Basic electrical plan... 2 car garage

[TNToy]

Okay. Here's the deal.

What I NEED is pretty straightforward:
* Two 220V breakers outlets, one each for a welder & compressor.
* A 110V breaker for the fluorescent lights I plan to add.
* A 110V breaker for the extra power outlets that are needed.

Here's what I'd LIKE
* 2 different 20A 110v outlets, instead of having all the plugs added running off of one breaker. A drill, a grinder, a couple of cordless tools chargers, and a radio together could eat up 20A pretty quickly.
* More 220V service. I'll have a plasma cutter eventually.

The main panel is in the master closet, diagonally opposite from the garage on the floor plan. So I'm going to install a subpanel in the garage. So I only need one double-pole breaker of the correct rating in the current box. Installing 2 slim-line breakers will make SPACE for it.

But how do I know if I have the free electricity for it? There is no gas in this house - they didn't even plumb the lines. Every major appliance is electric. Heat, oven, dryer, etc. Can I add up the power used by the most things that COULD be run at once, and figure out how much unused potential I have?

Is 15A a reasonable breaker size for 4, 6, or 8 couple of fluorescent fixtures? I keep forgetting to look at how many watts they consume. Right now, there's 3 un-covered 100W light bulbs in the ceiling. I BELIEVE that I could run three or four fluorescent fixtures off of that same amount of power? I'm thinking 2-bulb 4' fixtures. Probably the cheaper T12's.

How do I find out how much service I have? Is 200A pretty typical?

I've got a fairly large (25x30ish) 2-car garage to work with. Going to be building a lot of benches and shelving in here.

Assuming I can figure out how much power I can feed to the garage, and someone can point me to a chart that shows what size romex I'll need to run... I'd LIKE to install an 80A or 100A panel in the garage.

Here's a pic of where I'm starting... See that outlet the freezer is plugged into? That's the ONLY one in the whole garage.

 

[TNToy]

Forgot... is there a site that deals with the PLANNING aspects like this?

I know how to properly wire everything in this place, install the subpanel, fish the wires through the walls, get everything properly grounded and what-not...

But it's the planning stuff that's the issue...

How do I figure out what my current demand or load is? How should I size the wire for this ~100-foot run?



If nothing else, I wish the main box was closer. A hundred feet of 6,8, or 10-3 romex is NOT cheap.

 

[Junkman]

Put a 100 amp sub panel in the garage, and a 100 amp breaker in the main box. I doubt that you are ever going to come close to using the total 200 amps that the service will give. The breakers are to protect the wiring, not the appliance. If you were running the oven, all 4 burners, the electric heat, the electric dryer, and a lot of other heavy demand appliances all at once, you might get to trip the main, but I doubt it. I can't ever remember hearing about a main tripping unless it is a result of a catastrophic failure of the wiring or it is hit by lightning.

 

[bmwpower]

You need to complete a "Demand Load Calculation". Here is the place I learned how to do mine:

www.selfhelpforums.com

Very good site. A lot of friendly guys willing to help.

Here is my thread, working through my calc:

http://www.selfhelpforums.com/showthread.php?t=2011

 

[Bib Overalls]

How do I find out how much service I have? Is 200A pretty typical?

Locate your main breaker. It should be marked with it's trip capacity. It will be at the top of your main panel or possibly in a box under (or near) your meter. If it says "200 Amps" that is what you have. At one time 100 amps was common. And before that 50 amps. And I have even seen old houses with 30 amps of service. But almost all houses built in the last 20 years or so have 200 amp service.

I agree with the others. Run a 100 amp sub off your main panel. Buy a panel with room at least ten and (preferably more) breaker spaces. In residental wiring eight recepticles/devices on a breaker are common. But in a shop I would put no more than four. And at my workbench I would put two gang boxes on dedicated circuits. All 110 outlet circuits should be made with 12 guage conductors (wire) protected by 20 amp breakers. Lighting circuits can be made with 14 guage conductors protected by 15 amp breakers.

From the picture, it looks like you have finished walls. Will you be snaking Romex through the walls or running wires in conduit?

 

[Junkman]

BMW..... I went to that site and read your calculations. I am wondering why you even consider the lift in the calculation. The motor runs for no more than 30 seconds and how often is that? I agree that a load calculation is necessary if you are going with a lot of heavy use items, but in most instances, most homes never get anywhere near close to what the actual service is. If you really want to know the correct answer, check with your utility and see if they will do a load calculation for you. I don't know if they still do it, but at one time, in CT, the utility would set up a meter that would graph your electrical demand for 24/7 to make sure that you had a proper service.

 

[Charles (in GA)]

From another board........ This is a discussion pertaining to how many flourescent lights you can put on a timer. A breaker would be the same calculations, just slightly different numbers of lights in the end. The discussion centers on Power Factor and why with flourescents, expecially the older magnetic ballast type, you don't want to come anywhere close to what the simple volts x amps = watts and watts divided by volts = amps formulas, will give you.

The Question......
Could somebody tell me how to figure out how many 40 watt florecent bulbs will work with a timer that says 8.3 amps. I think that 100 watt is close to 1 amp, am I close? If I am I am guessing thst timer would handle 8 100 watt incandesant bulbs and 20 of the 40 watt?

The answer, in two parts...........
Its a lil cornfusing but when I try n explain it sort of helps refresh the whole thing all over again in my old brain. Years ago I could spit it out in my sleep but havent worked with it for a long time. It helps to look at a vector diagram showing the voltage and the lagging inductive current and the in phase resistive current elements. The Power Factor (if I recall correct??) is the cosine of the angle between the Voltage and Current i.e if pure resistive and they are in sync theres no angle (0 degrees) between and the cosine of 0 is one i.e. Unity Power Factor BUTTTTTTT if they are out of phase say an inductive motor load where the current lags the voltage thennnnnn theres an angle between the two and the cosine of that angle has a value so the power factor may be say 80% the bottom line remains that "apparent power" what a straight watts calculation would yield DOES NOT EQUAL 'REAL POWER' what the utility has to generate i.e current to energize the inductors magnetic field PLUS current in the DC resistive part of the inductor (its wire resistance)

John (rusty on this but knew it well a good while back, still interesting to me, however)

and the second part of the answer.........
Again as I posted below and explained, due to the Power Factor problem I NEVER used near as many fixtures/lamps as the straight watts calculations might indicate i.e. I used like 10 or 12 100 watt units (40 + 40 + ballast) on a 20 amp branch circuit.

NOWWWWWWWW lets say you have 4 fixtures each with two 40 watt tubes plus a ballast,,,,,,,,,,,,, lets say thats "about" 100 watts each,,,,,,,,,, then 4 of those would be a rough total of 400 watts,,,,,,,,,,,400 watts divided by 120 volts = 3.3 amps SOOOOOOOOOOOOOOOOOOOOOOOOO Yes a timer rated to carry n switch 8.3 amps ought to work fine

BUTTTTT REMEMBER this doesnt take into account the possibly lousy Power Factor of the ballast as some, especially the older, are poor as its an inductive load (its a transformer)

ANOTHER BUTTTTTTTTTTT still if the timer is rated at 8.3 amps and your load is only 3.6 (but thats if youre using a pure resistive unity PF which the ballast is NOT load) THATS A SAFETY FACTOR OF DOUBLE so you ought to still get by fine. (Those would have to reallyyyyy be poorrrrrrr ballasts if an 8.3 amp rated timer couldnt handle what computes to be a 3.6 amp resistive load) Just be aware if you use watts and treat the ballast as resistive (which its NOT) I wouldnt push things right up to the limit and use so many lamps the straight wattage calculations might say its 7 or 8 amps !!!!!!!!!!!

Watts = Volts x Amps and thats for a pure resistive Power Factor = unity 1 load. Howeverrrrrrrrrrr if the load is inductive (current lags the voltage) the apparent power DOES NOT equal the real power. It takes lagging current n energy to build and maintain the magnetic field surrounding the inductor PLUS it takes in phase (resistive) current to flow throug the straight DC resistance of the ballast. The utility hates poor power factor cuz they have to generate n supply energy for BOTH the lagging current to maintian the magnetic field of a motor/inductor PLUS the in phase resistive current SOOOOOOO their generators have to work harder n theres more inefficiencies.

Hope this helps, DO NOT use so many fixtures the wattage calculations go up near the amps limit of the device TO SOLVE THIS EXACTLY we would need to know the exact loads and power factors but a safety factor of two is sureeeeeeeee plenty. Not knowing the power factor and just guessing I sure wouldnt go much over 5 or 6 amps using straight wattage calculations but 3 to 4.5 or should be fine regardless.

Sorry we cant give any exact answer.

John, A Long Retired EE and a tad rusty on all this butttttttt if you use conservative raitings and ESPECIALLY if you use modern high PF ballats there shouldnt be any problems

I hope they don't mind my reposting, but I have eliminated last name references and don't tell you where I got it, so...........

Charles

 

[bmwpower]

BMW..... I went to that site and read your calculations. I am wondering why you even consider the lift in the calculation. The motor runs for no more than 30 seconds and how often is that? I agree that a load calculation is necessary if you are going with a lot of heavy use items, but in most instances, most homes never get anywhere near close to what the actual service is. If you really want to know the correct answer, check with your utility and see if they will do a load calculation for you. I don't know if they still do it, but at one time, in CT, the utility would set up a meter that would graph your electrical demand for 24/7 to make sure that you had a proper service.

The calculation is supposed to show worst case scenario, ie. what would happen if I had the A/C going, the air compressor, a large power tool, etc. AND the lift were to run. It's possible, but not highly probable.

With close to 100A running in my garage and well over 100A running in my house, the main breaker may trip.

 

[kbs2244]

On the watts to amps thing. I know it is not dead on, but it has a built in fudge factor going in the right direction if you just figure that 100 watts is an amp.

 

[TNToy]

Locate your main breaker. It should be marked with it's trip capacity. It will be at the top of your main panel or possibly in a box under (or near) your meter.

That's obvious. It's gotta be outside: I've got a 100A one in there labeled ELC HEAT, and a 60A BREAKER LABELED MAIN.

I know there's no way I've got 60A or 100A service in a home with electric EVERYTHING. I'll check out by the meter later, when it's not raining.

From the picture, it looks like you have finished walls. Will you be snaking Romex through the walls or running wires in conduit?

That's another good question. I'm trying to do this fast so I can start tearing down a Ford Ranger... and I want airtools for that, and good lighting.

I have full access to the attic over the garage. I want to simply bolt the box to the wall, run conduit up the outside of the wall, and into the attic, where it switches to bare romex and gets fed back down through conduit into the surface-mounted breaker box. How are you SUPPOSED to make the transition from conduit to bare romex? Do I need a box at the top of each conduit run? Or can you simply bend a 90 at the top of it inside the attic?

From another board...

(Long, italicized post follows)

Uh... I read that twice, and saw nothing resembling an answer.

How many watts does a typical 2 bulb, 4 foot fixture draw, and how many are usually fed off of a 15A breaker? How many on a 20A breaker?

 

[TNToy]

Also, I forgot this...

The run will be 75-100 feet from the main panel to the sub panel. Assuming I want 100A service in there, what size where needs to be run? My best guess is #6 for the hots & neutral, and #10 for the ground.

However, I can't find that chart that people always post showing current vs. length of run to determine wire size. Someone got the link handy?

 

[tanky321]

Also, I forgot this...

The run will be 75-100 feet from the main panel to the sub panel. Assuming I want 100A service in there, what size where needs to be run? My best guess is #6 for the hots & neutral, and #10 for the ground.

However, I can't find that chart that people always post showing current vs. length of run to determine wire size. Someone got the link handy?

Run #3 copper for the hots & neutral. #6 for ground.

 

[TNToy]

I've never even seen #3... only 2 and 4.

Is it readily available?

If I downsize to 80A service, can I run #4?

 

[tanky321]

I've never even seen #3... only 2 and 4.

Is it readily available?

If I downsize to 80A service, can I run #4?

#3 is readily availible. I run #3 at work all the time. #4 will be fine for 80A.

 

[bmwpower]

#3 is readily availible. I run #3 at work all the time. #4 will be fine for 80A.

Home Depot doesn't seem to sell #3, so I went with #2 for my 100A.

 

[tanky321]

Home Depot doesn't seem to sell #3, so I went with #2 for my 100A.

Hmm. I tend not to buy anything electrical related at home depot, because its much easier to get it through work. #2 is fine, thats probably what I would go with too if I couldnt find it. The determining factor is length.

 

[TNToy]

Yeah. I know.

Related to that question: Can you direct me to that table everyone always posts showing length of run, current needed, and the resulting wire size you must use?

 

[boiler7904]

I have full access to the attic over the garage. I want to simply bolt the box to the wall, run conduit up the outside of the wall, and into the attic, where it switches to bare romex and gets fed back down through conduit into the surface-mounted breaker box. How are you SUPPOSED to make the transition from conduit to bare romex? Do I need a box at the top of each conduit run? Or can you simply bend a 90 at the top of it inside the attic?

You will need to have a j-box at the transition from romex to wire in conduit. They make fittings that clamp the romex to holes in metal boxes.

You might want to check out Mike Holt's website. He's an electrical guru and has all kinds of interesting and useful info on his site as well as a forum.

Mike Holt

 

[Stuart in MN]

If you're running continous romex through the conduit with no splices, you don't have to have a box at the end, just a bushing so the edges of the conduit don't scrape the insulation. If you're running individual wires, yes you do need a box like boiler7904 said.

I think Mike Holt's forum is for electrical professionals only, unless it's changed since the last time I was there.

 

[wilbilt]

Can you run Romex inside conduit?

I always thought that was a major no-no. Of course, my "current" copy of the NEC is dated 1975......

 

[TNToy]

CAN you run romex in conduit? That's what I'd like to do...

 

[bmwpower]

CAN you run romex in conduit? That's what I'd like to do...

You can, but it's much easier with individual wires.

 

[tanky321]

You can run romex in conduit, but like stated before its a PITA as far as a voltage drop table, I dont trust anything but the NEC. Ive seen online calculators that are way way off.

 

[TNToy]

Got a link to the NEC's code on this?

Dammit, I've been searching this site, and DIY, and 2 others, and I keep finding reference to the NEC's code on this. But no one bothers to POST the section on the code that says "Runs of ___ feet needing ___ amps require ___ gauge cable"...

Heck, is there are formula for this per the NEC? I own a calculator...

 

[Bib Overalls]

In my pole barn construction shop I started the outlet circuits with Romex at the sub-panel. I ran them along the top of the wall perlin that is set at 8' above the floor. The outlets were wired using "handi" boxes mounted to another wall perlin set 4' above the floor. A 1/2" conduit runs up from the "handi box" outlet to another "handi box" on the 8' purlin. The Romex feed runs through the upper "handi boxes" and is secured with cable clamps. In the conduit I run individual connectors. Connections are made in the upper box with wire nuts. Simple, easy, and meets code in respect to protecting cables/wires from abrasion in work zones.

 

[Charles (in GA)]

Got a link to the NEC's code on this?

Dammit, I've been searching this site, and DIY, and 2 others, and I keep finding reference to the NEC's code on this. But no one bothers to POST the section on the code that says "Runs of ___ feet needing ___ amps require ___ gauge cable"...

Heck, is there are formula for this per the NEC? I own a calculator...

Wished it was that simple, its not. Here is the NEC in its entirety if you want to look

http://www.nfpa.org/freecodes/free_access_agreement.asp?id=7005SB

The NEC recommends but does not require that you maintain a voltage drop of 3% or less when determining wire sizes and runs. The complicated portion is depending on whether you are going to run any portion of the wire in a area that gets hot, such as an attic, or what type of insulation is on the wires (determines the temp rating of the wire), if you are running the wire in conduit, how many wires are in the conduit, and some other factors. These items determine how much, if any, de-rating of the wire is necessary. Its possible to have a 12 gauge wire, normally accepted to be good for 20 amps, that after derating, might be good for less than 10 amps.

General rule of thumb is that if you keep a 120v run under about 60 ft of wire, you will stay within the voltage drop requirements. Double that for 240v. Fact is, I do not recall any tables in the NEC that deal with wire lengths............

Charles

 

[Kapt]

I'm in the planning stages of my wiring and also will be running 100A to my garage. Look at table 310.15(B)(6) of the NEC and 310.16. One says #4 OK for 100A and the other says #3. Not sure which one applies to you.


HTH, Tom.

 

[Charles (in GA)]

Also, I forgot this...

The run will be 75-100 feet from the main panel to the sub panel. Assuming I want 100A service in there, what size where needs to be run? My best guess is #6 for the hots & neutral, and #10 for the ground.

However, I can't find that chart that people always post showing current vs. length of run to determine wire size. Someone got the link handy?

For 100 amps, Table 310.15(B)(6) will you that you need at least a #4 copper or a #2 Aluminum wire for services and feeders of 100 amps. 250.122 gives us a table that says for equipment grounding (not service or feeder, I cannot find that right now) that for 100 amps, you need a #8 ground if copper.

Charles

 

[bmwpower]

Regarding the NEC code....I guess the easiest thing is to run larger wires than you need to account for any derating, voltage drop, etc. I think if you run #2, you should be able to bypass all those calcs.

 

[boiler7904]

Regarding the NEC code....I guess the easiest thing is to run larger wires than you need to account for any derating, voltage drop, etc. I think if you run #2, you should be able to bypass all those calcs.

That might work but why would you want to pay for heavier copper than you really need to? #2 is also harder to pull and unneccessary if you don't really need to. I can also see where if the run is long enough that just guessing #2 is ok will result in that being undersized to.

 

[bmwpower]

Voltage drop calculator:

http://www.electrician2.com/calculators/vd_calculatoradv.htm

It looks like #4 will be fine for a 100 foot run with a load of 100A. Remember, the load is really never going to be 100A all the time, so you should be fine with #4.

I wanted to oversize mine feeders, so the next size I could source locally was #2.

 

[TNToy]

I had another idea, too...

I'll do some checking tonight when I get home. But I'm pretty sure the three existing garage lights (simple 100W bulbs) and the opener are on their own 15A breaker. If so, I'll simply install several (probably 6) 4" twin-tube flourescent fixtures on that circuit in place of the existing lighting.

That removes the requirement for 15-20 amps from the subpanel. So I could get away with #4 and an 80A setup:

20A (110V) - Wall outlets
20A (110V) - More wall outlets
20A (220V) - Welder
20A (220V) - Air compressor

... Total of 80 Amps.

 

[TNToy]

Oh yeah: For the third time:

Those of you who've finished your garages - how many flourescent fixtures are typically installed on a 15A circuit before it becomes overloaded?

Anyone know how much juice a 1/2 HP door opener pulls? Given that it's probably over-rated at 0.5HP... I belive that works out to less than an amp?

 

[bmwpower]

Oh yeah: For the third time:

Those of you who've finished your garages - how many flourescent fixtures are typically installed on a 15A circuit before it becomes overloaded?

Anyone know how much juice a 1/2 HP door opener pulls? Given that it's probably over-rated at 0.5HP... I belive that works out to less than an amp?

Depends on what the fixture draws. With a 1A fixture, you can install a maximum of 15 fixtures. You just cannot exceed the circuit capacity.

Found a manual on a typical opener ...see bottom for amperage output (5A):

http://www.garaga.com/produits/78/documents/en/PATS_Brochure.pdf

 

[TNToy]

Okay, so a typical flourescent fixture draws an amp? I know it's not as simple as figuring it based on the wattage of the two bulbs, because the ballast has to consume some power as well.

I guess next time I'm at home depot I'll take a look at the fixtures and look for their current draw.

5 amps sounds goo. I don't know where I came up with 1 amp for an opener before... you can't even run an electric drill on 1 amp, and an opener definitely has a larger motor than that.

 

[Charles (in GA)]

Okay, so a typical flourescent fixture draws an amp? I know it's not as simple as figuring it based on the wattage of the two bulbs, because the ballast has to consume some power as well.

I guess next time I'm at home depot I'll take a look at the fixtures and look for their current draw

I presented the discussion on Power Factor to point out that its not as simple as saying that you have two 40 watt tubes per fixture times however many fixtures, etc. You really need to know the actual current draw (amps) of the fixture, as given on its data plate. Lighting is considered continous load and in such cases you must not exceed 80% of the rated breaker capacity. If you have a 20 amp breaker, do not load it with more than 16 amps. If you have 15 amp breakers, do not put more than 12 amps on it. Another way of doing this is to take your total amp load of the lights you want on one breaker and mutiply that by 125% to determine the minimum breaker size needed. (ie. 15 amps of lights times 1.25 equals 18.75 amps. This would be OK on a 20 amp breaker, but not on a 15 amp)

Continous is defined as drawing loads for more than three hours nonstop.

Charles

 

[TNToy]

I understood that part. I was just curious what the typical fluorescent fixture draws...

I'll just look at the specs next time I visit a big box store.

 

[JDHolmes]

I understood that part. I was just curious what the typical fluorescent fixture draws...

I'll just look at the specs next time I visit a big box store.

I read most so let me chime in.

You figure for every 100' of wire, go up one wire size.
#10 wire will handle 30 amp
#8 = 40
#6 = 50
#4 = 70
#2 = 100

If you're going 100' or more, table drops down.

You can run about 6 outlets in the garage on a 15 amp circuit. I would, however, put in 20 amp breakers and run #12 wire with them. My house is wired with 15 amp breakers and the Christmas lights blow breakers all season. Don't forget your GFCI's.

If you're running outside sheet rock, you'll run in emt conduit minimum but if you have no sheetrock, run the romex through the studs, no conduit needed.

Breakers can be given 80% of their rating. That is, a 20 amp breaker can get 16 amps of juice. If your compressor pulls 26 amps, 30 amp breaker is too small. (30*.8 = 24). 100 amp breaker in the garage should only pull 80 amps total at full load. Compressor and welder with lights on will go a long way to getting there.

One thing to remember about electricity though that I didn't see posted. You can push electricity too far and usually the end result is a fire. You CANNOT too careful with electricity. If you start popping breakers, something's wrong and it should be fixed.