Connecting Sub-panel

Discussion in 'Shop Talk' started by Jena, Feb 15, 2005.

  1. Jena

    Jena Well-Known Member

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    I have all my wiring done and it all works as expected when I use the by-pass thing. I'm ready to connect it up.

    Again, I have a 70 amp breaker sitting in a box by itself. It was connected to a fuse box, which I will dispose of. I need to connect the 70amp breaker to my sub-panel.

    What size wire do I use? All the circuit breakers are in the sub-panel, so basically whatever wire I use needs to be able to handle the entire load for the barn, including the well pump. My handy-dandy book shows wire ratings up to 50 amps for 6 gauge. Do I need something that big? Bigger? If bigger, where the heck can I find that?

    My husband was going to use an old piece of 10 gauge wire, without a ground. He said that I didn't need a ground in the sub-panel because the main is hooked to a ground rod. He said just hook up the red, black and white on the neutral. I told him that the main being connected to a ground rod didn't mean a darn thing if that ground wasn't connected to everything else. Is that right? I know I'm right....what good can it be if it is not connected? He scares me. Burn my darn barn down...grumble, grumble...if y'all tell me he's right, I will apologize :)

    Jena
     
  2. Ross

    Ross Moderator Staff Member Supporter

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    You're right you need that ground or you need to ground the sub panel. Not sure what size wire, I ran #2 to my 50 amp sub panel but I was thinking there'd be another barn after that one. Home Depot here has heavy wire, but I'd only be guessing what you need.
     

  3. fordson major

    fordson major construction and Garden b Supporter

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    never hurts to go bigger wire.yes the sub needs grounding, you are replacing the main panel with breaker panel? and theres a throw before the panel?have to look later right now way to early and to little sleep
     
  4. TheBlueOne

    TheBlueOne Well-Known Member

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    How far is the run from the 70 amp breaker back to it's source of power?
    Assuming it's not a loooooooong way back you should use #4 AWG wire with a ground. I believe Home Cheapo carries either #4 or #3 in a Type USE cable which will give the the ground wire which you do need. In addition, drive a 5/8" galvinized ground rod at the remote panel and use #6 AWG bare copper to attach to the ground bar.
    Long runs would need a larger size wire to minimize voltage drop, depending on the loads you're running.
     
  5. Jena

    Jena Well-Known Member

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    The 70 amp box is connected to the service wire, which goes back to the meter pole...probably 100 feet. The sub-panel is within a foot of the 70amp breaker.

    Jena
     
  6. Rowdy

    Rowdy Well-Known Member

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    Grounding is one of the most important, yet least understood things about electrical work for alot of people. A well grounded system is a safe system. It does little good to have a surge protector on a valuable computer if there is a poor grounding system, since the surge protector just dumps the surge back onto the neutral and in the end onto the ground. That doesn't really apply to a chicken coop, but grounding saves lives every year, and so does GFCI.

    TheBlueOne is right on, drive a rod and connected it to the ground bar of your sub panel. In fact if your main is only hooked to one ground rod, go back there and drive at least one more, or even better two more. NEC states that two are the minium, unless you can prove a resistance of 25 ohms or less.

    When you do drive the ground rod on the subpanel, make sure you use a connector that is listed for direct burial, such as an "acorn" clamp, or cad welding. Please do not just wrap the wire around the ground or use hose clamps. The ground rod only helps if it has a good low resistance connection to the system. You will also be better off if you can place the rod some place that is fairly damp, such as near a downspout of a gutter.

    Speaking of the ground and the subpanel, it's ground and neutral should be wired slightly different than a main panel. It would not hurt to be sure that the ground bar and the neutral bar on the subpanel are not bonded together. Depending on the brand of box, they could be connected by a strap of metal, a wire, or a screw through the neutral bus into the metal box. The first two are easy to see, the last one should be with a green screw, but even so, running a continuity test between the ground bar and neutral bus is easy. (Though to be sure you are just testing the subpanel's bond you might unhook the incoming neutral to the subpanel. Once it is determined that the ground and neutral are not connected in the subpanel just make sure all the neutrals are all hooked to the neutral bus and all the grounds to the ground bar.

    Jena, it sounds like your coop is about to be a bright and well powered place. I'm glad to hear that your electrical adventures are all coming togehter!
     
  7. agmantoo

    agmantoo agmantoo Supporter

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  8. Jena

    Jena Well-Known Member

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    The sub-panel is not bonded, as per the book I bought. There was a big screw sticking out to bond it (it's a Siemens panel). I removed the screw as it sits there just begging to be tightened.

    Hubby does not understand ground vs. nuetral. He keeps telling me they are the same, but I know they are not. The only place they are together is in the main panel.

    I will go get some more ground rods. I have connections at the coop, so they will give me theirs (I use those for my electric fences too).

    The current ground wire goes under the barn so it's hard to tell what it's connected too, but it is connected.

    Jena
     
  9. aaatraker

    aaatraker Well-Known Member

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    Jena, you said the wire for the 70amp breaker goes back to the meter pole, does it come out of your main panel or is it a seperate feed to the barn? A sub-panel would be feed from the main panel so the 70 amp breaker would be feed from the main panel
    Is there a seperate meter for the barn? if there is, don't throw the grounding screw away you will need it.

    The grounding and bonding would be different on a main panel.

    kurt
     
  10. Runners

    Runners A real Quack!

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    I don't know what this is for, haven't been around here in awhile... so maybe this has already been covered.

    Beware of grounding loops. This happens when the new ground rod you drive has less resistance to ground than the original ground rod at the service entrance. One of the reasons why GFIC are a good idea is because it's a crap shoot what kind of ground the branch or sub panels have. The GFIC provides that extra protection.

    Depending on the actual location and configuration of the sub panel, it may or may not call for a ground rod, instead calling for GFIC. The last thing you want is to 'become' the easiest path to ground.... soooo... if there's a question, find a REAL electrician and have him sign off on it. The permit (usually under $50) and his blessing can keep your insurance intact - if an accident happens.

    Use that load/voltage drop calculator to size your wire according to your breaker/needs; or if you've only got such-n-such wire to work with, then use it to size your breaker/fuses.

    BTW - more people get shocked & killed off the neutral & ground than off of "hot" leads. They assume its not carrying current and get careless.

    (sorry if this was already mentioned, NEC stuff is always getting more complex)
     
  11. morrowsmowers

    morrowsmowers Well-Known Member

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    As some have already said, you should not ground a sub panel with a rod. That will cause the entire system to be grounded thru the sub panel if the main ground fails for some reason. You need to run 4 wires from the house to the sub panel. 2 wires to carry the 240 volt hot, one for a neutral, and one for the ground. The bus bars in the sub panel will separate the 240 into 120 unless you have installed any 240 breakers in the sub panel. Also, you do not install a bonding screw in a sub panel -- it is grounded back to the main panel and thus you need a ground bar in the sub panel and not a bonding screw. It is preferred to run your wiring in conduit for protection and it will also make it easier to repair if something happens later. Ground and neutral are two entirely different things even thought they usually go to the same bus in your panel. It becomes a lengthy technical discussion to explain all of the differences but some people have found out the shocking details personally by assuming the opposite!!!

    Ken in Glassboro, NJ
     
  12. Jena

    Jena Well-Known Member

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    There are two meters on the meter pole. One goes to the house, the other serves everything else. From the meter pole, a few service lines run out to the different farm buildings. One for this barn, one for the bin, one for the feed shed, one to another barn. Each building has it's own panel or whatever. For example, the bin just has a big breaker, while the feed shed has a whole slew of stuff in two different panels.

    The way I understand it is that my 70 amp breaker is basically a main panel, it just happens to only serve this barn. Therefore the nuetral and ground are bound on it (they are connected to the same lug. That's how it was before and how I put the new stuff in). If I went looking, I would find that that whichever panel is "first" at the feed shed, is wired the same way, or should be. Correct? That bin has a ground rod on it's breaker...the other barn is questionable, but then that whole wiring deal in that one is another nightmare for another day.

    The feed shed wiring is good and I haven't messed with it. It was all professionally installed and there are things in there that look awful foreign. It works and the service guy has been out for different reasons and never said a word about the wiring being a problem, except for one problematic mouse catching area, but the installation is sound.

    So far, I haven't gotten shocked or anything. I worked all day setting up my brooders for the chicks. Got all the lights plugged in, etc. No problems so far.

    I have not put in a ground rod...and not sure if I should. 70amp breaker does have a ground rod under the barn (right next to the skunk, but that's a different post).

    Jena
     
  13. fordson major

    fordson major construction and Garden b Supporter

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    do any of your water pipes have a ground clamp to them ? this is the way they are grounded here as well as three other ground rods driven deep in the drip lineof the eves. glad to here it went well but beware it's cotagious! first thing you know you'll have the house rewired then the neighbours......!chicks should be happy and safe with all the effort you put in.