0

We will be installing a 125amp sub panel in our pole barn which is about 115 feet from the main panel. We will use 125amp breaker in the main panel and run conduit the entire run. From what I have read we can use 2/0 aluminum. Was looking at using 2/0 2/0 1 4 MHF. Is there a better choice that we should be using? Thanks for the input.

6
  • 2
    We will be using this space as an arcade area, 10-15 arcade games, 4 TVs for the gaming cabinets and another -10 tvs for sports. 36k mini split, frozen drink machine and a popcorn machine. Various other items. 23 led canned lights.
    – Bryhud
    Oct 8, 2021 at 0:22
  • 1
    Sounds like a fun place! And actually does sound in the range of 100 A if everything is going at once. The more typical barn usage we see in questions is a shop with lights + a few tools. Oct 8, 2021 at 0:34
  • Yes we figured we would go with 125 amp breaker, though it might be overkill better to have it if we need it.
    – Bryhud
    Oct 8, 2021 at 0:38
  • 2
    Make sure you get a really big panel. You will likely have to have almost every circuit on AFCI, GFCI or both. And if you can easily do so (which you should be able to do when finishing the inside of a barn) put in a lot of separate circuits. It might be that you put in a 200A subpanel *because that's what gets you a good deal on a big panel and that's OK - the breaker in the main subpanel has to match the subpanel feed wires but the main breaker (which is technically there to be a disconnect) in the subpanel can be larger. Oct 8, 2021 at 0:58
  • 1
    1200 sq foot space.
    – Bryhud
    Oct 8, 2021 at 1:58

3 Answers 3

2

There are 2 separate questions that need to be split off. It's very similar to the posted speed limits on a road vs. the speed rating on your tires.

The size of the feeder supplying the sub panel.

This needs to correspond to the actual or likely usage you will have at the sub panel. For instance if you have a 12,000 VA of EV charger and 3600 VA of other loads, that's 15,600 VA or 65 amps. So you would need a feeder and supply breaker ready for at least 65 amps.

The ampacity limit of the sub panel.

This only needs to be greater or equal to the above number.

The main consideration here is on sub panel size should be to get plenty of breaker spaces. The #1 problem we see with subpanels is "I need to add a circuit, but my panel is out of breaker spaces". Well, that problem was caused by bad choices earlier, which in this case is "Right now!" Spaces are cheap. Aim to finish the project with at least 50% of spaces unused.

This may result in a panel whose amps are quite a bit larger than the first number. That is fine.

Your panel and wire size

The breaker must protect the wire based on its amp limits. However, if that breaker is not made, you round up.

So at your size, it's a labeling game. If you are ferociously committed to calling this a "125A" feeder, then you must use 2/0 aluminum wire (since 1/0 is only good for 120A).

However if you are willing to label this a "120A" feeder, you may use 120A wire (1/0). Since 120A breakers are not made, you use a 125A breaker. You must pinkie-swear never to plan to draw more than 120A.

125A is the largest breaker of reasonable size and availability, so it's a good choice.

1
  • 1
    I'd like to see the pinkie-swear reference in the NEC. :D ROFL
    – FreeMan
    Oct 8, 2021 at 12:28
1

You have plenty of feeder space, don't worry

Calculating the arcade cabinets and TVs at 180VA/unit (the miscellaneous receptacles number from NEC 220.14(L), which isn't too far off for arcade cabinets from the quick Google search I did, and a pretty generous allowance for modern LCD TVs) and adding 1500VA for the concession machines gives us 6900VA of plug load. Atop that, we add the 36kBTU minisplit: using an 18.5 SEER LG single-zone heat pump as a reference, we wind up with 23A * 230V * 1.25 (for being the largest motor in the space) = 6613VA for the minisplit. Finally, the lights are calculated based on standard square footage lighting loads; treating this space as a club of some sort, we get 2VA/ft² or 2400VA for your 1200ft² space.

Adding this all up and dividing by 240V, since we don't have enough receptacle load for demand factors, gives us 15913VA, or around 66-67A at 240VAC. This means that a 125A feeder is quite ample for the task at hand, with no shortage of expansion room if more is needed in this occupancy, and your 2/0-2/0-1-4 MHF will have no trouble handling what you have in store.

You'll want plenty of panel space, though!

However, you'll want plenty of loadcenter spaces in this setup, since your feeder is indeed good for 150A (although with some caution since your neutral is limited to 100A of maximum imbalance), and loadcenter spaces generally go fast! I'd recommend a 30-space or 32-space, 125A, main breaker loadcenter as a minimum here; if you want to go to a 40-space or 42-space, 200A, main breaker loadcenter instead, that may be worthwhile given the cost differential is only about $100.

Keep in mind that you'll need to fit accessory grounding bars to the load center, as well as pulling the loadcenter's bonding screw and running a 6AWG copper grounding electrode conductor to the grounding rods or grounding electrode for the barn. Note that unlike on a main panel, this grounding electrode conductor lands on the grounding bar; if you're wondering how it can get into the breaker box to begin with, that's the job of a part known colloquially as a "Kenny clamp" that is used to clamp single wires to knockouts.

Finally, you'll need a few gadgets that you don't normally put in a house

Finally, we'll need to power a few things that don't normally go into houses, as this really is a small assembly space, especially given its size. The closest thing to what you have in IBC 1004.5 is what they consider a "gaming floor" (their examples are casino-based, but I suspect arcade gaming counts all the same since they mention slot machines in the Code text), which is 11 gross ft²/occupant, or an occupant load of 109 people for your 1200ft² barn. This is enough to put you well outside of the 50-person rule that allows small assembly occupancies to be treated the same as business occupancies (office type spaces) by the IBC.

Going into more detail, your occupancy is somewhere between an A-2 (food/beverage consumption) and an A-3 (miscellaneous recreational) occupancy in the IBC system, given that food consumption and preparation are incidental to the function of the occupancy. Either way, you'll need at least two ways out of the barn that are outswing doors with panic hardware and combination exit sign/"bugeye" emergency light fixtures, as well as perhaps a couple more combination emergency light fixtures to serve as directional exit signs, or simple "bugeyes" to provide additional emergency egress lighting, depending on how much the space is divided up. (Don't worry about the pricetag -- combination exit sign/emergency light fixtures are standard, off-the-shelf parts that a lighting supplier can get you for $50-odd a piece, and the orange borg has panic hardware for $100 a unit, which can be fitted to a standard 30" exterior door hung outswing with jamb pin screws in the hinges.)

The other big question is whether you'll need to fit fire sprinklers or not; this is something you will need to talk with your AHJ (local building official and/or insurer) about, since it depends on whether they see your barncade as an A-2 occupancy (like a casino or nightclub with a kitchen and/or full service bar) or an A-3 occupancy (like a pool hall or dance hall with no food or drink service). This also determines whether you'll need to install a fire alarm panel, as sprinklers in a non-dwelling need an alarm panel to supervise the system (aka let folks know that some clown shut the sprinklers off).

0

2/0 can handle 150 amps when less than 200 feet. I hate to run at max and considering conductor count, underground and long length, I like your decision to use 125 amps.

I am not sure where you are getting the 2/0,2/0,1,4 feeder wire because the new wire is 2/0,2/0,2/0,1. Considering your wire sizing and application, there is nothing wrong with the old wire you spoke of assuming that you do not intend to get an inspection.

Don't forget to keep neutral separated from ground. If the garage is disconnected, remember to add couple of ground rods out by the new sub.

4
  • There are so many cable types I was sure what to go with. SER I read shouldn’t be put underground, so we landed on the MHF. The big box stores have limited supply on a lot of stuff so we were looking at the online stores which would have both the 2/0 2/0 1 4 and the 2/0 2/0 2/0 1. The ground rods are on the list.
    – Bryhud
    Oct 8, 2021 at 1:35
  • 2/0-2/0-1-4 is a standard MHF size -- in fact, the supplier I usually check doesn't have 2/0-2/0-2/0-1 in MHF Oct 8, 2021 at 1:46
  • @Bryhud try real electrical supply houses. Box stores only sell the popular stuff, they're not there to be an everything store, they mercilessly cut out anything the computer says doesn't sell well. E.G. they'll sell a conduit system, sell right ells, but not left ell's because they don't sell enough. Better to find an electrical supply you like and buy all you can from them. Also often cheaper! Oct 8, 2021 at 2:05
  • The 2/0-2/0-1-4 will be fine. I looked up the wire and found 2/0-2/0-2/0-1 and assumed that it is a new code. Electrical codes are getting completely out of control. There is nothing wrong with 2/0-2/0-1-4.
    – Paul
    Oct 8, 2021 at 2:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.