6 AWG to 100 amp subpanel?

Discussion in 'Electrical Forum discussion & Blog' started by seattle_steve, Nov 13, 2011.

  1. seattle_steve

    seattle_steve New Member

    Messages:
    28
    Location:
    Seattle, WA
    I'm installing a sub-panel for a new addition. My load calc suggests a 50amp load for the sub-panel. So, I'm planning a 50amp feeder breaker in the main panel with #6 feeder wire to the sub-panel. But, the local retail stores don't carry (Siemens) panels smaller than 100amp. I checked with the local inspector (Seattle) and he said that it's common practice to feed a larger sub-panel (e.g., 100amp) from a smaller main feeder breaker/wire (e.g. 50amp, #6 wire).

    The problem is that the 100amp main breaker in the sub-panel I bought lists a wire gauge range of "4 - 3/0". I assume this means I cannot connect #6 wire to it? I don't want to size up the feeder wire/breaker, so what are my options? Are there 100amp sub-panels that will accept smaller wire? BTW, the inspector mentioned that I might run into this issue, but I didn't really follow his recommended solution. Best I could tell, he was suggesting shimming the wire somehow at the 100amp breaker/connecter. That doesn't seem right to me... Is there some sort of adapter available for this situation?

    Thanks.
  2. Chad Schloss

    Chad Schloss Member

    Messages:
    330
    Location:
    USA
    i just wired the same panel in my garage with 6/3 using the 100a siemens panel. worked for me.
    Last edited: Nov 13, 2011
  3. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    Just because it works does not make it ok or a code compliant installation.

    You should splice a short piece of #4 onto the #6 and terminate the #4 on the breaker lugs.
  4. seattle_steve

    seattle_steve New Member

    Messages:
    28
    Location:
    Seattle, WA
    Thanks Jim. By "splice" do you mean simply twist-with-wire-nut as you would with smaller gauge splices?

    Steve
  5. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    I think you need a panel without a main and infeed thru a 50 amp breaker.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,274
    Location:
    New England
    That would be good, but as long as the wire feeding the subpanel is protected to the size of the wire, it doesn't really matter.
  7. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,560
    Location:
    North Carolina
    Use a split bolt or a Polaris
    [​IMG]
    [​IMG]
    That would be backfed and that is what is being done with the 100 amp breaker
    What Jim said
  8. Chad Schloss

    Chad Schloss Member

    Messages:
    330
    Location:
    USA
    so you use a split bolt then? so electrical tape over that is supposed to be safer than terminating #6 on the main breaker??!!? this would be the first post of over 100 that i have read that would choose this route. strange..
  9. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,560
    Location:
    North Carolina
    It is about time you learned something ;)
    If the breaker says that a #4 is the smallest conductor then a #6 would not be compliant. To use a split bolt of a polaris is the best choice at that time.
    So yes i suppose that I am saying that to use the proper size conductor is safer than using something that is non-compliant.

    EDITED TO ADD:

    I got to thinking while driving to school this morning about a statement you made here;
    I would hope that someone would not just use electrical tape over a split bolt. First one should cover the split bolt with the backing that comes off rubber tape and then cover with a couple of layers of rubber tape before using 3M on the outside.

    Vinyl electrical tape by itself is almost useless in most cases simply because it will dry out and under heat turn to carbon. Just as the carbon that we use in our grills to cook hamburgers the tape will smolder for days before igniting something in its surroundings.
    Last edited: Nov 15, 2011
  10. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    I think you left out the putty before the rubber tape. Whats with using the backing? It doesnt stick to anything, so saran wrap might be better. Putty takes the bumps out, tapers out and makes a clean shot. Now the tape lays clean. And I have never seen scotch 33 dry out and peel off, even after 12 years underwater. If we are talking harbor fright, I agree.

    I would think seeing a 100 amp breaker will cause the next guy to hook up his 80 amp welder in that place. Seems unsafe if not unreasonable to do that. Lot of ado and time for not buying the right breakerlesss panel in the first place.

    Our 'lately' mexican made breakers I have seen trip at 40 amps and some at 60 amps, so 2 would be a good backup.

    by the way, if he used an 'inline' set screw connector made for #6, it would likely slip right into the 100 amp terminals made for up to 3/0. That would be quick and clean and he need only insulate any part protruding.
    Last edited: Nov 15, 2011
  11. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,560
    Location:
    North Carolina
    Using the backing keeps the rubber from getting into the threads of the split bolt and makes for a cleaner disassembly but of course someone without experience wouldn’t know this. There is no need for rubber putty if using the rubber tape.
    Spoke like a true well man. The installation is not going into a hole in the ground but instead is going in a panel exposed to the rise and fall of the temperatures or its environment. Without a doubt there will be dust and other flying’s in and around the tape. All this will dry out any tape but it takes experience to know things like this.

    and anyone with experience would know that the welder would trip the 50 amp breaker supplying the 100 amp panel and then the next guy with the welder would know that the panel would not carry the load.

    are they not supposed to trip when they exceed their ratings?

    What is protruding?
  12. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,062
    Location:
    Cave Creek, Arizona
    quote; I would think seeing a 100 amp breaker will cause the next guy to hook up his 80 amp welder in that place. Seems unsafe if not unreasonable to do that.

    What is "unsafe" about it? The 50 amp breaker in the main panel will protect the #6 wire, and as soon as he tries to use the 80 amp welder and the 50 amp breaker trips he will have to reconsider his installation.
  13. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Why not skip the suprise phase of the next guy in? And you have redundant safety for the installation and not a big wad of rubber in the box.


    Are not 1.78$ Vi-agara tablets from india supposed to be legitimate and safe? Been to India? Is not the steering wheel on my jeep Patriot not supposed to fall off, as stated in my recent recall? Are not certain Firestone tires not supposed to delaminate at high speed and kill several families?

    I'll take that as agreement for a clean repair. But some are long and might protrude well out of the terminals.

    Maybe you dont use scotch 33, but its the gold standard, and as a topping over putty and rubber tape its fairly ornamental anyway. Over time it welds into a impenetrable mass and does not fall off. Hot, wet or cold. I cant imagine not using 15 cents of putty to get rid of all the sharp protrusions and bumps in the splice - makes the tape lay flat and clean. Makes the 'wrap' quick and easy. If you really want to get safe, brush on a coat of abs cement over the vinyl tape top coat.
    Last edited: Nov 16, 2011
  14. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,560
    Location:
    North Carolina
    All this time I thought that the Jeep was made in Belvidere Illinois here in the good ole USA.
  15. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Toyota had more recalls last year than Dodge, so its a universal failing.

    The issue on the Jeep are a few rivets, most likely sourced from China or Mexico. Because we sold our machine tools to them, and closed our high school shops.

    Scotch 33 IS made in America.
    Last edited: Nov 17, 2011
  16. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,560
    Location:
    North Carolina
    Balvalve

    I don’t know why nor do I much care but you are quick to jump on the bandwagon condemning items that are made in other countries but in your last two post here you have pointed out the failures of equipment that is made and assembled here in America at the same time pointing the blame on others.

    This shows a lack of knowledge of what you are trying your best to discriminate against. I would recommend that if you have a problem with items made in other countries that you address this issue with the elected officials and let them know if there is not something done to remedy the issue you will vote differently next election than you did in the last election.

    This is how to get action about what you are so quick to post about. The way you are addressing the issue by posting on a DIY web site is gaining nothing.

    Balvalve

    Here is a link to 33 vinyl tape
    http://www.alliedelec.com/Images/Pr...PECIALTY-MKTS_PRODUCTION-SUPPLIES_6174725.PDF

    Read it carefully.
    Last edited: Nov 17, 2011
  17. bsperr

    bsperr Member

    Messages:
    74
    Location:
    Athens, GA
    I might be missing something, but you should be able to find a 100A main lug only (mlo) subpanel that accepts 6 gauge wire. You might even be able to convert your current subpanel with the right size lugs. It seems like that would be easier unless you really want the convenience of a main breaker on your sub, in which case you can backfeed the mlo panel w/ a 60A breaker like ballvalve suggested (of course you would lose two potential spaces in your panel).
  18. SteinEE

    SteinEE New Member

    Messages:
    2
    Location:
    Illinois
    Not to overcomlicate things but if you are using 75 Degree rated equipment you could use #8's THHN with a 50A C.B in stead of #6's.

    You can change out the lugs. I am sure you can go to a local electrical shop and find these.

    What I don't like about this is the coordination issues. I think it is bad practice to have overcurrent devices upstream trip before local overcurrent devices. You would need to make note of where this new sub panel was fed from in case it trips.

    If this addition is a seperate building or structure you will need to look at NEC 250.32 for Grounding and Bonding Requirements.
  19. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,560
    Location:
    North Carolina
    If using NM cable it must be sized from the 60 degree column not the 75 degree.
  20. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    I think you started this with mention of "Canadian" drugs. But if a few get the message, its better than 1000 disposed letters to congress. I had 2 congressman partners, and I can tell you that only paid lobbyists have any pull with them.

    Writing to a politician has the value of perpetual motion devices. I am addressing national security, patriotism, and the education of our children in mechanical matters. Electricity and death fits right in there. These cannot be legislated into the national personae. Kids from farms, immigrants and the Amish, and variations therof provide our only hope for craftsman of the future. I do not have the time to write to each school in America and ask that they re-open the metal and wood shop that is now filled with computers.

    So whats with your latest conundrum about Scotch 33? Ask the electricians on the street if they know of any better? And my '33' boxes all have American flags on them, so this must be especially esoteric.

    I DID notice the part where they suggest putty under it in splices.

    I Do buy imported items, but try and find alternatives. Your electrical students are not getting work in Hong Kong, so what stays here, circulates here. Worked on a monster bridge replacement years ago. Buy American requirement. But no foundrys exist any longer for such heavy castings in America, so we had to go to China. Every piece was off spec, holes misdrilled, and some metallurgy-welding made monstrous pieces unuseable. 6 months of onsite repairs. Every third gigantic bolt failed testing, and all were trashed, finally found them in Ohio. That should explain my scepticism of Mexican circuit breakers and Chinese rivets. Here is my Scotch 33 link.

    http://www.grainger.com/Grainger/SCOTCH-Black-Plastic-Electric-Tape-2A226?Pid=search
    Last edited: Nov 19, 2011
Similar Threads: subpanel
Forum Title Date
Electrical Forum discussion & Blog Calculating subpanel/feeder size Oct 26, 2014
Electrical Forum discussion & Blog Yet Another Garage Subpanel DIscussion Jun 20, 2014
Electrical Forum discussion & Blog Subpanel location, mounting on the joist Jan 31, 2014
Electrical Forum discussion & Blog Subpanel Sep 13, 2013
Electrical Forum discussion & Blog Separating Ground & Neutrals to Create Subpanel Aug 23, 2013

Share This Page