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Powering a shop


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In the spirit of trying to be helpful, I wanted to do a little (well it might not end up little) write up on powering peoples shop, new and old. Let me preface this with this ONLY applies to within the USA and even then you should ALWAYS check your local code and follow it. If you have never run electric or are not confident in doing it yourself, hire a licensed electrician to do it for you or contact your local inspector. Most of the time either one will be more than willing to answer questions. Remember, it does not take a strong shock to stop your heart (.5mA can) and it only takes one wrong connection to burn down the structure. 

This write up assumes a typical house style service with single phase 250V. I can answer questions about different voltage and 3 phase if you have them.

Ok, lets hop into it!

How Much Power Do I Need?

This is probably one of the most common questions I get asked. There really isn't a simple answer to this question as it has too many variables most of the time. The "correct" answer would be to contact an electrician and have them do a load calculation to determine what your draw will be and then size the service accordingly. This is somewhat determined by the size of the structure you are trying to power. My little 10x20 shed wouldn't even fit enough equipment inside it to justify a 200A service would be an example.

The highest amperage a typical house panel can feed to another sub-panel is 125A (not 100% correct, but for simplicity sake). If you need more power than that, it gets a little more complicated and that is when I would highly recommend having an electrician do the work. If you have a larger shop, it might be easier to have a second service installed from the power company (if they are willing to do it. Most have certain requirements that need to be met before they will agree to do it!). This would provide you with an entirely separate service from your house and have its own metering.

There are meters that can be purchased that can split your primary power into two services but that will 100% require an electrician to do as it involves dealing with the power companies feed into your home. NEVER touch ANYTHING at the meter and past it (towards the street/pole). It is a felony to tamper with any of that and CAN EASILY result in your death. You typically do not own the meter and anything upstream as it is the property of the power company and most modern meters are "smart" and will alert the power company and authorities if tampered with.

 

What Panel Should I Install?

I am going to try to avoid getting super technical with panels but will probably fail.

Your typical electrical panels (excluding commercial grade) only come in a few amperages. Those amperages are 60A, 125A, 150A and 225A. You might be thinking "I have seen 100A before!" and you would be correct. What I listed are buss ratings whereas a 100A panel is (typically) a 125A buss panel with a 100A rated main breaker. If you check and read a panels description, it will tell you what the bussing is rated for. Panels only come in two styles, main breaker and main lug. Main lug panels will be the ratings I listed and not contain and means of shutting off the power to itself (the main breaker). Most are typically field convertible and can have a main breaker installed later. You will need to review your local code to determine your disconnect code and if you must use a main lug or main breaker panel.

Panels also come a wide variety of spaces. The amperage typically determines how many spaces a panel will have. 60A is normally a sub-panel fed via another panel and normally only has 6-8 spaces, a 125A panel can have up to 24 space, a 150A can have up to 30 spaces and a 225A can have up to 60 spaces. There are exceptions, but those are the "normal" sizes. It is better to always oversize the panel. If you think you maybe fill 20 spaces, get a 30! It is a royal pain to change a panel out once it is wired up, but can be done. Plan for expansion! One of those worst things you can do to a panel is start to fill it with tandems (also known as piggyback breakers).

 

What Wire Should I Use?

This is very much determined by your local code. The codes are different enough from county to county, state to state that I couldn't give you a truly accurate answer. Also due to liability reasons, I can not suggest any sizing when it comes to wire. Just know that the primary purpose of a typical breaker is not to protect you, but the wire. It is always best to oversize the wire going to a sub-feed panel to permit expansion. If the wire is rating for 150A you can put a 150A and smaller breaker on it (as long as the wire itself will fit in the breaker). NEVER OVERSIZE A BREAKER! If you put 20A rated wire on a 30A breaker, you risk the wire melting and causing a fire!

Wire comes in all kinds of styles/ratings, but for simplicity sake I will only talk about the ones you are likely to see.

NM-B

This is your typical house wire and is normally referred to as Romex. It comes in 2 and 3 wire (ground is not normally included in the conductor count). It has had various types of outer jackets over the years, but modern Romex has a PVC nylon jacket (NM stands for Non-Metallic and refers to the jacket). It is very uncommon to see this wire beyond 6 gauge, but they do make it larger. Comes in both copper and aluminum with copper being the industry standard. If you plan on using aluminum, all devices (outlets/switches) and connections MUST be rating for aluminum wire.

MC

Internally, MC is identical to Romex. The difference is the outer jacket. Rather than having a PVC nylon jacket, this cable has a metal sheathing/armor to protect it from damage. There are more restrictions on where you can use this cable, but you typically see it in applications where there is no choice but to run it outside a wall and exposed. It is cheaper to run vs single conductor wires pulled through conduit. You must see if your local code allows MC before using it. This also can come in copper or aluminum but can have a great deal more conductors and can get much, much larger in gauge ( I have seen 8 conductor 750MCM before. 750MCM is roughly the size of a 50 cent piece).

SEC/URD

SEC (service entrance cable) and URD (I sadly don't remember what this stands for) are your typical wires that feed your houses panel. SEC is normally a dull gray cable that has several other individually insulated conductors within an overall jacket. It is very heavy duty stuff and does not bend/flex easily. It comes in SER (service entrance riser), which is meant to be run overhead and SEU (service entrance underground) which is meant to be directly buried. SEU does not typically get very large in gauge however. URD is direct bury rated, but is typically sleeved with conduit for protection. URD has two different ratings, USE-1 and USE-2. USE-1 can NOT enter any form of structure. USE-2 is rated to go into a structure, but your local code may still not allow it. Both SER/U and URD are normally aluminum wire. They do come in copper, but it is very uncommon as the weight becomes very unmanageable due to being larger wire and have multiple conductors.

THHN/XHHW

This is the single strand wire that is used in just about every application you can think of. It is the industry standard wire. Both Romex and MC use it within their overall jackets. For the most part, THHN and XHHW are interchangeable but not always. XHHW is regarded as a slightly tougher cable whos jacket can withstand wet areas better. To use this cable, it MUST be placed in conduit and there are very, very few exceptions to that. This comes in both copper and aluminum but the norm is copper. 

 

What Conduit Should I Use?

This section will be short. As always, review your local code before installing any conduit. 

There are actually quite a few different kinds of conduit, but I will stick with the main 3.

PVC

This is the typical conduit everyone is familiar with. It is a plastic conduit that is typically buried in the ground. It comes in 2 variations, schedule 40 and schedule 80. Schedule 40 is the regular kind that is used for a wide variety of applications. Schedule 80 is normally identified with a yellow stripe down its length. Schedule 80 has a thicker wall compared to 40, so has less capacity. If the conduit is ever subject to any form of impact, schedule 80 must be used. All parts/pieces are glued together.

EMT

This is the metal tubing you see running everywhere in buildings. It is a thin gauge metal and can be used all over inside a building. It is not normally used outside as it will rust away, but it can be used outside if needed. Uses set screw and/or compression fittings

GRC

Typically referred to as rigid conduit, this is the heavy duty stuff. It is galvanized so it can be used outside, it is impact resistant, can be buried and is HEAVY. a 10' stick of 4" weights around 130lbs and is not fun to use. It has threaded ends so that all its pieces are screwed together, but compression fittings due exist (and are really expensive). This is typically used as the pipe going up walls/pole in place of schedule 80 PVC as it is very unlikely to ever break.

 

That is all I have for now. I will try to keep adding to this as well as clean it up as time goes on. If anyone ever has a question, feel free to ask me :lol:.

 

 

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My electrician suggested I get an externally rated panel and so not have to deal with the code to have a clear space in front of it.  (He suggested this after seeing how much cruft was piled along the walls of my shop.)

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The panels are typically double the cost of their indoor counterparts, but code normally states you must have I think its 3 feet in every direction clear of the panel so it is easily accessible. Outdoor panels are a pain. They are heavy, more prone to rust and falling apart and are a good deal more expensive on average, but sometimes you can't avoid them.

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Climate!   "prone to rust"  is more an issue where you are at; as you get over 4 times as much water in precipitation  and not many days when the relative humidity is in single digits! "Kiln Dried" Wood has to be "seasoned" before use to allow it to adapt to our low humidities.

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I had a student from the local college whose summer job was removing killer bee hives from rural west Texas oilfield equipment---nothing like wearing a complete protective suit in West Texas Summer Heat!

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That sounds...not fun.

I had a electrician tell me once how he went out to do a typical service call and when he opened up the panel, had a copper head staring him in the face. Said he slammed the cover shut so hard he nearly broke it! Its amazing what critters somehow find their way into things.

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This is what i know about electricity: call an electrician. 

I have done some pretty crazy things in my life, i have been in some really dangerous situations, some i may should have not walked away from, but electricity scares the bejeebus outa me. 

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That's a good thing Billy lol.

People can do plumbing and be fine. Worst case is a line backs up or you get wet. Electric will burn down your home and possibly kill you.

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I remember the first time a new apprentice saw me do hot connections on a service entrance,  He asked how I turn the power off to do it, and I told him we dont...  The look on his face when I grabbed the line and stripped off some insulation to make the splice LOL

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My mom's boyfriend is a lineman and the level of comfort he has working on live circuits was very... shocking.. to me at first. I'm pretty sure I had the same look on my face a few times while I was watching him. He says the majority of the work he does is done live.

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I will work on a simple 120V circuit hot. That just..."bites". 240V is a nope from me. I've been had by 240V and it isn't anywhere near as fun as 120V. 0 out of 10 would not recommend. I have watched people work on stuff live that would make you just wonder why? But the equipment was unable to be shut off. I watched a guy work on a 800A 600V disconnect hot (he was wearing full arc flash gear) and while talking with me and another field guy, failed to notice another Alan key in his set flipped out and it caught another lug he was working on. The resulting arc explosion sent him back several feet into a wall and welded his Alan key set to the lugs. Scared the crap out of us, but thankfully he was fine.

Have you ever watched videos of lineman installing spacers on transmission lines? Those are pretty crazy. I have been in sub-stations where stuff has enough juice running through it that it has the potential to arc out several feet and get you. I have a high dislike of being in areas where you can literally hear the electric humming and crackling. You can actually build up a static charge being in areas like that and its not fun when you have to touch metal again!

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I am not a lineman, But there is some over lap with the sub stations and service connections I have worked on, and FYI 120v has an arc flash danger zone of 10 feet, so dont fool yourself

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O wow, I actually did not know that one. It would be interesting to see a simple 15-30 amp 120v circuit jump that far (and probably terrifying). I wonder if it only happens at really high amperage. I will have to look into that one and talk to some of the regulars guys who come in.

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That is correct. I don't know why, but I seem to never include gas in my plumbing generalization. My mind seems to always stick it with HVAC for some reason. 

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I spent 15 years in a house that originally had gas lights and most rooms originally had a vented gas heater in it, (4 double flue chimneys!).  I added back in a small gas heater in the bathroom: Central Ohio, Structural brick house, corner room bathroom, *cold*!  to warmest room in the house with the small heater.

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