Electrical Factors




	NOTE: Electrical practices and suggestions in this guide are based on North American practices. For regions and areas outside North America, local electrical codes will take precedence over North American electrical codes. An example would be the recommendation that the PE (Protective Earthing) conductor be green with yellow stripes. This requirement is a North American directive and does not override the local code requirements for a region or area outside North America. Local Authority Has Jurisdiction (LAHJ) and should make the final decision regarding adherence to region-specific or area-specific electrical codes and guidelines. The LAHJ acronym is used throughout the section to denote that local authority has jurisdiction.

Proper design and installation of a power distribution system requires specialized skills. Those responsible for this task must have a thorough knowledge and understanding of appropriate electrical codes and the limitations of the power systems for computer and data processing equipment.

In general, a well-designed power distribution system exceeds the requirements of most electrical codes. A good design, when coupled with proper installation practices, produces the most trouble-free operation.

A detailed discussion of power distribution system design and installation is beyond the scope of this information. However, electrical factors relating to power distribution system design and installation must be considered during the site preparation process.

The electrical factors discussed in this section are:

Computer room safety
Power consumption
Electrical load requirements (circuit breaker sizing)
Power quality
Distribution hardware
System installation guidelines

Computer Room Safety

Inside the computer room, fire protection and adequate lighting (for equipment servicing) are important safety considerations. Federal and local safety codes govern computer installations.

Fire Protection

The National Fire Protection Association’s Standard for the Protection of Electronic Computer Data Processing Equipment, NFPA 75, contains information on safety monitoring equipment for computer rooms.

Most computer room installations are equipped with the following fire protection devices:

Smoke detectors
Fire and temperature alarms
Fire extinguishing system

Additional safety devices are:

Circuit breakers
An emergency power cutoff switch
Devices specific to the geographic location for example, earthquake protection

Lighting Requirements for Equipment Servicing

Adequate lighting and utility outlets in a computer room reduce the possibility of accidents during equipment servicing. Safer servicing is also more efficient and, therefore, less costly.

For example, adequate lighting reduces the chances of connector damage when cables are installed or removed.

The minimum recommended illumination level is 70 foot-candles (756 lumens per square meter) when the light level is measured at 30 inches (76.2 cm) above the floor.

Working Space for Server Access

The recommended working space for performing maintenance on the server is three feet. The work space shall permit at least a 90° opening of equipment doors or hinged panels. When planning for the working space area, consider whether access to the server will be at the front, side, or rear of the server.

Power Consumption

When determining power requirements, you must consider any peripheral equipment that will be installed during initial installation or as a later update. Refer to the applicable documentation for such devices to determine the power required to support these devices.

Electrical Load Requirements (Circuit Breaker Sizing)




	NOTE: Local Authority Has Jurisdiction (LAHJ) and should make the final decision regarding adherence to country-specific electrical codes and guidelines.

It is good practice to derate power distribution systems for one or more of the following reasons:

To avoid nuisance tripping from load shifts or power transients, circuit protection devices should never be run above 80% of their current ratings.
Safety agencies derate most power connectors to 80% of their current ratings.

Power Quality

The intended source voltage for Telco systems is -48 VDC. The hp Integrity cx2600 Server is designed to operate over the range of -40 to -60 volts DC nominal. The server utilizes a DC to DC power supply to provide stable operation with a uniform internal voltage.

Sources of Voltage Fluctuations

Voltage fluctuations, sometimes called glitches, affect the quality of electrical power. Common sources of these disturbances are:

Fluctuations occurring within the facility’s distribution system
Utility service low-voltage conditions (such as sags or brownouts)
Wide and rapid variations in input voltage levels
Electrical storms
Faults in the distribution system wiring (such as loose connections)

Power System Protection

The hp Integrity cx2600 Server can be protected from the sources of many of these electrical disturbances by using:

A dedicated power distribution system
Power conditioning equipment
Over- and under-voltage detection and protection circuits
Screening to cancel out the effects of undesirable transmissions
Lightning arresters on power cables to protect equipment against electrical storms

Precautions have been taken during power distribution system design to provide immunity to brief power outages. However, testing cannot conclusively rule out loss of service. Therefore, adherence to the following guidelines provides the best possible performance of power distribution systems for HP computer equipment:

Dedicated power source—Isolates an hp Integrity cx2600 Server power distribution system from other circuits in the facility.
Low-voltage detectors—Shuts equipment down automatically when a severe power disruption occurs. For peripheral equipment, these devices are recommended but optional.

Distribution Hardware

This section describes wire selection and the types of raceways (electrical conduits) used in the distribution system.

Wire Selection

Use copper conductors instead of aluminum, because aluminum’s coefficient of expansion differs significantly from that of other metals used in power hardware. Because of this difference, aluminum conductors can cause connector hardware to work loose, overheat, and fail.

Raceway Systems (electrical conduits) (LAHJ)

Raceways (electrical conduits) form part of the protective ground path for personnel and equipment. Raceways protect the wiring from accidental damage and also provide a heatsink for the wires.

Any of the following types may be used:

Electrical metallic tubing (EMT) thin-wall tubing
Rigid (metal) conduit
Liquidtight with RFI shield grounded (most commonly used under raised floors)

Building Distribution

All building feeders and branch circuitry should be in rigid metallic conduit with proper connectors (to provide ground continuity). Conduit that is exposed and subject to damage should be constructed of rigid galvanized steel.

Grounding Systems

Power Distribution Safety Grounding (LAHJ)

The power distribution safety grounding system consists of connecting various points in the power distribution system to earth ground using green (green/yellow) wire ground conductors. Having these ground connections tied to metal chassis parts that may be touched by computer room personnel protects them against shock hazard from current leakage and fault conditions.

Power distribution systems consist of several parts. HP recommends that these parts be solidly interconnected to provide an equipotential ground to all points.

Main Building Electrical Ground

The main electrical service entrance equipment should have an earth ground connection, as required by applicable codes. Connections such as a grounding rod, building steel, or a conductive type cold water service pipe provide an earth ground.

Electrical Conduit Ground

All electrical conduits should be made of rigid metallic conduit that is securely connected together or bonded to panels and electrical boxes, so as to provide a continuous grounding system.

Power Panel Ground

Each power panel should be grounded to the electrical service entrance with green (green/yellow) wire ground conductors. The green (green/yellow) wire ground conductors should be sized per applicable codes (based on circuit over current device ratings).




	NOTE: The green wire ground conductor mentioned above may be a black wire marked with green tape (LAHJ).

Computer Safety Ground

Ground all computer equipment with the green (green/yellow) wire included in the branch circuitry. The green (green/yellow) wire ground conductors should be connected to the appropriate power panel and should be sized per applicable codes (based on circuit over current device ratings).

A ground lug is provided on the chassis rear panel. Refer to “Grounding”.

Dual Power Source Grounding

When dual power sources are utilized, strong consideration should be given to measure voltage potentials. The use of dual power might create an electrical potential that can be hazardous to personnel and might cause performance issues for the equipment.

Dual power sources might originate from two separate DC sources. Voltage potentials from ground pin to ground pin of these sources should be measured and verified to be at or near 0.0 volts. Voltage levels that deviate or are measured above 3.0 volts should be further investigated. Increased voltages might be hazardous to personnel, and should be further investigated.

Cabinet Performance Grounding (High Frequency Ground)

Signal interconnects between system cabinets require high frequency ground return paths. Connect all cabinets to site ground.




	NOTE: In some cases power distribution system green (green/yellow) wire ground conductors are too long and inductive to provide adequate high frequency ground return paths. Therefore, a ground strap (customer-supplied) should be used for connecting the system cabinet to the site grounding grid (customer-supplied). When connecting this ground, ensure that the raised floor is properly grounded for high frequency.

Power panels located in close proximity to the computer equipment should also be connected to the site grounding grid. Methods of providing a sufficiently high frequency ground grid are described in the next sections.

Raised Floor High Frequency Noise Grounding

If a raised floor system is used, install a complete signal grounding grid for maintaining equal potential over a broad band of frequencies. The grounding grid should be connected to the equipment cabinet and electrical service entrance ground at multiple connection points using a minimum #6 AWG (16mm2) wire ground conductor. The following Figure 3-1 “Raised Floor Metal Strip Ground System” illustrates a metallic strip grounding system.




	NOTE: Regardless of the grounding connection method used, the raised floor should be grounded as an absolute safety minimum.

HP recommends the following approaches:

Excellent—Add a grounding grid to the subfloor. The grounding grid should be made of copper strips mounted to the subfloor. The strips should be 0.032 in. (0.08 cm) thick and a minimum of 3.0 in. (8.0 cm) wide.
Connect each pedestal to four strips using 1/4 in. (6.0 mm) bolts tightened to the manufacturer’s torque recommendation.
Better— A grounded #6 AWG minimum copper wire grid mechanically clamped to floor pedestals and properly bonded to the building/site ground.
Good—Use the raised floor structure as a ground grid. In this case, the floor must be designed as a ground grid with bolted down stringers and corrosion resistive plating (to provide low resistance and attachment points for connection to service entrance ground and HP computer equipment). The use of conductive floor tiles with this style of grid further enhances ground performance. The structure needs to be mechanically bonded to a known good ground point.

Figure 3-1 Raised Floor Metal Strip Ground System

Equipment Grounding Implementation Details

Connect all HP equipment cabinets to the site ground grid as follows:

Attach one end of each ground strap to the applicable cabinet ground lug.
Attach the other end to the nearest pedestal base (raised floor) or cable trough ground point (nonraised floor).
Check that the braid contact on each end of the ground strap consists of a terminal and connection hardware (a 1/4-in. [6.0-mm] bolt, nuts, and washers).
Check that the braid contact connection points are free of paint or other insulating material and treated with a contact enhancement compound (similar to Burndy Penetrox).

System Installation Guidelines

This section contains information about installation practices. Some common pitfalls are highlighted. Both power cable and data communications cable installations are discussed.




	NOTE: In domestic installations, the proper receptacles should be installed prior to the arrival of Hewlett-Packard equipment. Refer to the appropriate installation guide for installation procedures.

Wiring Connections

Expansion and contraction rates vary among different metals. Therefore, the integrity of an electrical connection depends on the restraining force applied. Connections that are too tight compress or deform the hardware and cause it to weaken. This usually leads to high impedance, preventing circuit breakers from tripping when needed, or can contribute to a buildup of high frequency noise.




	CAUTION: Connections that are too loose or too tight can have a high impedance that causes serious problems, such as erratic equipment operation. A high impedance connection overheats and sometimes causes fire or high temperatures that can destroy hard-to-replace components such as distribution panels or system bus bars.

Wiring connections must be properly torqued. Many equipment manufacturers specify the proper connection torque values for their hardware.

Ground connections must only be made on a conductive, nonpainted surface. When equipment vibration is present, lock washers must be used on all connections to prevent connection hardware from working loose.

Data Communications Cables

Power transformers create high-energy fields in the form of electromagnetic interference (EMI). Heavy foot traffic can create electrostatic discharge (ESD) that can damage electronic components. Route data communications cables away from these areas. Use shielded data communications cables that meet approved industry standards to reduce the effects of external fields. These shielded communications cables must be grounded at both ends.