Prepare the Physical Site

Your computer system must have a stable, reliable source of electrical power to function properly. Your physical site must meet certain minimum requirements to provide the power your system needs. Please follow these requirements carefully.

By doing so, you can avoid a number of problems, such as lock-ups and file corruption, that can affect computers on overloaded, poorly grounded circuits.

It is critical all computer-related equipment be powered by circuits using the following electrical guidelines:

• Always follow local codes.
• Use a 120-volt 60Hz, single-phase power source for all computer-related equipment.
• Put the CPU and monitor on a dedicated 20 Amp circuit with an isolated safety ground (one hot, one neutral, and one isolated safety ground).
  
  Do not connect any electrical device other than the CPU and monitor to this circuit.
• Use a battery backup that offers line voltage regulation with transient protection and noise filtration to power the CPU and monitor. You can do this with a battery backup system, such as the Powerware 5119 Uninterruptible Power System, or equivalent.
• Connect peripheral devices, including terminals, printers, multiplexers, modems, and so on, using 20 Amp circuits with a maximum of three duplex receptacles per circuit.
  
  These circuits must be three wire, dedicated circuits with isolated grounds; do not daisy-chain neutrals or safety grounds from other circuits. Also, the load cannot exceed 60% of the circuit's rated capacity. For example, for a 20-amp breaker, the maximum load is 12 amps.
  
  DDMS recommends that all computer circuits originate from one electrical panel, if possible.
• Use receptacles with an isolated ground on computer circuits.
• Install a 420-Joule electronic surge protection device on all computer-related equipment.
• Place laser printers, copy and fax machines, electrical space heaters or other non-critical equipment on a circuit that does not contain computer equipment.
• Never cut or remove the third (ground) prong from the power cord plug.
• Avoid using extension cords. If one needs to be installed, use a three-wire SO or SJ cord with minimum #12 conductor.
• Make sure that each three-prong receptacle is properly grounded. If you're not certain, have them checked by a qualified electrician or contact LED Enterprises at 888-566-1615. (LED Enterprises are computer power specialists who can work closely with DDMS customers to ensure that their sites provide a good power source for their computer systems.)
• Ensure that computer panels have isolated safety ground and neutral bus bars. EXCEPTION: Computer Panel is the Main Service Panel.
  
  Use shoulderless set screws on all neutral and safety ground bus bars (one wire per set screw).
• Ensure that the voltage hot to neutral for computer receptacles is 120 (-9+6) volts.
• Understand that the sizing of the phase, neutral, and safety ground wires is critical. The National Electrical Code (NEC) specifies the minimum wire size you can use for personal and equipment safety. To obtain a higher degree of integrity for a computer circuit, make these wires one size greater than the NEC specifies.
• Verify the Xo bond (the bonding of the neutral and safety ground bus) at the main service entrance and new power sources, such as a step-down transformer.
  
  Install full-sized insulated wires from the Xo bond to reference points: cold water pipe, building steel and/or earthing ground rods (check local codes).
• Sizing of the safety ground reference to the sub-panels is critical. For distances of less than 100 feet, the size of the safety ground should be the same as that of the supply conductor. For distances of more than 100 feet, the safety ground should be one size larger than the supply conductor. This conductor should be insulated and reside in the supply conduit.
• It is extremely important that all safety grounds return to the service entrance to establish a single point of reference to earth. Refer to Section 250, paragraph 54 of the NEC.

If you need a battery back-up for your system, you can order one from LED Enterprises using this form (pdf). This form is in Acrobat format; you can print it, fill it in, and fax it. (To return to this page, click your browser's Back button.)