# Planning shop electric



## Bill7255 (Feb 23, 2012)

I have built a new shop and will have a electrician put in a 125 amp sub panel. In the past I have always installed 30 amp for receptacle and plugs on the 220V equipment and 30 amp breakers. This equipment is all 1980's or 1990's and I don't have any of the original manuals. They all have 3 hp motors, 2 Jet and 1 Baldor. Is it better to install 30 amp or should I install 20 amp breakers?


----------



## crank49 (Apr 7, 2010)

Those motors probably draw around 16 amps running at full load.
It takes about 60 to 80 amps for a second or two to start a motor like that.
You might trip a 20 amp breaker; especially if the machines have a high inertial load. You didn't say what the machines were.
I think I'd stay with #10 awg wire and a 30 amp breaker.

They do make breakers especially for starting motors that handle high inrush current. In that case you could by with #12 awg wire and a 20 amp breaker. Check the price of these breakers before going that way. Might be cheaper to go bigger.


----------



## Grandpa (Jan 28, 2011)

Depends on the brand and seller of the panel. You can get Cutler Hammer at the big box stores and I think the breakers are the same cost for 20 or 30 amp. I would go with 10 gauge wire because it will work with either of the breakers and it costs more than the breaker. Why run the risk of needing larger wire. If you use 30 amp breakers you are required to have 10 gauge wire. The breaker protects the wire. With 12 gauge and 30 amp breakers the wiring becomes a fuse to burn out.


----------



## RussellAP (Feb 21, 2012)

Stay with 30 amp. 20 will trip on start. Also use wire rated for 40 amp or you wires could get hot.


----------



## wapakfred (Jul 29, 2011)

My tools that have 3 HP (+) motors are all on 30 amp breakers for the reasons given above. I do have a lot of 240V/20A circuits for some of the other stuff, but I'd keep the big tools on the 30s.


----------



## Bill7255 (Feb 23, 2012)

Thanks all just doing my sanity check. I usually always over build which is fine until I need to take it apart. I will stay with the 30 amp


----------



## HorizontalMike (Jun 3, 2010)

Bill,
I did just as you are planning with the 125amp box, HOWEVER, several years later I now wish I had gone ahead and put in another 200amp box (like my main house panel). I say this because the 240v double wide breakers take up too much real estate in the 125amp box. I have 3-240amp breakers in mine. And that leaves just 6-120v breakers for everything else in the shop. And I have to run too the house panel in order to cutoff the entire shop, because the 100amp breaker is there and not in the shop.

IMO, buy the bigger box now because it doesn't cost that much more and it will give you much more flexibility in future expansion.










ALSO, while I first started with installing 30amp breakers on all of my 3-240v machines, I have since backed off on that practice. My G0690 TS still calls for 30amp, but my G0593 Jointer and 14in Rikon MS(wired 240v) have been changed to 20amp breakers. Remember, the breakers are there to protect the shop wiring and the machine. If you set the breaker amperage too high you will do more damage, not less. Take the time to match each machine with the appropriate sized breaker.

FWIW, all my 240v wiring is armored 10-3. My 120v is mostly 12-3, with some leftover 10-3 ran to make best use of the wire I had left.


----------



## teejk (Jan 19, 2011)

Mike…I think you are supposed to have a cut-off in remote locations. I goofed there because I misread the code. I looked for 100a "knife switches" but can't find any without breaking the bank.

I have a big panel in my shop and a friend suggested that I simply put a 100a breaker in the panel to accept the feed from the house instead of using the main lugs in the box. I would effectively be energizing the entire panel from that breaker that I would label as "main". I know it would be a double breaker situation (100a in the house to another 100a in the shop).

I relied on the diagrams in the store that said to get "main lugs only". So a question to any "sparkies"...why not install a "main breaker" panel in that situation? Square D sells the basis starter kits that include a handful of breakers so not that much more than the sub-panel + breakers purchased separately.


----------



## Charlie5791 (Feb 21, 2012)

You have to have a disconnect in a detached building. That *can* be a main breaker in the sub panel. So you'd have a breaker in your main panel and one in the sub panel. I *think* you can get away without the disconnect in the detached building if the sub panel there has 6 breakers or less. This was referred to as the "6 handle rule" when I was hanging around with electricians 

Call your building inspector if he's the one going to sign off on it. In my town they use an underwriter and you can call and ask a question. Don't rely on what you find here as this can vary a little from one jurisdiction to the next and while NEC might say you don't need a breaker under certain circumstances, your local guy might say, "Yeah, but we want one in there."


----------



## bigblockyeti (Sep 9, 2013)

30 amps is the way to go. If you run across some equipment with 5hp, you'll still be ok, instead of having to pass.


----------



## teejk (Jan 19, 2011)

Charlie…NEC adoption does vary by location but only because of a lag in adopting it. I don't think anybody can get in trouble for using the latest code even if your locality hasn't adopted it. New electric codes only seem to "add", never "subtract" from the previous version. Still waiting for an opinion from the sparkies about whether the best solution is to use a "main breaker" sub-panel in the detached building even though it feeds from a breaker in the main panel.


----------



## Charlie5791 (Feb 21, 2012)

OK. Fair enough. You made me get up and go out and look at mine. Done to code, *by* a licensed electrician, *and* inspected by an independant underwriter.

I have a 60 amp (double) breaker in the basement main panel (200amp main panel). It feeds my subpanel about 100 ft away in a detached shop building. The sub panel in the shop has a 60 amp (double) breaker, but instead of being labeled "Main", it's labeled "Principle" and it shuts down everything in the shop. I don't know if that's in any way important, but this is about 2 years old so it's pretty recently done.

That help?


----------



## teejk (Jan 19, 2011)

"Principle" and "main" are the same thing Charlie…that's your cut-off (disconnect"). I wonder why they don't simply use a main breaker panel instead??? Like I said previously, the SQ D panels are not that much more money when they come with a handful of breakers. All I can figure is that if the main on a main panel goes bad, it is a lot of work whereas if the breaker energizing the panel goes bad, it's a pretty easy fix.


----------



## HorizontalMike (Jun 3, 2010)

My MAIN panel with the 100amp shop breaker, is outside the house and straight-line visible from the garage/shop. My shop panel is a *GE PowerMark Gold 125 Amp 6-Space 12-Circuit Convertible Main Lug Outdoor Load Center* . The unit may be converted to a main breaker and offers top or bottom feed.

I don't think I would be required to convert it, since the main feed is outside and within eyesight, <50ft away. I fed the shop panel with 2/0 Triplex Aluminum Service Drop Cable in one straight overhead run to the shop.

*All that being said, going with a larger panel is never a bad idea.* I now find my 125amp panel marginal.


----------



## icsparks (Sep 17, 2013)

The NEC 225.32 States that the disconnecting means shall be located either inside or outside the structure served or where the conductors pass through the building and it shall be readily accessible located *nearest the point of entrance of the conductors*. Go with a panel that has a main breaker in it that serves as a disconnecting means. The 6 breaker rule only applies if the sub-panel is only a six space panel.


----------



## Grandpa (Jan 28, 2011)

Mike brought up another good point. Size the service properly or above for the shop. I did all the calculations and mine was right at the teetering point for 2/0 copper. I used 3/0 copper because my good friend was renting a trencher and replacing his at the time. I am 245 feet from the meter to my shop so that all figures in.


----------



## HorizontalMike (Jun 3, 2010)

I probably wouldn't pass if I built it today… however I put this up in 2003. No other electrical conduction paths of any kind, completely stand alone other than the service feed from the main panel. Neutral is bonded to ground, and since this is completely isolated I added a grounding rod at the base of the box. If this were not completely isolated, this second ground rod would be an issue.

FWIW, I actually lost a bunch of electronics in my observatory once, just because of the CAT5 and telephone line being attached to my observatory PC that was attached to my telescope controller on my "isolated" pier. Burnt the PC, telescope controller, both camera control circuits, and all the hubs, protective power strips, etc. *When they mean ISOLATED, they mean isolated.* This was a nearby lightning strike that came in on the telephone line and the "secondary" ground (observatory pier) that was created by the electronics hook up, killed everything near that secondary ground loop. My indoor stuff was fine. The observatory was directly fed from the main panel.


----------



## teejk (Jan 19, 2011)

Mike…Later codes (2009???) require "single point grounding" that nobody seems to understand but I guess it is related to lightening and getting "imbalance" when different ground rods are installed from a single power source. Code requires all grounds come back to a single point (in my case the 2 copper driven rods at the service entrance). My inspector required me to install a grounding point for satellite/cable/telephone although none of those guys seem to know the code at all and drove their own separate ground rods (a big problem I guess on passing inspections).

No big deal with my shop since the 100a service was done with 4 wires and when I installed it I left off the big green screw that would have bonded the ground to the neutral (I don't know the science behind that either other than insurance should either one would fail…in the whole scheme of things they all come back to the main service panel where the 2 are bonded).

I did have a weird experience a few months ago in the shop. A 30×56 steel building constructed such that the outside shell is one big lightening rod isolated from the inside (2×6 ladder framed). I drilled a tiny hole to get some coax out for radio reception. During a lightening storm I got to see blue flashes following that wire (path of least resistance I guess).


----------



## Charlie5791 (Feb 21, 2012)

I have 2 ground rods. Opposite corner of the house. When the second one was installed, I had to run a #6 copper all the way around to the "main" ground rod to bond them. (outside, not through the house).

Interestingly, if you have 2 ground rods and they are NOT bonded, you can actually develop electrical potential between them. Something about the earth acting as a conductor or something. Reminded me of a big battery.


----------



## teejk (Jan 19, 2011)

Charlie…I have two ground rods at the service entrance into the house only a few feet apart and they are tied together with a piece of wire (probably 6ga copper or thicker). I don't have the code handy but that's what it required. I had to install a grounding block to one of them to accept the telephone etc. but that is no where near 6ga. The block connects to the grounding rod and then has a series of slots that take the ground wires from everything else with a set screw.

Inside the house I have the main service panel that grounds to those rods. It feeds a subpanel in the house (I needed 2 panels solely because current code soaks up breaker slots like a sponge when you have a well and septic pump and central air and required GFCI circuits in kitchens and bathrooms and garage) and cost wise it was cheaper to energize a panel on one end of the house rather than "home run" all wires back to the main panel.

It also feeds my shop building with a 4 wire 100a wire. Long story short, everything comes back to the main panel and those 2 ground rods.

Code says that on a remote building I need to isolate the neutral and ground in the shop (even though in the main panel they come back together). I guess that is to provide some safety in case something happens to either the ground or the neutral wire. No big deal because it is a single green screw that comes with the panel.


----------

