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    12dbsinad's Avatar
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    Any electricians on here? Sub feed question.

    In part of construction of the new garage/shop I am planning out power. Here are my thoughts:

    - I would like to install a outdoor load center near my barn. My need for this is for outdoor outlets for horse buckets, pool pump, outdoor wood boiler and I'd like to move the feed for the barn to the sub panel(there is no panel in the barn). Right now it goes underground into the main panel. I would then like to run power to the garage from this outdoor panel. the outdoor panel would be 130' from the main panel, and the garage is 200' from the sub panel.

    - Can I daisy chain 2 sub panels like this? I understand the loads would need to be calculated. If I did a 125 or 150A outdoor sub panel, could I run a 100A sub to the garage? I did my calculations on wire size from the main panel to the outdoor panel and plan to use copper USE #2 direct burial for the 2 hots and neutral and a #6 for the bonding ground. According to my calculations I can run a 150A load up to 131' @ 3 percent voltage drop. I plan on using aluminum 4 wire to the garage but have not done any calculations yet.

    My biggest concern is keeping it all to code. I am not a NEC nut that knows the book like a bible. Thanks for any help!
    Last edited by 12dbsinad; 10-05-2019 at 11:24 AM.
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    Quote Originally Posted by 12dbsinad View Post
    In part of construction of the new garage/shop I am planning out power. Here are my thoughts:

    - I would like to install a outdoor load center near my barn. My need for this is for outdoor outlets for horse buckets, pool pump, and I'd like to move the feed for the barn to the sub panel(there is no panel in the barn). Right now it goes underground into the main panel. I would then like to run power to the garage from this outdoor panel. the outdoor panel would be 130' from the main panel, and the garage is 200' from the sub panel.

    - Can I daisy chain 2 sub panels like this? I understand the loads would need to be calculated. If I did a 125 or 150A outdoor sub panel, could I run a 100A sub to the garage? I did my calculations on wire size from the main panel to the outdoor panel and plan to use copper USE #2 direct burial for the 2 hots and neutral and a #6 for the bonding ground. According to my calculations I can run a 150A load up to 131' @ 3 percent voltage drop. I plan on using aluminum 4 wire to the garage but have not done any calculations yet.

    My biggest concern is keeping it all to code. I am not a NEC nut that knows the book like a bible. Thanks for any help!
    Sounds like you need someone to provide you with a one line diagram. If you are an electrician then you would not be asking for this basic information. Will there be permits and inspections done? I only want you to do it once and do it right so I think you need more than internet advice for this type of install.
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    12dbsinad's Avatar
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    Quote Originally Posted by pappa View Post
    Sounds like you need someone to provide you with a one line diagram. If you are an electrician then you would not be asking for this basic information. Will there be permits and inspections done? I only want you to do it once and do it right so I think you need more than internet advice for this type of install.
    Who said I was an electrician? I said I was planning out the job, not doing it. You COULD do what I am asking but the rules change every year and some people know the book because they deal with it everyday. I am not asking for detailed instructions here so I think you took my post wrong.

    Thanks for your concern though.
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    Local Codes need to be followed if you do.

    I have done this but the panel lugs need to be approved for 2 wires of the type your using.


    Question: Can a subpanel have power supplied from a*circuit*breaker into another subpanel? In other words, can*you*daisy-chain subpanels?
    Answer:*Yes.
    The main electrical service panel is where branch circuits originate. A branch circuit consists of the circuit conductors between the final over-current device protecting the circuit and the lights, receptacles and equipment supplied by the branch circuit.
    There are three main types of branch circuits:
    General-purpose branch circuits for illumination and other general purposes
    Appliance branch circuits that supply power in the kitchen for countertop receptacles, such as small appliances
    Individual branch circuits that only supply one utilization equipment, such as a central heating gas furnace, an electric clothes dryer, an electric range and so on.
    The*main service panel also may contain fuses or circuit breakers that supply “feeder” conductors to downstream subpanels. A feeder consists of the circuit conductors that originate at the main service panel and are routed to the subpanel, in which there are branch circuit over-current devices for the downstream branch circuits.
    You could daisy-chain a feeder from the main service panel (Panel A) to a subpanel (Panel B), and then run another feeder from Panel B to another subpanel (Panel C). There really is no limitation to this concept, as long as every set of feeder and branch circuit conductors are properly sized and rated in amperes, and each feeder and branch circuit has the proper over-current protection (fuse or circuit breaker).
    Always check with your local electrical inspector about the specific code requirements in your area.*
    Question answered by John Williamson, Chief Electrical Inspector,*Minnesota Department of Labor and Industry*
    John Williamson has been in the electrical industry for 40 years and is a licensed master electrician and certified building official. John has worked for the state of Minnesota for over 23 years and is the Chief Electrical Inspector. For the past 25 years John has also provided electrical code consultation to various book and magazine publishers.

    I like doing this when the runs are long and the building is big like my Daughters Shop. Solves voltage drop problems and a way of using the power in a building better. So I have 3 sub panels in a row and one main panel feeding them and the other circuits in the building. Was not sure that later more power would be needed and this covered moving big tools around and not re/wiring circuits all the time.
    Last edited by JD4044M; 10-05-2019 at 11:45 AM.
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    Quote Originally Posted by 12dbsinad View Post
    Who said I was an electrician? I said I was planning out the job, not doing it. You COULD do what I am asking but the rules change every year and some people know the book because they deal with it everyday. I am not asking for detailed instructions here so I think you took my post wrong.

    Thanks for your concern though.
    I am a retired electrical inspector and I figured you weren't an electrician. Sorry if I offended you. It is best to seek help from someone who is knowledgeable in the code and installations. I could design it and install it to code for you but it is a lot of work to do it over the internet. If I lived nearby it would not be a problem. Don't want to see anyone or anything hurt due to an improperly torqued conductor or improperly installed grounding system. It is not a DIY type of endeavor you are asking about!
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    12dbsinad's Avatar
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    Quote Originally Posted by pappa View Post
    I am a retired electrical inspector and I figured you weren't an electrician. Sorry if I offended you. It is best to seek help from someone who is knowledgeable in the code and installations. I could design it and install it to code for you but it is a lot of work to do it over the internet. If I lived nearby it would not be a problem. Don't want to see anyone or anything hurt due to an improperly torqued conductor or improperly installed grounding system. It is not a DIY type of endeavor you are asking about!
    I am not offended. All I wanted to know was it still feasible. I am basically planning out for budget purposes. I do plan on doing most of the work myself like digging trenches and mounting the panels, I am not hiring that stuff out as I am very capable. All work WILL be inspected through the local inspector.
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    The NEC allows (or more correctly, doesn't prohibit) daisy chaining of sub-panels. But you do need proper load calculations and you have to watch how things are wired very closely.

    Keep in mind that your 3% max voltage drop should be calculated from the main panel for both sub-panels. If you run from a main panel -> sub panel A -> sub panel B, your wiring load calcs for the main -> sub A have to also meet requirements for your main -> sub B distance.
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    Quote Originally Posted by JimR View Post
    The NEC allows (or more correctly, doesn't prohibit) daisy chaining of sub-panels. But you do need proper load calculations and you have to watch how things are wired very closely.

    Keep in mind that your 3% max voltage drop should be calculated from the main panel for both sub-panels. If you run from a main panel -> sub panel A -> sub panel B, your wiring load calcs for the main -> sub A have to also meet requirements for your main -> sub B distance.
    Thanks Jim. Obviously I can't daisy chain 2 panels of the same amperage, correct? Is there a minimum amperage reduction requirement for the second panel? For example, can I run a 100A sub off a 125A, or does it need to be a 150A?

    Just trying to get a rough idea on wire size for budget. Copper is big bucks but I can run a size smaller (main panel is tight)
    Last edited by 12dbsinad; 10-05-2019 at 11:56 AM.
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    Quote Originally Posted by 12dbsinad View Post
    Thanks Jim. Obviously I can't daisy chain 2 panels of the same amperage, correct? Incorrect
    Is there a minimum amperage reduction requirement for the second panel?No

    For example, can I run a 100A sub off a 125A,Yes, or even vice vresa or does it need to be a 150A?

    Just trying to get a rough idea on wire size for budget. Copper is big bucks but I can run a size smaller (main panel is tight)
    The code doesn't say what size one panel has to be to able to feed another panel. It does says that equipment needs to sized for the loads to be served. Does that make sense? Example, my barn has a 100A panel fed from my 200A sub-panel, but it is fed by a 90A breaker. The 90A breaker is the over-current protection, and the 100A breaker in the barn is now a disconnect.
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    Quote Originally Posted by kylew View Post
    Example, my barn has a 100A panel fed from my 200A sub-panel,
    I'm thinking that 200A panel is your "Main" panel. Does that 200A panel feed your house direct from your Service entrance/Meter?
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