Service at key panel is 200A. Subpanel is 125A. Desire 100A ceded to Subpanel 100ft far (run). Have the right to I usage 100A breaker in Main and also run 2-2-2-4 cable to the lugs in the 125A Subpanel?


Make sure your subpanel has sufficient spaces

The #1 wrong sizing subpanels is gaining just sufficient spaces to perform the job today. Then later, they shot to add more loads, an especially 240V tons that gobble increase 2 spaces each... And also they discover a full panel. This is made also worse by the allure that "12 spaces/24 circuits" - that second figure has been a finish lie for number of years, currently that many circuits require AFCI or GFCI breakers, which take it a full space.

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"Running out of breaker spaces" should just never happen, provided that extra breaker spaces expense less 보다 $2 every today. Spend $30 extra and also get a nice, large panel. Target to end up with at least 50% that spaces unused.

Don"t use copper

The #2 mistake is utilizing copper wire for feeder. That"s just silly. Not only is aluminum proven and reliable because that feeder, the old feeders never ever had problems from being aluminum, not just did they improve the metallurgy, but the lugs room aluminum. For this reason the clever novice creates the dissimilar metal matchup rather of staying clear of it.

Copper is likewise wastefully expensive contrasted to aluminum, which creates an irony if the person additionally cheaped out on a small panel. Whoo, saved $30, wasted $400.

Honestly the key reason copper feeder exists is consumers affected by the aluminum ooga-booga. Like numerous moral panics, there is a nugget of reality at the facility of it, but it uses to small-appliance branch circuits only (receptacles, lighting, dryers etc.), and is conveniently managed. No house inspector is ever going to blink an eye in ~ a 100A aluminum feeder.

Aluminum is a really lightweight material, almost 1/4 the weight of copper, through fewer atom spaced furthermore apart. Atoms space what lug electricity, for this reason the wires should be physically bigger (by 2 numerical wire sizes). Also so, the cable is notably lighter.

Wire sizes

First, at 100" that distance, you do not need a wire dimension "bump" for voltage drop. The wire salesmen love to exploit two misconceptions: First, friend shouldn"t compute voltage drop based on breaker trip, however rather on handy load, i.e. What friend actually intend to run. (and the breaker have to be at least 125% of that, for code reasons). Second, 3% is not in code anywhere, and also it"s ridiculous. An extremely often, the voltage drop calcs will pressure you to bang wire dimension at 3.01% autumn - the smaller size would compute to 3.35% drop, and also that"s perfectly fine. 4.15% is fine. 5.03% is allowable. Password is concerned with total voltage drop indigenous the meter to the final outlet; don"t permit that to exceed 8% without a good reason.

Anyway, you"re nowhere near to even needing come think about voltage drop. Even the wire salesman won"t introduce a bump before 115".

Given that you room at 100A, you just pull it the end of NEC Table 310.15(B)(16). Use the 75 level C column, unless you have a cable type which mandates use of the 60 degree C column. And, girlfriend round approximately the next available breaker size. That way usually:

100A is #3 copper ($600/100ft) or #1 aluminum ($175/100ft).125A is #1 copper or #1/0 aluminum (you require to call it 120A feeder, but you gain to round as much as 125A breaker because 120A is no made.) If you require full claimed 125A you"d require 2/0 aluminum.

As friend know, the subpanel ampacity have the right to be greater than the feed breaker ampacity. Girlfriend don"t require a key breaker in the sub, if it"s in the exact same building.

Oh. You"re in PVC conduit.

Okay. Readjust of arrangement for the wires, then.

You desire to use individual wires no cable. (the external jacket makes cable an extremely stiff - too stiff for achievable pulling through conduit. That can it is in done however you"ll need an electrician"s truck complete of pulling tools, and also the whole point of is not needing to speak to the electrician, eh? :)

In this case, you usage individual wires. Such as XHHW-2, THWN-2, or USE-2. (the "2" just means it"s the 2nd revision of the spec for the insulation, and also as such, offers it an ext features, such as higher temperature.)

You aren"t stuck with the cable"s default ground cable size. You deserve to use any kind of ground wire that NEC patent (6 AWG Cu or 4 AWG Al). Due to the fact that it"s one outbuilding, you will need the floor wire in addition to the floor rods. Both space mandatory; one bring away human-generated fault current ago to source, and the other takes herbal lightning/static electrical power to planet (which is that source).

If you simply bought the cable, then cut off a few inches and also see if the wires are individually labeled through markings. If so, you have the right to remove the sheath and use the wires in any type of application their markings allow.

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If you should run several of it open minded (e.g. ~ above joists as cable) and some in conduit, you either carry out the functions in cable (hard pull; obtain bigger conduit, it"ll help!) or friend can change from one wire kind to the various other in any kind of appropriate (large here) junction box with allowed splices.