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Old 04-08-2012, 10:26 PM   #1
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Subpanel for the workshop

I have 100 Amps main panel. There is only two empty slots left. I could replace couple 15Amp breakers with a double so I could get potentially one more free spot.

I'm setting up a woodworking workshop in the basement in another area from the main panel. Current needs in the workshop is two 110V 20Amp circuits running at the same time (dust collector and another machine) + 15Amp lighting (I might actually use existing lighting circuit in the basement or combine). However, I'd like to wire two 220V circuits for the future (better dust collector and better table saw / jointer). 2hp machines would only consume 8 Amp of 220V and I don't think I will ever need to beyond that to 3hp that draws up to 15 Amp 220V.

I think the best options would be to install a 220V subpanel in the workshop area so the first question is do I need 40 Amp or 60 Amp subpanel? Its not that far but 40 Amp conduit is cheaper and easier to work with. I think 40Amp would be sufficient.

The second question is whether my 100Amp main panel is enough. Upgrade to 200Amp would be quite expensive and I believe I'm not allowed to do this upgrade myself. I think my current panel is rated up to 125Amp so I could replace the main breakers if my main feed supports that load (I guess I will have to call my Hydro provider?).

Thanks in advance for your replies. I'm in Canada, Ontario if that matters WRT local codes.



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Old 04-08-2012, 10:37 PM   #2
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Before deciding amperage for the panel you need to look at what your main panel is powering now. Electric dryer, heat or air conditioning, water heater or any other large electrical load needs to be considered. If you have no major appliances which consume a large load then you need to consider what your future needs will be in both your home and workshop. It's not rocket science, but a little bit of planning will go a long way.


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Old 04-08-2012, 11:37 PM   #3
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I'd suggest going a step further and actually doing a load calculation. It'll give you a rough idea of what size service you should have before and after wiring up the shed. You can find a bunch of help online for doing the calculation. For example the City of Naperville is one of many that created a spreadsheet to help out

When thinking about the amperage for the workshop, remember you're going to be kicking yourself if you find you need to upgrade in the future. Going with 60 Amp right now isn't going to be much more work or expense. I'd be surprised if PVC conduit was more than a buck a stick more expensive. Now if you want to go IMC or RMC, then it gets to be a different story.

Finally if you do find that you want to upgrade your service to 125, remember there's more to it than just swapping the main breaker. You need to ensure that the POCO's drop, the meter & socket, and you're lines from the POCO's drop to your main breaker are all rated for 125. You may also find that you need to upgrade your grounding electrodes.
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Old 04-09-2012, 10:17 AM   #4
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You can upgrade the work shop with a sub panel fed from the two (2) empty breaker slots in the existing main service panel. It is not required for you to upgrade the service. Rarely will all the circuits be under load and you might just find you have plenty power for both the house and the workshop. So install all the electrical you want in the new workshop. Then if required you can always upgrade the service.
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Old 04-09-2012, 07:43 PM   #5
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Based on the house size, our local code dies require 100 Amp. For a single family residential house, of size larger than certain threshold, 100Amp is required but there is no code requirement to automatically require more than 100Amps. I'll try to do the calculations - I've just bought a local electrical code book but there are quite a few details to consider.

My major 220V appliances are Drier 30A, A/C 30A and Stove 40A. The rest are 15A circuits and there are 19 of them plus 3 dual 15A kitchen split plugs.

In the service size table, a house of my size with up to 12kw range, 4kw drier and 3kw water heater (which I don't have - mine is gas) - service minimum is 100 Amps. Electric hot water boiler and furnace would require some upbraid as well as baseboard heating but I don't have it.

There are guidelines god hot tub and spa but all lower powered appliances (and it spells out examples of central vac up to 12.5A and etc) included in base load. Not sure if my workshop qualifies for base load too but without specific guidelines, I could only assume so.

Thanks for all replies so far. I do tend to chose 60Amp subpanel and not saving on more expensive wire.

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Old 04-09-2012, 07:56 PM   #6
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With dryer ac and stove going all at the same time with the rest of the circuits you are probably using around 75 amps. Do you have an electric water heater too?

You can always upgrade if you start tripping a main. I would go with what you want at the shop.


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