The problem with writing about residential electricity is that I have to include a disclaimer to the reader advising them to do nothing with the information I share. So why write at all? Because it is an exploration of information as complicated as Tax law and twice as deadly. So, promise me you will do nothing with the information I am about to share.
The basic info, if you don't have time to read further, is 1) if you are putting a basic sub panel immediately next to the primary circuit panel, then you can buy a 125A Main Lug load center. It doesn't matter if you only need 60 amps. Just get the 125 because it serves the same purpose. A Main Lug Load Center won't have its own main breaker and will only have a service disconnect on the primary panel of an amperage hopefully more than you plan on using in the panel but no more than 125A. Got it? 2) If you are putting a sub panel some distance away or out of sight of the primary panel, then buy a "125A Main Breaker Panel" which will include a double pole service disconnect for that panel specially designed for the top of the lugs of a panel. If it doesn't say "Main Breaker" then you are going to have to back feed the whole panel with your basic double pole 220V breaker if you desire (or code requires) a service disconnect in the panel itself. This is what I did because it's a few dollars cheaper, but the time spent in hunting down the right components is not worth it. If I had to do it again I'd just buy the basic 125 Main Breaker Panel because it's plug and play and requires no further research and assembling of components.
Off the top of my head, I wanted a sub panel 30 feet from the main panel in a detached garage. I used 2'' grey conduit glued together and probably should've used rigid conduit buried about 18 inches deep and it's so obvious that I really pray no one in the future digs it up accidentally since I didn't put caution tape over it when I buried it. Bigger conduit is better in case someone wants to run larger wire for a hot tub or welder in the future. I used #6 black, red and white and a #10 ground. This went to a 125 amp main lug panel with a 60A breaker at the main panel and a 60Amp breaker back fed disconnect on the sub panel. I was required to hammer 2 TWO ground rods and run a ground wire to one and then the other, but I hammered only one ground rod. And the ground bar is not bonded to the panel since this is a subpanel.
Read on if you want more details.
Subpanels are as common as pigeons, but this last month I've really dug into them and still I did not truly get all the information I needed until I finally purchased nearly the correct panel.
It's a common issue: you have a detached garage that has no power. You want power in the detached garage, but not simply a single light or outlet, but multiple outlets, a dryer outlet, a washer, a car lift...etc. So you really want an additional circuit panel in the garage. That makes sense. So you decide how many circuits, what you will use, etc, and determine what size wire you will need, which will determine what size conduit you will need, and what size breaker to use to feed your additional breaker panel. But then you have meticulously customized your breaker panel in your mind and then go shopping and realize you have a choice of a 125A, a 150A or 200A. Well, wait, you only have a 100A main panel, so that would make no sense to have a subpanel that is larger than your main panel. It's not like you can buy a $20 bill with a $5 bill, right? You can't provide 200A, magically, from a 100A panel, so why purchase a 200A panel?
And that is just the beginning of an exploration of a simple, yet detail oriented topic. It's interesting, yet requires a binge of information that can really test your aging brain and make you pretty sure you have dementia, but not so sure that you want to see a neurologist. It will test you. The physical technique is pretty basic, but the research is intermediate.
The whole problem comes from overthinking the concept of panels. They do not come pre-packaged in a box customized for your needs. Nope. That would be too easy. I could probably make a living packaging sub-panels for someone's custom design. A big box store will carry few options for your project, but one of them will probably work.
Multi-space panels require an exclusive main disconnect when they are not adjacent to the main panel supplying them power. Code requires this and it makes sense if you are envisioning turning off power to a sub-panel by sprinting across a yard to the primary panel. A panel in a detached garage 30 feet from the main panel will require a main shut off switch. Right? But if you have customized on paper that you need 75Amps to run your treadmill and electric dryer and lights....then you will find that no such multi-panel exists. You have to build it from other panels. Or, I've learned, you simply buy a 100A main breaker panel and run wire from a 75A breaker in your main panel...and ignore the 25A discrepancy between the two items. You can't use more than 75 Amps, so who cares if the panel is rated for 100Amps? Your sub panel breaker will say 100A, but it's being fed by a 75A breaker in the main panel. That discrepancy bothered me at first, so I tried to figure out a way around it. I wanted a 75A sub panel with a 75A Main breaker that would MATCH the 75A branch circuit breaker in the main panel that feeds the sub panel circuit. Simple? No, it's not simple. Because no such '75Amp Main Breaker" panel exists that I know of. Manufacturers are not going to package panels for every customized demands customers come up with. The problem is a disconnect between the customer who is required to determine his needs...and the products offered, which will likely not correspond exactly to his needs.
Add to this quandary the issue of cost and value and Oggy's unemployment insurance being maxed out and cancelled, and you now have a classic home owner problem....how to get things to work, as cheaply as possible, but correctly and 'by the book'.
Fortunately, I have more time than money lately so I can learn about the details that I've only touched on in the past. I have learned that there are times when the numbers not matching is very bad. Right? We know instinctively that a 120V circuit should have 120V on it and not 440V. That's simple. Wire rated for 220V should not have 440V passing through it. 20A outlets should not have 50A equipment plugged into it.
So if I have a sub-panel with 100A breaker that is being fed from a 75A breaker then my instinct is that I have done something wrong. I'm right to be cautious and to ask questions. My motto is that electrical work is very easy: either you know what to do or you do nothing. See? Easy. Studying electrical work is like diving into real estate law or tax evasion codes. It's insane. It's not easy. If it were easy then there would not be millions of products with specification pages running into the billions. The research, the learning, the book work, is extremely time consuming and requires focus and a scientific method. But the actual hands on work of basic residential electricity, once you know what to do, is in the range of the average home owner. So, how do you know what to do? How do you wade through the insane number of false leads and bad info, let alone the expensive code book? Time. You spend lots of time learning, following false leads, taking each step to a conclusion. And then making mistakes. See, you should never do anything unless you know what to do. But you will still make mistakes. How is this possible. You can't make a mistake if you knew what to do, right? If you made a mistake then you didn't know what to do. Ah, such is life. You don't know, until you know, and then it might be too late. But if it's not too late, then you move forward.
I hit a gas pipe with a pick axe the other day. It was buried 4'' deep in the middle of my lawn. I knew I'd have a surprise but nearly blowing up the neighborhood was bigger than I thought. I dented the pipe. But didn't rupture it. So I taped it up and moved on. What else could I do? I found out why they buried it 4'' deep when I tried to dig 18'' deep to put the conduit. The ground after 10'' is as hard as concrete and also filled with debris. They, whatever idiot buried this gas pipe, gave up at 4''. I gave up at 10''. Even if you had told me I had a gas pipe buried 4'' deep in my lawn I would've hit it with the first swing of the pick axe, which has a 5'' tip. Ponderous.
So, sometimes the numbers will not match, and you should investigate. Your wire is rated for 60A...but your welder requires 80A of current. Is this a allowable or not? Your sub panel has a main breaker of 100A, but it is fed from a 60A breaker in your main panel. Is this allowable or not? How about this....your sub panel has a 60A back-fed breaker coming from a 100A breaker on wire that is 12 gauge in conduit that is 2'' in diameter. Is this allowable or not?
See, it's a trade with specific details but one thing I've learned is that trying to make "everything match" is sometimes a path to problems, and sometimes a path to avoid problems. IN the case of a subpanel with a 100A main breaker, being fed by a 60A breaker in the main panel....that's actually fine. The 100A sub panel can't get more current than 60A, You can 'try' to access 100A due to some flawed hope that your 100A sub panel will provide it, but the 60A breaker in the main panel will trip. You can't get 100A through a 60A breaker, even if there is a 100A breaker between the 60A breaker and the appliances. More importantly, you won't be able to easily find a 60A main breaker panel because they aren't common, aren't pre-packaged, and have to be custom assembled by YOU. And you will be assembling the 60A sub panel with a 60A main disconnect from a 60A breaker in the main panel simply because you want all the numbers to match, but this is not required for it all to work or for it all to be in line with the electrical code. It's your own code that you are obeying, and that's fine, but in this case you will find that getting the numbers to all match is twice as expensive and time consuming than simply having the numbers not match. And it will all work with both approaches.
The terminology isn't helping either. There are Main Breaker Panels. And Main Lug Only Boxes. But a Main Lug Only box can be converted to a Main Breaker box. And there are Service disconnects, and sub panels. But a sub panel can have a main disconnect. So these terms are all jumbled and a person thinking of a main breaker might think they are talking about a main panel, but the main breaker is just the disconnect to any panel, not necessarily a sub panel or a service source panel. The vocabulary is not self explanatory unless you are a veteran of residential electricity projects.
Main Breaker panels will be pre-packaged and ready to go out of the box, but they only come in a few amperage ranges. Changing the main disconnect on one of these is possible but it's not something you'll likely find in the same store you bought the panel. It's special...and looks like this bolt on variety.
Main Lug Only panels are rated for only a few amperage ranges, but can be customized using back-fed basic double pole breakers to a much wider range of amperage. They are also cheaper because they don't use any fancy equipment other than a retainer clip on the back fed breaker. But using a back-fed breaker basically detours the original design of the panel. It's permitted but one has to wonder if this is the best solution when a panel is designed to either have no main disconnect or only be converted with a main breaker like the one pictured above, but you go and get a $9 appliance breaker and control current to the two legs by screwing the hot wires from the main panel directly into the breaker, where the downstream wires usually go, and use it as main disconnect switch. Is that sensible? Instead of using a breaker to send power downstream to an appliance, you put wires in the downstream lugs and use the breaker to send power 'upstream' to the panel legs. Power doesn't care if it's going upstream or downstream in relationship to the breaker. But we're all accustomed to seeing breakers control downstream appliances and a back-fed breaker has a hot panel in the downstream direction that is sending power 'backward' into the panel. I can definitely see this leading to error. But you can customize the panel and get all the numbers to match.
I guess it's possible if you have 200A service to your house and you use a panel rated for 125A then you can have a double pole 125A breaker on the main panel and control current to a prepackaged 125A main breaker panel and you will not have to customize or modify anything and all the numbers will match. But this is only one scenario and my experience is that we estimate our needs and then find that nothing is prepackaged to fit exactly those needs, the prepackaged products will fit 'within the maximum threshold of those needs' and that turns out to be good enough.
So, sometimes, it's up to your own choice what to do. You can spend more to assemble your custom panel, or you can use a pre-packaged 100A sub panel with a main disconnect and feed it with a 60A breaker. But you can't get any more current than 60A from it. And that might bother you because the main breaker says "100A". It's like a lie, staring you in the face. This panel is rated for 125A, has a 100A main breaker, but is only capable of 65A because that's the size of the breaker in the main panel that is across the lawn. I have a hard time embracing that lie. I want the numbers to tell the truth. I want a breaker that is rated for 'Truth'. And they don't sell those at the big box stores.
P.S. do nothing with the information I have shared.
Subpanels are as common as pigeons, but this last month I've really dug into them and still I did not truly get all the information I needed until I finally purchased nearly the correct panel.
It's a common issue: you have a detached garage that has no power. You want power in the detached garage, but not simply a single light or outlet, but multiple outlets, a dryer outlet, a washer, a car lift...etc. So you really want an additional circuit panel in the garage. That makes sense. So you decide how many circuits, what you will use, etc, and determine what size wire you will need, which will determine what size conduit you will need, and what size breaker to use to feed your additional breaker panel. But then you have meticulously customized your breaker panel in your mind and then go shopping and realize you have a choice of a 125A, a 150A or 200A. Well, wait, you only have a 100A main panel, so that would make no sense to have a subpanel that is larger than your main panel. It's not like you can buy a $20 bill with a $5 bill, right? You can't provide 200A, magically, from a 100A panel, so why purchase a 200A panel?
And that is just the beginning of an exploration of a simple, yet detail oriented topic. It's interesting, yet requires a binge of information that can really test your aging brain and make you pretty sure you have dementia, but not so sure that you want to see a neurologist. It will test you. The physical technique is pretty basic, but the research is intermediate.
The whole problem comes from overthinking the concept of panels. They do not come pre-packaged in a box customized for your needs. Nope. That would be too easy. I could probably make a living packaging sub-panels for someone's custom design. A big box store will carry few options for your project, but one of them will probably work.
Multi-space panels require an exclusive main disconnect when they are not adjacent to the main panel supplying them power. Code requires this and it makes sense if you are envisioning turning off power to a sub-panel by sprinting across a yard to the primary panel. A panel in a detached garage 30 feet from the main panel will require a main shut off switch. Right? But if you have customized on paper that you need 75Amps to run your treadmill and electric dryer and lights....then you will find that no such multi-panel exists. You have to build it from other panels. Or, I've learned, you simply buy a 100A main breaker panel and run wire from a 75A breaker in your main panel...and ignore the 25A discrepancy between the two items. You can't use more than 75 Amps, so who cares if the panel is rated for 100Amps? Your sub panel breaker will say 100A, but it's being fed by a 75A breaker in the main panel. That discrepancy bothered me at first, so I tried to figure out a way around it. I wanted a 75A sub panel with a 75A Main breaker that would MATCH the 75A branch circuit breaker in the main panel that feeds the sub panel circuit. Simple? No, it's not simple. Because no such '75Amp Main Breaker" panel exists that I know of. Manufacturers are not going to package panels for every customized demands customers come up with. The problem is a disconnect between the customer who is required to determine his needs...and the products offered, which will likely not correspond exactly to his needs.
Add to this quandary the issue of cost and value and Oggy's unemployment insurance being maxed out and cancelled, and you now have a classic home owner problem....how to get things to work, as cheaply as possible, but correctly and 'by the book'.
Fortunately, I have more time than money lately so I can learn about the details that I've only touched on in the past. I have learned that there are times when the numbers not matching is very bad. Right? We know instinctively that a 120V circuit should have 120V on it and not 440V. That's simple. Wire rated for 220V should not have 440V passing through it. 20A outlets should not have 50A equipment plugged into it.
So if I have a sub-panel with 100A breaker that is being fed from a 75A breaker then my instinct is that I have done something wrong. I'm right to be cautious and to ask questions. My motto is that electrical work is very easy: either you know what to do or you do nothing. See? Easy. Studying electrical work is like diving into real estate law or tax evasion codes. It's insane. It's not easy. If it were easy then there would not be millions of products with specification pages running into the billions. The research, the learning, the book work, is extremely time consuming and requires focus and a scientific method. But the actual hands on work of basic residential electricity, once you know what to do, is in the range of the average home owner. So, how do you know what to do? How do you wade through the insane number of false leads and bad info, let alone the expensive code book? Time. You spend lots of time learning, following false leads, taking each step to a conclusion. And then making mistakes. See, you should never do anything unless you know what to do. But you will still make mistakes. How is this possible. You can't make a mistake if you knew what to do, right? If you made a mistake then you didn't know what to do. Ah, such is life. You don't know, until you know, and then it might be too late. But if it's not too late, then you move forward.
I hit a gas pipe with a pick axe the other day. It was buried 4'' deep in the middle of my lawn. I knew I'd have a surprise but nearly blowing up the neighborhood was bigger than I thought. I dented the pipe. But didn't rupture it. So I taped it up and moved on. What else could I do? I found out why they buried it 4'' deep when I tried to dig 18'' deep to put the conduit. The ground after 10'' is as hard as concrete and also filled with debris. They, whatever idiot buried this gas pipe, gave up at 4''. I gave up at 10''. Even if you had told me I had a gas pipe buried 4'' deep in my lawn I would've hit it with the first swing of the pick axe, which has a 5'' tip. Ponderous.
So, sometimes the numbers will not match, and you should investigate. Your wire is rated for 60A...but your welder requires 80A of current. Is this a allowable or not? Your sub panel has a main breaker of 100A, but it is fed from a 60A breaker in your main panel. Is this allowable or not? How about this....your sub panel has a 60A back-fed breaker coming from a 100A breaker on wire that is 12 gauge in conduit that is 2'' in diameter. Is this allowable or not?
See, it's a trade with specific details but one thing I've learned is that trying to make "everything match" is sometimes a path to problems, and sometimes a path to avoid problems. IN the case of a subpanel with a 100A main breaker, being fed by a 60A breaker in the main panel....that's actually fine. The 100A sub panel can't get more current than 60A, You can 'try' to access 100A due to some flawed hope that your 100A sub panel will provide it, but the 60A breaker in the main panel will trip. You can't get 100A through a 60A breaker, even if there is a 100A breaker between the 60A breaker and the appliances. More importantly, you won't be able to easily find a 60A main breaker panel because they aren't common, aren't pre-packaged, and have to be custom assembled by YOU. And you will be assembling the 60A sub panel with a 60A main disconnect from a 60A breaker in the main panel simply because you want all the numbers to match, but this is not required for it all to work or for it all to be in line with the electrical code. It's your own code that you are obeying, and that's fine, but in this case you will find that getting the numbers to all match is twice as expensive and time consuming than simply having the numbers not match. And it will all work with both approaches.
The terminology isn't helping either. There are Main Breaker Panels. And Main Lug Only Boxes. But a Main Lug Only box can be converted to a Main Breaker box. And there are Service disconnects, and sub panels. But a sub panel can have a main disconnect. So these terms are all jumbled and a person thinking of a main breaker might think they are talking about a main panel, but the main breaker is just the disconnect to any panel, not necessarily a sub panel or a service source panel. The vocabulary is not self explanatory unless you are a veteran of residential electricity projects.
Main Breaker panels will be pre-packaged and ready to go out of the box, but they only come in a few amperage ranges. Changing the main disconnect on one of these is possible but it's not something you'll likely find in the same store you bought the panel. It's special...and looks like this bolt on variety.
 |
| This bolts to the top of the hot legs of a panel. Then the hot wires go into the top lugs. It's 5x more expensive than a similar double pole appliance breaker that does the same thing but is installed in a circuit space by clipping onto the hot tabs and rail rather than at the top of the two hot legs. |
Main Lug Only panels are rated for only a few amperage ranges, but can be customized using back-fed basic double pole breakers to a much wider range of amperage. They are also cheaper because they don't use any fancy equipment other than a retainer clip on the back fed breaker. But using a back-fed breaker basically detours the original design of the panel. It's permitted but one has to wonder if this is the best solution when a panel is designed to either have no main disconnect or only be converted with a main breaker like the one pictured above, but you go and get a $9 appliance breaker and control current to the two legs by screwing the hot wires from the main panel directly into the breaker, where the downstream wires usually go, and use it as main disconnect switch. Is that sensible? Instead of using a breaker to send power downstream to an appliance, you put wires in the downstream lugs and use the breaker to send power 'upstream' to the panel legs. Power doesn't care if it's going upstream or downstream in relationship to the breaker. But we're all accustomed to seeing breakers control downstream appliances and a back-fed breaker has a hot panel in the downstream direction that is sending power 'backward' into the panel. I can definitely see this leading to error. But you can customize the panel and get all the numbers to match.
I guess it's possible if you have 200A service to your house and you use a panel rated for 125A then you can have a double pole 125A breaker on the main panel and control current to a prepackaged 125A main breaker panel and you will not have to customize or modify anything and all the numbers will match. But this is only one scenario and my experience is that we estimate our needs and then find that nothing is prepackaged to fit exactly those needs, the prepackaged products will fit 'within the maximum threshold of those needs' and that turns out to be good enough.
 |
| Here you can see my main lug only sub panel that I have converted to a a Main Breaker by using a standard double pole breaker (bottom left) to control current to the two rails. This works, but took more time to assemble the parts than a simple 125A main breaker panel that comes with everything in a box. |
So, sometimes, it's up to your own choice what to do. You can spend more to assemble your custom panel, or you can use a pre-packaged 100A sub panel with a main disconnect and feed it with a 60A breaker. But you can't get any more current than 60A from it. And that might bother you because the main breaker says "100A". It's like a lie, staring you in the face. This panel is rated for 125A, has a 100A main breaker, but is only capable of 65A because that's the size of the breaker in the main panel that is across the lawn. I have a hard time embracing that lie. I want the numbers to tell the truth. I want a breaker that is rated for 'Truth'. And they don't sell those at the big box stores.
P.S. do nothing with the information I have shared.
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