What causes fuses to blow
1. As for the first cause (a short), check all your wires and connection points to ensure they are snug. If a connection point is heating up when the power is on (e.g. extension cord connectors) it indicates a poor connection and the power should be disconnected and the connectors inspected.
2. Demand is too high if the power requirement exceeds the rating of the fuse (and typically there is a buffer as electricians install a circuit with the fuse rating being 20% over the maximum anticipated demand). For BREWHA customers, it is important to ensure that the power supply is understood correctly, and that the correct heaters chosen for the supply. BREWHA offers 208V and 240V heaters and each are designed to provide 5500W of heating at that voltage. Since resistance heaters are designed for output based on the anticipated volts, if a 208V heater is purchased, but is supplied with 240V, the power output will exceed 5500W and the amps will also be higher. Voltage coming to your brewery varies by location and even time of day since local demand on the electrical grid causes it to change. So if the supply is higher than the rating, fuses might only occasionally blow.
3. Solid state relays (SSR) inside the control box enable the brewer to interrupt the amount of power going to the heaters, to permit less than 100% output. Being able to control heater output is useful during mash and fermentation, when reduced power to the heaters can reduce the risk of scorching, and during the boil, to enable control over how much water is being boiled off. Without the SSRs, the power would either be only fully on, or fully off. Power flowing through the SSRs however, does generate heat, and as the temperature of the SSRs increase, they become less effective, drawing more current. So to keep them operating well, it is important to ensure that the box is ventilated and the cooling fan (on larger controllers) is working optimally. During heatup on the fan cooled controllers (this is especially true when the cooling fan was installed in an orientation to draw air out of the box) it is recommended to keep the lid closed so that the fan moves fresh air throughout the box, rather than just past the front plate and out the side. For the single heater controllers without a fan, it is recommended to keep the lid open, and always installed on a wall (never lying flat on a table). Also, the air filters (on some controllers) can severely restrict air flow (especially if dirty) so should not be used unless the controller is in a very dusty environment. For optimal performance, the air temperature inside the control box should remain below 45C/113F.
Volts and amps are relatively easy and inexpensive to confirm and there are lots of videos online about how qualified personnel would go about that. To check heater functionality the resistance can be measured with an ohm/multimeter. The two formulas you need (there is math in brewing!) are: Ohms=Volts/Amps and Amps=Watts/Volts (for the 9500W three phase heaters the Watts for each rod are 1/3 of total).