Another shop electrical run

Question

Looking for advice and/or affirmation of my thoughts. I have read other posts and nothing quite fit just perfectly for the direction I am looking to go. But I might be over thinking this.

I am about to wire up a shop/garage in my backyard, clearly LOL. The electrical wire distance from my house's load center to the shop's predicted load center location is 160'(+/-5ft) including up and down walls. I have 200-amp service to the house. I would like 150 amp to the shop. I haven't quite settled on a shop load center location but it will be within the 175'.

I basically have no equipment bought yet, I have read a lot of others posts about buyer regret from not researching first, and at least learned some wisdom from their mistakes. I did get some breakers form an estate sale but didn't find out that breakers were manufacture specific AND series specific. Unfortunately, they are Square D homeline breakers, but it was a buck a breaker so... But I've digressed.

I am going to be upgrading my house's load center (currently an unknown brand) as it is 25+ y/o and more than came with the house in 1980. That coupled with some house electrical rewiring and additional outlets, best to replace it.

I have been eyeballing the Square D QO plug on neutral load center 200-amp for the house's replacement and the Square D QO 150 main breakers plug on neutral load center for the new shop setup.

I am considering URD401000 - 4/0 Urd Sweetbriar Alu for the wire from house to shop. I am open to arguments for copper verse aluminum, but the cost was, of course, cheaper. Also, the direct burial makes it easier for me as well. I have considered 1/0 Cu THHN (and 4awg THHN ground wire?). My house is located in the county, so codes apparently allow for the direct burial Ai. Cost isn't the top priority, doing this correctly is, but cost is still a part of the calculous, of course. I am willing to trench and grey PVC conduit some THHN. Have shovel, will travel.

Is there a better load center I should considering? Is there a reputable manufacture with pass through lugs available that don't cost an arm and a leg like square Ds? I only chose square D because my other shed has a QO series in it (hence how I discovered that the series matters just as much as the manufacturer when I tried to use the breakers, I got so cheap.). I despise GE products in general, so I avoided them. I have a siemens for another load enter but I haven't been all that impressed with the prewire job that it came with inside for RV hook ups.

I need a separate ground rod 5/8" by 8'. I can't put the rod Stright down (solid rock about 3' down so I plan on a horizontal 30" deep placement with 8awg wire to the shop's panel. Do I need two still? I read somewhere that it needs to have 25 ohms resistance, or it you need two at least 6ft apart. how do I measure the resistance? the soil is dry and cracked so I would figure I have infinite resistance right now.

These are the questions battling in my head. I sure I have missed something in the other posts I read, I just wish I had more experience. So, what am I not covering and missing in my designs? Am I going the correct direction or am I all over the place and need to reassess my concepts? Thanks in advance.

I found this QO2150

As a side note, the shop will be future proofed for EV charging, RV power (50 amp 240), and support for a 4.0-ton AC (30 amp I believe), as well as the obligatory shop 120 psi 80 gal air compressor (30 y/o Cambell Hausfeld but still worthy) and probably a small welder at some point. I do realize that I am approaching max load with just those items running at the same time but realistically by the time I am forced to get an EV I won't have the 5th wheel anymore. and even then, the 5th wheel doesn't use the max load even when cooking and using both a/c units I'm still only at 40amps total between each L. and what are the actual odds of all those things kicking off at the same time, as I write this I know it will happen now.

I had an electrician over (for a different project) who mentioned connecting my shop power to the secondary lugs on at the meter enclosure (the meter enclosure is sperate from my load center and on the outside of the house opposite of my load center which is on the inside of the garage. How do I determine if this is plausible. I say the tamper seal... I was tempted to just cut it and take a peek but haven't yet.

Thanks again

Answer 1

A few things:

• Aluminum vs. copper

Yes, save your money and use aluminum. But wire size will depend on capacity and that will depend on load calculation, more below. Personally I would recommend conduit + wires rather than cable, but that becomes a cost issue. 160' is a significant distance. It is long enough that conduit, wire and cable costs are all significant and worth comparing. It is also long enough that renting equipment (or hiring a contractor) to do trenching is reasonable, in which case 24" for direct burial may not be so bad. At shorter distances where doing the work by hand makes sense, the 6" burial depth for EMT is very attractive.

• Panel Brand/Type

Square D QO is a good choice. So is Eaton CH (my favorite, but I am a definite amateur - Harper likes it and my electrician likes it so I like it). And everyone has their favorite. Go with whatever works for you, and yes using the same type (but different sizes) for the two buildings makes sense.

• Lugs

I am not so sure about the point of using the pass-through lugs from the meter or main panel. That would force you to a higher rating, which means bigger wire. In addition, depending on your local code cycle, you may have to put in a meter main with a breaker feeding each panel anyway.

• LOAD CALCULATIONS

This is the biggie. You MUST do a load calculation at each level:

• Total utility service
• Main panel (including workshop if that is fed from the main panel)
• Subpanel (workshop)

Load calculation is not "I think". It is a specific complicated formula based on building size, required circuits (kitchen, bathrooms, laundry, etc.), HVAC and other permanent loads and a bunch of other things. You can put a 150A panel in the workshop, but you can only feed it 150A (3/0 AWG minimum wire size) if you have 150A to spare in your service load calculation. Unless you have gas appliances and a tiny house, I don't see how you will have 150A to spare out of a 200A feed. You might be able to roughly split 50/50 - 100A for the house and 100A for the workshop, and if you do that then you can also use much smaller wire (1 AWG).

• Ground Rods

I need a separate ground rod 5/8" by 8'. I can't put the rod Straight down (solid rock about 3' down so I plan on a horizontal 30" deep placement with 8awg wire to the shop's panel. Do I need two still? I read somewhere that it needs to have 25 ohms resistance, or it you need two at least 6ft apart. how do I measure the resistance?

This may be jurisdiction dependent. For example, in my area, according to my electrician, some jurisdictions require two ground rods (or one rod with a test but NOBODY does the test because it is so much easier to just put in a 2nd ground rod), some require a copper water pipe ground + 1 ground rod. And he was prepared for my house at inspection time in case the inspector insisted on two rods + water pipe (inspector didn't, but it was not a battle that my electrician felt worth fighting if it happened). But unless your workshop has copper water pipes going into it through the ground, it is a pretty safe bet that two ground rods is the answer. You will likely need larger than 8 AWG wire to the ground rods, but it is dependent on feeder size.