How to LOTO a PV system

While site specific, general shutdown procedures are the same for PV systems as for standard electrical systems:

1. Announce the shutdown and state the magnitude of the energy (i.e., voltage and current levels).
2. Use a clamp meter, such as the Fluke 393 FC CAT III 1500 V True-RMS Clamp Meter with iFlex to test voltage and continuity.
3. Open circuit breakers, fuses, and leads between modules.
4. Once you have verified there is no voltage in each component, apply the lock and tag to each component with the worker’s name, date, energy sources, isolating devices, magnitude of stored energy, and work being performed.

For PV systems you need to control both the DC (before the inverter), and the AC (after the inverter) sides of the circuit. The steps below describe the process of LOTO procedures for systems that are grid-tied, in which the inverter senses the grid and shuts off when there is no grid voltage present. You should always follow all your organization’s safety and maintenance procedures, as well as NEC regulations when working on PV systems.

DC-side LOTO

PV modules will always have voltage, so you need to LOTO the PV source circuit conductors, which run from the modules to the combiner box, to prevent the DC power from energizing the DC side of the inverter.

1. Disconnect fuses in the DC combiner box to remove parallel connections and isolate individual strings.
2. LOTO the output circuit from the combiner to the DC recombiner, which is found in large-scale PV systems between string combiner boxes and a central inverter.
3. LOTO source circuit leads, also known as home run wires, that run from the modules or battery bank to the combiner box. The leads are the positive and negative ends of a PV string, which is a group of modules connected in series. Use a plug lock or apply a tag without a lock if a lock on the leads is not feasible.

AC-side LOTO

On the AC side, incoming power from the grid will be present and precautions must be taken to isolate and deenergize the PV system.

1. Remove the fuses in the AC combiner, which connects multiple string inverters in large scale systems.
2. LOTO the AC recombiner output circuit between the AC combiner and the grid connection to ensure there is no voltage from the grid.
3. LOTO the low voltage (LV) side of the transformer. If the LV side is not de-energized, AC power may be present on the AC recombiner or central inverter.