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Thread: Looking for some help on garage sub panel

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  1. #1
    DIY Junior Member knied1's Avatar
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    Default Looking for some help on garage sub panel

    This subject may have been beaten to death, but here is my plan, and I have a couple questions.

    I am running a sub panel to my garage, I have already purchased the panel box for the garage from Home Depot, it was on sale, and included the 100amp main, 1 - 30 amp (240) and 2 – 15 amp breakers. My garage is detached from the house, and total run from box to box is almost 50 feet. I currently have 100 amp service to my house, but am planning to upgrade to 200 amp in the next year or 2. I understand that I can only send 50 amps to the garage (half of my service) but I want to put 100amp wire / cable depending on what you prefer to call it, and sub panel, this way when I upgrade my service I am all set to send more power to the garage. I also know I need a permit, and an inspection, the permit is $100, and inspection is $68, cheap enough to not risk burning down the house i WILL be getting them. My town code DOES allow for the home owner to do the work I just need an inspection to close out the permit.

    This is my plan, and I am asking this so that I can have 100% everything ready and done only one time, so your input will be appreciated.

    • 2-2-2-4 aluminum (Home depot called it 100amp feed, I may have the numbers and dashes wrong I’m going by memory, but I am planning to use aluminum 100 amp feed)
    •1 ” pvc conduit buried 18” deep ( I understand I can use 1 but I figure 1 ” would be easier to pull the wire)
    o I have not purchased the wire or conduit yet would it make sense to run 2” conduit?
    o There will be about a 15 foot run inside the house. Is this supposed to be in conduit?
    • 50 amp breaker in my house panel, and leave the 100 amp in the sub panel in the garage, using it as a main disconnect, but I will label the box as 50 amp house supply.
    • Since I am running 4 wire I understand I need to tape both ends of one wire white marking it the common, obviously one wire to either side to the 50 amp breaker, and the other to the ground.
    o I am running 4 wires I am being told I do not need a grounding rod at the garage, and if it put one there I am increasing my risk of lightning strike. Is this true or was someone having fun with me?

    What am I missing? understand that i am also planning to upgrade my house service, and want this install able to accomidate future upgrades.

    I am planning to run a welder, and just the basic home shop type tools. I currently only have 20 amps of service in my garage, and am sick of using my generator welder. This will allow me to get rid of that, and pick up a regular 240 volt.

    Thanks for any help you can offer please understand that I am not up on the electrical lingo, and may ask some questions that seem dumb.

  2. #2
    DIY Junior Member knied1's Avatar
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    sorry one more question
    I am told that the common and ground wires CAN be on the same bussbar in the house, BUT the ground and neutral need to be on separate bussbars in the panel. Is this true? and what is the difference?

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by knied1 View Post
    sorry one more question
    I am told that the common and ground wires CAN be on the same bussbar in the house, BUT the ground and neutral need to be on separate bussbars in the panel. Is this true? and what is the difference?
    The difference between the grounded neutral and the equipment grounding conductors are as follows;
    The grounded neutral conductor is a current carrying conductor that completes the circuit from the transformer back to the transformer just as the way a flashlight works. From the end of the batteries through the light bulb back to the batteries.

    The Equipment Grounding Conductor is installed in the event that there is a fault in the system where exposed metal will be energized it will carry the faulted current back to the source in order to open the overcurrent device be it a fuse or breaker. The only time the EGC will carry current is when something goes wrong.

    The two are tied together in the service equipment where the fault current travels from the service panel to the transformer via the neutral. The equipment grounding conductor does not carry current unless something has gone wrong.
    If the two are tied together anywhere downstream from the service then they both will have current on them making any exposed metal between the two points hot.

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    DIY Junior Member knied1's Avatar
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    jwelectric thanks for the input but i need to hit you up again.

    The wire is 4 wire aluminum, and all 4 wires are insulated individually, one has a yellow stripe. I understand that i need to be sure of the W, or UF labeling on the wire before i purchase it, and 90 amps is more than enough for what i am planning. This being said...... he told me i only need 1 1/4" conduit, but i am assuming it would be easier to pull the wire if i went with 1 1/2" or 2" conduit. the difference in cost between 1 1/4" and 2' is sooo minimal i do not care about the few extra dollars, and does the conduit need to continue into the house all the way to the panel? What would you recomend for conduit? At the same time is there a different wire you would recomend for a DYI`er. I want the wire in conduit incase i need to pull something like a phone line, or need to replace wire things like that. (planning on PVC conduit)

    As far as the grounding rods....You are saying 2 rods 6 feet or more apart, do I run 1 wire to each? or wire to the one rod, and then a jumper for lack of a better term to the other. I am also assuming the rods need to be 8 feet long.

    thanks again
    Last edited by knied1; 08-31-2012 at 08:08 AM.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    The bigger the conduit the easier it will be to pull. What you don’t want to do is install a low voltage conductor in that same conduit be it telephone or cable as it is neither the voltage rating and it will distort the signal. For these run another 1 inch conduit.

    If the conductors are single strand conductors and this sounds like what you describe then it will need to be in conduit from end to end but if it is URD again it sounds like what you describe then it can’t enter either building so a junction box will need to be set and transitioned to another type of conductor. I suggest 2 SE-R cable for entering either of the buildings. This can be 2-2-4-4 or what ever they have on hand as long as the first two numbers are 2.

    Yes two 8 foot rods at least 6 feet apart and you can install one conductor to the first rod and then install a “bonding jumper” to the second rod.
    Last edited by jwelectric; 08-31-2012 at 09:03 AM. Reason: for corrections

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    DIY Junior Member knied1's Avatar
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    How far are you allowed to run URD inside a structure?

    In the garage i would need to run it about 3 feet, to the panel, and in the house it would be about a 10 foot run into the panel. It seems to me it would be safer to have one run for panel to panel instead of 2 junction boxes, and splices.


    Thanks

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    Electrical Contractor/Instructor jwelectric's Avatar
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    2-2-2-4 for a remote panel is good for only 90 amps so installing a 90 amp breaker will be good for now or after the service is changed.

    If the conductors are to be installed underground make sure that there is a W in the lettering on the conductors. If they are selling you URD or trailer cable as some call it, it cannot enter either building. Set a junction box on the outside and terminate the URD and install SE-R four conductor cable to the panels.

    Unless it is a cable it will need to be in pipe from end to end. If it is part of a cable it must be type UF.

    If it is aluminum conductors then all four must be insulated and identified by tape for the equipment grounding conductor green and for the grounded neutral with white or gray.

    At the garage a grounding electrode system must be installed. If there is none available then drive two rods at least 6 feet apart and install a grounding electrode conductor to them. This conductor can be a solid uninsulated conductor.

    The use of the word common is not correct. The four conductors will consist of two ungrounded (HOT) one grounded (neutral) and one equipment grounding conductor. In the remote panel the neutral and EGC must be isolated from each other with the grounding electrode conductor landing on the EGC terminal bar which will be bonded to the panel enclosure. The neutral will need to be isolated from contact with the grounding.

    Just for the record there is no such thing as a
    Quote Originally Posted by knied1 View Post
    and may ask some questions that seem dumb.
    All questions are needed when doing something that one lacks knowledge about. Where the problems with questions comes into play is when someone is told that something will not work but one keeps asking questions about how to do it. If it cant be done why keep asking questions? These are the dumb questions and you have not asked one yet so keep them coming.

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    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by knied1 View Post

    I am running a sub panel to my garage, I have already purchased the panel box for the garage from Home Depot, it was on sale, and included the 100amp main, 1 - 30 amp (240) and 2 – 15 amp breakers.
    I have absolutely NO idea why you think you need 100 amps out in the garage. I have installed a few 50 amp services for real gear heads, but most guys are happy with a 30 amp service. Square D makes a great little panel with six slots. Two slots for the 30 amp main (or 50), two more slots for a 240v circuit, one 15 amp circuit for the lighting, and one 20 amp circuit for all the power tools not of 240v.

    IF you want AC as well, some tandem breakers will fit fine. Same for a fridge, if you must.

    Are you intending to run a factory in there? How many guys will be working simultaneously? How many of your power tools can YOU work simultaneously?

    The Square D panel costs about $17 at Home Despot. I swear by it.

    Seriously, what sort of power demand do you think you are laying on the system?

    You do understand that when you say "100 amp" that means two 100 amp 120v circuits, yes?

    You could hold electrocutions in there based on your plan.

    My whole 1800 sq ft home with a 4 ton AC in LA runs on a 100 amp panel.

    You are way over killing this project.

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    DIY Junior Member knied1's Avatar
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    I know that immediately I am over killing it, BUT within the next few years I am going to have a mill, and lathe in the garage, before you call me out they are both single phase 220. My father is retired and when he sells his house I can have them…….. Right now my son and I work in the garage at the same time, I know I am doing the welding, and he is grinding or cutting…... When I get the machines in there it is very possible I will be working on one, and he will work on the other.
    If I am going to do the work now to send a feed to the garage it seems stupid to only send 30amps out there so that in a few years I can tear it all out and do it again.
    Yes for the next year, two, three, I will only have a 50 amp breaker for 100 amp line, but at least I am ready. When the time comes all I would have to do is switch out breakers and the garage is all set, and if my plan falls thru then I only spent maybe an extra $100, and not re-spend several hundred. I know I bought the panel too early, but it was on sale for $28.00 and included all the breakers. I have not bought the conduit or wire yet.
    Will I need a full 100 amps?..... I don’t know…… I DO respect your opinion, and appreciate the fact that you may be trying to save me money, and hassle, but my opinion is if I’m going to spend the time and money, I may as well make sure I only have to do it once.

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    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by knied1 View Post
    If I am going to do the work now to send a feed to the garage it seems stupid to only send 30amps out there so that in a few years I can tear it all out and do it again.
    Of course you should only do the work once and anticipate your future needs.

    Based on what you are saying here, yes, 30 amp is possibly too little.

    As for the mill and the lathe, they are 240v. You understand, I hope, that that means that they draw half as much ampacity on the hot leg(s), yes? If the same motor is wired to run at 120v and it is eating 5 amps (which is a big motor) at 240v it will draw 2.5amp per leg.

    Go find out how much the lathe and the mill draw. I bet combined they don't add up to more than 20 amps.

    Likewise the welder you want to use and the grinding and cutting. The grinding and cutting happens at 120v.

    You can go ahead with your enormous panel, but I am quite sure that you don't need more than 50 amps out there.

    As I say, I have a 1800 sq ft house with a 4 ton ac in LA running without any difficulty on a 100 amp panel.

    How you think you need more than half that is a mystery to me, but I'll let the other guys chime in.

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    DIY Junior Member knied1's Avatar
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    I did an amperage calculation, before I started looking into upgrading the electrical, Lets ignore the things like clocks, radios, cordless battery chargers, and go with the following. 5 lights at approx 1 amp each 5 amps total, Welder at 24.8 (start up) amps Angle grinder 8 (start up) amps, Air compressor 9 runnng, 12.8 (start up) to electric heaters 12.8 amps 25.6 amps total, Mini powder coater 22 amps, this totals 98.2 amps,

    I obviously will not have everything running at the same time, but lest assume lights, Welder, Air compressor, heaters, and a grinder, that equals 76.2 amps,

    Now add into the mix a lathe, or mill, instead of the grinder......

    Do I need to run all of this at the same time?..... No, but why not have the ability if I’m going to upgrade anyway.

    I do not disagree that if I wanted to I could get away with only 50 or 60 amps, but why be in a situation where I can say I wish I would have done this , or changed that?
    Yes when i calculated required amps i used worst case start up amps, and not running amps, but doesnt that add a safety factor?

    Nothing would agrevate me more than being in the middle of a weld, or a cut on either the lathe or mill and have the breaker trip.
    Last edited by knied1; 09-05-2012 at 12:08 PM.

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    DIY Senior Member Homeownerinburb's Avatar
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    Again, I think you are not understanding that when you install a 100 amp panel with a 100 amp service behind it, you have TWO 100 amp legs, which each return down the neutral, unless they are part of a 240 circuit, in which case they return down each other.

    Two 12.5 amp heaters? One on one leg, one on the other.

    The welder of course is 240v. That is a powerful welder you have there. It is drawing current from both legs simultaneously.

    All the 120v stuff is drawing from one leg or the other, and returning down the neutral.

    So if you have a 50 amp panel you have a total potential of 100 amps. If you have a 100 amp panel you have a potential to deliver 200 amps, assuming you can perfectly balance the load.

    In my youth I was a film electrician. We often had to struggle to get the load balanced within a few percent. One day we were on a huge project and were using all of the generator's capacity. Just plugging in a 5k lamp (4.8amps) was enough to shut down the whole system.

    Do what you think best. Copper is expensive.

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