Seems to be alot of confusion over wiring, amps, loads, contactors, timers and the like, so I thought I would try and cover some of the basics.
Electricity should be shown a healthy respect, at the end of the day it can kill, and not just from shock, bad wiring can cause fire very easialy. Not the best plan.
Wiring Basics.
All wiring should be colour coded (there are a few exceptions, and i'll cover some later) ALWAYS make sure the right colours get connected together.
Brown/Red = Live
Blue/Black = Neutral
Green/Yellow = Earth
When connecting wires, use appropriate connectors. Junction boxes are ideal as are Central Heating wiring centres, though there are other connectors you can use. At the VERY LEAST use terminal blocks and insulation tape. I'm not recommending that, but bear minimum. Make sure screws are tight, don't leave loose connections. When stripping cable, don't strip to much, and don't damage the remaining insulation.
Also use the right cable. Flex is ideal, minimum 6mm, 10A rating. Earths should always be connected, if the appliance dosen't require an earth, still connect it to the junction box so the cable lenght is still protected by the earth.
You also need to be aware of what load your wiring is subject to. Load is measured in Watts (W), it's the amount of power flowing through a circuit. You can work it out using the following equation
P=IxV where P=Power (watts/W), I=Current (Amps/A) and V = Voltage (Volts/V), as the equipment should be rated in Watts, and we know the voltage, what we need to find is the current, so we re arrange the equation to I=P/V, so 3000w divided by 230v = 13a
Lets do an example to make it clear, let's say we have 500w of HPS lighting, 50w of Fans, and a 20w Heater. Thats a total of 570w. So 570w / 230v = 2.5a. So your main fuse would be 3a, and your cable and connectors would have to be rated to atleast that. With the exception of fuses, bigger load capacity is better. Fuses should be sized to the circuit.
Lighting
There are a few differant types of light used in growing, Flourescent and CFL, HPS and MH. All are ballasted in one way or another. The ballast will draw far more on start up than the rating of the bulb this is called inductive load. General rule of thumb is twice as much. So a 250w bulb ans ballast will draw 500w on startup. Remember to allow for this when working out your ratings, if we go back to the calculation above it works out like this : 1070w/230v = 4.65A, so you would want a 5A fuse.
Timers
There are a veriety of timers available, for starters forget the cheap plug through ones, there meant for table lamps etc. By far the best solution is an immersion heater timer. Around £15.00 at electrical wholesalers, should handle around 3kw (3000w) and inductive loads. Max rating around 13a. Perfect for most setups.
If your timer won't handel the load, your going to need a contactor, this is basically a relay where a low power circuit activates a higher power one. If you need a contactor though it's cheaper to buy a new timer.
Fans (AC)
Fans are pretty low power, but still need wiring correctly. Many people seem to think that a dimmer is fine as a cheap fan control. Wrong.
AC fans are set to work at set voltage (230v) and frequency (50hz) for the UK. A dimmer adds resistance and reduces the voltage. The possibility exists that the fan can stall, the windings then heatup until they either melt, or combust. A fan speed controller reduces the frequency to control the speed of the fan correctly.
Some fans wiring is not colour coded. If this is the case one wire is live and the other is neutral, it dosen't matter which is which.
With everything, make sure you follow manufacturers instructions. Keep yourself and family safe, and if your in doubt ask before turning it on.
I hope people find this useful, and it keeps people safe.
Mellow
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