I’ll start by saying that this project is at the “probably about six months from now” stage where I’m just starting to make plans. I’ve done a fair amount of house wiring, but I will definitely be working with a licensed electrician on this one.
I have overhead lines running from a pole along the street to my house. I’d like to shift these underground, at least part of the way. They pass above and close to a separate garage building, so my idea was to bring the service down into the garage, install a panel there, and run the service underground from the garage to the house (a distance of around 100 feet). I know I’ll need an in-ground conduit of Schedule-40 PVC, buried 30" deep.
But if I install a panel in the garage, what is now the main house panel will wind up as a sub-panel, right? Are there problems with that?
I realize I’ll have to run four conductors (hot, hot, neutral and ground) from the garage panel to the house. As this is 200-amp service, they will have to be substantial (will 0-0-0 work?). Do all four conductors need to be the same size, or can the ground and/or neutral be smaller? Can these conductors be separate, and thus pulled one-at-a-time through the conduit? (This sounds much easier than having to pull some giant bundled 4-conductor cable).
Any other thoughts on this project would be appreciated.
According the ampacity chart in this PDF document, 2/0 should be satisfactory for your 200-amp service. But, considering the long run, you’ll probably want to bump up to 3/0 (code may even require so; I’ll check if I can find my copy).
Don’t know how it works in your area, but Where I live you have to call the Electrical company out for a meter spot (They tell you where you can bring the service in) I wanted to do the same thing, bring the service in to my garage and run underground to my house then to a new main panel. I was told no.
The neutral(grounded conductor) must be the same size as the hot legs. The ground(grounding conductor) can be of a smaller size.
The house panel will become a subpanel which will some rewiring to accommodate that. Neutrals need to be non-bonded to that panel. If you can make room I would probably add a new bar with a lug sizable for the new neutral and leave the 1or 2 already in there as grounding bars.
For the conduit I would probably use 4" to make it an easy pull and pull all the wires at the same time. If you wanted to use a smaller conduit you could do it by sliding the pcs over the wires rather then pulling the entire length(note assembling a conduit in this manner is not to code but it is a standard procedure for many electricians)
Interesting. I spoke with a guy (lineman) from the electric company who seemed knowledgable and claimed to have seen this sort of thing before. He pointed me to a web page where they outline the requirements, and basically said that if an electrician certifies that the new setup is to Code, they will do the switch.
I will clearly have to get their blessing before proceeding.
I don’t know where you live, but around here where it can freeze a bit, the unofficial recommendation is to go with Schedule 80 pipe. It costs a little bit more but it’s a bit stronger (thicker wall). Code should have no problem with a stronger pipe, at least not that I can find in the 2008 book that I have here.
Moreso than the strength of the pipe, pay very close attention to the specs of pipe diameter, radius and number of bends - service entrance wiring is STIFF. Don’t up the diameter without asking either - if you run 6" pipe thinking it will make for an easier pull, you may find that the utility-provided “meter can” only accepts 4".
Also look into direct-burial SE cable, AKA USE, or Undergound Service Entrance. If you can just trench and lay, vs trench, run pipe and pull cable, it’ll save a bunch of time and labor. My neighborhood is all underground service, and it’s only in pipe for the vertical section where it comes out of the ground and runs into the meter can.
Not long ago, I needed to get four #6 strandeds through 75 feet of flex with three 90 bends. I wound up pulling the wires with the flex laying straight on the ground, then routing and mounting the stuff. Once it’s up, who’d know the difference?
With the service going into the garage and then running to a subpanel in the house, you have grounding issues to look into. Generally, as 2 separate buildings, you will need an approved grounding rod installed at both buildings. It’s likely your garage does not have one now.
Works fine with flex. The code issue is that assembling PVC after the wires have been pulled invites getting PVC cement on the wire’s insulation. Which may cause some melt damage to the insulation which is Not a Good Thing.
I expect you already know that, but some other readers may not have picked up on that.
Though I will certainly defer to my electrician on such matters, this matches my understanding: the system has a single ground, at the main panel. So I will need a proper grounding rod near my garage.
I don’t usually work with electrical systems, but what I have taken away from the NEC training I received is that multiple grounds are ok, but there is only one point of connection between the ground and the grounded conductor (nuetral) and that connection is at the service entrance.