sub panel in garage
#1
sub panel in garage
I am working on a project to put a sub panel in a detached garage. From what I've gleened from websites and this forum the proper way to do this would be THWN wire in PVC conduit buried a miniumum of 18".
My questions are this, given that the panel will be approx 80' from main panel and I will feed it with a two pole 50 A breaker what wire size and conduit size is appropriate. I think 6 AWG in a 3/4" PVC is correct but..
Also I believe I can transition from the THWN to NM once inside the basement of the house using a junction box, any problems there?
Also what is the deciding factor if I need to run a seperate ground to the panel.
My questions are this, given that the panel will be approx 80' from main panel and I will feed it with a two pole 50 A breaker what wire size and conduit size is appropriate. I think 6 AWG in a 3/4" PVC is correct but..
Also I believe I can transition from the THWN to NM once inside the basement of the house using a junction box, any problems there?
Also what is the deciding factor if I need to run a seperate ground to the panel.
#2
What you said sounds good.
If you have a noncurrent carrying metallic path such as a metal water pipe connecting the two buildings then you must install a four wire feeder being two hots, one neutral, one grounding conductor. A four wire feeder dictates that you separate the neutral and grounding bars in the panel of the second building and install a grounding electrode conductor also on that second building.
If you have no noncurrent carrying metallic path between the two buildings then you may install a three wire feeder installing a new grounding electrode at the second building. A three wire feeder dictates that the neutral and grounding bar in the panel in that second building be married together as one entity.
Hope this helps
Wg
If you have a noncurrent carrying metallic path such as a metal water pipe connecting the two buildings then you must install a four wire feeder being two hots, one neutral, one grounding conductor. A four wire feeder dictates that you separate the neutral and grounding bars in the panel of the second building and install a grounding electrode conductor also on that second building.
If you have no noncurrent carrying metallic path between the two buildings then you may install a three wire feeder installing a new grounding electrode at the second building. A three wire feeder dictates that the neutral and grounding bar in the panel in that second building be married together as one entity.
Hope this helps
Wg
#4
In that junction box, what is the best way to connect such large wires? I was preusing the local home center and couldn't spot anything suitable for wires larger than #8 -10.
Seems like a foolish question, but what do splice the big boys with?
Mondo
Seems like a foolish question, but what do splice the big boys with?
Mondo
#5
i've gathered that i can run a four wire service and that i need to add a "grounding electrode", pretty sure this means grounding rod. I've seen elsewhere that the rod must be 1/2" x 8' but i'm a little unclear on wether or not i need two if there are no other grounding electrodes in the garage(water pipes etc).
Any thoughts on how many ground rods i need to add and how far below the surface does the top of the rod need to be?
Answereing the question above regarding slicing #6 wire, i think the correct way to do this is with "burndys" they are a cable clamp. i've also seen inline cable splices, sort of like a butt slice you would crimp but the larger ones have set screws.
thanks
Any thoughts on how many ground rods i need to add and how far below the surface does the top of the rod need to be?
Answereing the question above regarding slicing #6 wire, i think the correct way to do this is with "burndys" they are a cable clamp. i've also seen inline cable splices, sort of like a butt slice you would crimp but the larger ones have set screws.
thanks
#6
The NEC states that any grounding electrodes listed in 250.50 must be used as the grounding electrode system IF AVAILABLE. 250.50 lists water pipe in contact with earth for 10' or more, rebar in concrete, wire mesh in concrete, a grounding conductor that encircles the building located below the footing of the structure, and others. If non of the above is available then you must use a made electrode such as a steel plate or ground rod etc. The NEC requires a grounding electrode to meg less than 25 ohms to ground. This leaves it open to interpretation of the AHJ [electrical inspector] in your area. Some AHJs put the burden of proof on the electrician to prove that one ground rod megs less than the maximum of 25 ohms to ground. Some AHJs put the burden of proof on the AHJ to prove this 25 ohm limit is not being met before a second ground rod is required. No one seems to want to perform a megging of a ground rod. If the AHJ pushes it then it would be much easier to install the second rod rather than go through a documented megging process to read the ohms to ground the rod produces. Electricians take the easy way rather than buck the AHJ.
A ground rod is required to be protected from physical damage. If you bury the end of the rod below sod then you have performed that function of protecting the rod and its connection from physical damage.
A large conductor can be spliced by use of a key tap, split bolt, H clamp, or any other compression connection listed and labeled for the conditions and the size and type of conductor. Split bolts seem to be the norm.
HandyRon has a good point. YOu may not have a noncurrent carrying metallic path between those two buildings now buy may desire to install one at a later date. Installing an equipment grounding conductor as a part of the feeder serving that accessory building would give you future options to install a non current carrying metallic path such as a water pipe at a late date. Most commonly water is served to an accessory buildng in black plastic rather than metallic piping though in my opinion.
Remember that if you do install an equipment grounding conductor as part of that feeder connecting to the accessory building to separate the grounding and neutral bar in that panel in that detached structure.
Also remember that you must have a main breaker in that panel in that accessory building unless you have a maximum number of breaker switches of 6 for branch circuits that these 6 breakers may serve as main breakers just remember you have a limit of up to 6 main breaker serving a building.
Hope this helps
Wg
A ground rod is required to be protected from physical damage. If you bury the end of the rod below sod then you have performed that function of protecting the rod and its connection from physical damage.
A large conductor can be spliced by use of a key tap, split bolt, H clamp, or any other compression connection listed and labeled for the conditions and the size and type of conductor. Split bolts seem to be the norm.
HandyRon has a good point. YOu may not have a noncurrent carrying metallic path between those two buildings now buy may desire to install one at a later date. Installing an equipment grounding conductor as a part of the feeder serving that accessory building would give you future options to install a non current carrying metallic path such as a water pipe at a late date. Most commonly water is served to an accessory buildng in black plastic rather than metallic piping though in my opinion.
Remember that if you do install an equipment grounding conductor as part of that feeder connecting to the accessory building to separate the grounding and neutral bar in that panel in that detached structure.
Also remember that you must have a main breaker in that panel in that accessory building unless you have a maximum number of breaker switches of 6 for branch circuits that these 6 breakers may serve as main breakers just remember you have a limit of up to 6 main breaker serving a building.
Hope this helps
Wg
#7
Wg, just to be clear on your last point concerning the need for a main breaker in the sub panel.
If the sub panel has more than six breakers then it needs a main breaker? Otherwise, none needed?
Does it make any difference if these six breakers are single pole or two pole? I'm probably going to have 2 two pole and four single pole.
Thanks for your help, grounding info was clear and very helpful.
I'm definitely going to pull a fourth grounding wire in the pipe. I think I can make that ground a #8 THWN rather than a #6. Does this sound right for a 50A service?
If the sub panel has more than six breakers then it needs a main breaker? Otherwise, none needed?
Does it make any difference if these six breakers are single pole or two pole? I'm probably going to have 2 two pole and four single pole.
Thanks for your help, grounding info was clear and very helpful.
I'm definitely going to pull a fourth grounding wire in the pipe. I think I can make that ground a #8 THWN rather than a #6. Does this sound right for a 50A service?
#8
You are fine with what you are saying. Just remember that if the panel in the detached garage is with an equipment grounidng conductor installed with its feeder to that detached garage the panel must be wire as a sub panel with the neutral bar and grounding bar separated from each other yet this is a detached structure and a ground rod will be requried. Also being a detached structure it must have a main breaker with a maximum number of main breaker totalling 6. The stroke of hte hand counts as a main breaker. A single pole or a double pole is considered as one stroke of the hand therefore counted as one main breaker whether single pole or double pole breaker.
If you are installing initially 6 breakers whether you have double pole or single pole then then can be the 6 main breakers. However if it were me I would buy a panel that has room for expansion and install the main breaker in your case or you won't be able to add branch circuits to that panel in the future.
Hope this helps
Wg
If you are installing initially 6 breakers whether you have double pole or single pole then then can be the 6 main breakers. However if it were me I would buy a panel that has room for expansion and install the main breaker in your case or you won't be able to add branch circuits to that panel in the future.
Hope this helps
Wg