Announcement

Announcement Module
Collapse
No announcement yet.

sub panel wiring grounding question

Page Title Module
Move Remove Collapse
X
Conversation Detail Module
Collapse
  • Filter
  • Time
  • Show
Clear All
new posts

  • sub panel wiring grounding question

    i currently have a sub panel in my garage feeding off the main in the house. i would like to update the box as its an older no-longer-made brand box and i want to add some more circuits to it for my woodshop

    my problem is the way its wired currently it doesnt have a dedicated ground bar in the box. the neutral bus bar has the green bond strap connected connecting it and the box and all nuetral and ground wires are running to the neutral bar, which from everything i can find online says that this is a big NO-NO. however we bought the house last year and our house inspector did not catch this (although she caught many other electrical problems)

    my question is when i add the new box should i install and wire it the same way or wire it correctly with a ground bar and with the green bonding strap disconnected?

    from what ive read you are supposed to leave the strap off so the ground wire cant become energized if a nuetral wire became disconnected. common sense tells me i should leave the strap disconnected on the box and seperate the neutral and ground wires but im afraid that there may be a reason it was installed the way it was so i figured id ask first. thanks in advance for any help

  • #2
    Re: sub panel wiring grounding question

    Do you have a seperate ground wire feeding the panel?
    Is the cable feeding the panel large enough for the extra load you are planning to add?
    If the answer is no, then consider replacing the cable and seperate the wires in the sib.

    Comment


    • #3
      Re: sub panel wiring grounding question

      Is your garage attached to your house or is it a separate building? In either case you want to have a ground bar in the new sub-panel and a very good earth ground connected to it. As for bonding (connecting) ground and neutral, that's a no if the garage is part of your house and a yes if the garage is free standing in which case the sub-panel is the point of service entrance for the garage. In any case you want to be sure the cable is heavy enough.

      Please try to provide more info if you can.

      Hint: No matter what codes may state, always think on the side of safety. A ground bar is totally worthless and dangerous unless there is a very good connection to a very good earth ground.

      Comment


      • #4
        Re: sub panel wiring grounding question

        ahh geezz i didnt even consider that. no there is not a seperate ground feeding the panel just red black and white wires coming from the house to the garage (detached) im not sure what size the wires are. currently there is a 50 amp breaker at the main house panel feeding the garage. i plan on keeping that and just addin the new sub panel box to get a few extra circuits as right now there is 1 220 volt 30 amp circuit and 2 20 amp circuits. i want to have the 1 220 circuit and maybe 4 20 amp circuits. the sub panel is an old GTE sylvania box and i cant find replacement breakers for it otherwise id just swap in some 1/2 size breakers

        Comment


        • #5
          Re: sub panel wiring grounding question

          Be real careful here with a feeder (no longer referred to as a subpanel) in a detached structure.

          If the sub-panel is in the same structure as the main then you MUST have separate grounding and neutral conductors.

          If it is in a detached structure like a garage, outbuilding, shed, shop, it varies.
          The latest NEC (2008) requirement is the same. You need a separate ground and neutral conductor, plus your red and black hots. Previous NECs did allow a "3-wire" feeder such as what you have. The insulated neutral serve as both the neutral and grounding conductors. This was only allowed under certain conditions, such as not having ANY metallic paths between structures, like phone/catv/water pipes/etc.

          A detached structure supplied by a feeder always requires a grounding electrode (ground rod).

          You may want to check with your local electrical inspector before doing any work on upgrading that subpanel. Ask him what he wants to see in place first before doing any work.

          One thing that cannot be stressed enough is that the neutral is a CURRENT carrying conductor. It is not a substitute or a replacement for a ground period. The ground wire on the other hand is not a current carrying conductor. That is why the neutral wires are insulated. There is often a misconception about the role of the two wires which comes from the fact that the neutral wire is intentionally grounded at the main service panel only. This allows ground-faults (or "short circuits" to ground) a direct return path back to the source of power, the utility transformer. Having the ground wires bonded to the neutral makes it possible for the circuit breaker to trip out easily under such conditions.

          When and if you were to connect the current-carrying neutral wire to the ground wires "downstream" (as in a feeder) then it becomes possible for some of that current to follow what is called a parallel path -- over the bare grounding wires -- instead of the insulated neutral wires -- as it finds its way back to the source. That's why the neutral and grounds are separate in a feeder and in an outbuilding, a ground rod is used. Hope this helps explain enough.
          Cheers,
          Jim Don

          Comment


          • #6
            Re: sub panel wiring grounding question

            Do yourself a big favor and somewhere near the sub-panel but outside drive in a copper plated 5/8 or 3/4 x 8 foot ground rod. Run a #4 bare copper wire from it to the grounding bar inside the new sub-panel. No matter what else you really will want-need to do this. Be sure to use a good brass/bronze acorn ground clamp on the ground rod. Drive it so there's a few inches above ground. If you can't get it all the way into the ground with say 4" sticking up, take a hacksaw and cut off the top. Now if only 1/2 of it gets into the ground and you hit a rock, try to get it out and start again. If you just can't pull it out, cut it off a bit below ground level and then cover it up with dirt. Be very sure where you drive in ground rods that you don't damage the foundation of the building or drive it into underground cable or pipes. KNOW what's down there before starting.

            As to whether the neutral gets bonded to the case and thus ground in the sub-panel depends on local codes and as Jim stated if there's anything other than the electric feed line connecting the garage to your house. If there is, then normally you need to bond them.

            I strongly recommend calling in a good licensed electrician before you start doing any major work. You can buy and mount the sub-panel and install breakers in it, but leave the main power connecting up to the electrician to do. Also, if there is a need to pull new cable from your house out to the garage.

            As for the panel, I would look at Cutler-Hammer type CH or Square D type QO. Both are good and you'll be able to get breakers for them for a good long time. Leave the economy grade stuff alone.

            Something you should talk to the electrician about is to install a fused enclosed safety switch beside the sub-panel as an emergency power disconnect. In case something goes very wrong out in the garage being able to quickly shut off power can really save the day for you. I like to size and type the fuses so they will blow just before the breaker feeding it would trip.

            For safety it is a good idea to install a small fully automatic emergency light in your garage if you use it as a workshop. I'm sure you can figure out why this is a good idea. Hint: Power failure at night = all goes dark = dangerous

            For under $100 for the emergency light (try to find one approved for slightly damp locations) and an easy install connecting it to the breaker for your main lighting circuit, this is cheap life insurance.

            If anyone else reads this, please really consider installing some simple emergency lighting in all dangerous areas of your place. Stairways and kitchens come to mind along with basements. I put in about $400 worth of them in my place (garage included) and have been most thankful for it.

            Now please call in a good electrician to inspect what you have and make recommendations on improvements. Some of this is not a DIYer type project and you do not want to get hurt or have other troubles later on. People that do their own work and not have it totally to code end up in real messes with their insurance company and sometimes the law.
            Last edited by Woussko; 06-30-2008, 09:22 PM.

            Comment


            • #7
              Re: sub panel wiring grounding question

              Originally posted by JimDon View Post

              One thing that cannot be stressed enough is that the neutral is a CURRENT carrying conductor. It is not a substitute or a replacement for a ground period. The ground wire on the other hand is not a current carrying conductor. That is why the neutral wires are insulated. There is often a misconception about the role of the two wires which comes from the fact that the neutral wire is intentionally grounded at the main service panel only. This allows ground-faults (or "short circuits" to ground) a direct return path back to the source of power, the utility transformer. Having the ground wires bonded to the neutral makes it possible for the circuit breaker to trip out easily under such conditions.

              When and if you were to connect the current-carrying neutral wire to the ground wires "downstream" (as in a feeder) then it becomes possible for some of that current to follow what is called a parallel path -- over the bare grounding wires -- instead of the insulated neutral wires -- as it finds its way back to the source. That's why the neutral and grounds are separate in a feeder and in an outbuilding, a ground rod is used. Hope this helps explain enough.
              Cheers,
              Jim Don
              Very well said, Jim

              I really hope that sometime they revise the NEC so it reads in simple language about all the safety issues people must take seriously regarding grounding and neutral conductors. A big forced update regarding the use of conduit for grounding is needed too. SAFETY FIRST before all else.

              Fear the flowing electrons. Stay alive
              Last edited by Woussko; 06-28-2008, 07:07 PM.

              Comment


              • #8
                Re: sub panel wiring grounding question

                The whole grounding, bonding outbuildings can be confusing. They used to commonly run the triplex cables out to them and there was no ground wire.

                The code is letting us use ground plates buried a couple feet deep instead of a groundbar. What happens if the ground dries out?

                Comment


                • #9
                  Re: sub panel wiring grounding question

                  Here's a page that has good diagrams for NEC 2002 detached structure.
                  Diagrams are half way down the page. JUst put http: in front of the URL.

                  //www.selfhelpandmore.com/home-wiring-usa/accessory-structures-to-dwellings/wiring-a-detached-garage-2002.php

                  Comment


                  • #10
                    Re: sub panel wiring grounding question

                    Originally posted by Woussko View Post
                    Something you should talk to the electrician about is to install a fused enclosed safety switch beside the sub-panel as an emergency power disconnect.
                    detached building/structure, code says it needs a main anyway so he should get a sub panel with one already in it... also run a #8 bare copper for the ground rod.. and here we use 2 ground rods, no further than 8' apart no closer than 6' apart not in a spot people walk though... and definitely call a qualified electrician preferably IBEW j/k on the IBEW part

                    Comment


                    • #11
                      Re: sub panel wiring grounding question

                      so, now youv'e got a 4 wire feeder to a sub panel with the neutral isolated, the grounding conductor tied down to the sub panel box itself and to 1 or 2 ground rods with a #8 bare.

                      Youv'e just tied your house main service electrode conductor to 2 seperate grounding systems.
                      That's a no no.
                      If the main service grounding electrode conductor fails or is a poor ground, the garage may carry a fault current from the main.The new ground system at the garage is not designed or intended to do so.

                      Comment


                      • #12
                        Re: sub panel wiring grounding question

                        Thanks swampfox this is what the forum is for its a give and take and i feel as though i speak for everyone here when i say we appreciate you asking a question and having the decency to stick around and offer advice in your area of expertise!

                        Comment


                        • #13
                          Re: sub panel wiring grounding question

                          no sweat brother

                          Comment


                          • #14
                            Re: sub panel wiring grounding question

                            In some cases it might pay to run everything in the shop through a disconnect switch that can be locked out. This would allow all power to be removed from the shop tools making it safer if you have kids or others who might not be well versed in proper use of power tools.
                            ---------------
                            Light is faster than sound. That's why some people seem really bright until you hear them speak.
                            ---------------
                            “If I had my life to live over again, I'd be a plumber.” - Albert Einstein
                            ---------
                            "Its a table saw.... Do you know where your fingers are?"
                            ---------
                            sigpic http://www.helmetstohardhats.com/

                            Comment


                            • #15
                              Re: sub panel wiring grounding question

                              Bob D has a great point. A fused, enclosed safety switch would work well. They are great in the event you need to shut off power fast in case of emergency. If you'll be in the garage or shop at night, I recommend a small fully automatic emergency light in case of power failures or if you have to shut off power. There's nothing worse than being in a dangerous area and not being able to see the hazards only to trip and fall or worse.

                              If you look carefully at the handle (see picture) you'll see where you can use a small padlock to lock it from being moved up to the ON position. A second padlock or some heavy wire twisted to keep kids from opening the front cover is a good idea too.
                              Attached Files

                              Comment

                              Working...
                              X