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I want to run 60 amps (240 volts) to a subpanel, with a primary load of 40A. Because of the distance (270' between panels plus 165' from subpanel to pump) I am upsizing conductors to #2 Al. The 60-amp breaker only takes wires as large as #4. Is the proper way to do this to use an insulated, inline splicer like Polaris or Ilsco make and splice a short run of #4 wire inside the main panel? I can find a 22K AIC 60-amp breaker that takes #2, but that seems like it's not the best way to go. I've also heard some people just cut off a few strands to make the wire fit, but that also doesn't seem like the right way to go.

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    I can find a 22K AIC 60-amp breaker that takes #2, but that seems like it's not the best way to go. Assuming it's actually listed for use in your panel, why would you think it's "not the best way to go", given that it solves the problem directly and quite possibly has cost similar to if not less than a pair of suitable Polaris connectors?
    – Ecnerwal
    Oct 25, 2023 at 0:15
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    What is the distance? What brand/type of panel? Oct 25, 2023 at 0:18
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    So 270+165 = 435'. OK, that is a long ways. How many Amps does the pump actually draw? Oct 25, 2023 at 1:45
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    I think you misunderstand must be "installed on a circuit capable of delivering fault current greater than 10,000 amps." It is NOT "you can only install a QPH if the circuit can deliver > 10,000A". It is actually "If you have a circuit that could deliver greater than 10,000A then you MUST use QPH instead of QP". There is absolutely nothing wrong with using QPH even when you don't have any possibility of 10,000+A. Oct 25, 2023 at 2:02
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    I believe it generally has to do with utility service size - i.e., how much power could possibly flow over the wires given the limits of the utility transformer, wires, etc. Typically it is 22k for a main breaker and 10k for the branches. Basically don't worry about it for an application like yours. Really a non-issue except that QPH gives you larger wire size connections. Oct 25, 2023 at 2:35

3 Answers 3

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Cutting off strands is a code violation ...and just stupid.

The proper options are to use a breaker (correctly listed for use in your panel) with suitable connections built in, or to splice from the largest wire your breaker takes to the wire you want to run by any suitable (listed for the purpose) means.

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60A subpanels are an entirely fictional thing.

The idea that this is a 60A subpanel is a fiction you created in your mind. There is no such thing. A 60A subpanel would either need to be 60A rated - it's not, it's rated 70A, 100A or 125A. Or, it would need to use 60A wire - go look in Table 310.15(B)(16) and you'll observe there is no such thing as 60A wire.

So the inconvenient "60A" is all made up, and we are not bound to that non-reality in any way. We can "make up" something better, provided we stay within legal constraints. The wire is 90A and the panel is at least 70A. The ground wire, #8 Cu or #6 Al, constrains you to 100A.

I believe you will find the 70A breaker of your panel line will accept 2 AWG wire directly. And that's it. Problem solved.

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  • Maybe, but the point was to limit voltage drop by limiting amps. If I put in a 70 amp breaker, then there is nothing to stop anyone from adding circuits or loads and defeating the purpose of upsizing in the first place? I want to follow code, but I also want to protect the expensive well pump.
    – cjc
    Oct 25, 2023 at 19:05
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    @cjc I call that a "nanny breaker" when its only purpose is to protect you from voltage drop. But voltage drop is NOT the bogeyman some make it out to be; it's a minor inconvenience at most, and 3% is a complete lie. Nothing will struggle with 5% drop. You only need to deal with it if you're in Canada. Oct 25, 2023 at 20:01
  • I really don't know much about induction motors, but I've read a couple times that insufficient voltage is hard on them. I didn't size the wire down the well. But depending what the pump actually draws at startup, that adds another 2-4% voltage drop. Anyway, I like to build things to last, since we already do enough maintenance and repair work around here. Even an extra year of pump life seems worth it.
    – cjc
    Oct 29, 2023 at 19:08
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    @cjc well pumps are built to be much deeper than that, and they don't upsize the well wires. They are well aware of the voltage drop issue down a long well, and build the motors specifically to endure it without damage. You have zero evidence that another % of voltage drop will extend a well motor's life. You are wasting money making a mountain out of a molehill, and pretending blind overdesign improves safety. No, intelligence does. My advice is to use the 70A breaker and use good judgment about adding loads to that panel in the future. Feel free to use the Polaris connectors instead. Oct 30, 2023 at 0:26
  • Good to know. I did notice that manufacturer's directions for running off a generator didn't seem to meet 230 volts.
    – cjc
    Oct 31, 2023 at 2:03
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2 AWG aluminum is a good choice because of pricing and future expansion. It can handle up to 90A, assuming there are no voltage drop issues. So the key questions are: What is the actual distance? and what is the actual load?

As it turns out, there are two distances involved:

  • main panel to subpanel = 270'
  • subpanel to primary load (pump) = 165'

In certain ways they could be considered together, but for simplicity (and for more common use in similar questions) I'll keep them separate for now.

Using a very conservative 3% (not really necessary in most cases, except Canada), 2 AWG aluminum will handle:

  • 306' at 40A (target for this question is 40A, and 306' > 270')
  • 255' at 48A
  • 219' at 56A
  • 191' at 64A
  • 170' at 72A

But wait a minute, you said 60A and I suggested up to 90A, so what are those crazy numbers???

They are 80% of the breaker size. Generally speaking, if loads are continuous, such as EV charging, water heating, HVAC, etc. then you have to provision 125% of the expected usage. So a 60A circuit (defined by breaker size) will, most of the time, not have more than 48A on it. And a 90A circuit will not have more than 72A on it. The voltage drop is based on what is actually being used, not hypothetical maximums (except possibly in Canada).

Larger circuits and/or longer distances are possible, up to the standard limit of the wire (90A for 2 AWG aluminum) if you allow for more than 3% voltage drop.

A key point is that you can use a larger breaker than you actually need, as long as your wire is large enough and as long as the destination panel can handle it. Most panels have a bus rating of at least 100A, so that part is easy. A subpanel in a different building from the main panel does need a disconnect. So that might mean using a big "main" panel (but with ground bar added and neutral-ground bond removed) that happens to have a nice big main breaker (100A or larger, even 200A is fine) which you then use as a disconnect. You just can't (maybe you could, but really shouldn't) use a subpanel with a 60A breaker as a disconnect if your feed circuit is more than 60A. But all that is no big deal - big panels are actually not very expensive compared to small panels.

The final step then is to figure out breaker sizes that can accept 2 AWG wire:

  • Eaton CH - 60A and up
  • Eaton BR - 60A and up
  • GE - 70A and up
  • Square D QO - 60A and up (except GFI, but you generally don't use that on a long feed - put the GFI in the subpanel on individual circuits)
  • Square D Homeline - 60A and up
  • Siemens QP - 70A and up
  • Siemens QPH - 60A and up

There are some other brands out there. But the end result is that at least with most of the top breaker lines there really isn't any issue at all, unless the labeling indicates otherwise. And if there is, bump it up to 70A or 80A or even 90A to solve the problem.

As far as Siemens, QPH can always be used in place of QP. QPH has a higher maximum interrupt rating - i.e., it is designed (or at least rated) to handle a massive overload better than QP. No harm in using a QPH. But a QP 70A will also work just fine.

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    The breaker protects the wire, so unless I'm missing something, it seems like you could use a 70A breaker in the main panel and then backfeed through a 60A breaker in a different brand subpanel. It's a goofy way to do it though when, as you say, bigger rated panels are so cheap.
    – KMJ
    Oct 25, 2023 at 1:32
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    @KMJ I don't know if there is any code against such a setup. Arguably even if the subpanel had a 60A bus it wouldn't matter - the 60A subpanel breaker would protect it. But goofy and really no reason to do it. Better to oversize and have expansion room. Oct 25, 2023 at 1:39
  • @manassehkatz-Moving2Codidact I used 40 amps expected usage to calculate voltage drop based on what I know will be in the pumphouse/shed.
    – cjc
    Oct 25, 2023 at 2:04
  • Aha! Now we actually have some real numbers... Oct 25, 2023 at 2:08
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    @manassehkatz-Moving2Codidact thought you were questioning KMJ backfeeding, comment deleted Oct 25, 2023 at 13:35

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