How to safely use an inverter in an off-grid solar power system

Power inverters convert 12 or 24V battery voltage up to 230V mains voltage to power appliances that need this. For this reason, they are commonly used with off-grid solar power systems at festivals, and in remote locations. This blog post shows how to ensure that they are used safely.

The formal guidance in this area is provided by the HSE in their document (GS50 edition 4)  'Electrical Safety in Places of Entertainment'. Please click the text to download this for free. Its a long document, so we have reproduced a few key clauses here.

■ Ensure installations and equipment are properly insulated and correctly earthed.

■ At outdoor venues earthing should be by earth rods.

■ make appropriate use of residual current devices (RCDs).

■ Protect sockets for audio equipment with Type A or Type B RCDs having a tripping current of 30 mA. 

■ Locate RCDs in readily accessible positions at the sub-circuit distribution board level to get maximum benefit (each RCD can protect a maximum of six sockets).  

■ Operate the RCD test button at least monthly and test it annually.

■ If a 30 mA RCD trips, it is an indication that there is a fault. Do not ignore it.

Below are a few basic guidelines to assess the risks and steps to follow to ensure that inverters are used safely.

An appliance is plugged directly into the Inverter: If this is the only application, then the risks are minimal, as long as the power cord on the appliance is  less than a meter long. There is no need to provide earthing or an RCD.

An extension lead is in use to power multiple appliances: In this case, the following steps need to be taken.

1.    A metal stake has to be used to provide a local earth, and the earth point on the inverter has to be connected to this.

2.    An RCD device has to be used to protect the user from dangerous earth leakage currents that could flow under fault conditions.

3.    The Neutral has to be bonded to the Earth at the Inverter to stop the Neutral voltage drifting.

Below is a schematic of the set-up.

  

The photos below show the set-up. The RCD switch on the inverter (photo on the right) connects the Neutral to the Earth internally. The RCD is shown (photo on the left) plugged into the inverter. The make and model of the inverter is shown in the middle photo.

The photo below shows the Earth rod, which is connected to the Earth point provided on the inverter.

What are Residual Current Devices (RCDs)? These detect any leakage current of greater than 30mA and break the circuit. They are used to prevent electrocution. The reason that they are set to 30mA can be seen from the diagram below. This shows that currents above 30mA is extremely harmful to humans.

Plugs and sockets for outdoor use: The type of waterproof, 230V plugs and sockets that must be used outdoors, is shown here. 

We hope the information here is useful, when setting up an inverter for use in off-grid applications. Please contact us if you would like more information. seggy@sf-innovations.co.uk