subpanels
- Thread starter pelican
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electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
Re: subpanels
Yes
Yes
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: subpanels
I would just like to add a comment on the reason why we isolate the neutral from the ground wire in any sub-panel.
If the neutral wire and the ground wire were bonded togeather in a sub-panel, you would have un-wanted currents flowing over the ground wire as well as the neutral wire. The only time that current should be on the ground wire is when you an electrical fault to ground.
I would just like to add a comment on the reason why we isolate the neutral from the ground wire in any sub-panel.
If the neutral wire and the ground wire were bonded togeather in a sub-panel, you would have un-wanted currents flowing over the ground wire as well as the neutral wire. The only time that current should be on the ground wire is when you an electrical fault to ground.
Re: subpanels
In some subpanel, the ground and the neutral buses are together. I only seen that in a 100 amp service. That is only subpanel I install was 100 amp.
Now I seen in a 200 amp subpanel the ground and the neutral buses are not together. I guess that will answer my ? Why was it always like that.
In some subpanel, the ground and the neutral buses are together. I only seen that in a 100 amp service. That is only subpanel I install was 100 amp.
Now I seen in a 200 amp subpanel the ground and the neutral buses are not together. I guess that will answer my ? Why was it always like that.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: subpanels
You must read the panel label to see if a panel is for service equipment only. These panels will not have the neutral bar isolated from the can. Most panels will have a jumper bar that is allowed to be removed and the side that has the bonding screw will be for the grounding conductors and the isolated side will be used for the neutrals. But you must look at the label to see if this is allowed. Also there are some panels that will only have enough terminals for the neutrals, if NM cable is used then you will have to order the grounding bar kit that is listed for that panel. Also these panels will need this grounding bar kit since they don't identify the neutral bar for the connection of grounding conductors (408.20) . T&B is one of those such panels.
You must read the panel label to see if a panel is for service equipment only. These panels will not have the neutral bar isolated from the can. Most panels will have a jumper bar that is allowed to be removed and the side that has the bonding screw will be for the grounding conductors and the isolated side will be used for the neutrals. But you must look at the label to see if this is allowed. Also there are some panels that will only have enough terminals for the neutrals, if NM cable is used then you will have to order the grounding bar kit that is listed for that panel. Also these panels will need this grounding bar kit since they don't identify the neutral bar for the connection of grounding conductors (408.20) . T&B is one of those such panels.
Re: subpanels
friebel, If the EGC is insulated who cares if neutral current flows on it? I know this is a silly question but really, If its insulated who cares? the only problem I could see is the EGC might not be able to handle all the fault current if it already has some neutral current on it, and depending how its bonded at the panel you could have current on the panel enclosure and that couuld be a shock hazrd.
friebel, If the EGC is insulated who cares if neutral current flows on it? I know this is a silly question but really, If its insulated who cares? the only problem I could see is the EGC might not be able to handle all the fault current if it already has some neutral current on it, and depending how its bonded at the panel you could have current on the panel enclosure and that couuld be a shock hazrd.
luke warmwater
Senior Member
Re: subpanels
And, maybe the person working on the system?
CODE, for one. 250.32(B)(1)
And, maybe the person working on the system?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: subpanels
The current rating of one panel versus another is irrelevant. The fact that a panel may or may not be service-rated is also irrelevant. The main has the neutral and ground bus bonded, and it has to be service-rated. Any and all sub-panels, whether or not you buy one that is service-rated, must have the neutral and ground buses separated.
It?s not a silly question, for there is no such thing. What you have to realize, however, is that the EGC is connected to the exterior metal surfaces of every electrical device in the building. That puts every metal object in parallel with each other. Thus, while the insulated EGC is carrying current, and while a person might not care about that, current could also be flowing through the door of the electrical panel as well as the door of the refrigerator, through the lamp stand, through the lighted make-up mirror, and (I suppose it would not be impossible) through the kitchen sink.
The current rating of one panel versus another is irrelevant. The fact that a panel may or may not be service-rated is also irrelevant. The main has the neutral and ground bus bonded, and it has to be service-rated. Any and all sub-panels, whether or not you buy one that is service-rated, must have the neutral and ground buses separated.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: subpanels
"If the EGC is insulated who cares if neutral current flows on it? "
Two issues.
1. The EGC can be a raceway such as EMT. EMT fittings are not designed to carry current, except briefly under fault condtions. A loose connection can result in heating of the surrounding material, if wood, this is called pyrophoric carbonization.
2. If the EGC is emt, and carrying neutral current, if you open up the emt, and come in contact with it, under a series condition you could recieve a severe shock or die.
For a good explaination of the above, I recommend Mike Holts Grounding and Bonding text. Its $30 and well worth it.
"If the EGC is insulated who cares if neutral current flows on it? "
Two issues.
1. The EGC can be a raceway such as EMT. EMT fittings are not designed to carry current, except briefly under fault condtions. A loose connection can result in heating of the surrounding material, if wood, this is called pyrophoric carbonization.
2. If the EGC is emt, and carrying neutral current, if you open up the emt, and come in contact with it, under a series condition you could recieve a severe shock or die.
For a good explaination of the above, I recommend Mike Holts Grounding and Bonding text. Its $30 and well worth it.
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: subpanels
To: jes25, I hope that the explanation that Tom Baker gave to you, that it has convinced you that we must isolate the egc(equipment grounding conductor) from the neutral in any sub-panel, and the reason why we need to do this.
I know when I started out as an apprentice electrician many years ago, we did not isolate them. As time goes by we do get smarter, hopefully. Take care. bob friebel
To: jes25, I hope that the explanation that Tom Baker gave to you, that it has convinced you that we must isolate the egc(equipment grounding conductor) from the neutral in any sub-panel, and the reason why we need to do this.
I know when I started out as an apprentice electrician many years ago, we did not isolate them. As time goes by we do get smarter, hopefully. Take care. bob friebel
physis
Senior Member
Re: subpanels
I've read this whole thread and noticed that nobody has pointed out the specific code that says you can only have one main bonding jumper at the main panel. After looking for about 15 minutes, although I've read it a few hundred times, I can't find this code. For those of you who remember, yes, I still hate the way the NEC is written!!! Back to the subject, the code is very clear about the main bonding jumper (and there is only one allowed) I just don't know how one would find it. (I need the CD)
I'm curious why nobody has sited this code yet.
I've read this whole thread and noticed that nobody has pointed out the specific code that says you can only have one main bonding jumper at the main panel. After looking for about 15 minutes, although I've read it a few hundred times, I can't find this code. For those of you who remember, yes, I still hate the way the NEC is written!!! Back to the subject, the code is very clear about the main bonding jumper (and there is only one allowed) I just don't know how one would find it. (I need the CD)
I'm curious why nobody has sited this code yet.
- Location
- Massachusetts
Re: subpanels
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