I will answer your questions in turn, and then add a few notes at the end -- the code for pools is complex, partly because they are bespoke installations for the most part and partly because of how pool electrical safety evolved over time.
- You actually cannot do this -- the wire run must be in conduit as per 680.25(A)(1). You can use Schedule 80 PVC or RTRC-XW for the entire run provided the stub-up is protected from physical damage (i.e. being clobbered with a mower or whatnot -- 4x4 corner posts around the panel should do the trick, as would mounting it in a drained pump room or pit using an outdoor enclosure, provided clear working space is maintained). Otherwise, you're stuck with RMC or IMC (NOT EMT) -- likely red brass to avoid corrosion.
- That 125A number is overkill, requiring a 1/0 or 2/0 triplex in Al. I'd recommend instead using individual XHHW-2 Al conductors instead of a triplex (with an 8AWG copper THWN-2 or XHHW-2 wire for the EGC, of course) -- this will be easier to get through the conduit than a triplex, and also isn't liable to short the neutral to ground unexpectedly if you're running it in red brass. (Conductor/subpanel sizing advice is below, if you wish it.)
- You are correct -- never bond neutral and ground in a subpanel.
- Your overall plan seems sound, provided the subpanel is correctly placed (it cannot be within 5' of the nearest edge of the pool).
Additionally, given the type of pool you are dealing with, there are a few additional points to consider:
- You'll need a convenience receptacle somewhere outside 6' but within 20' of the pool -- this can be at the subpanel, attached to the lighting circuit and protected by its GFCI. (While you don't need GFCI protection on a lighting circuit that's feeding listed low-voltage ground-free luminaires -- it's cheap insurance.)
- Your branch circuits will need to be run in conduit as well -- either red brass RMC or IMC, or Schedule 80 PVC or RTRC-XW if you wish to use nonmetallic conduit. In any case, you must run an insulated EGC with the branch circuit.
- EQUIPOTENTIAL BOND ALL THE THINGS. If it is conductive, not a hot or a neutral, and is within 5' of the pool, don't take a chance -- just hook it up to the equipotential grid. In your case, since your pool is vinyl-lined, you do not need to run the grid under the pool, just as part of the perimeter paving -- 12" O.C. 8AWG bare copper is used for at least 3' beyond the sides of the pool, with cadwelded (i.e. exothermically welded) or otherwise listed connections. You'll also need to hook this grid up to the pool pump motor's ground wire (which is where it'll tie into the electrical system's equipment grounding system -- for a double-insulated pool pump, just run an EGC down to the pump's j-box as normal and tie the equipotential bond wire to it there), and to an underwater equipotential bonding electrode made from corrosion-resistant materials that has a minimum of 9 in^2 of surface area and can't be damaged by pool activity if there is no bonded metal in contact with the pool water. Also, I recommend running another bare wire from the grid to the subpanel itself, directly -- this is insurance against the EGC connection at the pump motor getting undone.
As to that forum that told you not to bond the equipotential grid to the house grounding system, whoever was posting that there is full of baloney, to put it extremely mildly. NEC 680.26(B)(6)(a) explains it most clearly (strong emphasis mine):
(a) Double-Insulated Water Pump Motors. Where a double-insulated water pump motor is installed under the provisions of this rule, a solid 8 AWG copper conductor of sufficient length to make a bonding connection to a replacement motor shall be extended from the bonding grid to an accessible point in the vicinity of the pool pump motor. Where there is no connection between the swimming pool bonding grid and the equipment grounding system for the premises, this bonding conductor shall be connected to the equipment
grounding conductor of the motor circuit.
Finally, as to that 125A number, it's hooey -- the pool pump motor is 8FLA@240V as per Table 430.248 and uses a 20A breaker from table 430.52, not the whopping 60A fib that you were told. In fact, that 60A number that they're giving you just for the pump is enough to leave 1200VA (600 per leg) for lighting and convenience receptacle loads after the 10A max load from the pool pump and the 40A number given for the heat pump -- which is well over three times the 180VA/outlet the Code tells you to allocate to general receptacles and outlets that aren't covered by other loads.
With that information in hand, we can run 4 6AWG THWNs for the feeder, just as you propose, and 14AWG for the pool pump as 430.22 specifies a conductor rating of 125% of FLA, or 10A in your case. (You can also use 14AWG for the receptacle/lighting circuit -- nothing says it has to be 20A.)
Your options are a minimum of #1 aluminum or #3 copper.
Since it's only 65 feet I wouldn't upsize it for voltage drop.
You don't need service entrance or direct burial type cable if you are running conduit underground you can use type THWN wire. Individual wires not cable. If you don't want to run conduit you can buy direct burial type wire like You are talking about.
Good luck and stay safe!
Best Answer
SER cable isn’t legal underground, so cross that off the list.
URD also called Mobile Home feeder, comes in 3-wire or 4-wire, so it’s an option. It’s legal for direct burial underground, but not for use indoors without conduit as if it was Romex or something.
So the real question is, what happens at the ends of the conduit? Does the conduit go straight into the panels at both ends? Or does it just sorta end, and then ??? to get over to the panel? I do not recommend the latter, as that ??? can get rather messy with wires this large.
If it’s conduit all the way
Then don’t use cable. Because the wires are bound to each other, cable is excessively stiff and a real pain to “pull”. You can buy individual wires, either THWN or XHHW. (All THWN is dual-rated THHN). You simply buy three full-size wires for hots and neutral, and one appropriately ground-sized wire for the ground.
Note that URD is simply THHN or XHHW wires glued together. If your conduit is continuous, then gluing the wires together is bad, and works against you. Get the wires individually.
You need #1 Al. Do you need a wire size bump?
Voltage drop is proportional to actual load, and cannot see the number on the breaker handle. Therefore we do not calculate voltage drop based on breaker trip. We calculate it based on the actual, expected, or permitted load on the wires. For instance you’re only allowed to plan for 80A on a 100A circuit, so you’d never, ever calculate voltage drop based on 100A. Never!
At less than 180’, I don’t even bother crunching the numbers to see if a wire size bump is worthwhile. It’s not. So you’re right on the cusp. Anyway, we don’t do wire size bumps for distance. We do them for distance and load. So let me ask - how much thinking did you do about loads?
In short, if it’s the second one, and you’re close, I’d do the bump to 1/0 Al wire. Otherwise fuggedaboutit, just stick with #1 Al.
If you bump hots, bump ground too.. #1 Al maxes out at 100A, and that means a #8Cu / #6Al ground is sufficient. However, if you do a wire size bump to 1/0, that maxes out at 125A, and that means you MUST have a #6Cu/#4Al ground. When you bump the hots, bumping the ground also is mandatory per Code. That’s because ground wires have voltage drop too, and theirs is worse, because they only carry fault current!
Don’t “Nanny Breaker” yourself. If you decide on a wire size bump to 1/0 AL, you might as well use the 125A breaker that you are entitled to. That way, you can the entire 125A of your feeder on the occasions when you do need it and are willing to “endure” the “scary, terrible” 3.7% voltage drop, woo woo. You don’t need a “100A nanny breaker” to protect yourself from voltage drop. Unless you are in Canada, because they say you do.
Did we mention BIG panel? Buying extra spaces at install time is extremely cheap. Adding spaces after you run out is extremely expensive. As such, we really like to see people splurge on excessively sized panels (in terms of numbers of spaces). If a 125A feed breaker seems like a buzzkill because your panel is only 100A, that implies a too-small panel. Take it out and swap it now, while it’s still super easy to do. That’s one mistake NOT to double-down on.