BREWHA recommends that home brewers consider having a GFCI (GFI) installed between a power source and an Electric Water Heating Element. A GFCI is defined as:
A ground fault circuit interrupter or Residual Current Device (RCD) is a device that shuts off an electric circuit when it detects that current is flowing along an unintended path. It is used to reduce the risk of electric shock.
You have probably already seen a 120V GFCI as most washrooms have one installed on the receptacle used for shavers and hair dryers.
Breaker boxes (the electrical panel often found in laundry rooms) will prevent too much overdraw but a GFCI will respond faster than a breaker to any deviation in electrical current.
A GFCI can be installed in an existing breaker box (if not already there), or one can be added on the line servicing your brewing setup. GFCI panels that service outdoors spas/hot tubs (240V/40A) are readily available at Home Depot, Amazon or other electrical or hardware stores and at around $200 are relatively inexpensive. Speak with an electrician for details.
A method that does not require electrical install, but works only with non-digital power boxes* is to purchase a 240V extension cord that has a GFCI built in to it. One end connects to the Heating Element cord, and the other end plugs into the Power Box. A GFCI extension cord can be purchased from electrical wholesalers such as Stay Online and McMaster-Carr (Model 7348K42). The cord should have an L6-30 plug and receptacle, to work well with the Heating Element and Power Box.
(*Some portable GFIs do not work with the Digital Power Box on <100% power output as the power output reduction causes the GFI to trip. If you are using the Digital Power Box it is recommended to use a GFI—such as the spa panel discussed above—placed prior to the Power Box.)