Running a sub panel off a sub panel
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  1. #1
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    Running a sub panel off a sub panel

    I have never done it, I thought it was against code.
    But electricians I work with, who are pretty much electricians in name only were talking about doing it.
    So I searched around some and it doesn't appear to be against code?
    Maybe its just bad practice?
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  2. #2
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    Re: Running a sub panel off a sub panel

    Not sure.

    I have a sub box off my garage sub box ... but it only houses a gfi breaker for a hot tub
    I used to have ..... 220/30amp


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  3. #3
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    Re: Running a sub panel off a sub panel

    The limitations are overload. Common practice to run a 100 amp sub to a remote portion of a house, or commercial building, then a second, either farther, or a remote building.
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  4. #4
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    Re: Running a sub panel off a sub panel

    That's good news because I am running power out to a well house.
    The well is about 400 feet away from the house.
    There is an out building and animal pen area with a 100 amp sub panel in between the house and well.
    I was just going to run the well house breakers off the out building and animal pen sub panel.
    Putting a small sub panel out there at the well would make more sense.
    old Miller spectrum 625
    Lincoln SP-135 T, CO2+0.025 wire
    Miller model 250 and WP-18V torch
    Craftsman 100amp AC/DC and WP-17V torch
    Century 115-004 HF arc stabilizer
    Home made 4 transformer spot welder
    Home made alternator welder

  5. #5
    Join Date
    Mar 2018
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    34

    Re: Running a sub panel off a sub panel

    After many years as a residential and light commercial construction contractor and as a home builder I'm unaware of any restriction to running sub-panels of any number off sub-panels. As long as everything is properly sized the overcurrent protection beaker/fuse upstream is still going to provide overcurrent protection as required.

    You do need to keep the grounding/earthing rules in mind and it would be a good idea to check with your local electrical inspector. My understanding is that if the sub-panel is in the same building as the feeder panel you ground/earth the sub-panel back to the feeder panel. If the sub-panel is in a detached structure it needs a separate grounding system at the detached building (IE ground rod{s} or other ground/earth as allowed or required locally).

    You'll also want to allow for the potential voltage drop due to distance by either using larger conductors or ensuring that your well pump will work at the lower voltage present out at the end of the line. You might need a boost transformer.....

    It is worth considering that well pumps don't mind running as they experience most of their strain in starting, particularly deep well pumps which have to start out by pushing the column of water sitting above the pump in the water pipe. So a bigger pressure tank would lower the number of starting cycles and put a lot less strain on the pump over time.


    Best regards,


    Lance

  6. #6
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    Re: Running a sub panel off a sub panel

    In both cases a service entrance panel, (NOT ALL BUILDINGS HAVE ONE), is the only place you connect grounded, (white) to grounding, (green). Everything downstream must have both green, and white. They must not connect.

    Where I live, most buildings have cellars. The most common arrangement is to have three wires to the meter, three to the cellar, where the service disconnect is inside the breaker panel.

    Others have a disconnect incorporated in the meter enclosure. Either way, the enclosure with the service disconnect gets the bond of neutral to earth ground. Nowhere else should there be a connection. Everything else gets four conductors, and isolated neutral. The sheet metal of all boxes are connected to bare, or green, the neutral buss is insulated from the box.

    Remote buildings also need an earth ground system. If concrete rebar of 20 feet is available, use it. Otherwise, typically two 8' ground rods, or water supply.
    Last edited by Willie B; 07-12-2018 at 07:22 PM.
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  7. #7
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    Re: Running a sub panel off a sub panel

    I'm going to run the well pump with no check valve and pump the water to an open tank.
    The well is 120 feet deep with water at 108 feet.
    old Miller spectrum 625
    Lincoln SP-135 T, CO2+0.025 wire
    Miller model 250 and WP-18V torch
    Craftsman 100amp AC/DC and WP-17V torch
    Century 115-004 HF arc stabilizer
    Home made 4 transformer spot welder
    Home made alternator welder

  8. #8
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    Re: Running a sub panel off a sub panel

    Not a residential building but, I have several sub panels. My shop has 600 amp 480 delta service, I have a sub panel near my main panel, that goes to a sub panel 170 feet away, that goes to a sub sub panel 100 feet away. The first sub is a 400 amp panel wired at 200 amps, the sub sub is 100 amps. There was actually three other sub panels in the shop when I got it, two have been decommissioned, one completely removed. It is a big shop 35K sq ft.
    Steve from SoCal now in Hutch

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  9. #9
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    Re: Running a sub panel off a sub panel

    The only problem that I have seen arise with this is people don't check the wire capacity of the main wire coming in. Say you have a 3 sub panel line running. How many people actually check the wire size from sub to sub in all runs.

    I do believe that if you have more than 1 sub, your required to label where it came from so panels can be easily traced. Disconnects are not included in labeling.

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  10. #10
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    Re: Running a sub panel off a sub panel

    All panels that don't include the only service disconnect should have labeling as to where the power comes from.

    For that matter, all circuits should be labeled CORRECTLY. I constantly see circuits labeled "outlets" or "lights". When a circuit doesn't work, I spend a lot of time finding what is on the circuit.

    I urge a rudimentary floor plan with electrical devices having circuit numbers.
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  11. #11
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    Re: Running a sub panel off a sub panel

    My panels are all named and, every circuit is ID'ed at the terminus. I addition to my 480 three phase panels I have transformers for 240/120 delta service with several breaker panels throughout the shop. Mapping the panels was one of the first things I did when I moved in. The fab area of my shop has bus duct to power cranes and fab equipment, for a large open area that is a really nice feature.
    Steve from SoCal now in Hutch

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    And a whole bunch of machines

  12. #12
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    Re: Running a sub panel off a sub panel

    It can save so much time when you have a failure, and might save your life.

    Labeled switches: Turn them off to confirm that they supply what they say they supply.

    Unlabled switches: turn them off, and wait until something doesn't work, then turn them on to confirm. If nothing fails to work, they may be abandoned circuits serving no load. If you can't find a load, disconnect.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

  13. #13
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    Re: Running a sub panel off a sub panel

    We find the fastest way to label the panel is to shut them all off then turn on one at a time and walk through with testers and plug in lamp holders.
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  14. #14
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    Re: Running a sub panel off a sub panel

    In a commercial, or industrial building, I agree. Inside a residence I am uncomfortable, and I sense residents are uncomfortable with me crawling under their furniture. I suggest they draw a simple floor plan, and identify each opening, (as my father always called them) The code book uses the term outlet. Ya gotta be multi lingual to be an electrician.

    After identifying as much as possible, I use an extension cord, and light, or a vacuum cleaner. I plug in, and flip breakers until it stops working. I urge people to never do this with their spouse. The inevitable miscommunication is the stuff divorces grow from.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

  15. #15
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    Re: Running a sub panel off a sub panel

    Sometimes the home owners try to help. We know where the 20 amp circuits go and we can find them pronto. They slow us down when they try and help like "the hall light is out" or when looking for the 15's "It might be the dryer". Just shuddup and let us get outa here lady.
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  16. #16
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    Re: Running a sub panel off a sub panel

    Why not run a check valve on the pump?
    Lowering start current/voltage is the only reason I can of?

  17. #17
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    Oct 2014
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    115

    Re: Running a sub panel off a sub panel

    Quote Originally Posted by drujinin View Post
    Why not run a check valve on the pump?
    Lowering start current/voltage is the only reason I can of?
    Thinking because he is flowing into a open tank not a pressure tank so nothing is going to back up pressure against the pump (or check valve). The suction side I guess it would help keep water from falling out but it surely has a check valve already in the foot that should keep the water from falling out.


    Dropped in a new 60 foot deep well/jet packer system today. Waters back on. 6 years the well wasn't used and it rotted the return pipe pretty bad.

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