Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 03-08-2008, 01:15 PM   #16
General Contractor
 
joasis's Avatar
 
Join Date: May 2006
Posts: 876
Share |
Default

Question regarding a Sub-panel


I enjoy seeing the posts work out where everyone is on the same page....now, the one offending post is gone, let's keep this civil, thanks guys, Jay

__________________
Ladwig Construction
Hennessey, Oklahoma
405 853 1563



joasis is offline   Reply With Quote
Old 03-08-2008, 01:20 PM   #17
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,004
Default

Question regarding a Sub-panel


Quote:
Originally Posted by DaleB View Post
I have a question regarding a sub panel. My understanding is that if you're putting in a sub panel it must be of a lower amperage than the main panel. The guys at the Home Depot said that you could run a 100amp sub panel off of a 100 amp main panel. Is this right?? I alwasy thought that you needed the lower amperage in the sub panel to kick off anything in the sub panel but not the main panel. If you have a 100 amp main and sub panel won't that cause problems?? Any information will be appreciated. Thanks.
It would be prudent to check the labeling for the maximum bus stab rating or maximum branch circuit breaker allowed. It will usually be listed as the combined amp rating rating per stab (each stab will have 2 breakers connected to it) or it will be listed as maximum branch breaker allowed. For a 100 amp mains panel I think when you closely examine the label it will not allow a 100 amp breaker on a buss stab. As an example Square d usually states " sum of branch breakers not to exceed xxx per bus stab". This is almost always less than the main breaker rating in most residential load centers.

Just my thoughts.
Stubbie is online now   Reply With Quote
Old 03-08-2008, 01:33 PM   #18
Licensed Electrician
 
jrclen's Avatar
 
Join Date: Feb 2008
Location: central wisconsin
Posts: 982
Default

Question regarding a Sub-panel


Quote:
Originally Posted by Stubbie View Post
It would be prudent to check the labeling for the maximum bus stab rating or maximum branch circuit breaker allowed. It will usually be listed as the combined amp rating rating per stab (each stab will have 2 breakers connected to it) or it will be listed as maximum branch breaker allowed. For a 100 amp mains panel I think when you closely examine the label it will not allow a 100 amp breaker on a buss stab. As an example Square d usually states " sum of branch breakers not to exceed xxx per bus stab". This is almost always less than the main breaker rating in most residential load centers.

Just my thoughts.
Interesting Stubbie, I've never seen that. Of course I've not looked either. Is that on a QO load center? No inspector has every called me on it either. I guess I better spend more time looking at the label. You are 100% correct about it being prudent to check.

Last edited by jrclen; 03-08-2008 at 01:52 PM. Reason: the last sentence seemed like a good idea to add
jrclen is offline   Reply With Quote
Old 03-08-2008, 06:59 PM   #19
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,004
Default

Question regarding a Sub-panel


To my knowledge all load centers have a bus stab rating. For what it is worth this is something that was brought to my attention by a NACHI inspector about a year or so ago. I frankly had never paid any attention to that on a panel label. I have a 25 year old Challenger/Sylvania 200 amp breaker panel that states " sum of branch circuit breakers installed not to exceed 125 amps per branch circuit bus stab." this just to show as an example how old this specification has been around.
I can't say as I have ever talked to anybody in the trade that has ever paid any attention to that specification. The inspector that showed me this does right it up when he finds it. I have never met a codes official however that has written that up as a violation. I simply bring it up as food for thought. I'll spend a little time to see if I can locate the information and provide some links to verify what I have stated. I don't think I would change how I do things as I think we have all put 100 amp sub-feeds in 100 amp mains at sometime in our careers. This is just one of those technicalities that is often times overlooked at least it has by me for many years.. I've never heard of it being an issue as far as overheating the bus stab but then again I don't have the data to say one way or the other.

EDIT: A quick search on the Seimens site shows a 70 amp as the maximum branch breaker for a 100 amp panel and 100 amps is the maximum branch breaker for a 125 amp load center... if the bus is aluminum. I don't see it specified for the copper bus load centers. So this may be a key difference worth noting. I have not been able to locate this information at the square d site. A Qo panel has copper busses so it could be that it will allow a branch breaker equal to the mains.
Attached Thumbnails
Question regarding a Sub-panel-bus-stab-rating.jpg  

Last edited by Stubbie; 03-08-2008 at 07:37 PM.
Stubbie is online now   Reply With Quote
Old 03-08-2008, 08:38 PM   #20
Member
 
Join Date: Mar 2008
Posts: 32
Default

Question regarding a Sub-panel


John,
Thanks very much for your concern. Actually, it's not my place but a friend's so let it burn. Seriously though, thank you very much, I usually have a good understanding of what needs to be done but got thrown for a loop on this for some reason. One last thing though, I guess I don't understand why your use four wire on the sub panel but there is only three wire coming in from the service drop itself. I know it pertains to grounding issues but that's where I get lost. (I did some reason reading last night but now I'm even more confused) Is there a simply explanation for a dummy? PS- I think you might have a good idea with having someone check this out rather than being the buddy that burned his buddy's place down. Thanks.
DaleB is offline   Reply With Quote
Old 03-08-2008, 09:11 PM   #21
Member
 
Join Date: Nov 2007
Posts: 101
Default

Question regarding a Sub-panel


sorry to butt in here.

but i am also planning for a subpanel off my Cutler Hammer 200 Amp Main Service panel. I have 6 open slots but need 14 circuts (finishing my basement) thats the reason for my subpanel addition.

My question is.
Coming out of the main do I need to put a Circuit breaker that feeds the Subpanel? or do I just wire from the bus bars?

Thanks all.
luweee is offline   Reply With Quote
Old 03-08-2008, 09:18 PM   #22
Electrician
 
Join Date: Aug 2007
Location: Connecticut, Litchfield
Posts: 2,015
Default

Question regarding a Sub-panel


Quote:
Originally Posted by luweee View Post
sorry to butt in here.

but i am also planning for a subpanel off my Cutler Hammer 200 Amp Main Service panel. I have 6 open slots but need 14 circuts (finishing my basement) thats the reason for my subpanel addition.

My question is.
Coming out of the main do I need to put a Circuit breaker that feeds the Subpanel? or do I just wire from the bus bars?

Thanks all.
You need a circuit breaker.
chris75 is offline   Reply With Quote
Old 03-08-2008, 09:32 PM   #23
General Contractor
 
joasis's Avatar
 
Join Date: May 2006
Posts: 876
Default

Question regarding a Sub-panel


Quote:
Originally Posted by DaleB View Post
John,
Thanks very much for your concern. Actually, it's not my place but a friend's so let it burn.
Now I can't help but ask why you are doing this anyway? If you were in Oklahoma, this would be illegal, plus exposing you to liability if anything ever went wrong. You can do your own electrical work, and assume the risks for it, but are you ready to accept the risks for doing something you really need a license for?
__________________
Ladwig Construction
Hennessey, Oklahoma
405 853 1563



joasis is offline   Reply With Quote
Old 03-09-2008, 11:39 AM   #24
Licensed Electrician
 
jrclen's Avatar
 
Join Date: Feb 2008
Location: central wisconsin
Posts: 982
Default

Question regarding a Sub-panel


Quote:
Originally Posted by Stubbie View Post
To my knowledge all load centers have a bus stab rating.
Thanks for pointing that out Stubbie. I'm going to look for that from now on. To late to go back 40 years and fix all the ones I've done without looking.
jrclen is offline   Reply With Quote
Old 03-09-2008, 12:16 PM   #25
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,004
Default

Question regarding a Sub-panel


Update

I've had time to do a detailed search on bus stab ratings including e-mail contact with some of the manufacturers. Since it is the weekend I won't get replies till Monday.
What I have discovered is this.... for modern panels for current listings on the manufacturer catalogs the only panels I have been able to verify bus stab ratings are Seimens. Square d and GE, Cutler hammer for current listings are not showing a bus stab rating in the specifications I have been able to access. So will have to wait for replies from those manufacturers and I will share those when I get them.
So at this point I would say the proper response should be...... ' be sure to check the panel specifications label to be sure you do not have a limit on amperage for an individual bus stab.' I am starting to get the gut feeling this may be a bus material thing.
Stubbie is online now   Reply With Quote
Old 03-09-2008, 12:21 PM   #26
Licensed Electrician
 
jrclen's Avatar
 
Join Date: Feb 2008
Location: central wisconsin
Posts: 982
Default

Question regarding a Sub-panel


Quote:
Originally Posted by DaleB View Post
John,
Thanks very much for your concern. Actually, it's not my place but a friend's so let it burn. Seriously though, thank you very much, I usually have a good understanding of what needs to be done but got thrown for a loop on this for some reason. One last thing though, I guess I don't understand why your use four wire on the sub panel but there is only three wire coming in from the service drop itself. I know it pertains to grounding issues but that's where I get lost. (I did some reason reading last night but now I'm even more confused) Is there a simply explanation for a dummy? PS- I think you might have a good idea with having someone check this out rather than being the buddy that burned his buddy's place down. Thanks.
It sounds like you're coming around Dale. And now that I know this is not your own house, I most strongly recommend your buddy hire a qualified electrician.

If you were at my local tavern and were providing the beer, I would happily give you a detailed lesson in grounding, bonding, 4 wire feeders, and keeping the ground and neutral separate in the sub panel. But we're not there, so I'll just give you this link to get you started. That way I can head down there now without typing a long dissertation.

http://mikeholt.com/mojonewsarchive/...s~20021206.htm

I hope it clears things up for you.
jrclen is offline   Reply With Quote
Old 03-09-2008, 12:26 PM   #27
Licensed Electrician
 
jrclen's Avatar
 
Join Date: Feb 2008
Location: central wisconsin
Posts: 982
Default

Question regarding a Sub-panel


Quote:
Originally Posted by Stubbie View Post
Update

I've had time to do a detailed search on bus stab ratings including e-mail contact with some of the manufacturers. Since it is the weekend I won't get replies till Monday.
What I have discovered is this.... for modern panels for current listings on the manufacturer catalogs the only panels I have been able to verify bus stab ratings are Seimens. Square d and GE, Cutler hammer for current listings are not showing a bus stab rating in the specifications I have been able to access. So will have to wait for replies from those manufacturers and I will share those when I get them.
So at this point I would say the proper response should be...... ' be sure to check the panel specifications label to be sure you do not have a limit on amperage for an individual bus stab.' I am starting to get the gut feeling this may be a bus material thing.
Thanks for taking the time on this Stubbie. I haven't learned anything new for a few days now, so I'm over due. I'm sure some others here will be enlightened also.
jrclen is offline   Reply With Quote
Old 03-09-2008, 01:06 PM   #28
Member
 
Join Date: Mar 2008
Posts: 32
Default

Question regarding a Sub-panel


John,

Again thank you. I got thinking that I had bought a book about wiring and got looking at it. It actually came from Home Depot- I spent time looking it over before buying itand it pretty good. It did a great job of explaining all of this to me and it had pictures. An even shorter explaination for me is that you (NEC-they) don't want the neutral and grounds traveling back to the main panel and then possibly to the transformer. So, you separate the two in the sub panel and let them travel to ground there rather than all the way back to the main panel and then grounding out from there. Again, thanks very much- I too learned something so its been a good day.
DaleB is offline   Reply With Quote
Old 03-09-2008, 01:21 PM   #29
Licensed Electrician
 
jrclen's Avatar
 
Join Date: Feb 2008
Location: central wisconsin
Posts: 982
Default

Question regarding a Sub-panel


Quote:
Originally Posted by DaleB View Post
(NEC-they) don't want the neutral and grounds traveling back to the main panel and then possibly to the transformer. So, you separate the two in the sub panel and let them travel to ground there rather than all the way back to the main panel and then grounding out from there.
The tavern can wait a bit. I have to help you out here. The current does travel back to the main panel. The neutral current travels back to the main panel on the neutral wire. At the main panel it is connected to the service neutral and travels out that wire to the transformer.

A ground fault, or short, is the only time we want current to flow on the grounding conductor (ground). And that current, in the event of a short, will flow back down that grounding wire to the main panel. There it is bonded to the service neutral and travels out to the transformer on that wire. The high current flow on that low impedance (resistance) path is what trips the circuit breaker to stop the fault.

If we bonded the neutral and ground together in the sub panel, we would have neutral current flowing in the ground wire as a parallel path. And we don't want that.

I'll throw one more thing at you. Those ground rods and water pipe connections have nothing to do with any of this. They serve unrelated functions. Electricity does not want to travel into the ground. It wants to return to the source where it came from, in this case, the transformer.
jrclen is offline   Reply With Quote
Old 03-09-2008, 01:36 PM   #30
Member
 
Join Date: Mar 2008
Posts: 32
Default

Question regarding a Sub-panel


That is what I was trying to say but you said it MUCH better. I have the idea and again thanks. I guess I'm a great example of knowing just enough to be dangerous. Thanks.

DaleB is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Glass Fuse Panel box question? pouncerw Electrical 4 10-05-2009 09:01 PM
Multiple Sub Panel Installation Handyman2007 Electrical 26 12-31-2007 05:47 PM
breaker panel question chadvavra Electrical 11 08-10-2007 09:20 AM
Main panel design question amakarevic Electrical 13 06-04-2007 04:35 AM
3 phase panel question curse21 Electrical 2 08-18-2004 10:17 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.