Been lurking for awhile getting ready to install a 60 amp sub-panel for my back yard.

I have everything I need figured out except for three important items as I get conflicting stories depending on who I ask or what I look up:

  1. Where should I place the sub-panel? As close to the main box as possible or at the end of the garage where the hole will be drilled for the outside runs? Does one method have more advantage than the other?

  2. What size wire should I run from the main to the sub? Some say 6 is fine since it's under 50 ft, others are telling me for 60 amps you have to use 4.

  3. What size wire is adequate coming from the sub-panel breakers to the individual circuits? I was going to use 10 AWG, but was told that was over kill and I should use 12.

The images below show what the runs will look like and also the breakers I am planning on putting in the sub-panel.

There may be a few location changes if I can't access the area under my deck like I think I can, and yes I will be burying the wire running to the batting cage and pool equipment.

I will be hiring an electrician for some of the work, but the more I can save doing myself the better. I am handy and have messed with power before, just not this much at once. Normally it's just running inside stuff.

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  • Have you already purchased the subpanel? – ThreePhaseEel May 11 '19 at 13:32
  • And the conduit, for that matter? For an indoor run, EMT would cost less, be more compact, and spare you the need to purchase a grounding wire as it's an acceptable grounding path under NEC rules if properly bonded. Runs don't look excessive, so 12Ga for 20A and 14 Ga for 15A should be fine for wire sizes. – Ecnerwal May 11 '19 at 14:13

Put the subpanel closest to where the branch circuits exit

I would put the subpanel as close to where the branch circuits exit the house as possible. This prevents routing and spacing/derating issues with a "bundle" or "trunk" of branch circuit wires from biting you in the butt when you go to hook the branch circuits up to the subpanel.

I'd use 4AWG aluminum for the feeder between the two panels

The folks who say 6AWG is sufficient for 50A are correct, as 6AWG copper wire can handle 55A when limited to a 75°C maximum temperature, which is the general limit for wires connected solely to distribution equipment. However, at 60A, you are at the threshold where aluminum wires become a cost-effective choice. As a result, I would use 4AWG aluminum THWN or XHHW-2 in the conduit for the hots and neutral, along with an 8AWG bare copper ground wire.

Your choice of conduit is fine

While 2" conduit may sound like overkill, it's a good choice here as oversizing the conduit both makes the pull easier and provides plenty of space for future expansion. One could use EMT instead of PVC if they wished to not have a ground wire in the conduit, but that's up to you, really. One note with PVC, though, is if this garage is not a conditioned space, then you'll need to use expansion joints in the run to keep it from doing the worm on you!

Either way, you will want to provide ample pull points to avoid needing to ask your electrician to swoop in with his truck full of pulling tools and bail you out. While the inside bends from wall to ceiling will need to be made using prefabricated sweeps, any 90° bends in the ceiling-supported run should be made using LL or LR conduit bodies instead.

Given your outside wiring scheme, I would go "trunk and branches" here

Given the diagram you gave for your outside wiring scheme, I would run conduit (1" Schedule 80 PVC will do for this) for the main outdoor runs. In particular, the run from the panel to the first receptacle and from that receptacle to the deck/firepit lights should be done this way, with the pool wiring run as a separate conduit homerun from the panel to provide room for future upgrades to the pool setup.

In the homerun from the panel to the first receptacle box, then, we have:

  1. a 14AWG THWN hot/neutral for the batting cage lights
  2. a 12AWG THWN hot/neutral for the receptacles
  3. a 14AWG THWN multiwire (hot/hot/neutral) branch circuit for the remaining lights
  4. and a 12AWG bare or green THWN ground wire

This conduit gets stubbed up to the first receptacle box, a 2-gang FSS box that has an extra 1/2" nominal (7/8" actual) knockout field-made in its bottom (with a step drill or hole saw) in addition to having 1" hubs molded into the box. The 1/2" knockout gets used for a 1/2" PVC conduit sleeve (with appropriate fitting) that protects a 14/2 UF cable going down into the ground for the batting cage lights, while the other 1" hub is used for the conduit onward to the deck/fire pit lights. In this conduit, we have the 12AWG for the receptacle branch circuit, the 14AWG multiwire branch circuit for the deck and fire pit lights, and a 12AWG ground wire.

When we reach the deck/fire pit light switch location, we stub up into a 2 gang FSCC box with 1" factory hubs. This box houses the light switches, or if you prefer, just splices with the light switches in a 2 gang FSC box mounted further up on the structure. From the light switch box, we then head up to the light fixtures in more conduit; if you need to, you can split neutral in half at the switch box and have two neutrals in the conduit from the switch box to the lights, even.

The other stub-down, then, can either be a 1/2" conduit to the ground with a reducer at the box if you are running a 12/2 UF to the other receptacle location, or 12AWG THHN in conduit (either 1/2" or 1", your pick) for the entire run to the other receptacle if you prefer.


One other note is that when you are installing panels these days, 2017 NEC 110.14(D) requires that you use a torque tool (torque wrench or screwdriver, reading in inch-pounds in practice) to tighten all lugs on devices labeled with torque specifications to that labeled torque. Even if your jurisdiction has not adopted the 2017 NEC yet, it's a good idea to do this anyway, lest your electrical system loses you the race.

  • I like the multi-wire branch circuit, as long as it is only lights. Lights don't need GFCI, which is the achille's heel of MWBCs. – Harper - Reinstate Monica May 11 '19 at 16:09
  • @Harper -- that's the idea, yeah :) – ThreePhaseEel May 11 '19 at 17:04
  • @Harper I for one really appreciate you and TPE answering the electrical questions. Keep up the good work! – Kris May 11 '19 at 18:03
  • thank you for the super detailed explanation. That answers everything that I need. – Craig Andrews May 11 '19 at 20:15
  • The panel I was looking at getting was this... Model # HOM2448M100PCVP Square D Homeline 48-Circuit 100-Amp Main Breaker Plug-On Neutral Load Center – Craig Andrews May 11 '19 at 20:26

Place the subpanel wherever convenient for now/future use

I gather you're contemplating a subpanel right next to the main panel because the latter is full. That's fine.

However if another location is also convenient, feel free to put it there, complying with law of course, and with a preference toward keeping it out of the weather. (even outdoor rated panels do poorly outside, and that is far more so with GFCI/AFCI breakers, which are required nowadays).

Do take consideration for difficulty of routing the feeder from the main to the subpanel. I strongly recommend metal conduit - you may be more familiar with PVC piping, but EMT conduit is quite easy to work with once you get the hang of it, provides better physical protection, and provides a grounding path.

If you put the subpanel right next to the main panel, definitely use EMT, and put at least 3 pipes between the two panels. There are advantages to having these pipes be <24" long.

Get a B.I.G. panel

I mean in terms of spaces. If you lurk around here, you've certainly heard our standard advice. And since I gather you're out of spaces, you certainly understand the problem! Right now, you can have a couple dozen spare spaces for the price of a couple of pizzas... and zero extra work. But later... that'll cost you the price of a panel and a day + of solid, regretful work. Yowch.

My "go-to" subpanel is a 30-space. They can be had very inexpensively.

Of course that means a panel with a main breaker much larger than 60A. That is fine. There is nothing wrong with feeding a 200A panel from a 60A feed breaker. The 60A breaker will assure the 200A panel does not overload. And since you're in the same building, your panel doesn't even need a main breaker; a main-lug panel will be fine.

Make up your mind: cable -- OR -- conduit + wire

One trope we see a lot is people specifying conduit, and then wanting to run cable inside it. They go to cable because that's all they know.

But cable is very stiff, and is rather hard to pull through conduit. (and I bet that was your first thought when you considered it!) So it requires quite large conduit, and novices often get what physically fits there in the big-box store. This makes the pull even harder than normal, enough to make you swear off conduit forever! What a shame, it's wonderful when used as intended.

Cable also has two problems: Physical protection (cable can't provide this directly), and wet locations (standard Romex aka NM cable is NOT wet-rated). Conduit solves these - and EMT is better for physical protection since it bends rather than shatters.

If you lay conduit, which I recommend - then you are better off putting individual wires in the conduit. These are sold in spools in individual colors. The wire is colloquially called "THHN", but the wire actually sold is dual-rated THHN/THWN-2 (dry and wet). Sometimes you see XHHW, which works too.

For size 6 AWG and below, you need colored wire - black for hot conductors (and using 2 blacks is absolutely fine), white for neutral, and if you run in PVC conduit, green for ground. (EMT is the ground). For size 4AWG and above, you can buy all black and mark the wires with tape on both ends.

You can use copper or aluminum for the feeder to the subpanel. If you use aluminum, you must "bump" 2 numeric sizes (remember smaller==larger). Aluminum got a bad rap because of inappropriate use in small branch circuits, but that never applied to feeder. It's a good choice for feeder. Price it both ways.

If the subpanel will be right next to the main panel, I would use copper, just because it's easier to bend (smaller gauge) and while significantly more expensive, you won't use enough of it to care.

Voltage drop

You seem concerned about voltage drop. We don't even need to think about voltage drop until the wire length exceeds 120' for a 240V/feeder run, or 60' for a 120V run.

But even so, calculate voltage drop based on the actual normal loads, never, ever, ever on the breaker rating. And forget 3% - it's a good rule of thumb but 4-5% is also acceptable if there isn't too much other voltage drop. Especially, the normal wire will often calculate out to something like 3.4%, and the online calcs will recommend a size bump because of 0.4%. That's silly.

Feeder wire size

If the breaker is 60A, you need #6 Cu or #4 Al. Why? Looking at table 310.15(B)(16), we are required to use the 60 degrees C column, because the circuit is <100A. (>=100A allows 75C). Both these wires rate at 55A, and we are allowed to "round up" to the next available breaker.

  • For a 70A breaker, #4 Cu.
  • For 80A, #2 Al.
  • For 100A, either #3 Cu or #1 Al. (It may be weird to get 30 extra amps for a 1-unit size bump, but remember - we can use the 75C column at 100A).

2" conduit is a very good choice of size, and will make for an easy pull in any of the wire sizes we discuss here.

And for a novice, first-time pull, using #6 Cu is fine. It's easy to work with, it'll land just fine on a 60A breaker without pigtailing, and the project will go smoothly. However, you do need to buy natively colored white wire for neutral and (if in PVC) green or bare wire for ground. The ground can be undersized.

Branch circuit wire size

Remember we calculate voltage drop based on actual load, not breaker rating. You are always allowed to upsize wire size.

With 120V circuits, my rule-of-thumb is a size bump every 60', but with an extra 30-40' thrown in because the circuit should never be loaded up to breaker rating. Below about 100', I don't worry about it.

The breaker size defines the circuit size.

14 AWG is only legal for 15A circuits, but myself, I do not use 14AWG anywhere. I don't even own any #14.

12 AWG is legal for 15A or 20A circuits. It is the minimum for 20A.

10 AWG is the minimum size for a 30A circuit, but may also be used for 15/20A circuits.

  • Awesome. Between the 2 answers I have a lot to think about. – Craig Andrews May 11 '19 at 20:18

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