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.
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.
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.
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.