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I looked up size for #2 and it says just over a quarter inch. I'm concerned a 60amp breaker won't fit a #2. I have an older Bryant panel. Maybe breaker manufacturer makes a difference or I must order a special one?

I have along run 100+ft which has forced me to use aluminium and a #2.

  • Using aluminum (AA-8000 alloy) is a good thing, but what's the load on the other end that necessitates a wire size bump for voltage drop? What is the actual amp draw of the load when running? The usual blunder is to do the v.drop calc on the ampacity on the breaker rather than the ampacity on the load. In 240V circuits the 3% typically happens at 110-160' depending, not that 3% is even all that critical. – Harper Jun 26 '18 at 16:37
  • there is already been a long discussion of wire sizes at my other post so won't respond here. diy.stackexchange.com/questions/140898/… – DKebler Jun 26 '18 at 20:21
  • If I run the calc at 100amp at 5% says #1. If I run 80amp 5% then I can do #2. An 80amp double pole breaker costs 3x times a 60amp. Even though my load center can handle 125 I don't ever see drawing anywhere near 60amps ever. In fact rarely even 20amps total for my tiny trailer. If need be one could go up to 80 or maybe even 100 amp breaker in the future like if a new owner pulls in a huge RV. Even though I personally don't need this much I wanted to run big enough wire for "resale". – DKebler Jun 26 '18 at 21:38
  • Well then, do your load calcs for 20A@3% if that's your expected load. Take a) the resulting figure, and b) the minimum wire size required for that breaker even if the wire length were 1'... And use the larger of the two. Sorry, I missed the part where your remote service was 50A. You didn't ask and I honestly didn't give upsizing for voltage drop any thought since the run is only 100'. A 100' run of 240V is almost always below 2.5% drop, so I don't even bother running the math unless it's 120'+. – Harper Jun 26 '18 at 22:05
  • I,ll say this though, your situation is absolutely an ideal situation to not worry about oversizing wire. Your length is just long enough for upsizing to maybe have merit, but still short enough, and of an ampacity, that the differential cost is very low... And the capacity headroom is nice. So even though I don't think you need 2Al, if I was spending my own money I wouldn't lose any sleep over it and would maybe even do it too. – Harper Jun 26 '18 at 22:44
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On the side or front of the breaker, there is a label that says what the maximum wire size is that you can use. This label is required by UL when the breaker is made. It may have fallen off however. If so, you can look on-line for a similar breaker. Bryant is now part of Cutler Hammer, their version of that breaker is called a BR series with the BR standing for Bryant. The breaker is unchanged from when Westinghouse owned the Bryant line (Westinghouse was bought by Eaton years ago, Eaton owns Cutler Hammer). So any technical specs on a new version are going to be the same.

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    A quick look at their catalog says that a BR160 will accept a wire size from #8 to 1/0, so #2 is not going to be a problem. – JRaef Jun 26 '18 at 16:27
  • Yes, BRyant is an alright, modern panel, and a mainstay of the big-box stores. In fact, an electrical supply guy recently showed me a BR double-stuff breaker right next to the equivalent CH breaker, CH being their superior industrial line that is physically narrower. The BR handles were notably narrower than they needed to be, and the handle shapes were identical. Eaton is clearly putting CH guts in BR bodies. That makes BR better. – Harper Jun 26 '18 at 16:53
  • There is no more Bryant, it's just a marketing gimmick to make it appear to have differentiation. All Eaton breakers come from the exact same factory... – JRaef Jun 26 '18 at 19:32
  • @J.Raefield. Got a link to those specs? All the online vendors like baybreakers had no specs. If I could have found them I won't have had to ask here. – DKebler Jun 26 '18 at 21:41
  • @DKebler here you go – ThreePhaseEel Jun 26 '18 at 22:31
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If in doubt, transition in the panel

A proper electrical supply house will cheerfully sell you an inline insulated lug splice made of plated aluminum. Aluminum-bodied lugs play well with both aluminum (obviously) and copper, hence their broad use. You then continue with #6 copper for the last 8" from the splice to the breaker.

I go to electrical supplies because they have good selection and I prefer insulated lug splices that barely fit the largest wire - that way the wire opening is just the size of the insulation, and I don't have to do any additional work to insulate it. Torque 'em!

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