Mains power supply

  • Star earthing

As a general rule, all mains power for a “PA system” and any associated “back line equipment” must come from one “Star Point”to reduces the problems of earth loops. This “Star Point” should be as close as possible to the power amplifiers. When a three-phase supply is being used, the PA should be fed from a single phase where possible .The desk and back line power must always be fed from a single phase. This prevents the possibility of the equipment the performer comes into contact with being fed by the more lethal voltages present in multi phase supply, keeping the shock hazard at a minimum.

All earth connections must be connected. If a break in the earth is necessary to stop an earth loop a ground isolator must be used with its earth switch open, do not disconnected a mains earth. This maintains the safety earth while breaking the signal earth.



Note the microphone multicore should be run along side the mains power for the front of house desk to minimise the area of the earth loop between the mike signal cables and the system power.


  •  Mains power Protection

The whole of the power system for the PA system must be protected against earth faults by a 30 mA. earth leakage breaker. Each circuit being fed from the distribution board must be protected from excessive current flow greater than the cabling can cope with using either fuses or over current breakers.

It is preferable that the mains distribution system’s protection is divided up into sensible sub systems. So if a piece of equipment or mains wiring fails, the protection only isolates the part of the system where the fault is, not the whole system.


  • Portable appliance test

A regular PAT must be done on all mains equipment and cables. Every time any mains equipment or cable is used, it must be visually examined for insulation damage and if found, any damage must be repaired before it is used (even though the next PAT is not due)

  • Recommended sub division of mains power

 Circuit 1 Front of  house

  1. Front of house desk
  2. Front of house effects rack

 Circuit 2 Monitor control

  1. Monitor desk
  2. Monitor effects rack

 Circuit 3 Monitor amps

  1. Monitor amps
  2. Monitor system controllers

 Circuit 4 Front of house amps A

  1. Amps A
  2. Amps A system controllers

 Circuit 5 Front of house amps B

  1. Amps B
  2. Amps B system controllers

 Circuit 6 Stage power front

  1. Stage power front left
  2. Stage power front right

 Circuit 7 Stage power rear

  1. Stage power rear left
  2. Stage power rear right



About John Maggs

I have been in the industry and supported many events for many years. I pride myself in providing a personalised service and deliver a first class service.