No announcement yet.

O T Electrical

  • Filter
  • Time
  • Show
Clear All
new posts

  • O T Electrical

    I need to install a 50 amp w/ breakers
    distribution panel on the outside of my house.
    The meter is very close to the area I need the

    Our main breaker box is on the other side of the house.

    Two questions;

    Can I just hook the distribution panel into the load side
    of the meter?

    If so does the distribution panel need a main breaker.

    olf20 / Bob

  • #2
    You don't say where you are so all of this could be just general guidance. In the US things are governed by the NEC (National Electric Code) and any applicable local codes which will supplement and perhaps override it.

    I could be wrong, but I believe the NEC allows multiple distribution panels. The NEC requires an outside, accessible disconnect on the exterior of a building. If your meter has a disconnect switch I believe you will be OK with this: most do. In that case, be sure to wire the new panel from downstream of that disconnect. Among other reasons, this is for the safety of people like firemen who often must enter a damaged building. They want to turn off the gas and electricity before entering.

    Yes you do need a main (50A) breaker since you will probably be running feed wires that are only rated for that current. They need the protection provided by that breaker. You should check the local codes as it may be required to install that 50A breaker at the meter location, ahead of those feeder wires. I am sure some others will chime in on this.

    Don't be afraid of talking to your local code officials. You may incur an inspection fee, but they will guide you, answer any questions, and make sure that your installation is safe. In most localities they will not force you to hire an electrician if you look like you know what you are doing. That inspection fee is cheap insurance. And having it inspected and approved by the local officials may go a long way in protecting you from any legal liability in case something happens.
    Paul A.
    SE Texas

    Make it fit.
    You can't win and there IS a penalty for trying!


    • #3
      My HVAC (air conditioner) was done the way that you are proposing. The meter has a distribution panel on the load side with two breakers. One goes to the main panel and is rated 100amps. The other goes to the HVAC on the far side of the house and is rated 30 amps st 220V.

      I have everything except the HVAC available when running on my backup generator. The transfer switch is in line with the 100 amp main feed that goes to the main panel.

      At the end of the project, there is a profound difference between spare parts and extra parts.

      Location: SF East Bay.


      • #4
        Thanks for the replies! I got the breakers for anything
        I feed from the panel.
        Do I need a main breaker? In other words
        a main breaker in the distribution box.
        All these outdoor boxes come with lugs, or main.
        Big difference in price, not that $$ is a big deal.
        My main electrical guy is on vacation for two weeks.
        Thanks again!
        olf20 / Bob


        • #5
          Yes - Don't connect your new panel without a fused disconnect or main breaker, but that's "here". Where are you? Were you planning to connect live or break the seal and remove the meter? You are not installing a "sub-panel"; it is effectively another main panel.-

          More importantly, you need to get your electrical advise based on your local conditions, and it sounds like you need someone with experience to fit the required equipment.


          • #6
            You need a main breaker or mains fuses.

            The reason is that breakers vary in the amount of current that they will actually break. The usual 15 or 20A breaker is not made to break the large current available from the power line directly, and actually may fail to open. The "main" breakers are made to do that. Installing the lower rated breakers without a main might be similar to just not bothering to use any breakers.

            Not smart to try to install the box "hot" yourself. Unless you know what you are doing, and have suitable equipment, it is hazardous (obviously). The obvious issue of shock is one thing, but the other is that the high fault current (remember the breaker rating issue?) means that there is also a possibility for a very high current arc. You probably would not want to find yourself holding a large welding arc in your hands, a foot from your face.

            Most electricians have to work hot sometimes, but will shut off power if that is possible. There is no percentage in being a "hot dog". Pull the meter, or, better, get it done by an electrician.

            Keep eye on ball.
            Hashim Khan


            • #7
              Bob, if you have to pull the meter make sure you get permission from your power provider to break their seal. Doing so without permission could get you a very large fine, up to $500 and possibly more.

              I used to work for our provincial electrical utility and I would give an electrician permission to pull our meters but I would never give a homeowner permission because sometimes the meter sockets insulators would be broken and pulling that meter would result in a non fused/non breakered high amperage short with resultant very high energy and very dangerous arc flash. Electricians are at least more knowledgeable about such things and are more likely to be careful and wary about the possibility of that happening.
              Location: Saskatoon, Saskatchewan, Canada


              • #8
                Typical commercial and residential circuit breakers are generally rated for 10,000 amps interrupting rating, from 15A to 200A or so.



                To get an idea of the maximum available current for a typical residence, consider that the pole pig may be rated about 50 kVA, and have about 3% impedance, which means that its own internal impedance will limit short circuit current to 33 times nominal rating. So 50 kVA/240 V is 208 amperes continuous. A bolted short across the output of the transformer will be no more than 208 * 33 = 6875 amps RMS. By the time one considers the additional impedance of the line from pole to panel, it will be even less. So a 10kA interrupting rating is safe.

                However, a circuit breaker is only required to safely interrupt such a high current, and not necessarily survive in operable condition. Typical survivable current for a MCCB is on the order of 10x-20x, at which it will trip "instantaneously", which is actually often as long as 2-3 cycles, or 33-50 mSec. Fuses are typically rated at least 50kA RMS IR, and most are 100kA to 300kA. They also may be peak current limiting, so they will actually open before the current reaches the peak current available, so circuit breakers with lower IR may be used downstream. The fuse will trip much more quickly than the CB, faster than 1/4 cycle, so it will not even trip.
                Paul , P S Technology, Inc. and MrTibbs
                USA Maryland 21030


                • #9
                  That is true. BUT......

                  Much depends on where you are. If you are closer to the substation, line impedance will be less. The pole transformer "probably" is fairly high impedance, but might not be, depending. The panels are made to cover every situation that is possible, with a margin of safety, because circuit breakers vary. If you want to be reasonably sure that you interrupt 5000A, rate the breaker for 10,000. Then the probability is that all of them will do 5000A OK,

                  The main breakers are usually rated higher than others.

                  Fuses are very reliable and can be made to let only a known energy through. Then anything after that in the circuit need not break a higher current.

                  The whole issue of "protection co-ordination" is a big one, with lots of details that cannot be covered in a few sentences. So, one follows the rules for what capacity each type and location of breaker or fuse must have.

                  Keep eye on ball.
                  Hashim Khan


                  • #10
                    I'm in USA, Illinois. I also thought that it should have a
                    main breaker, but so few were offered I thought I should
                    ask. Like I said my electrician is on vacation for two weeks
                    and I thought I would get some parts ready.
                    Thanks again for all the info and help!
                    olf20 / Bob


                    • #11
                      As I recall your not actually required to have a Main breaker, the Code just requires six or less breakers, disconnects or other means to remove power from the building. Article 230 of the NEC covers it in great detail. Your assuming your 20 amp breaker has to disconnect 10,000 amps directly from the sub station. There are fuses on the transformers feeding your building. Those fuses as our local squirrel population has proved from time to time do work.
                      Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router


                      • #12
                        Here is some general info, might be a bit techie


                        Here is utility data sheet data for the fault current capability. See page 58 of the first document, page 2 of the second. The number is higher in some cases than the numbers suggested above, but that will vary with the drop wire length, and other site specific points.



                        Keep eye on ball.
                        Hashim Khan


                        • #13
                          That's all fine, but those are service or company rules, not NEC.
                          Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router