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UMC Wiring

Discussion in 'Roadster: Technical' started by W.Petefish, Aug 30, 2011.

  1. mpt

    mpt Electrics are back

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    Yep, that's good to know.

    @donauker: Indeed, but, a 5-20 or 6-20, etc. might be found on circuit with a few other outlets and a 30A breaker no? Could be good to get at that extra few amps.
     
  2. donauker

    donauker Member

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    Only in violation to the code. All wire and receptacles must be rated at or greater then the breaker. Under an overload situation the 20 amp outlet could meltdown/burn without throwing the breaker.

    Also a 20 amp or greater outlet must be wired with only one receptacle per breaker.
     
  3. mpt

    mpt Electrics are back

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    Oh, that's interesting; I must check the breakers wired in my garage; I was able to pull 40A from a 5-20... For only 30 seconds whilst I tested to see if it was possible mind you. No breakers tripped and the wiring remained cool. On each side of the garage I have a string of 5-20's daisy chained through a GFCI outlet, sounds like not to code.
     
  4. donauker

    donauker Member

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    Actually I got that part wrong. Receptacles rated higher then circuit are not a problem, so multiple 5-20s should be OK. The somewhat confusing one is the 5-15 which can be used for 20 amp circuits as long as there are multiple outlets per circuit. One duplex 5-15 can handle 20 amps but each outlet would be limited to a 12 amp device.
     
  5. doug

    doug Administrator / Head Moderator

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    Annoying that these things are labeled for their peak rating instead of continuous.
     
  6. S-2000 Roadster

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    I don't think it's peak versus continuous rating so much as a built-in understanding that continuous usage should only be 80% of maximum rating. In other words, I think the ratings are consistent with reality, it's just that you should never use anything at its full rating, at least not if you want to be safe. Engineering design always allows at least 10% overhead for variances and tolerances. I don't think there's a safe way to mark everything with the exact same number just to make it easy to match like numbers with like numbers. Personally, I think it's important to be aware of planning on the 80% continuous usage out of the actual 100% rating that is marked.
     
  7. mpt

    mpt Electrics are back

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    Oh, I'd better ease back on the go pedal then, 'cause I use that at 100% rating quite a lot. Perhaps this is why my rear tires are all used up after six months.
     
  8. bonnie

    bonnie Oil is for sissies.

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    I made it 6 1/2 months before I had to replace. :)
     
  9. S-2000 Roadster

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    Ha! What I find very interesting is that Tesla Motors hides the 100% from us in so many ways.

    A "full" charge is only 4.1 V, and a "range" charge is still only 4.15 V, and both of these are shy of the actual 4.2 V capacity of the batteries that any laptop would use when charging to 100%

    Even with traction control turned off, the Tesla motor does not put out full torque, otherwise the wheels would spin. Rather than rely upon driver finesse, the computer manages to hold back from 100%

    But, hey, I'm used to high-performance tires wearing out quickly, it's all according to their treadwear rating.
     
  10. dpeilow

    dpeilow Moderator

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    Just to reiterate - the 80% rule is true in the US but in Europe we rate things at their continuous load capability.
     
  11. doug

    doug Administrator / Head Moderator

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    This is just convention. It's done differently (and in my opinion more sensibly) on the other side of the pond.
     
  12. TEG

    TEG TMC Moderator

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    Trying to pull 80% (40amps) off of a socket labeled 50 amps at an RV park can sometimes be hit-or-miss too.
    When the sockets are exposed, outdoors, and used heavily they can start to get 'dodgy' after years of use.

    Sometimes a little safety margin isn't a bad thing.
     
  13. VolkerP

    VolkerP EU Model S P-37

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    It appears to me that opinions here are biased by what everyone is used to. As pointed out with the acceleration example, there are many situations where all of us want to go to 100% spec. And overclocking hardware without additional cooling is simply exploring that safety margin in a CPU design.

    "What's that? I wanted my steak well done."
    "Sure darling, but I thought to go on the safe side and do it just 80%"
     

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