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
    So, back to the topic...

    Thanks for all the suggestions. I do prefer to have a main cutoff on the sub-panel. It seems like Siemens 100-amp panels all require #4 minimum for the main breakers. So, I'm thinking I might take the suggestion to return the panel I bought and just get a "main lug" panel (without a main breaker) and backfeed a 50 or 60amp breaker to use as the main breaker in the sub-panel. Anyway, that's how I read one of the suggestions.

    And, from a little research, it sounds like backfeeding means simply attaching the feeder wires (red & black) to the 50 or 60amp breaker (instead of the panel's lugs). Is that correct? And I assume the neutral and ground attach to their normal lugs/terminals. Although, now that I think about it, will I have the same problem with the neutral: minimum #4? Hmm...I'll check the panel specs again.

    Thanks.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    You could just trash the 100A breaker and replace it with a 50A one, too. Since you already have the panel, and would have to buy a 50A breaker anyway, it seems like the easiest. that would have to proper sized lugs.
  3. seattle_steve

    seattle_steve New Member

    Messages:
    28
    Location:
    Seattle, WA
    Yeah, unfortunately (or not?), Siemens builds the main breaker into the panel -- it's physically attached at the top of the panel and isn't a regular breaker that slides into one of the slots. Same with the breaker's lugs -- they don't seem replaceable.

    In the meantime, I bought a Cutler & Hammer panel today to check it out, even though I wanted to stick with the same brand (Siemens) as my main panel, since I have extra Siemens breakers, it will be easier to swap the breakers between panels, etc. The C&H panel's lugs do seem to take smaller gauge wire (and its main breaker does just sit in one of the regular breaker slots, unlike the Siemens). However I'm not impressed with the apparent quality of the C&H innards. It just looks cheap compared to the Siemens.

    So, plan for tomorrow: take back both the Siemens and C&H panels and get a Siemens main lug panel + a 60amp breaker to backfeed as the main.

    As far as the neutral lug wire size: I've noticed at the store that they sell these separately, so I'm guessing if the Siemens neutral lug says min #4, I can add a new neutral lug that accepts a smaller wire?
  4. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    There is a reason why the main is mounted to the panel.
    408.36(D) Back-Fed Devices. Plug-in-type overcurrent protection devices or plug-in type main lug assemblies that are backfed and used to terminate field-installed ungrounded supply conductors shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means on the panel.

    When you get this50 or 60 amp breaker, in order to back feed the breaker it MUST be secured to the panel to prevent someone from pulling it out while it is still energized. So don't forget to get the lok-down kit that goes with it.
  5. seattle_steve

    seattle_steve New Member

    Messages:
    28
    Location:
    Seattle, WA
    Interesting. Makes sense. After a little more research it sounds like I'll also need a "breaker retaining clip" to meet this requirement. I've added it to my list.
  6. seattle_steve

    seattle_steve New Member

    Messages:
    28
    Location:
    Seattle, WA
    Ok, I've given up on Siemens. I took a look at the documentation for the 125A main lug. Turns out they only (apparently) support 3 specific breakers for backfeeding the panel. Not surprisingly, none of these was available at Home Despot. In addition, the 3 breakers were all in the 100-125Amp range, so even if I was able to find one, no doubt I'd be back at square one with the wire size issue.

    So, I bought a 100amp Square-D Homeline main breaker panel. Its main breaker lists a wire range from #12(!) and up. The quality of this panel still seems somewhat inferior to the Siemens (e.g., aluminum "connector plate" (?) instead of copper), but definitely a step up from the C&H panel.

    So, I think I've resolved the panel/breaker/wire-size issue. Thanks again for all the responses.
  7. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    You have resolved it, but it seems a shame for the next guy unless you leave him a big tag in the box saying the main breaker will not operate as a protective device, but only as an on-off switch. With all the rules in that big NEC book, I think they really missed one here.
  8. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    The breaker that supplies the feeders will do the protecting and as you pointed out the main is nothing more than a switch to turn the panel on and off
  9. ActionDave

    ActionDave Electrician

    Messages:
    351
    Location:
    Colorado
    I would argue that it is one example of the code behaving as it should. There is nothing unsafe about the set up.
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    One way to think about this is the wall switch, rated at 15A that is controlling a 100W light bulb...works fine, lasts a long time, perfectly safe.
  11. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Fine, but would you feed this single 15 amp breaker with a 100 amp main, with the "real" 20 amp breaker perhaps 500' away in a basement?

    I see some homeowner in the future deciding the 100 amp main is shot because his outlet is dead, and changing that before he finds the real infeed device. Simply an illogical and perhaps unsafe situation for what he might think he can add to that panel.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    As long as the wire is protected, it is safe...you're totally wrong on that. Now, convenience may be another matter. A black marker writing the main panel breaker number and it's amperage for the subpanel would be a simple way to indicate what the main supply to it is.
  13. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,327
    Location:
    Houston, TX
    I think that the page may have turned, and everyone is not on the same page.


    Be careful Playing with electricity.


    Have a Great Thanksgiving Holiday.
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