What's on the circuit
Usually lighting circuits are protected by a 15 Ampere breaker. This means that if the total circuit current draw is greater than 15 Amperes, the breaker will trip and open the circuit. It's suggested to only load a circuit to 80% capacity, so the total current draw should only be ~12 Amperes (1440 Watts). The first step in determining if you should add a new receptacle to a circuit, is to determine what's already there and how much power it's sucking. There are many list available online that list the typical wattage of various appliances, that can be used to estimate how much power you're currently using.
Turn off the breaker for the circuit at the main service panel, and make a list of all the items that lost power. Add up the wattage of all the items, and determine if your circuit can handle the load you plan to add.
Electronics and motors don't mix
When motors start (vacuum, circular saw, drill, etc), they draw a large amount of power for a short amount of time. If these items are connected to a circuit that also supplies lights, you may see the lights dim briefly when the motors start. This may or may not be a problem for lights, but you may find that sensitive electronics (TV, computer, etc) don't like it so much.
Blow a fuse, wander through the dark
It's often recommended to keep light circuits separate from other circuits. This is done for the simple fact that if you trip the breaker, it's nice to not be standing in the middle of a pitch black room because of it.
Imagine this
You get your project all ready to be cut, you line the saw up, pull the trigger, and click. You're standing in the dark.
Circular saws tend to be rated 12-15 Amp, which means they'll push most circuits to the limit all by themselves (15A * 120V = 1800W). This is why it's a good idea to not mix lighting and motor loads.
Is the wiring already in place
In some cases, only 2 wires exist at the switch (excluding the equipment grounding conductor). There will be a wire carrying electricity to the switch, and another that carries it to the light when the switch is on (closed). In a situation like this, you'll have to run more wire to connect a receptacle.
In other cases, the power for the circuit passes through the switch box. This is the perfect situation, because you can use the power at the receptacle before interrupting it with the switch. In this situation, you should see 4 wires (2 cables) in the box (not including the equipment grounding conductors, which may or may not be present).
These combination switch and outlet devices typically have four screws:
- 1 silver screw connected to the neutral side of outlet
- 1 brass screw connected to one side of the switch
- 2 dark screws: one is connected to the hot side of the outlet, the other connected to one side of the switch. There is a removable tab that connects the two dark screws together.
The silver screw needs to be connected to the neutral (white) wire.
Leaving the tab in place, you have two ways to connect the hot (black) wire:
- To have the outlet controlled by the switch, connect the hot (black) wire to the brass screw. The dark screws then become a switched hot that you can use to control another device.
- To have the outlet always on, connect the hot (black) wire to one of the dark screws. The brass screw is now a switched hot for controlling another device.
If the tab is removed, then your switch and outlet are disconnected from each other. Wire them as separate devices. If you want to control the outlet with the switch, you'll need to run a wire from the switched side of the switch to the hot side of the outlet.
Best Answer
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.
Earth leakage, a life saver! It is easy to install however it can be costly, but its worth it!
Cables, this flex cable is commonly used
Cables, a shielded copper core flex cable, for extra safety!
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.