Electricians help...my electrical plan. Long and complicated.

[Smoking Joe]

I know it’s long, but I’m **** about details, and you can never be too safe with electricity.

I am wiring up my detached (edit)garage for use as a personal auto-shop. Please review my plans and tell me what you think. I do not have a copy of the NEC yet, the Florida Code laws I recently purchased did not include it as expected. I have talked to an electrician at Lowes and reviewed a couple of electrical books that I have. I am attempting to use the correct terminology so feel free to correct me if I am referring to something incorrectly.

My current house breaker is a 150 amp breaker. My external garage currently has one 20 amp (12 ga wire) branch which operates the overhead lights (8 4-bulb T-10 fluorescent light ballasts), 5 double-outlet boxes, and a ½ HP 115v, single phase roll-up garage door opener. (I will leave this branch in place, but it will be reduced to two double outlet boxes and the garage door opener. One fluorescent bulb will be plugged into one outlet for emergencies). All new wiring will be done for 20 amp circuits or greater. I want to be able to handle electric tools when plugged in, and be able to expand circuits in the future.

SWITCHES
My switch box will consist of 5 gangable boxes and 1 double-socket box (attached below with an EMT connection). The switch box which will be connected to a 4 11/16” X 2 1/8” J-box with 3/4” EMT. All switches are 20 amp switches. The J-box will be affixed to the wall, below the ceiling. 12/2 NM-B romex will feed the box from the different circuits. All switches will be end-line switches. The 3/4" EMT will contain individual 12 ga wires. (My fill capacity for this J-box is 18. I will be using 14 wires, with possible later expansion of a switch (2 wires). I was planning on using the EMT as the ground, with the ground wire from the feeding romex grounded to the J-box, as well as the the neutral bar in the sub-panel [correct me if this is wrong]).

OUTLETS
All my outlets will consist of double outlet boxes (4 outlets). The circuits in this branch consist of 12/2 romex. The romex is protected below the ceiling line to the box by 3/4" EMT. All EMT is capped with a plastic bushing to protext romex.

SUB PANEL
I will need 6 branches in the garage, 3 of which will need to supply 240 single phase power to major appliances (auto lift, AC, air compressor). I will run power from my main breaker to a sub-panel in the garage. This run will exit the main breaker box on a 75 amp (or 100 amp) breaker, exit the house in a 2 1/2" PVC conduit, which travels under the concrete sidewalk, and up the inside of the concrete block wall of the garage. It exits the concrete block and enters 2 1/4" EMT to the sub-panel. 110 to each busbar and a neutral to the neutral bar. (Is there a need for a ground wire? What size/type conductors should I use)? I am trying to decide whether to run the sub-panel off of a 75 amp breaker or a 100 amp breaker. I have measured each busbar in the main breaker box for max load on start up of all major appliances. I don’t remember these numbers I’ll have to get them when I get to work where they are written down. I am inclined to use a 75 amp breaker. 12/2 romex will run out of the sub-panel, protected by 2 1/4" EMT. The romex will be connected to various circuits in 1-2 4 11/16” J-boxes at the top of the 2 1/4" EMT above the sub-panel.

The 6 branches will consist of the following circuits (Table 1). (I need an explanation on 240 V circuits to include info about the conductors and breakers). The sub-panel is a GE wafer(?)-style (really thin breakers) 8 position breaker box [PowerMark Gold 125Amp 3 wire].

Table 1________________________________________________________________
Branch 1: Air Conditioning (240v, 30 amp breaker)

Branch 2: 8 4-bulb T10(?) fluorescent overhead lights, 2 double-outlet boxes, 2 circuits. Longest run is 45’, 12/2 romex. (light ballasts are made with 16 ga wires).

Branch 3: Spot lights - 8 x 100 watt bulbs (2 bulbs per unit, 4 units). The spotlights are evenly distributed on two circuits. Longest run is 55’ 12/2 romex, 20 amp breaker and switch.

Branch 4: Automotive lift (240, 30 amp, single phase). Have not purchased the wire/cable yet. Run will be 20’ long.

Branch 5: Air compressor (240, 30 amp, single phase [21 amp peak power]). Have not purchased wire/cable yet. Run will be 23’ long.

Branch 6: 6 20-amp double-outlet boxes, one circuit. 12/2 romex. Cables will combine in a 4 11/16” J-box above sub-panel. Power will run 6’, from sub to J-box, on 12 ga wire, inside 3/4” EMT.
----------------------------------------------------------------------------------------
A future branch will consist of an exhaust fan to vent automotive exhaust.


Thanks for reading this post...and the help.

 

[mrb]

there are a few issues with your plan.

It sounds like this is a detached garage -if so you cannot leave the existing circuit and install a subpanel. Only allowed one circuit to a detached structure.

You need 4 wires to the detached garage -two hots, a neutral, and a ground

You mentioned 14 wires in one EMT. You will need to calculate your derating for these conductors, typically more than 9 current carrying conductors in a conduit causes you to have to bump up a wire size. Use two conduits instead of one.

Grounds do not connect to the neutral bar in the subpanel. They connect to the ground bar. The neutral has to stay isolated from the can in the subpanel.

GE subpanel = garbage. Get something better -sqd homeline or (better) QO

You need two ground rods 6ft apart at the detached garage

If you have more than 6 breaker handles you need a main at the garage (use a bigger subpanel and backfed breaker with holddown or a main breaker panel)

If you have an 8 position breaker box you are already out of room as the 240v breakers take two spaces and I count 9 in the list you have

Pull a permit for your work and have it inspected.

 

[Charles (in GA)]

By "External Garage" do you mean "Detached" as in not connected to the house? This is important as certain things electrical are different if the garage is detached, vs attached.

As far as the code book, the NEC is created by the National Fire Protection Association (NFPA) which is a private organization and as such, copyrights all of its material. You can, and should obtain a copy of the code, whichever cycle Florida and your county or municipality is using. Easiest is to get it from Amazon.

2011 version of the NEC, paperback edition

Forget the NEC "handbooks" and other stuff, just get this code book. I also HIGHLY recommend a third party guide book of some sort to lead you thru many of the code requirements, the one I use, which has code references and makes it easy to jump from book to book, is the Illustrated Guide to the 2011 NEC in Paperback by Charles R. Miller

If you need an older code version, both the NEC and the illustrated guides are available from Amazon for the 2008 and 2005 and I think the 2002 versions of the NEC.

If the garage is detached and has a circuit currently supplying it, you will have to disconnect that circuit from your house when you run the subpanel, and reconnect that circuit to the subpanel in the garage. You cannot have more than one circuit supplying a building.

You are using way too small of a breaker panel. Eight positions is not enough. Get one with anywhere from 16 to 30 spaces and you will be OK. The cost is only slightly more in the big scheme of things.

You must run FOUR wires from the House to the Garage, two hots, a ground and a neutral. You cannot run jacketed service entrance cable (which has a spiral wrapped ground in it) in conduit, you will need to use separate conductors).

Using EMT for the ground is legal, but not the best. If you have a connection come loose, something as simple as a set screw work loose, then you stand a good chance of losing the ground. I highly suggest running a green ground with your hots and neutrals in the various branch circuits.

Pulling romex in conduit is difficult, even a straight run of some length will test your patience and abilities. It is best if you run conduit all the way, not just partial runs, and pull THHN individual wires in the conduits.

Many subpanels will not come with a ground bar. They will have a insulated from the box neutral, but no ground. You will have to buy a ground bar and install it in the panel, that is what all those small holes in the back of it are for. I just now looked at MRB's post, he has said much of the same things I have. I will not say a GE panel is bad, I have used them a couple of times and see no real problems with them. I prefer a Siemens panel, easy to get, large selection of sizes and types, and circuit breakers are easy to find for it. They work.

Not sure what you need to know about 240v circuits, you run two hots, usually use a black and a red, and a green ground. Most 240v circuits do not need a neutral, unless its something like a clothes dryer that needs a neutral to operate a 120v timer or motor. You use a double pole circuit breaker, which is really two breakers riveted together and have a connector for the handles so they trip together (except Square D QO, which has one handle and both breakers in one housing).

You cannot run a "gang" of romex out of a panel using one large conduit. The romex must be clamped at the panel, in connectors approved for such. Its not uncommon to see what you describe, but not legal.

You do not mention a disconnect. You are required to have a disconnect on the detached building, either outside (many times required by local code) or inside at the subpanel (bare minimum required by NEC).

Amperage you supply the subpanel will be dependent on the wire size you use, and the rating of the subpanel. #2 AL wire is NOT suitable for 100 amps.

Charles

 

[Smoking Joe]

Thanks guys,
It is a detached structure. I'll remove the original circuit. I was going to remove it originally, and thought it would be good in case I ended up tripping the 75 amp breaker on the main breaker box, so I would have some light and the ability to exit the garage door in the event of a major accident in the garage. It's not that big of a deal, I can always hang a battery-back up emergency light.

I'll change the sub-panel. It says it supports 8 spaces, 16 circuits. I test fit the breakers in the sub-panel and they all fit, but they were the half-slot sized breakers (three of which came with the sub-panel). Charles, I know what you mean about the ground bar. I was annoyed when I got home, and had to go back to home depot and get the ground bar. Also, I will get one with a main. I wondered why it didn't come with one. I noticed a lot of them didn't.

"Grounds do not connect to the neutral bar in the subpanel. They connect to the ground bar. The neutral has to stay isolated from the can in the subpanel." Thanks, I typed this part incorrectly.

Reference the ground for the sub-panel: Do I need both a ground cable from the main breaker, plus two ground stakes 6' apart? Also, how close do the ground rods have to be to the sub-panel and the structure. The concrete slab for the detached garage comes right up against the house, creating a five foot breazeway between the two structures. The concrete extends 12' and 20' on either end of the garage. The far side does not have concrete, but is 20' (straight line distance) across the garage, which would have to have the ground cable routed 42' up through the ceiling and back down the other side. I could always bore holes in the concrete in the breezeway, but I'm not sure how I would sink an 8' grounding rod in that tight space (suggestions welcome).

"You mentioned 14 wires in one EMT. You will need to calculate your derating for these conductors, typically more than 9 current carrying conductors in a conduit causes you to have to bump up a wire size. Use two conduits instead of one." I thought I might have to do this, and bought enough stuff to run two conduits. I don't understand how to calculate the derating for the conuctor...how do I do this?

"Using EMT for the ground is legal, but not the best. If you have a connection come loose, something as simple as a set screw work loose, then you stand a good chance of losing the ground. I highly suggest running a green ground with your hots and neutrals in the various branch circuits." Ok, I was trying to save on my fill calculation. If each circuit has a ground, do the total number of grounds count as 1 wire or 5 (hypothetical number) wires?

Finally, the PVC underground was laid into the concrete by the previous owner. I cannot change it. I'm just glad he had the foresight to put the PVC in. I may be using the wrong term...it's the grey thicker PVC for electrical. Is it still called PVC?

"You cannot run a "gang" of romex out of a panel using one large conduit. The romex must be clamped at the panel, in connectors approved for such. Its not uncommon to see what you describe, but not legal." Is there no difference when the romex is being run in conduit as protection verses run in the conduit as a system? It would only be 3 cables from the box, expanded to four in the future. The current box has enough punch-holes where I could clamp them all and then route them through the conduit. It seemed to make more sence to me attache the conduit, cap it with a bushing and run them through. But if that is not permissible I will change it.

Thanks for the responses guys...especially late at night.

 

[walrus]

EMT is fine for a ground, if installed and supported properly. Its a common practice and who is to say a wire nut won't come loose?

 

[Aceman]

The first thing you need to do is a load calc for your home.

 

[Smoking Joe]

The first thing you need to do is a load calc for your home.

I have. The numbers are at my office. I will bring them home tonight and post it. I also measured the load across each line under surge (had friends turn on all major appliances at one time, while another read both lines. I also measured under normal operation with all items turned on. Plus I did a variation with the hot tub under different conditions to determine the draw of the hot tub under normal use, heating-up, and with the jets on.

Give me a few hours and I'll put the numbers into a readable format on here.

 

[mrb]

measurements do not equal a load calc. Buy the appropriate year NEC for your jurisdiction and read article 220

 

[Falcon67]

The sub-panel is a GE wafer(?)-style (really thin breakers) 8 position breaker box [PowerMark Gold 125Amp 3 wire].

I have the same panel in my shop with the thin breakers. It's a good panel, and makes for a nice compact install IMHO. The ground bar is readily available and the breakers are fairly priced. I have a disconnect where my shop feed comes off the meter can - you may want to back feed that panel or go up to a similar panel with a main in it. Being able to kill the power in the panel when doing add/move/change adds a safety factor.

Note, our (ex) house has a 100 amp panel and I took my 60amp shop power for the shop off the meter can, BEFORE it got to the house panel. Had the Poco set up the same at the new house - 100 amp tap at the meter can, before the 200 amp house panel.

 

[Smoking Joe]

going to try and pick up a copy of the NEC tomorrow at the library.

Then I will do the load calc. It may tell me, but if not do I calculate in my planned items in the shop?

 

[MrMark]

A couple of random answers to your questions:

Grey electrical conduit is PVC. You can use the same glue as the plumbing version but I would use the gray glue specifically for electrical conduit. It doesn't get primer. It is a sign of a hack to see purple primer or the blue plumbing glue on conduit.

There is only one ground required for each pipe. That ground is just one wire but it does not count for derating; it does count for permissible conduit fill. Only conductors (phase and neutral) count for derating. For box fill calcs, something you did not ask about, all the grounds together count 1. It is foolish, imo, to rely on the emt conduit for ground. It is simple to include the green wire, play it safe.

Derating: there is a table that you must consult if you go over the 9 conductors in the pipe. Break it up. There is no good reason to use one big pipe. Keep your pipes at 3/4 and less than 9 conductors.

You can put romex in conduit but I wouldn't unless necessary with a short piece for physical protection.

 

[Smoking Joe]

no NEC from th elibrary. I'll order one from Amazon.com. I'll proceed with some of the minor stuff until I get the book.

By the way, I remember reading somewhere about GFI's in detached garages. Is there a code requirement for the outlets to be on a GFI.

Also, what are peoples opionions on arc protected breakers?

 

[mrb]

only put arc fault breakers where required by code. they will cause you nothing but trouble in a garage.

 

[Smoking Joe]

Ok, I have a copy of the NEC. I would like to ask some questions for clarification on some things. I am not being a smart *** in my questions, I don't want to mis-interpret the code, and your experience will probably catch some mistakes.

"It sounds like this is a detached garage -if so you cannot leave the existing circuit and install a subpanel. Only allowed one circuit to a detached structure."
Under 225.30, A it says that I can have a separate branch go to a detached structure for Emergency systems. Does my idea of powering an emergency light and the garage door opener for an immidiate exit in an emergency fall under this category? That was my only intent for having a secondary source of power.

Planning on using #4 Cu for my feeder from the main panel to the sub and using #8 Cu for my ground. The total length of wire will be about 20'. This accounts for the length down the wall, underground, under the breezeway, and up the wall. The distances between buildings is 5'. (does this sound right?)

I think I have to use single wires (THHN/THWN) through the PVC conduit. How do I protect the feeder/nuetral wires from the house main breaker to the exterior wall where it will travel through the wall into a LB fitting down into the conduit.





btw- How high off the floor should my outlets be. right now they are 12 inches. Do they all have to be GFCI protected?

please clarify the definition of a recepticle in the context of calculating the number of "recepticles" on a branch circuit. I have 8, two-recepticle outlets on one branch and 6 on the other. Does this cound as 8 and 6, or 16 and 12?

 

[jeffmoss26]

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