Chapter 2. Site Preparation Concepts

This chapter provides a general overview of the planning process, and provides a more detailed discussion of the issues involved in the site preparation than is provided in the individual chassis chapters (chapters 3 through 8).

Not all of the items listed here apply to every installation. For example, if the system being installed is a single small workstation, the delivery route probably does not present a problem. However, it is a good idea to at least briefly consider each question for any system installation.

Chapter 1, “Planning the Installation” of this guide provides a checklist for site preparation. Chapters 3 through 8 provide detailed specifications for each chassis described. This chapter provides the theory behind the checklist and system specifications. It explains what the specifications mean, and why they are important.

Physical Location

This section addresses the issues to consider when choosing a physical location for a new system.

Selecting a Delivery Route

The best final location is no good if you can't get the system there. Answer the following questions before planning a delivery route for the new system:

  • Will the packing crate fit through doorways and hallways and on elevators?

    The relevant dimensions can be found in chapters 3 through 8. Just measuring the width of the halls, for example, is not enough. Look for corners where the system might get stuck, check width and height of doorways and elevators, and so on.

  • If the packing crate can't be transported to the final destination, can you unpack the system somewhere else?

    Often it is possible to unpack the system in a hallway or on a loading dock, then roll the system to its final destination.

  • Is the floor strong enough?

    The rack systems can be very heavy. Look up the floor loading figures in chapters 3 through 8 and verify that the floor along the delivery route can handle the weight.

  • Is the elevator capable of lifting the system?

    If the intended delivery route includes an elevator, check its weight capacity and size against the system specifications detailed in chapters 3 through 8. If they are available, use freight blankets on elevator sides. Use straps to keep the chassis from shifting while being moved in an elevator.

  • Are there any steep angles, bumps, sharp changes in level, or thick carpeting along the delivery route?

    The large systems are equipped with wheels. However, the wheels are designed only for relatively smooth, level surfaces. Ramps, sliding door channels, rough flooring, and even thick carpeting may present difficulty. If in doubt, arrange for additional assistance.

  • Did you check that the leveling feet are fully retracted?

    Caution: Some systems have screw-in leveling feet. Moving the system with these feet extended can cause severe damage to the chassis. These feet sometimes unscrew during shipment. Before unpacking or moving a system, ensure that the leveling feet are fully retracted.

Selecting a Final Location

There are a number of issues to consider when selecting a location for the system. Answer the following questions before selecting a final location for the new system.

  • Will the system interfere with normal traffic through aisles, hallways, or entranceways in the intended location?

  • Will the intended location allow the convenient performance of routine operations, such as loading and unloading tapes or other media, attaching cables, and so on?

  • Is the floor of the intended site strong enough to support the system, and any planned future expansions?

    Large systems are often installed in machine rooms with raised floors. Pay particular attention to floor-loading and weight distribution in this case.

    The floor loadings listed in the tables in chapters 6 and 8 are total chassis weights averaged over the chassis's entire footprint. Since the chassis typically sit on four casters or four levelers, the point loading is drastically higher.

  • Will the system fit in its intended location?

    Refer to the relevant section of chapters 3 through 8 for system dimensions.

  • Will the systems be maintainable?

    Even if it fits, the system must still be maintainable. Using the measurements provided in chapters 3 through 8, make sure you will have enough room to open the doors, remove boards, and accomplish other routine tasks.

  • How does the intended location fit with future expansion plans for the site?

  • Is the location subject to flooding, extremes of humidity or temperature, or any other factor making it inappropriate for sensitive electronic equipment?

    Generally speaking, SGI systems are designed for use in typical office computing environments: the air temperature should not be too high and should not fluctuate dramatically, air should circulate freely, and it should be relatively dust-free, and the system should not be exposed to any caustic or corrosive chemicals or vapors. Refer to the environmental specifications listed in the appropriate tables in chapters 3 through 8 for details.

Electrical Requirements

Some SGI systems require electrical resources beyond what may be found in a typical office environment. The following sections describe those requirements in general. These sections, along with the data presented in chapters 3 through 8, can help to determine the exact requirements for the new system.

Voltage Requirements

  • What voltage does the system require?

    SGI systems may be shipped with many different voltage configurations. Even some of the smaller systems may require 208 volts, which may need to be specially installed at the site. Refer to the “Power and Cooling” table in the relevant section of chapters 3 through 8 for the voltage requirements of the chassis in question.

  • Is the required voltage available?

    Make sure that the required voltage is available, and is within a reasonable distance of the intended location. If it is not, the site will need to be wired for the required voltage.

Different voltages are available in different countries. Japan uses a low voltage of 100 volts and a high voltage of 200 volts. The United States and Canada use a low voltage of 120 volts and high voltages of either 208 volts or 240 volts. Some other countries use 220 volts or 240 volts, but many have now switched to a 230-volt standard.

In this book, “120 volts” is used to refer to the low range (and, except where otherwise indicated, includes Japan's 100 volts), and 208 is used to refer to the high range (and, except where otherwise indicated, includes Japan's 200 volts, as well as the 220 volts, 230 volts, and 240 volts used in various other countries).

Power Requirements

  • Is there enough power for the system?

    Even one SGI system can require more power than is routinely available in an office environment. A roomful of them will almost certainly require some specially installed electrical circuits. Refer to the “Power and Cooling” table in the relevant section of chapters 3 through 8 for the power requirements of the chassis in question.

    Note: Most configurations will never draw the wattages listed as “maximum” in this guide. However, it is generally a good practice to install wiring capable of supporting the system's maximum potential wattage. If you need power figures for your specific configuration, ask your SGI representative.

Power is measured in volt-amps (VA) and in watts. Both numbers are important in preparing wiring, power conditioning, and cooling.

A system's VA rating is a function of the voltage and amperage of a system. A system's watt rating is that system's VA rating multiplied by its power factor (see “Power Factor”). You can convert among amps, volts, VA, power factor, and watts using the following formulas:

VA = amps × volts
VA = watts ÷ power factor
watts = VA × power factor
amps = watts ÷ (volts × power factor)

Using this information and the information provided in the “Power and Cooling” tables in the relevant sections of chapters 3 through 8, you can determine the site power requirements.

If, after adding up the power requirements of all the devices in the room, you find that the total is even close to the limit of what the existing wiring can support, you should probably install additional power circuits to support the systems.

Grounding Requirements

  • Will all the chassis be at the same ground potential?

    Warning: Any difference in ground potential greater than 500 millivolts (0.5 volts) between two chassis connected with CrayLink or XTown cables can cause severe equipment damage. For further information, see “Chassis Branch Circuit Grounding” in Appendix B.

Power Factor

The “Power and Cooling” tables in chapters 3 through 8 include a listing for power factor. “Power factor” is a number between zero and one representing the portion of the power drawn by a system that actually delivers energy to the system. A system with a power factor of one (sometimes called “unity” power factor) is making full use of the energy it draws. A system with a power factor of 0.75 is effectively using only three-quarters of the energy it draws.

Many SGI systems are power-factor corrected, and thus have a power-factor of one, or very close to one. Some SGI systems and peripherals do not have this correction built in.

Caution: It is very important when selecting an uninterruptible power supply ( UPS) or standby power supply ( SPS) to take the system's power factor into account. For more information, refer to “Power-Line Treatment” in Appendix C.

Inrush Current

The “Power and Cooling” tables in chapters 3 through 8 include a listing for inrush current. “Inrush current” is the peak current that flows into a power supply as AC power is applied. The inrush current is usually much higher than the nominal current. This temporary increase is due to the charging of the input filter capacitors in the power supply, and is limited only by the input impedance of the power supply and the wiring supplying power to the system.

The inrush current often far exceeds the rating of the electrical outlet to which the system is connected. If the system is connected directly to “wall power” (that is, it is not on a UPS or SPS), this is typically not a problem. The peak inrush current lasts for only a part of one AC cycle (that is, less than 1/60 of a second). This is not long enough to damage wiring, and in most cases will not trip a circuit breaker (though this depends on the delay curves of the circuit breaker).

Caution: It is very important when selecting a UPS or SPS to take the system's inrush current into account. Unlike power-company lines, these power-protection devices may not be able to supply the current required during power-on, even if they are sized appropriately for nominal current loads. For more information, refer to “Power-Line Treatment” in Appendix C.

It is possible for the inrush current drawn by a device to cause a slight drop in the line voltage. Though it is very brief, this drop can, in unusual situations, be enough to cause problems in other devices on the same line.

Inrush current is a characteristic of the power supply (or supplies) in a system. The inrush current values listed in the “Power and Cooling” tables in chapters 3 through 8 apply whether the system is heavily or lightly loaded. Therefore, though a lightly loaded system may draw less power while it is running, it may still draw a very large inrush current at the moment it is powered on.

Total Harmonic Distortion

The “Power and Cooling” tables in chapters 3 through 8 include a listing for total harmonic distortion (THD). Total harmonic distortion (sometimes also called harmonic factor) is a measure of the extent to which a waveform is distorted by harmonic content. This rating tells how much the power supply in the system affects the quality of power delivered to other systems supplied by the same transformer.

While the term total harmonic distortion can be applied to either voltage or current, the figures listed in this guide all apply to current.

Thermal Requirements

It is important that SGI systems be kept within their rated thermal range.

  • Will the ambient air temperature surrounding the system be within the required range?

    Refer to the “Power and Cooling” table in the relevant section of chapters 3 through 8 for temperature ranges for the chassis in question. Typically, the upper limit of the temperature range is more likely to be an issue than the lower limit.

Heat Output

All of the systems detailed in this guide have a maximum rated operating temperature. Exceeding this temperature greatly increases the rate of hardware failure, and in many cases causes the system to simply shut itself down.

All the electrical power consumed by a computer system must end up somewhere. For ordinary air-cooled systems, the place it ends up is in the surrounding air, in the form of heat. Every watt drawn by a system is eventually dissipated as heat. This tends to raise the temperature of the air in the room that houses the system. Some method is therefore needed to keep the temperature within the required range. The typical method is to install additional air conditioning capacity.

Air Conditioner Terminology

Air conditioner capacity is generally measured in Btu per hour ( Btu/hr), in tons, or in KiloJoules per hour (KJoule/hr).

A Btu, or British thermal unit, is the amount of energy needed to change the temperature of one pound of water by one degree Fahrenheit.

One ton of air conditioning removes 12,000 Btu of heat energy per hour.

One KJoule is the amount of work or energy equal to 1 × 1010 ergs, or one watt-second.

The more systems installed in a given area, the larger the air conditioning capacity required. It is important to calculate the total thermal load of the computer systems you will be installing and determine if the existing air conditioning system can handle the additional load. If not, you must provide additional cooling capacity.

Calculating Thermal Load

The thermal load can be determined as follows:

  • Add up the wattages of all the items in the room.

  • Calculate Btu/hour by multiplying the total wattage by 3.41.

  • Calculate the KJoules/hour by multiplying the total wattage by 3.23.

  • Calculate tons of air conditioner load by multiplying wattage by 0.000285
    1 KBtu/hr = 1000 Btu/hr
    12,000 Btu/hr = 1 ton of air conditioning load

    Caution: The calculations described here give results that represent the equipment's theoretical maximum thermal output. These calculations, and the “maximum” thermal figures given in the individual chassis chapters (chapters 3 through 8), are based on maximum rated wattage. Even if a system approaches this maximum rated wattage occasionally, it is highly unlikely it will do so for very long. For these reasons, the “maximum” thermal figures quoted in this guide are truly worst-case figures.

Some sources quote “typical” thermal outputs, which may be significantly lower than the numbers listed in this guide. Sizing the air conditioning system for “worst-case” thermal output, however, helps to minimize system problems later. If these maximum thermal figures represent a problem for your site, or if you have any other concerns about these figures, talk to your SGI representative.

When calculating required air conditioner capacity be sure to take into account not only the heat load from computer equipment already installed at the site, but also the non-computer equipment already installed or to be installed, and other factors, such as solar gain, outside ambient air temperatures, and even the number of people.Besides the computer equipment being added to a site

Thermal Gradient

The “Specifications” tables in chapters 3 through 8 include a maximum thermal gradient for each system. The thermal gradient is the rate at which the temperature changes, typically given in degrees per hour. Temperature changes that are more rapid than the given rating can cause damage to some of the components used in the systems.

Where not otherwise indicated, the thermal gradients listed apply whether or not the system is operating.

Cooling In Mission-Critical Installations

In mission-critical installations it is important to consider what would happen in the event of an air conditioner failure. Complete consideration of this topic is beyond the scope of this book. It would be a good idea, however, to consider the following:

  • Should the site have multiple air conditioning units, each able to maintain a safe temperature?

  • How long can the site run in the event of an air conditioner failure before the systems get too warm, and must be shut off?

    Can the air conditioner be repaired within this time?

Environmental Requirements

Electromagnetic interference (EMI), electrostatic discharge (ESD), vibration, and humidity can cause problems for computer systems.

Electromagnetic Interference

Electromagnetic interference (EMI) is caused by malfunctioning, incorrectly manufactured, or incorrectly installed devices that radiate electrical signals. Common sources of EMI include electronic, telephone, and communications equipment. EMI transmissions can be conducted or emitted.

Use properly shielded connectors and cables throughout the site to prevent the new systems from generating EMI.

Caution: Failure to use shielded cables where appropriate may violate FCC regulations and void the manufacturer's warranty.

Electrostatic Discharge

SGI designs and tests its products to be resistant to the effects of electrostatic discharge (ESD). However, it is still possible for ESD to cause problems ranging from data errors and lockups to permanent component damage. To protect the systems from ESD, use these precautions:

  • Minimize the use of carpeting at computer locations (or consider special static-reducing carpet).

  • Verify that all electronic devices are properly grounded.

  • Keep all chassis doors and access panels closed while the system is in operation.

  • Keep all screws, thumbnail-fasteners, and slide-locks fastened securely.

  • Use a grounded static wrist strap whenever working with the chassis or components.

  • Use antistatic packing material for storage and transportation.

  • Clear the site of all devices that create static electricity or are possible sources of EMI.


The SGI product line is designed for use in a typical office computing environment, requiring no special modifications or protection. If a system is to be installed at an industrial site, ensure that vibration does not exceed the limits given in the relevant “Specifications” table in chapters 3 through 8.


The “Specifications” tables in chapters 3 through 8 include a listing for maximum humidity levels for each system, both operating and non-operating. Exposure to humidity levels above the rated maximums, or exposure to condensation, can cause equipment damage.

Humidity Gradient

The tables in chapters 5 through 8 include a maximum humidity gradient for each system. The humidity gradient is the rate at which the humidity changes, typically listed in percent relative humidity per hour. Humidity changes that are more rapid than the given rating can cause damage to some of the components used in the systems.

Where not otherwise indicated, the humidity gradients listed apply whether or not the system is operating.

Ergonomic Requirements

In selecting a physical location, pay attention to ergonomic considerations. The location of a system often puts constraints on the location of the devices attached to it, such as monitors, keyboards, and so on. In this way, decisions made during the installation process can affect workers much later.

In addition to attached devices, consider issues of noise, temperature, air quality, and so on, some of which may be affected by the addition of the new system.


All of the acoustic measurements provided in this book are in dBa (decibels absolute) rather than dB (decibels). This is a measurement of weighted absolute noise power, and includes frequency corrections.

The acoustic measurements listed in chapters 5 through 8 are approximate. Acoustic values depend on many factors outside the control of the manufacturer. Room characteristics such as carpeting and wall coverings affect the noise levels at an installation.

If a site exceeds desirable noise levels, try these remedies:

  • Try alternate orientations of the systems (for example, point the fan away from people).

  • Reduce the quantity of flat reflective surfaces, such as glass, tile, or metal.

  • Add sound-absorbing carpet, wall coverings, and drapes.

  • Add sound baffles in critical locations (being careful not to block airflow).

  • Install ceiling tiles with sound-absorbing properties.

  • Modify office space to separate operators from hardware.

Local Regulations

Before installing a system, make sure to become familiar with any applicable local regulations. Since these vary dramatically by country and state, it is impossible to provide a complete list of such regulations. These regulations, however, might involve

  • power

  • emissions

  • other safety issues

  • ergonomic and health issues

  • telecommunications regulations.

Planning for the Future

  • Will additional systems be added to the site in the future?

    Even if the infrastructure in place can handle the site's immediate needs, what are the future plans? It is always much easier to provide enough space, power, air conditioning capacity, and so on, in advance than it is to add them later.

Converting Between U.S. Customary Measure and Metric Measure

Table 2-1 contains a list of conversions between U.S. Customary measure and Metric measure.

Table 2-1. U.S. Customary to Metric Conversions

U.S. Customary


1 inch (”)

2.54 cm

1 foot (')

30.48 cm

1 square foot (ft2)

0.093 m2

1 pound (lb)

0.4536 kg

1 lb/ft2

4.88 kg/m2

1 cfm

0.00047 m3/s

1 Btu

1055 Joules

1 Btu

1.055 KJoules


1 cm


1 m

10.76 ft2

1 m2

2.205 lbs

1 kg

0.205 lb/ft2

1 kg/m2

2127.66 cfm

1 m3/s

0.00095 Btu

1 Joule

0.95 Btu

1 KJoule

Fahrenheit to Celsius conversion

(F° - 32°) × 5/9 = C° 

Start with the temperature in Fahrenheit, subtract 32 degrees, multiply by 5, and divide by 9. The result is the temperature in Celsius.

Celsius to Fahrenheit conversion

(C° × 9/5) + 32° = F° 

Start with the temperature in Celsius, multiply by 9, divide by 5, and add 32 degrees. The result is the temperature in Fahrenheit.