0 volts if the neutral is bonded to the grounds at a remote panel the voltage drop on the neutral will be present between the grounds and earth. Without the bond there will be no voltage on the grounds without current on the grounding there is no voltage drop. the reason that the NEC allows for the bonding of the grounds and neutral at a remote building only when there is no other metal paths between the two buildings is that that the voltage drop of the neutral will be always less than the voltage drop of the earth so with a grounding electrode installed there will be no potential for shock hazard. If there was any metal paths then this path could have the main service grounding potential without the voltage drop that the earth would provide so the voltage drop of the neutral would have a voltage potential between it and this metal path.
hope this helps.
[ July 03, 2003, 02:47 AM: Message edited by: hurk27 ]
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