Running a dedicated 50A circuit to my garage.

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Old 01-18-17, 07:37 AM
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Running a dedicated 50A circuit to my garage.

Hi,

I know similar things have been asked before but I couldn't find the answer to my exact problem and since we're dealing with electrical wiring I'd like to get this right. Here's my situation:

            I know (read: think) that the best way to do this would be to add a sub-panel to my garage and add separate circuits from there but I don't want to do that and I don't think there's a point of having a 50A sub-panel (if there's such a thing). A 100A sub-panel would make more sense, but everything (wire, conduit, etc.) would have to then be upsized. I already have most of the things and I don't want to just throw them out.

            Does the way I described the circuit work? (i.e. not necessarily best but legal?) Is the wire size adequate? Can I add 2 outlets on the main 50A line, as I described?

            Any and all comments suggestions are much appreciated!

            Thanks,

            -Gabor
             
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              #2  
            Old 01-18-17, 07:49 AM
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            A feeder into a subpanel is a much better solution. You can feed the panel with less than 100 amps. The 100 is the maximum.

            You will not connect a neutral to the breaker. Neutrals connect to afci or gfi breakers.

            The wires need to be in the proper colors since you are using conduit.
             
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            Old 01-18-17, 07:57 AM
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            First of all, number 8 THHN is rated at 50 amperes, not 55. Second, nominal voltage is 240, not 220.

            A sub-panel is not only recommended, it is required in this instance. You cannot have 30 ampere receptacles on a circuit protected to 50 amperes.

            You need FOUR conductors; hot, hot, neutral and equipment ground.

            Plus the items that PC mentions.
             
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            Old 01-18-17, 08:42 AM
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            Thanks for both of your replies. I got the THHN ampacity rating from this chart.

            That I cannot have 30A receptacles on a circuit protected by a 50A breaker makes sense but then what about putting 50A outlets on it?

            I'm leaning towards just doing it via a sub-panel as you suggested, but want to understand what's going on.

            Thanks
             
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            Old 01-18-17, 08:51 AM
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            The 90[SUP]o[/SUP] C. column in Ampacity charts is only used for conductor derating purposes when you have more than three current-carrying conductors in a conduit. This is because there are very few circuit breakers or lugs rated to be used at 90[SUP]o[/SUP] C.

            You technically could use 50 ampere receptacles but then the branch circuit would be way bigger than either machine requires. Manufacturer's usually specify the size of the required branch circuit.
             
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            Old 01-18-17, 09:41 AM
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            Just checked the manuals of my machines and they all only specify the minimum breaker size. These machines all have thermal overload protection on their motors so I'm thinking the machine would shut itself down if it was overloaded and wouldn't rely on the breaker shutting it down anyways. (Is that thinking correct?)

            Thanks again for all the help!
             
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            Old 01-18-17, 10:57 AM
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            Yes, the starter on the machine, whether magnetic or manual, protects the motor from overload but it does nothing for short circuit protection, that comes from the branch circuit protection i.e. circuit breaker.

            For example, lets say the planer has a five horsepower motor on it. That's about 28 amperes at 230 volts. That means the connecting cord would be #10 conductors that are nominally rated at 30 amperes. Now let's say that somehow the cord is severely damaged near the machine and creates a short circuit. With a 30 ampere circuit breaker the CB will trip almost instantaneously probably causing no more damage than to the cord itself. However, with a 50 ampere CB the sparking at the damaged cord lasts for a second or two and might ignite some shavings from the planer. That, in turn, could cause more damages.

            Also, while not an absolute, generally speaking 240 volt machines have dedicated branch circuits.

            Or, you can think about it this way, any appliance will work on a circuit that will supply more amperage than the appliance requires but you don't plug a radio into the 50 ampere electric range receptacle.
             
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            Old 01-18-17, 11:09 AM
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            Alright, alright. I'll do it via a 100A sub-panel, feeding it 60 Amps. Thank you very much again for all your help!
             
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            Old 01-18-17, 11:26 AM
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            If you run 1-inch conduit (could use PVC) all the way you can use the #8 and a 50 ampere circuit breaker. The equipment grounding conductor only needs to be #10 copper for anything less than a 100 ampere CB. This way you can use the #8 wire and it MAY be sufficient but if not you can easily upgrade by removing the #8 from the conduit and replacing it with #6 or even #4 to increase the capacity to maximum of 70 or 90 amperes respectively.

            Note, as mentioned by PC #8 wire cannot be "re-identified" to different colors by a strict code interpretation. BUT many inspectors will allow a homeowner to use colored tape for re-identification. The prohibition is because requiring a contractor to stock different colors in sizes through #6 is not considered a hardship but for the homeowner it is often far less expensive to buy a full spool of one color than to buy three cut lengths of different colors. Check with your inspector before doing the work.
             
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            Old 01-18-17, 11:39 AM
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            I'll probably just run 6-3G NM-B cable in a 1" PVC conduit inside the basement and without a conduit in the crawl space (which is not damp). That way I can go to 60 Amps. Any reservations with this method?

            Also does the sub-panel feeder have to enter the main panel on top? Is it a must? I have very limited space on top of my main panel and it's hardly reachable...
             
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            Old 01-18-17, 12:19 PM
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            Also does the sub-panel feeder have to enter the main panel on top?
            No and often side or bottom is easier.
             
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            Old 01-18-17, 02:51 PM
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            Thanks that would be much easier. I read in a few posts including this one that it must enter the main at the top. Are they wrong or it's just a local strictness in their code?

            Do you happen to know the NEC section that is relevant here?

            Thanks!
             
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            Old 01-18-17, 03:12 PM
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            I think the issue was the size of the available knockouts. It is not a code requirement.
             
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            Old 01-18-17, 03:23 PM
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            If the panel is in an exposed area (like an open basement) you may need to add some framing members or plywood for support and protection of the cable below the panel, but given that there is no problem routing it that way. The cable just can't be hanging loose or exposed directly on the concrete wall.
             
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            Old 01-18-17, 03:26 PM
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            Ok great, thanks! There's no such problem. The main panel is behind a locked door in the basement and framed around.
             
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            Old 01-18-17, 04:14 PM
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            I read in a few posts including this one that it must enter the main at the top.
            I skimmed your link and saw nothing saying they had to. Can you quote or point to the statement in the link? In fact in many cases such as outdoor panels only the service wires enter the top of the panel. If no knock out you can always cut a hole with a hole saw.
             

            Last edited by ray2047; 01-18-17 at 04:33 PM.
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            Old 01-19-17, 07:09 AM
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            Right next to the 4th picture it says "when we ran these wires, we had placed the sub-feed (arrow 2) off to the side. This cable needs to enter the main panel at arrow 1, so we had to re-route the cable behind all those other cables". Arrow 1 points to the top...
             
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            Old 01-19-17, 07:56 AM
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            Right next to the 4th picture it says "when we....
            But they don't really give a reason. I agree with PCBoss
            I think the issue was the size of the available knockouts.
            They just didn't have another knock out and it was easier than making a new hole. Note sometimes the sides are difficult because of partial obstruction by the neutral bar though usually near the bottom below the neutral bar is good. Often bottom is easiest.

            In fact if you will look at pictures you will see when a subpanel is added next to main panel a nipple on the sides of each panel is used.

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