Electrical safety

The path that current takes from hand-to-hand passes through the heart.

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 12 V battery with dry hands, you should not receive no shock. If your hands are wet or sweaty it may be possible to get a shock as this will greatly lower the resistance of your skin and make it more conductive. Systems with nominal voltages above 24 V are capable of giving a shock, but it is generally accepted that a system with a nominal voltage above 50 V is required to be able to deliver a fatal shock. Nontheless, it is a best practice to take all possible precautions, including proper PPE and restricting access to unathorized personnel to avoid any accidents.

If a given 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 3000-20000 V, 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 A can cause a human heart to stop and far less to make you feel pain

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.

Safety with PV

Even with small amounts of sunlight, a PV module will produce voltage. There is no way to stop them from functioning - 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 have voltage and all necessary precautions should be taken.

Safety with energy storage systems

Most batteries do not have a way to disable them - they sit at a steady voltage waiting for a path through which they can supply current. Energy storage systems with a nominal voltage above 48 volts can deliver a potentially lethal shock, but also carry an additional risk due to the tremendous amounts of energy that they store that can be released very rapidly. If an energy storage system is short-circuited it can produce sparks and destructive amounts of heat that can destroy equipment and start fires instantly - this is called an arc flash. The potential for an arc flash increases with the size of the energy storage system. A small system with one or two 12V lead acid batteries with a low Ah rating will not be able to produce an arc flash, but as the size increases beyond this point, so does the potential for an arc flash.

One of the most common accidents that happens when working with batteries is the creation of a short-circuit in the battery bank by dropping a metal tool that provides a low resistance path between the (+) and (-) terminals of a battery. When installing or maintaining batteries, it is best to buy tools that are insulated. If insulated tools are not available where you work or cost prohibitive, then tools can be made less likely to create a short by insulating them with electrical tape.

Batteries should always be handled with extreme caution and carry additional hazards that go beyond electrical hazards. When working with energy storage systems of any kind, the bare minimum amount of personal protective equipment that should be worn is eye protection. Additional PPE should be worn in accordance with the risk created by the particular type of energy storage - this is discussed in more detail in the section that is dedicated to teach type of energy storage. See Lead acid battery safety for more information on safety related to lead acid batteries.

Lock out, tag out

A distribution panel that has been locked out and tagged out.

Following proper electrical safety procedures has saved many lives. One of the most important electrical safety guidelines is called Lock out, tag out. Lock out, tag out means that if someone is working on an electrical system that any potential power sources are disconnected and that the means to reconnect or energize them can only be operated by someone who is authorized to do so. In commercial and industrial environments this is done with a device that includes a lock and a tag that notifies all individuals who to contact about the locked out power source. It is often unnecessary on small projects to follow this same guideline exactly, but the principles of lock out, tag out should always be applied. In off-grid settings final connections should be left undone and marked with tape at the minimum. If the distribution panel or battery box has a lock, it should be locked if no one is working in the area to avoid any accidents.

Safety on new electrical systems

1. Identify if there are any other power sources of electrical systems.
2. Leave any connections that would connect a power source disconnected. These power source connections should be locked out and tagged out.
3. Complete all work possible before energizing the system.
4. Perform all necessary checks on the system.
5. Notify everyone in the vicinity that you are going to energize the system.
6. Energize the system and perform final performance checks.

See Commissioning for more information on energizing a newly installed off-grid system.

Safety on already existing systems

1. Communicate to anyone else that may use the system, or is in the area, that you are going to begin working.
2. Determine what the rated voltage and potential current that the electrical system you are working on can supply.
3. Disconnect the circuit or turn off the system.
4. Use a multimeter to measure to make sure that there is no voltage.
5. Perform lock out, tag out.