service at main panel is 200A. Subpanel is 125A. Desire 100A yielded to Subpanel 100ft away (run). Can I use 100A breaker in Main and also run 2-2-2-4 wire to the lugs in the 125A Subpanel?


Make certain your subpanel has enough spaces

The #1 mistake sizing subpanels is obtaining just enough spaces to do the project today. Climate later, they try to add more loads, particularly 240V loads that gobble increase 2 spaces each... And they discover a complete panel. This is made also worse through the allure that "12 spaces/24 circuits" - that 2nd figure has actually been a complete lie for several years, now that many circuits need AFCI or GFCI breakers, which take a full space.

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"Running the end of breaker spaces" should merely never happen, offered that extra breaker spaces price less 보다 $2 every today. Invest $30 extra and get a nice, big panel. Target to complete with at least 50% the spaces unused.

Don"t usage copper

The #2 mistake is using copper wire for feeder. That"s simply silly. Not just is aluminum proven and reliable for feeder, the old feeders never had troubles from being aluminum, not just did they enhance the metallurgy, however the lugs room aluminum. So 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 the end on a tiny panel. Whoo, conserved $30, wasted $400.

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

Aluminum is a very lightweight material, nearly 1/4 the weight of copper, through fewer atoms spaced aside from that apart. Atoms space what carry electricity, for this reason the wires must be physically larger (by 2 numerical cable sizes). Also so, the wire is significantly lighter.

Wire sizes

First, at 100" that distance, you execute not require a wire size "bump" because that voltage drop. The cable salesmen love to exploit two misconceptions: First, girlfriend shouldn"t compute voltage drop based on breaker trip, however rather on helpful load, i.e. What girlfriend actually suppose to run. (and the breaker should be at least 125% that that, for password reasons). Second, 3% is not in password anywhere, and also it"s ridiculous. Really often, the voltage autumn calcs will force you to bump wire dimension at 3.01% fall - the smaller size would compute to 3.35% drop, and that"s perfectly fine. 4.15% is fine. 5.03% is allowable. Code is involved with total voltage drop indigenous the meter come the last outlet; don"t permit that come exceed 8% there is no a good reason.

Anyway, you"re nowhere near to even needing to think about voltage drop. Also the cable salesman won"t recommend a bump before 115".

Given that you space at 100A, you simply pull it out of NEC Table 310.15(B)(16). Usage the 75 level C column, uneven you have a cable kind which mandates usage of the 60 degree C column. And, girlfriend round as much as the next accessible breaker size. That method usually:

100A is #3 copper ($600/100ft) or #1 aluminum ($175/100ft).125A is #1 copper or #1/0 aluminum (you require to contact it 120A feeder, but you acquire to round up to 125A breaker since 120A is not made.) If you need full asserted 125A you"d require 2/0 aluminum.

As friend know, the subpanel ampacity deserve to be better than the feeding breaker ampacity. You don"t require a key breaker in the sub, if it"s in the very same building.

Oh. You"re in PVC conduit.

Okay. Adjust of arrangement for the wires, then.

You desire to use individual wires not cable. (the outer jacket renders cable very stiff - too stiff because that achievable pulling through conduit. The can it is in done but you"ll need an electrician"s truck full of pulling tools, and the whole point of is not needing to speak to the electrician, eh? :)

In this case, you use individual wires. Such together XHHW-2, THWN-2, or USE-2. (the "2" just means it"s the second revision that the spec for the insulation, and as such, gives it much more features, such as greater temperature.)

You aren"t stuck to the cable"s default ground wire size. You can use any kind of ground wire that NEC permits (6 AWG Cu or 4 AWG Al). Because it"s an outbuilding, you will need the ground wire in enhancement to the ground rods. Both are mandatory; one bring away human-generated error current earlier to source, and also the various other takes natural lightning/static electricity to planet (which is the source).

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

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If you have to run some of it openly (e.g. On joists together cable) and also some in conduit, you either perform the functions in cable (hard pull; obtain bigger conduit, it"ll help!) or girlfriend can transition from one wire form to the various other in any type of appropriate (large here) junction box with allowed splices.