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I have a serious lack of outlets in my garage and that is a problem for a beginner carpenter. I have a light switch by my workbench and was curious if I could change it to a combination outlet + switch?

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@ppumkin is right. Think about this... A typical circular saw is 12Amp (12A x 120V = 1440Watts), which will put a 15Amp circuit at the safety limit ((15A x 120V) x 80% safety factor = 1440Watts). If you do run a circular saw on a light circuit, you will see the lights dim and possible trip the breaker. –  Tester101 Apr 3 '12 at 11:40
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3 Answers 3

Your profile does not indicate where you are from. If you are from the UK, then @ppumkin would be the guy to take advice from. If you are from the USA, I will add my 2 cents!

Short answer is maybe it is possible (I hear so many people cringing now!), truth is back in the 50's & 60's it was kind of accepted. If you have the feed in the switch box, then you can easily add a switch - outlet combination. However as others have warned this is not okay to run heavy tooling with! You should see what other circuits are on the breaker, and if it is the garage only (or lite loaded) you may want to add the outlet for small loads only! That means an occasional hand drill, drop light, etc. I would make the outlet a GFCI type (NEC code requirement for new installs). Some disadvantageous of this are:

  • If the breaker should trip on overload, you will be in the dark.
  • May not be code compliant, check NEC and local codes.
  • Limited to small loads only.

I agree with others, if possible the better way is to run a new circuit. Perhaps a split 120-220V circuit if you plan to do a workshop.

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Your profile does not indicate your location. ppumkin's answer is clearly influenced by European standards... and his answer is certainly correct, accurate and 'safe'.

But I would propose for North America, in his words: The Regulated and safest answer is No. The DIY answer is maybe.

It is common in North American residences to see lighting and outlets on the same circuit. Arguably in these days of low energy lighting fixtures, we tend to have much unused capacity on our 15A or 20A 120V lighting circuits.

How easy you are able to accomplish this would depend on where the power is fed. Sometimes power is at the light fixture with only two conductors being fed to the switch box; other times, you'll see power enter the switchbox then continue to the light. The later situation would be very handy in your circumstance. You could tap off the power to feed your combination switch/outlet.

Things do get more complicated though. For instance, in a garage, your outlet should be GFCI (not something I've seen on those combo switch/outlets). Also, as ppumkin points out, you could easily run into capacity problems depending on whether you're trying to run a 10W battery charger or a 2200W table saw.

Best advice might be to call an electrician for a quote to go over your options. The carpenter thing is a bug (I've been bitten by it), and you might find yourself wanting a subpanel (DB) in your garage to handle the big iron 220V tools in your future.

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@ pilotcam-Great minds think alike! I guess we called that one @ the same time :) –  SteveR Apr 3 '12 at 12:05
    
Im no just influenced by just European, but African too(which is influenced by both States and Europe, However it adopted EU electrical regulations.. because its cheaper) and in my opinion.. better. PS Remember that on 120Volts you get less wattage! 15Amp @ 120V = 1800Watts –  ppumkin Apr 3 '12 at 12:51
    
@ppumkin: Yes, but pilotcam's point is that a garage with its own dedicated circuit for its lights/outlets might fall well short of the 80% rated continuous load you're supposed to put on a circuit (in the case of a 15A 120V circuit, that's about 1450W). A garage with three 100W light fixtures (plenty of light) draws only 300W, leaving over 1100W for power tools, and as you generally only have one tool turned on at a time the "demand load" of a garage branch circuit is one of the lowest in an average house. –  KeithS Apr 3 '12 at 16:43
    
@KeithS - Yes. If that is the assumption and it gets stuck too. No problem. –  ppumkin Apr 4 '12 at 7:42
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The Regulated and safest answers is No. The DIY answer is absolutely not.

Why?

Running carpenter machinery of even the smallest type will use a good 300Watts? Then to the large saw tables or routers that can be anything between 800Watt and 2000Watts.. It can cause an electrical fire and will void any insurance of any kind in any country.

Light Outlet

By building regulation these should be about 1200Watts maximum.. That is 12 100Watt lights bulbs that is easily achieved in 3 rooms with 4 fittings... Also these wires are usually 1.25mm core which is way to small for heavy loads!

Solution

You will have to pull a SEPARATE, or find a separate socket that is handled by 1 breaker for this heavy machinery.

It might take a bit of work but this will be the best and safest way to do it. Pulling power from your DB(Distribution Board) you can put a new 15Amp breaker(220Volt) on the supply phase giving you extra 3300Watts just for your heavy tools. You also want to make sure to have earth leakage connected as this is a life saver in many cases!And that is no joke.

You would pull that using a 5mm2 Solid copper core cable. You can run it along the outside of the wall or in tubing but it MUST be in a shielded coating. If you run it within pipes within the walls unshielded wire is fine.

TIPS

When working on the DB, turn off the Main incoming power, usually a big switch before the DB in newer installations of somewhere outside your house. This can seriously hurt you if you don't.

A DB box should be neatly wired, like this.

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Earth leakage, a life saver! It is easy to install however it can be costly, but its worth it!

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Cables, this flex cable is commonly used

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Cables, a shielded copper core flex cable, for extra safety!

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Alternatives

If you really really cannot do it the proper way for whatever reason then you must seriously think about some safety precautions when connecting to your light switch. At least put a breaker 5amp(@220v = 1000Watts) after the light switch stop overload if any and then wire a plug in. Sometimes you can buy Isolated plugs with build in fuses. Try not to exceed 5AMP. This is highly unrecommended though.

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I like European wiring, it's so colorful. –  Tester101 Apr 3 '12 at 11:31
    
It not just in Europe, but Africa and Australia its the same. –  ppumkin Apr 3 '12 at 12:50
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