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Thread: Looking for some help on garage sub panel

  1. #16
    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.

  2. #17
    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.

  3. #18
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Homeownerinburb View Post
    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.
    So if you have a 50 amp panel you have a total potential of 50 amps. If you have a 100 amp panel you have a potential to deliver 100 amps.

    You are correct that current will travel on both legs of the 240 volt circuit with any unblanced load on the neutral.
    If the current is flowing on the two legs of the 240 volts then the current will not exceed what is between the two unless there is current on the nuetral and the amount on the neutral will be the higher leg minus the lower leg.

    In other words if the panel was protected with a 50 amp breaker and there was 50 amps on one leg and 40 amps on the other leg the neutral would be carrying 10 amps. The total amps on the breaker would be 50 amps not 90 amps.

  4. #19
    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by jwelectric View Post
    So if you have a 50 amp panel you have a total potential of 50 amps. If you have a 100 amp panel you have a potential to deliver 100 amps.

    You are correct that current will travel on both legs of the 240 volt circuit with any unblanced load on the neutral.
    If the current is flowing on the two legs of the 240 volts then the current will not exceed what is between the two unless there is current on the nuetral and the amount on the neutral will be the higher leg minus the lower leg.

    In other words if the panel was protected with a 50 amp breaker and there was 50 amps on one leg and 40 amps on the other leg the neutral would be carrying 10 amps. The total amps on the breaker would be 50 amps not 90 amps.
    Fine. Not to be pedantic: assuming all the loads are at 120v, and the panel is protected with a 50 amp breaker, then one could have a total of 100 amps of demand going.

    If one had a single 240v demand of 10 amp, then the total ampacity you could deliver at 120v would be 80.

    40 on each leg.

    Do you have an opinion on how much ampacity this guy actually NEEDS?

  5. #20
    DIY Junior Member knied1's Avatar
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    Homeownerinburb,

    I dont understand why you are pushing this soo much. My father had 50 amps feeding his workshop, and the breaker would pop every now and then, he raised it, since i will actuially be running more than he is i am going 100 amps. it is not like i am doing anything that is dangerious..... actually i am going far out of my way to make sure i am doing this the safe way. Since his breaker poped that is proof enough for me........ that is that.
    I do not disagree that when everything is at its running draw i will have more than i need, but it is not at all unrealistic that a compressor will cycle, heaters turn on and off to maintain heat, i do not want to be under powered.

    Have you ever used a saw, and the lights dimmed on start up, and you needed to move something to a different plug?

    Well trust me when you fire up a boreing mill the initial startup has a draw.

    can we get past this now???????

  6. #21
    DIY Junior Member knied1's Avatar
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    Quote Originally Posted by jwelectric View Post
    URD cannot enter either building for even one half inch. In the event of a fire the insulation is toxic.

    If you want to run from panel to panel the use THW conductors, the price will be a little higher but the benefits outweigh the price.
    jwelectric,

    I MUST be missing something..... I did contact my local town building code office, They forwarded me to the Electrical Inspector / Code Enforcement officer. I told him what i am doing, and asked if he had a recomendation on where to purchase my materials. He told me to just go to Home Depot, and get their 100 amp feed. I told him about how i was told the insulation is toxic if there was a fire, and he said that all wire insulation is toxic, and inside of conduit the intention is that my family would have more than enough time to excape........ I can only assume that there are some markings on the wire i am missing. I do know that it has URD on it, but are ther other markings that may dual rate the wire? Could the rules be different in different states?
    I am not saying you are wrong. If the wire is URD only i will go another route.

    I just simply like to understand as much as i can, I figure the more i know, and the more homework i do, the less mistakes i will make

  7. #22
    Electrician ActionDave's Avatar
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    Quote Originally Posted by knied1 View Post
    ........ I can only assume that there are some markings on the wire i am missing. I do know that it has URD on it, but are ther other markings that may dual rate the wire? Could the rules be different in different states?
    I am not saying you are wrong. If the wire is URD only i will go another route.

    I just simply like to understand as much as i can, I figure the more i know, and the more homework i do, the less mistakes i will make
    Most URD is dual rated- it has more than one set of letters URD, RHW or some other alphabet soup.

    I would go to Home Desperate and buy 2-2-4-6 tri-rated mobile home feeder, tag it to a ninety amp breaker to feed the shop, and never look back.

  8. #23
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Homeownerinburb View Post
    Fine. Not to be pedantic: assuming all the loads are at 120v, and the panel is protected with a 50 amp breaker, then one could have a total of 100 amps of demand going.

    If one had a single 240v demand of 10 amp, then the total ampacity you could deliver at 120v would be 80.

    40 on each leg.

    Do you have an opinion on how much ampacity this guy actually NEEDS?
    This is totally incorrect. The rating on the handle of a breaker is what that breaker will carry. A two pole 50 amp breaker is rated at 50 amps of 240 volts or it is rated at 50 amps per leg. They don’t add up.

    Look at your dryer and range breakers and the neutral conductor that is installed with each one. If the two poles of the thirty amp breaker would add to 60 amps they why is the white conductor supplying that dryer not a #6 instead of a #10 if the two added to 60 amps?

  9. #24
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by knied1 View Post
    jwelectric,

    I MUST be missing something.....
    As Dave has pointed out most URD is dual rated but a lot of times it is not.

    If the conductor is not listed in table 310.104(A) of the 2011 code cycle then it can’t be used. You won’t find URD listed there because it is a utility conductor and not one that is allowed to be installed in the premises wiring by us.

    Many inspectors think that if it can be bought at some supply house then it is okay to install. This if not true, it must be listed in the NEC or it can’t be used.

    Is it used? Yes many times but that don’t mean that it is right. I would never install URD for anyone for any reason simply because should the insulation burn someone might die. Never and I repeat never bring URD to the inside of any building unless it is a dual rated conductor.

    Edited to add;

    It is fine to install the 90 amp feeder to the garage if this is what you want to do. The 90 amp breaker you install to protect the #2 conductors you are installing is just that, 90 amps. It does not add up to 180 amps of 120 volts of current. It is 90 amps period.
    Last edited by jwelectric; 09-06-2012 at 04:53 AM.

  10. #25
    DIY Junior Member knied1's Avatar
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    OK, hopefuly this will be the last question....questions

    I am looking into the grounding rods, there are both Galvanized and Copper, I am assuming that copper is the way to go. Does 5/8" or 3/4" matter? Does the grounding rod have to be out side the structure, or can i core drill thru the sill plate, and concrete then drive the grounding rod inside the garage this way i dont have somethin to trip on, and trim around when cutting the grass.

    FYI i will be borrowing a 3/4" hammer drill from my work, and making up an adaptor for driving the grounding rod.

    Thanks again

  11. #26
    Electrical Contractor/Instructor jwelectric's Avatar
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    Outside and 5/8 galvanized drives easier than copper. Use a "T" post driver and it goes down very easy.

  12. #27
    DIY Junior Member knied1's Avatar
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    jwelectric,

    Thanks again

    Just an FYI

    What we do where i work is take a of pipe where the id is a little bigger than the diameter of the rod, and weld a piece of round bar to it, then if you set the hammer drill to hammer only mode it will drive the rod in super easy and fast. I looked around a little bit and we already have some made up for 5/8" and 3/4 diameters

    We drive 3/4" re-bar 20 ft long in no exageration about 2 minutes. We just dig a hole about the size of a pop can, and fill it with water set the end of the re-bar in the middle of the hole and drive it down.

    Where i work we build bridges, and sometimes need to drive re-bar to shore up for our crane matts.

  13. #28
    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by jwelectric View Post
    This is totally incorrect. The rating on the handle of a breaker is what that breaker will carry. A two pole 50 amp breaker is rated at 50 amps of 240 volts or it is rated at 50 amps per leg. They don’t add up.

    Look at your dryer and range breakers and the neutral conductor that is installed with each one. If the two poles of the thirty amp breaker would add to 60 amps they why is the white conductor supplying that dryer not a #6 instead of a #10 if the two added to 60 amps?
    Oh, jeepers.

    If he has a panel that has a 50 amp breaker, then he can have 50 amp of demand at 120v on one side of the phase and 50 amp of demand at 120v on the other side of the phase.

    50 plus 50 equals 100. No, he cannot have a 60 amp load on one side of the phase and only have a 40 amp demand on the other side, and have the breaker hold.

    I suppose there are people out there dull enough not to get that. I am not one of them.

  14. #29
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Homeownerinburb View Post
    Oh, jeepers.

    If he has a panel that has a 50 amp breaker, then he can have 50 amp of demand at 120v on one side of the phase and 50 amp of demand at 120v on the other side of the phase.

    50 plus 50 equals 100. No, he cannot have a 60 amp load on one side of the phase and only have a 40 amp demand on the other side, and have the breaker hold.

    I suppose there are people out there dull enough not to get that. I am not one of them.
    My friend if he has a 50 amp breaker and he has 50 amps of 120 volts on one side and he has 50 amps on the other side he would have a total of 50 amps at 240 volts and there would be no amps on the neutral.

    Using your analogy of 50 amps on one side and then 50 amps on the other side there would be 100 amps on the neutral which is not true. If there was 50 amps on one side and 40 amps on the other side there would only be 10 amps on the neutral.

    I suppose there are people out there dull enough not to get that and you are one of them.

  15. #30
    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by jwelectric View Post
    Using your analogy of 50 amps on one side and then 50 amps on the other side there would be 100 amps on the neutral which is not true.
    I wrote nothing of the sort and I don't understand why you insist on distorting my comments.

    And you can take your insults and insert them.

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