Emergency Power Supply
EPS or Emergency Power Supply is an option with Fox ESS inverters. It is a separate output from the inverter that is generated using the batteries when grid power is lost.
You need to specifically wire the inverter EPS output to loads that you want to power when the grid is lost. You cannot use EPS to power your whole house through your grid connection / consumer unit. You should note that:
- EPS output is limited to the power rating of your inverter
- Inductive loads, such as motors, can cause the EPS circuit to trip
More detail on the configuration, type of loads and switching that is required are provided in the Fox ESS H1/AC1(G2) User Manual
Fox provides 2 diagrams detailing how to wire the inverter for EPS when using the internal bypass mode:
Alternatively:
Internal bypass mode should not be used for hard wired EPS loads.
Where higher loads or whole house EPS is required, an external change-over or automatic transfer switch should be used.
The main consideration here is how EPS N is connected to local E when the inverter is operating off-grid for Class 2 installations (where applicances are not double insulated and EPS N must be bonded to local E).
In the UK, it is illegal to connect an off-grid power supply to any of the incoming grid connections - this is to avoid the potential for electric shock when engineers are working on the incoming cable and are expecting it will not be made live by the consumer. This includes not connecting EPS N to grid E when operating off-line. To achieve this, the following are required:
- a local earthing rod to ensure the earth conductors remain at ground potential in all normal and fault conditions
- a switch that links EPS N to local earth when the inverter is operating off-grid
- a switch that disconnects grid E from EPS N when the inverter is operating off-grid
An example arrangement with a 3 pole change-over switch is illustrated below:
During normal operation, the 3 pole change-over switch is in the 'up' position. Main and EPS loads are fed from the grid supply via the main and EPS consumer units respectively. Grid E is connected to the local earth (PME as recommended in 18th Edition wiring regulations).
In EPS mode, the 3 pole change-over switch is in the 'down' position. Loads connected to the main consumer unit are not powered. EPS loads are fed from the inverter via the EPS consumer unit. The third pole of the change-over switch disconnects grid E from local earth and connect EPS-N to local earth.
The change-over switch can be manual or automatic. An automatic switch is held in the 'up' position when the grid supply is present and drops to the 'down' position when the grid supply is lost.
Local regulations and established working practices must be followed at all times. Class 2 EPS installations should not be undertaken as a DIY job.
Inverter settings that configure EPS include:
- Enable / Disable: determines if the EPS output is active
- Bypass mode: determines if the internal or external bypass switch is being used
- UPS mode: keeps EPS active through power cycles