Electrical safety
Electricity presents a safety challenge as it creates hazards that we cannot see it. The only way to work safely with electricity is to follow all of the necessary precautions all of the time to avoid accidents. Even small electric shocks can be dangerous to humans as the rhythms of our hearts and brains function using electricity and a shock can disrupt these. As always with electricity, voltage, current and resistance all come to play when thinking about safety with electricity. Human skin has a certain amount of resistance that must be overcome for voltage to be able to pass through it. If you touch the positive (+) and negative (-) terminals of a 12V battery with dry hands, you will receive no shock, but a large battery can provide a dangerous amount of current if there is a path for it to flow. But if your hands or wet or sweaty this will lower the resistance of your hands, as water is an excellent conductor, and you may be able to receive a shock. At around 48 Volts electricity can begin to overcome the resistance of the skin on human hands, therefore this is often used as a guideline to distinguish voltages that are safer to work with and those that are more dangerous.
If a voltage is able to overcome the resistance of your skin, then current becomes very important. A static electric shock between your clothing and you may be 3000-20000V, but it does cause anything other than a momentary jolt. Current therefore becomes an important factor in determining how dangerous a particular electrical source is. It depends on the path that an electrical current takes, but as little as .1 or .2 amps can cause a human heart to stop.
Before working on any electrical system we should understand the voltage and amount of current that we are going to be working with. Nonetheless, the safest way to work with electricity is when circuit or system is disconnected and has no voltage. As we cannot see electricity, the only way to be completely sure that a system is off is by using a multimeter to check if there is currently any voltage. The basic steps before starting to work on any circuit or electrical system are as follows:
- Communicate to anyone else that may use the system or is in the area that you are going to begin working.
- Determine what the rated voltage and potential current that the electrical system you are working on can supply.
- Disconnect the circuit or turn off the system.
- Use a multimeter to measure to make sure that there is no voltage.
- Perform "lock out, tag out" which consists of locking the means of turning on a circuit or system to prevent unqualified people from turning it on or reenergizing it unexpectedly.
Safety with PV
Even with small amounts of sunlight, a PV module will produce voltage. There is no way to stop them from functioning. Therefore if there is sunlight, then it should be assumed that a PV module or an array are producing voltage. It is therefore necessary to proceed with caution at all times. Even covering a module with a tarp or opaque covering is typically not sufficient to reduce the voltage to zero as sunlight can still enter from the back of a module. In the case of PV, it is therefore very important on new installations to leave modules disconnected until all other work is finished. On existing installs, circuits connected to PV should always be treated as if they are live and all necessary precautions should be taken.
