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Old 03-10-2008, 10:27 AM   #1
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Load Center bus stab ratings


In a previous thread I was having a discussion on maximum branch circuit breaker ratings per bus stab or often called a load centers bus stab rating. Most manufacturers list this as the maximum combined circuit rating per branch circuit bus stab or just the maximum branch circuit breaker allowed. I emailed several of the manufacturers having the most common brands we see at DIY centers. My question to their technical departments was as follows " It is my understanding that all residential load centers have technical data limiting the amperage that can be connected to a a branch circuit bus stab and I am inquiring as to the specifics to this specification?" A product listing with a internet link would be much appreciated.

So far I have only heard back from General Electric Powermark Gold division. They attached the below link as a reference. With the added note that all load centers for residential applications are specific to type, bus material, and mains rating as to the maximum branch circuit breaker or maximum amperage as a sum of branch circuit breakers per bus stab. See page 13

http://www.geindustrial.com/publibrary/checkout/Catalogs%20and%20Buyers%20Guides|DET-222|PDF#search='det%20422'
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Old 03-10-2008, 10:49 AM   #2
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Load Center bus stab ratings


Maybe I am interpreting this wrong, but I read that as they are listing the maximum amperage branch circuit breaker allowed in each panel, not the maximum amperage allowed per bus.
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Old 03-10-2008, 11:58 AM   #3
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Load Center bus stab ratings


I don't think Stub is looking for a total bus rating. Just a rating per buss stab. IE: Maximum branch circuit rating.
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Old 03-10-2008, 12:02 PM   #4
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Load Center bus stab ratings


Speedy...Yes I read it per bus stab but you will see it two ways depending on the manufacturer. What brought this up was the question of a 100 amp branch breaker being installed in a 100 amp loadcenter to supply a sub-panel. My response was that the load center may not allow a breaker of that size to be installed without first checking the max. branch circuit breaker rating or bus stab rating. For instance if the bus stab rating is stated as maximum sum of branch breakers installed cannot exceed 125 amps per branch circuit bus stab.. You could not have a 100 amp and a 30 amp breaker connected to that stab. Meaning if I installed a 100 amp double pole breaker for a sub-feed, then across from it a 30 amp double pole breaker for a dryer. I would have 130 amps on both bus stabs as as a sum of the breakers. Which would not be allowed. Stated the other way if I had a 100 amp rated load center with a maximum 70 amp branch circuit breaker rating I could not install a 100 amp double pole to feed a 100 amp sub-panel.

Is that how you see it?

Last edited by Stubbie; 03-10-2008 at 12:10 PM.
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Old 03-10-2008, 12:04 PM   #5
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Load Center bus stab ratings


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Originally Posted by Speedy Petey View Post
I don't think Stub is looking for a total bus rating. Just a rating per buss stab. IE: Maximum branch circuit rating.
Gotcha.
It's amazing how different things read when you overlook a word
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Old 03-10-2008, 01:24 PM   #6
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Load Center bus stab ratings


Yes Stubbie. That's exactly how I read it.
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Old 03-10-2008, 05:32 PM   #7
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Load Center bus stab ratings


I didn't see anything on page 13. However on page 12 I read the notes at the bottom of the panel listing. Note 7 states maximum main or branch circuit breaker rating of 90A with copper and 70A with aluminum. Note 8 states 125A maximum branch capacity.

Did I miss something about the stabs? Also I question your interpretation about a set of stabs being a single stab. In other words breakers being across from each other needing to be added up to comply with the maximum allowed. That somehow doesn't sound right to me. I think it may be stretching things a bit to call the set of stabs for opposing breakers a single stab. But that's just me. I'd like to hear you and Petey weigh in on this further.

I concede the maximum branch circuit allowed on the bus might be limited by a manufacturers instructions or a UL listing. It's new to me, but there it is in back and white. And I have no problem at all with learning new things.

In the mean time, thanks Stubbie for bringing this up and doing the leg work to get us an answer. Or to get us a discussion about it. Either way.
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Old 03-10-2008, 05:52 PM   #8
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Load Center bus stab ratings


What I intrepret as a bus stab is each leg of the service has one bus stab as you move vertically down on a modern panel. Two single pole breakers will connect to the same bus stab on the same leg if installed across from each other. Many panels I have looked at in the last year including my own state " sum of branch breakers installed not to exceed xxx per branch circuit bus stab". To me this means the breakers rating when added cannot exceed the bus stab limitation. Simply as an example if the wording above stated 100 amps per bus stab I would intrepret that as the sum of both breakers double or single pole connected to that stab cannot exceed 100 amps. Maximum branch circuit breaker rating speaks for itself.
Page 13 shows the maximum branch breakers that ge allows installed in several of its load centers. Some are equal to the mains but several are less than the mains. They do not have a bus stab limitation only a maximum branch breaker allowed.
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Old 03-10-2008, 07:06 PM   #9
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Load Center bus stab ratings


I think, the bus stab is the area of the bus where a single breaker clamp attaches. But that's just my opinion. On the panel where a branch limitation is spelled out, say 70 amp, I do believe we can install (2) 70 amp breakers across from each other. Again, just my opinion. I would like to see a black and white on the bus stab limit to see exactly how it is spelled out.

Edit: Shoot, you already provided that in your post above. Now we need to know exactly what a bus stab is.

I have a commercial inspection in the morning. I will run this past the inspector for one more opinion.

Last edited by jrclen; 03-10-2008 at 07:11 PM. Reason: re read the post
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Old 03-10-2008, 07:29 PM   #10
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Load Center bus stab ratings


Stubbie, I asked this question over on the Code Guru forum also for an opinion. I'm itching for some answers on this.
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Old 03-10-2008, 07:54 PM   #11
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Load Center bus stab ratings


Great I would like clarification myself. I did find this over on Mike Holt......

http://forums.mikeholt.com/showthrea...highlight=stab

Last edited by Stubbie; 03-10-2008 at 08:02 PM.
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Old 03-10-2008, 08:47 PM   #12
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Load Center bus stab ratings


Did you see that Siemens label? It says "sum of qt breaker rating is not to exceed 110 amps per branch circuit bus stab." Two breakers installed opposing each other would be 2 branch circuits right? Good find on the thread though. I'm surprised it's only 2 pages long. I wish they would have hashed it out more thoroughly like usual.

I thought iwire had taken a stand until I read his post #7. But then stickboy posted #9. Then tallguy shoots that down with #10. And we are back to go.
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Old 03-10-2008, 09:24 PM   #13
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Load Center bus stab ratings


Actually I missed that, glad you pointed it out. Well if that is the case and they are only concerned about summing one tandem I'm not sure how you would ever get 110 amps. Two tandems across from each other that would be possible. So i guess we need to find out if a bus stab is one breakers connection or two breakers. I agree with you breakers opposite each other are two branch circuits in my opinion. If they are talking just one breakers connection then the need for that statement on the panel label is rather pointless.
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Old 03-10-2008, 09:34 PM   #14
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Load Center bus stab ratings


Quote:
Originally Posted by Stubbie View Post
Actually I missed that, glad you pointed it out. Well if that is the case and they are only concerned about summing one tandem I'm not sure how you would ever get 110 amps. Two tandems across from each other that would be possible. So i guess we need to find out if a bus stab is one breakers connection or two breakers. I agree with you breakers opposite each other are two branch circuits in my opinion. If they are talking just one breakers connection then the need for that statement on the panel label is rather pointless.
I agree the label seems to be saying a bigger than 55 amp tandem. I've never seen one.

Check out this one:
http://www.acehardwaresuperstore.com...58.html?ref=42
a 30-50-50-30. That would give us 80 on one side of the stab.
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Old 03-10-2008, 10:09 PM   #15
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Load Center bus stab ratings


All those features and still cheaper than one AFCI...
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