Fuse Protection

Fuses and Circuit Breakers are the primary means of protection – for technicians working on the system as well as for safeguarding your equipment and wiring against faults.

1) Do you need Fusing/CBs?

• YES
• Fusing, or other circuit protection devices, should be used to protect every connection within the system.

2) Where do you put the fuses/CBs?

• To maximise safety, both for technicians and for the equipment, each circuit and each device in a system should be guarded by a fuse or circuit breaker.

3) Why use so many fuses/CBs?

• The primary function of a fuse or circuit breaker is to sacrifice itself before the wiring is overloaded by an over-current event. Remember, when wiring is overloaded it catches fire! To be avoided at all costs!
• To ensure this, it is best practice to put fuses on every wire, preferably located as close as possible to the highest current end of the wire.

4) How to make the fusing more compact?

• Depending on how you want to build your enclosure, you can choose from a huge range of fusing methods. DIN-mounted fuses are easy to install, easy to label & identify and thus easy to access for testing & maintenance in-line fuses are more fiddly to install, can be hard to access for testing/ maintenance, but can be used to reduce congestion in an enclosure or to reduce
  the enclosure size
• Some Bus Bars allow integration of fixed POSITIVE fuses so can be good for reducing the amount of ‘equipment congestion’ in an enclosure

5) How to size the fusing/CBs?

• Fuses or circuit breakers should be sized for the system voltage, the maximum expected current of the equipment it’s protecting (or less than the wire it’s protecting!) as well as the fault current expected on the wire. Their trip time rating should also be suitable for the expected operating behaviour and/or possible fault characteristics of the equipment (i.e. some loads will have surge start-up currents and any fusing or DB’s on those circuits should be chosen to ensure the surge current doesn’t cause the protections to cut in).

6) When to use Double Pole protections vs POSITIVE only protections?

• Systems with common negative earth wiring design are usually OK with positiveonly fusing.
• Any floating circuits need double pole protection (equipment protective earthing does not count).
• Some equipment is designed for a specific earthing environment while some can be used in floating, positive OR negative earth environments (possibly with minor adjustments to internal fuse arrangements). Check the equipment you’re using is
  suitable for the system polarity of your site.
• Equipment designed for a specific earthing or fusing polarity may require special consideration when used in a system with different polarity. Be sure to check the manufacturer’s recommendations when designing the system.