Wiring a subpannel - wire size
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Wiring a subpannel - wire size
I'm putting a sub panel in a workshop built onto the house and after doing some research I would like to check what I've come up with. Always good to have a few more eyeballs on the plan to make sure mistakes are not made.
I need four 15 amp circuits (all 110V). I want to run 220V from the main service panel to the sub panel because it is going to be approximately 70 feet of wire.
From what I've read and how I understand it, I need to use 10/3 with ground connected to a double pole 30 amp 220v breaker in the main service panel. Since the sub pannel is technically in the house (work shop built onto side of house, extending house about 20 ft) the two hots will be connected directly to the two hot bars in the sub panel. Connecting neutral bar in sub panel to neutral bar in main panel, same with ground, but ground bar and neutral bar are not connected inside the sub panel. Install two 15 amp breakers on each bar.
Any glaring (or not so glaring) mistakes? I think I have it right but thats what worries me, that I got it right on the first draft with no mistakes.
Thank you
I need four 15 amp circuits (all 110V). I want to run 220V from the main service panel to the sub panel because it is going to be approximately 70 feet of wire.
From what I've read and how I understand it, I need to use 10/3 with ground connected to a double pole 30 amp 220v breaker in the main service panel. Since the sub pannel is technically in the house (work shop built onto side of house, extending house about 20 ft) the two hots will be connected directly to the two hot bars in the sub panel. Connecting neutral bar in sub panel to neutral bar in main panel, same with ground, but ground bar and neutral bar are not connected inside the sub panel. Install two 15 amp breakers on each bar.
Any glaring (or not so glaring) mistakes? I think I have it right but thats what worries me, that I got it right on the first draft with no mistakes.
Thank you
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Sounds reasonable. I think you covered all the points correctly. The only thing might add is that undoubtedly at some point in the future you may want to expand it. It might not be a bad idea to start out a little larger. It won't cost that much more and you will be glad yo did later when you want more circuits but if you think this is going to be all you need then go for it.
You also could run larger feed cable and still protect it at 30A and later up the panel and breaker. Just giving you some options.
You also could run larger feed cable and still protect it at 30A and later up the panel and breaker. Just giving you some options.
#3
I don't have a clear picture of this structure, but if you have any doubts, you might check with your inspector first to see if he rules this the same structure or a separate structure.
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I would run a 15 amp circuit for lights and all cord and plug tools on 20 amp general purpose receptacle circuit(s). Some power tools require individual circuits, if so, determine the branch circuit rating from the equipment load requirement.
If workshop addition declared attached this diagram will help.... based on 2005 NEC
As a side note your subpanel if less than 100 amps will be stingy on spaces maybe only 2 to 4 spaces. so be aware of this and make sure you panel has enough spaces. Most small panel ratings like 60 or 70 amps will use the tandem type single pole circuit breakers to get the maximum # of circuits. If your going to ever need a power tool at 240 volts then this can be come a problem without a panel change due to lack of sufficient breaker space.
There are some inspectors that would require a 60 amp feeder for any workshop, so just a heads up to that possibility.
If workshop addition declared attached this diagram will help.... based on 2005 NEC
As a side note your subpanel if less than 100 amps will be stingy on spaces maybe only 2 to 4 spaces. so be aware of this and make sure you panel has enough spaces. Most small panel ratings like 60 or 70 amps will use the tandem type single pole circuit breakers to get the maximum # of circuits. If your going to ever need a power tool at 240 volts then this can be come a problem without a panel change due to lack of sufficient breaker space.
There are some inspectors that would require a 60 amp feeder for any workshop, so just a heads up to that possibility.
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But if you go over 6 breakers or it is in a detached building you will need a main disconnect in the sub panel.
So now that we have all doubled your budget you can get started.
You will have to decide what your real needs are. Most of the time we over improve but there is no harm in that except it costs more. Every tool does NOT need its own circuit. If it is just you working then I really see no need to have even more than 2 or 3 circuits unless you need 220 for something.
So now that we have all doubled your budget you can get started.
You will have to decide what your real needs are. Most of the time we over improve but there is no harm in that except it costs more. Every tool does NOT need its own circuit. If it is just you working then I really see no need to have even more than 2 or 3 circuits unless you need 220 for something.
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But if you go over 6 breakers...
An mlo sub-panel does not require a main breaker if installed in the same dwelling/building as the service equipment whether the mlo has more than 6 breakers or not.
As of 2008 the differences for power and L&ABCP's has been eliminated and a main single throw disconnect is required for detached structures.
If you look at a mlo panel cover sheet you will see something like this..... it is important to note what is required of the panel to be service rated.
In others you will see a statement that says may be used as service equipment with 6 circuit breakers or less if the panel is not a L&ABCP.
Not trying to cause argument just wanting to discuss the common misunderstanding about the so called "six throw rule".
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I'm pretty certain it will be considered in house without a need for a main breaker in the panel. Worst case I'll install a small service disconnect next to the sub panel if they insist. I've already bought the sub panel and it does not accommodate a main breaker.
I should have been more clear in my original post about the 'workshop'. I build and paint models and figurines. 1 circuit for lighting (room lighting and spot lights), 1 for a 10K btu AC, 2 for outlets. Really only needed one for outlets but am putting in 2 just in case.
Many thanks to the comments and suggestions. I really appreciate it.
I should have been more clear in my original post about the 'workshop'. I build and paint models and figurines. 1 circuit for lighting (room lighting and spot lights), 1 for a 10K btu AC, 2 for outlets. Really only needed one for outlets but am putting in 2 just in case.
Many thanks to the comments and suggestions. I really appreciate it.
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Once you install a branch circuit(s) for lights or appliances you would now a have a L&BCBP and a main (single throw) disconnect would be required for a detached structure and the panel disconnect must be service rated.
An mlo sub-panel does not require a main breaker if installed in the same dwelling/building as the service equipment whether the mlo has more than 6 breakers or not.
As of 2008 the differences for power and L&ABCP's has been eliminated and a main single throw disconnect is required for detached structures.
In others you will see a statement that says may be used as service equipment with 6 circuit breakers or less if the panel is not a L&ABCP.
An mlo sub-panel does not require a main breaker if installed in the same dwelling/building as the service equipment whether the mlo has more than 6 breakers or not.
As of 2008 the differences for power and L&ABCP's has been eliminated and a main single throw disconnect is required for detached structures.
In others you will see a statement that says may be used as service equipment with 6 circuit breakers or less if the panel is not a L&ABCP.
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I'm not exactly sure what your getting at but the post was in response to your reply ( I thought maybe you would like to learn something). As for this being a DIY forum...do tell..... BTW he seems quite capable of understanding a bit above layman.....but if L&ABCP was not understood it stands for a panel that is classified as a "Lighting and Appliance Branch Circuit Panel". This is what Subspace is installing and is therefore relevant to the thread. Electrical installations are not always "layman" in terms of the many aspects you need to understand. I would let Subspace determine if reading my posts or diagram was over his head.
Now if you are interested in my opinion I think the post was primarily for you to read and then anybody else inclined which would include the OP. As for pursuing the issue I had no intention of doing so, it was simply relevant information nothing more or nothing less.
If I give wrong information in any of my posts I would expect a moderator or other member to correct me. Your response that a sub panel needs a main breaker if it is mlo and has more than 6 breakers in an attached or detached building/dwelling application needed some clarification. I thought this would be welcome.
Now if you are interested in my opinion I think the post was primarily for you to read and then anybody else inclined which would include the OP. As for pursuing the issue I had no intention of doing so, it was simply relevant information nothing more or nothing less.
If I give wrong information in any of my posts I would expect a moderator or other member to correct me. Your response that a sub panel needs a main breaker if it is mlo and has more than 6 breakers in an attached or detached building/dwelling application needed some clarification. I thought this would be welcome.
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No don't gt me wrong, all good info. It was just that I don't believe the original poster was looking for such a technical terminology ridden explanation. We are explaining in most cases at a novice level.
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Very good and noted ....lets carry on....
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Hey now! I just learned another term: L&ABCP
See? That is why I like coming to this forum...always new and exciting things to read which will expand my knowledge
Hey Bruto, how is it that people misinterpret what you say? I remember the time when I thought that you were criticizing my post on my subpanel install, but looking back on it, am I ever grateful. Now I love to be a teacher of 'objectionable current' to all who will listen The moral of my post is: lets all learn from each other!
See? That is why I like coming to this forum...always new and exciting things to read which will expand my knowledge
Hey Bruto, how is it that people misinterpret what you say? I remember the time when I thought that you were criticizing my post on my subpanel install, but looking back on it, am I ever grateful. Now I love to be a teacher of 'objectionable current' to all who will listen The moral of my post is: lets all learn from each other!
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I really don't see how it could be considered detached. I'll never add more than the existing 4 circuits. It's already 2 more than I really need.
It's a small town, everyone knows everyone. I'll be handing the inspector a beer as he comes in to check it out, just like I did when he came to look at the new addition. I did the electrical myself because we do not really have an electrician in town (he passed away several years ago). Have to get one out from about 50 miles away, thats not cheap. Town has several construction workers that commute though, was easy getting a contractor and labor for the add on as we all knew each other. And I handed them beer in the afternoons (tea in the mornings) to. If I hadn't, it been all over town how rude and snobbish I was They knew better than to drink to much before the end of the work day.
The inspection is really a formality. Don't get me wrong, he'll check it all out real good to make sure it's not dangerous. Thats about it. Then will sit on the porch, drink beer, and talk about the women, except when the wife brings us fresh beers. Then we'll be all quiet like, but she'll know anyways. No fooling the misses.
Much appreciate all the help everyone
p.s. Yall give Bruto some room, he's just a bit more picky on code than some I'm thinking. Besides, I believe he was just trying to be technically correct as well as busting a '6 throw rule' thats either a myth or out of date. Don't see that it concerns me directly, but thats ok.
It's a small town, everyone knows everyone. I'll be handing the inspector a beer as he comes in to check it out, just like I did when he came to look at the new addition. I did the electrical myself because we do not really have an electrician in town (he passed away several years ago). Have to get one out from about 50 miles away, thats not cheap. Town has several construction workers that commute though, was easy getting a contractor and labor for the add on as we all knew each other. And I handed them beer in the afternoons (tea in the mornings) to. If I hadn't, it been all over town how rude and snobbish I was They knew better than to drink to much before the end of the work day.
The inspection is really a formality. Don't get me wrong, he'll check it all out real good to make sure it's not dangerous. Thats about it. Then will sit on the porch, drink beer, and talk about the women, except when the wife brings us fresh beers. Then we'll be all quiet like, but she'll know anyways. No fooling the misses.
Much appreciate all the help everyone
p.s. Yall give Bruto some room, he's just a bit more picky on code than some I'm thinking. Besides, I believe he was just trying to be technically correct as well as busting a '6 throw rule' thats either a myth or out of date. Don't see that it concerns me directly, but thats ok.
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As of 2008 the differences for power and L&ABCP's has been eliminated and a main single throw disconnect is required for detached structures.
We just had a thread a few days ago (or more) where many of us were on opposite sides of the fence with regards to whether the OP needed a main or not in his detached garage. The inspector was saying he needed a main but others here (including a mod ) said 6 breakers were fine....
This has been buging me and I'd love to bookmark it in my NEC....
I even think that if a sub is installed out-of-reach of the service MBP, a main disconnect should be used regardless of structure classification.
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Hey Bruto... Anyway you can help me out and throw an Article # at me for this? This is what I was taught but I've torn thru 230 and can't find anything. Nothing but 1 to 6 breaker references in multiple places....
Article 408 is for panelboards aka load centers both residential and commercial/industrial.
If you have a copy of the 2005 code you will find that there is a classification for a Power Panelboard and Lighting and Appliance Branch Circuit Panelboard. It is important to know what makes a panel either a power panel or an L&ABCP if dealing with jurisdictions still on 2005 or before. It is also important to note what makes a panel suitable for service equipment. In most cases a single throw main is required if the panel is a L&ABCP and the service rated building disconnect is to be located in the panel.
In 2008 they dropped the difference between a power panel and L&ABCP. In other words the 6 disconnect rule for the most part applied to power panels as L&ABCP's required main single throw breakers in order to be service rated. So now with no differences all panel boards require main breakers unless you can apply one of the exceptions of 408.36. 408.36 allows "overcurrent protection" to be in the panel or anywhere on its supply side protecting the feeder to the panelboard as allowed in exception 2 but the panel must not exceed 42 branch circuits. BTW the 42 circuits was eliminated also in 2008 unless you are applying exception 2 of 408.36.
So for a panelboard that is mlo and is installed in the same dwelling as the service equipment you may have the overcurrent protection for that mlo panelboard located remote from it in accordance with 408.36 as the mlo is not required to be service rated. This changes when you supply an mlo in a detached structure (residential) and falls under Art. 225. The key there is that the disconnect (not overcurrent protection) must be service rated. So if you intend to have the 'disconnect' located integral to the mlo then you must have compliance with the manufacturer as to how that mlo can be made service rated. If we are dealing with 2005 then L&ABCP's will require a single main breaker in residential applications of detached structures. If in industrial/commercial applications mlo's are service rated by the manufacturer without a main breaker and can use the 6 breaker rule for the disconnect for detached structures Art.225.33. Now this is not easily explained and I have left a few holes as it is not something that can be explained in layman. You will find great controversy on this subject so be prepared for lots of disagreement.
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Awesome post tho. Thanks much. I'll re-read your above tomorrow along with referencing 08' as I do. It's a little late to be doing it now. I can barely understand parts of that book when I'm wide awake and refreshed.....
Usually what I've done is when I'm unsure of code specifics (when working as a sub/indep), I overkill. As with the MC thread... By installing a MBP as a sub instead of a MLO, you'd be meeting, if not exceeding, code. Your right, that's gets expensive quick. When I come across topics like this, I can't help but press the issue in an attempt to separate fact from fiction...
The NEC doesn't allow that to be done very easily, just by the way some of it's worded.
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The thing you need to remember is the NEC is written to cover all electrical installations not just residential. So it can be very difficult to interpret code and its exceptions if you do not have a wide knowledge of the industry.
#19
Very interesting post, Bruto. It's a lot to digest, so I think I'll take a read over it again when I have a reference book handy, but you do make a compelling argument for non-applicability of the 6 throw rule in outbuildings.
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This is a very complex subject. The six throw rule frankly has been allowed by many inspectors over the years for residential detached structures. I don't think there is much of a safety issue as much as code compliance. I believe the best explaination can be found in the 2008 handbook commentaries in Art. 408. but when you read that remember they are talking about overcurrent protection not the detached building disconnect. That disconnect must be service rated. It can be a single throw disconnect located at the nearest point of the entrance of the feeder or it can be in the form of a main breaker or back fed breaker integral to the panel. When you install a main breaker as the disconnect in the panel... the panel will almost always then become service rated and you are in compliance. The disconnect size in amperage is a result of Art.225.39 (2008) this may or not be the same as the overcurrent protection for the panel feeder... but it must not be more than the panel rating. In the case of a sub-panel in a structure that is not the same with the service equipment you can have the overcurrent protection at the service equipment and the disconnect can be in the form of a panel main breaker or remote single throw disconnect. So I could have a 60 amp overcurrent protection at the main dwelling panel and a 100 amp main breaker disconnect installed in a 100 amp rated panel at the outbuilding to satisfy the service rated disconnect of 225.36 as the panel requires a main to be service rated. As long as whatever option you chose for the "disconnect" at the detached building is service rated your good. The problem occurs with the six disconnect rule, under 2005 if the panel becomes a L&ABCP and I challenge anyone to put a panel in a residential garage that isn't one, the manufacturer requires a main breaker for it to be service rated. the panel specifications sheet like I posted earlier will detail the requirements. Some mlo's will say (assuming they are convertible to main breaker) suitable for service equipment if 6 breakers or less and the panel is not a L&ABCP. So if the breakers are all for power purposes and no neutral connections at or below 30 amps then the 6 disconnect rule can apply. When you look at a single family dwelling you often see the six disconnect rule being used at the service equipment but you will also note that none of the breakers is 30 amps or less connected to the neutral bus. Usually one of the breakers is supplying a mlo inside the home that is configured as the L&ABCP. This is still allowed under exception 1 of 408.36 (2008) so long as the panel is not split bus.
As of 2008 all panelboards need a single overcurrent device that complies with 408.36 or if the installation falls under the exceptions of that sub-section.
408.36 state that the overcurrent protection can be integral to the panel or anywhere on its supply side. This is where you get all the debate...however this is speaking of overcurrent protection and this works when the panel is located in the same structure with the service equipment. In these cases the "sub" panelboard can remain mlo as there is no requirement for a disconnect service rated or not for a sub panel fed from a breaker in the dwellings service equipment. The breaker in the service equipment panel satisfies 408.36 as far as overcurrent protection for the panel buses.
The confusion occurs when we get to art.225 and the mlo panelboard at the detached structure tries to comply with the service rating using the 6 throw rule as the service rated disconnect for the structure. This results from the failure to understand the compliance for service rating for a panel that is L&ABCP.
2008 having removed the distinction between power and L&ABCP's makes it pretty clear the panel needs a main breaker to be a service rated disconnect or a service rated single throw disconnect remote from the mlo panel located in accordance with 225.32.
My apologies for the thread highjacking as it may seem.....
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Bruto et all, Great post, as it answered similar questions I had related to putting in a wood working shop.
I do have one other question. Do you have a reference web site on wire / feed sizes for a sub panel? If the sub panel is 60amp feed, what would be the code feed? 8/3?
Im also curious about the plastic conduit. My walls are concrete block so I was planning on running conduit mounted to the walls. The plastic is much cheaper, but wasnt sure if this is ok to be outside a wall, since it isnt as ridgid.
Thanks in advance.
I do have one other question. Do you have a reference web site on wire / feed sizes for a sub panel? If the sub panel is 60amp feed, what would be the code feed? 8/3?
Im also curious about the plastic conduit. My walls are concrete block so I was planning on running conduit mounted to the walls. The plastic is much cheaper, but wasnt sure if this is ok to be outside a wall, since it isnt as ridgid.
Thanks in advance.
Last edited by Vanraw; 09-28-08 at 09:43 PM.