So I'm just in the process of running my electrical out to my formed pad. All I have right now is the gravel and want to get the electrical buttoned up so I can move forward with the pour.
The previous owner had buried a wire that was used for an RV plug. This is hooked up to a 50A breaker in the house. The house is a 200A service. Would it make sense to run another wire running off another 50A breaker in the house or should I just replace it and run a new wire big enough for 100A service in the shop?
It would be helpful to know EXACTLY what that existing cable is, in terms of both its AWG and number of conductors, as well as whether it is direct-burial rated or needs to be inside a conduit. I'm not familiar with the applicable codes in your area; but it is not unusual for there to be limits on how many wires/cables can be run through any one conduit.
If I can run 2 cables both off of 50A breakers, can these be tied into 1 panel or would I need 2 separate panels? I'm looking for the most cost effective way to do this since there is a wire there already that I would like to make use of.
Personally, I think you should take a somewhat longer view to this, and make sure you install something which will meet ALL of your needs as far into the future as possible. This is the perfect time to do that (while everything is still easily accessible); and thus, the "savings" of re-using that existing cable may well turn out to be relatively trivial in the overall scheme of things.
Given your mention of two 50A circuits, I'm guessing you plan to have some fairly serious electrical needs in that garage (i.e., compressor, power tools etc.?). Therefore, the way *I* would do it is to replace the existing cable which runs from your home's main service panel with one capable of AT LEAST 100A 120/240-volt split-phase service; then install a dedicated sub-panel in the garage to feed whatever branch circuits will be needed there. If it is feasible/cost-effective, I might even consider upgrading the main service panel to a larger-capacity one (not necessarily physically larger), then run 150A or 200A out to the garage; OTOH, this may well be overkill, depending on your actual plans/needs.
The shop is basically going to be used for parking 2 vehicles and then project vehicles in the other half. I do have a 220v welder to be hooked up and will be running in-floor heat. Other than that U shouldn't have much need for and huge power needs.
I gather that "in-floor heat" will be electric, as opposed to hot water? In which case, that will likely be a significant load in and of itself. Using this as a pot-shot example:
http://www.homedepot.com/p/WarmWalk...ting-Mat-Covers-180-sq-ft-WW120-240/203993037
That covers 180 ft.^2 (about the equivalent of one smallish garage bay) and draws 2,160 watts (or about 9.5 Amps @ 230V). Extrapolate from there, depending on the size of your garage. For a typical "large 2-car" garage with a floor area of perhaps 600 ft.^2, you'd need three times that much, or nearly 30A just for the heat (maybe more, given your far-north climate).
The welder will likely require its own dedicated branch circuit (from the sub-panel); the required ampere capacity will depend on the particular welder; but 30-40A is not uncommon.
Between those two things, you've already consumed 50-60A of your sub-panel's capacity, before you even get to lighting and other power tools. Now granted, you can "over-draw" the main breaker to some extent, based on the theory that you won't be using everything at once; but you should not push this for more than it is worth. In a perfect world, the sum of all your branch-circuit breakers does not exceed the main breaker capacity.
I realize the US codes and Canadian codes vary quite a bit but was just looking for an overall opinion and what is best to do. Thanks!
At this stage in the game, when everything is wide open, your mantra should be the old "Hot Rodder's Maxim":
Code:
If 'some' is good,
And 'more' is better,
Then 'too much' ought to be just about right.
One side note, with respect to your upcoming slab pour: Make absolutely sure that the slab is THOROUGHLY insulated, both from underneath and at all edges. Most folks use two-inch polyisocyanurate foam boards for this. That's fine, as far as it goes; but that "Hot Rodder's Maxim" also applies here -- in spades. The cost to make that two (or even three) layers thick before you do the pour is relatively minor, as compared to the savings it will provide over the long haul.
Good luck!
