Elect wire size

I have another electric question maybe someone can help me with. I have a out building 100 ft away from my panel. I have a 220 volt five hp compressor I want to use. Then I want to split off the 220 line for a 20 amp 110 v service. What size wire should I use? Thanks Stan

Ought alum, or 2 copper for entrance cable.

I would run number 6 wire from panel in house to building. I would put sub panel in building and do the 110v split on a breaker in the sub panel.

I think you could get away with #8 with a little less than 3% Voltage drop. #6 is better for starting the compressor. 1" Conduit.

That distance I would run the aluminum over head stuff like you have going into a house. My shop is about 150 feet form my breaker panel and that is what I did 25 plus years ago and have not ever had much problem with it.

I would go with 3 #6 THHN copper (2 lines and a neutral)and a #10 ground inside PVC conduit, underground. Feed off a 70a breaker from the house. Set a subpanel in the shop, drive a ground rod.

Good afternoon Chief, you ask "What size wire should I use?"

Lets do the math. A 5 HP 240 VAC Single Phase motor will draw in the vicinity of around 28 FLA which 8 Gauge Copper wire will handle HOWEVER that doesn't account for Voltage Drop. Therefore, I would use AT THE MINIMUM 6 Gauge THWN Copper. Bigger wire would yield less voltage drop and/or to allow for future expansion.

To feed say a 60 Amp 120/240 Volt Single Phase Three Wire SUB PANEL equipped with two pole Main Breaker in that remote outbuilding, you need to run FOUR Conductors out. Two Ungrounded Hots (L1 & L2),,,,,,,,,,One GrounDED Conductor Neutral,,,,,,,,,,,,,One Equipment GroundING Conductor. You will need to install and bond a Grounding Electrode (earth driven copper rod or rods or other suitable electrodes, check local authority or NEC) at the outbuildings electrical service. While the exact rating of the home panels circuit breaker which feeds the outbuilding depends on the wire size and type and enclosure, a 60 amp will likely suffice. DONT FORGET IN THE REMOTE PANEL THE NEUTRAL AND GROUND BUSSES (unlike in your homes main panel) ARE TO BE KEPT SEPARATE AND ISOLATED. The tubs case/frame is bonded to the Equipment Ground Buss but NOT the Neutral.

You could enclose the individual THWN conductors in buried PVC Conduit (so long as NOT under driveway and if so concrete encased or Rigid),,,,,,,,,,,,,,,,,If they make it???? you could direct bury 4 Conductor UF Underground Feeder Cable,,,,,,,,, You might get by direct burying Underground Service Entrance (USE) Cable if its manufactured with 4 Conductors (its typically 3 like to my home from the transformer). NOTE if you were to enclose an Equipment GroundING Conductor in metallic conduit, it needs to be insulated NOT bare as I recall. Heck you could use aerial cable if you like. I LIKE THE IDEA OF BURYING PVC CONDUIT and the use of individual THWN Conductors myself.

John T Longgggggggg retired Electrical Engineer and rusty on the latest codes SO NO WARRANTY but believe this is most likely correct, check with local authority or Utility providers and the NEC if adopted and it applies, versus anything posted here (where's Billy Bob and Bubba lol) is my best free advice.

Don't forget to multiply your motor load by 1.25 to arrive at you total amps. The code wants that when the wire is feeding the motor and other loads. John T. had it dialed in just follow his methods using 35 amps plus voltage drop as your load. Do it once do it right and be done with it.

The neutral bar in the remote shed panel needs to float isolated from the ground system. Otherwise neutral current will flow in the ground system.

This is what happens when water gets into a service panel. A two day job, the Electrician just finished replacing everything yesterday.

Sorry I cannot answer your question. Just wanted to say whatever you are doing, make sure it is done right. The expense and frustration is not worth it.

Per the tables in article 430 of the NEC, a 5hp motor at 220 volts, single phase, draws 28 amps. If you are not installing the receptacle, a #8 would work. Because you are installing the receptacle, use #6 and hire an electrician to help you.

Indeed, the ampacity of the wire must be at least 125% of the MAXIMUM "CONTINUOUS LOAD". 28 x 1.25 = 35 amps for which 6 Gauge suffices and still allows a permissible voltage drop. 6 Gauge would still be the MINIMUM I would use and I didn't factor in much for a single phase load like he mentioned. Heck 4 gauge wouldn't be unreasonable to allow for expansion.

John T

EXACTLY and that agrees with my post "DONT FORGET IN THE REMOTE PANEL THE NEUTRAL AND GROUND BUSSES (unlike in your homes main panel) ARE TO BE KEPT SEPARATE AND ISOLATED"

John T

Now to confuse everything. I already have a 110v line for lights only. Can I use those neutral and ground wires for my other 110 circuit, and 220 v ground. What ever I do it will be right, just getting information. Stan

110 all by itself requires 3 Conductors, a Hot and Neutral and an Equipment Ground.

Straight 220 (NO 110) all by itself requires 3 conductors, 2 Hots and Equipment Ground.

BOTH 110 and 220 requires 4 conductors (at a remote outbuilding sub panel) 2 Hots, Neutral, Ground

So if you already have some conductors out there, you just need to add however many extra are needed so you have 4 total if you want BOTH 110 and 220.

John T

Don't forget if the NEC considers the load as "continuous" the wires ampacity must be 125% of the FLA, therefore for 28 FLA continuous, the wire must have a minimum ampacity of 125% x 28 = 35 amps and then you have to take voltage drop into account which depends on the current and distance and wire size.

John T

100' is a long way for a compressor. I installed one 50' before with a #6 wire and ended up having to move it closer to panel. You would be better off installing the compressor close and piping the air to the building.

If you compare the cost of four strands of #2 aluminum USE (underground service equipment) versus a run of #6 copper UF (underground feeder), I think you'll find that USE is very cost effective. Using #2 will allow you to put a 100 amp subpanel in your outbuilding, leaving you plenty of room to grow.

Look at the plate on the motor for FLA. I don't know how they can do it, but a lot of those compressors put decals on them with exaggerated horse power rates! I was told to wire an installation for a 5 HP once. When the unit came the amps required matched a 1 1/2 HP motor. My installation was way bigger than what was required.

You would feed the panel with 220 two legs and then break out to the compressor from there. The requirments for the compressor may turn out smaller than you think.Wire size ? How many amp service panel ?

A 60 amp service out to the shed would also power a welder,fridge, microwave, big screen TV, heat and AC.