Data Center Glossary: Terms Engineers Use
Data center work has its own vocabulary. This glossary gives short, plain definitions of the terms you will meet most often.
Terms
| Term | Meaning |
|---|---|
| Availability | The proportion of time a system is operational. |
| Autonomy time | How long a UPS battery can carry the load. |
| ATS | Automatic transfer switch; moves a load between sources, such as utility and generator. |
| Busway / busduct | Enclosed conductors used to distribute power. |
| CRAC | Computer room air conditioner with its own compressor. |
| CRAH | Computer room air handler using chilled water. |
| Concurrent maintainability | Any component or path can be taken out for planned maintenance without affecting the IT load. |
| Containment | Physical separation of hot and cold air streams in a data hall. |
| CUE | Carbon usage effectiveness; carbon emissions per unit of IT energy. |
| DCIM | Data center infrastructure management software. |
| Demand factor | The proportion of connected load expected to operate at once. |
| Dual-corded | IT equipment with two power supplies fed from separate paths. |
| Earthing | Connecting a system to the general mass of earth. |
| Edge data center | A smaller facility placed close to users or devices. |
| EPMS | Electrical power monitoring system. |
| FAT | Factory acceptance test. |
| Fault tolerance | Continuing to operate through a single failure. |
| Generator set | An engine and alternator providing backup power. |
| Hot aisle / cold aisle | Rack arrangement separating exhaust and supply air. |
| Hyperscale | Very large facilities run by cloud and internet companies. |
| IST | Integrated systems testing of all systems together. |
| kVA | Kilovolt-ampere; unit of apparent power. |
| kW | Kilowatt; unit of real power. |
| Load bank | Equipment that provides an artificial electrical load for testing. |
| LOD | Level of development of a BIM element. |
| LV | Low voltage, commonly up to 1,000 V AC. |
| MCC | Motor control centre. |
| MV | Medium voltage, commonly from about 1 kV to tens of kV. |
| N | The capacity needed to serve the load with no redundancy. |
| N+1 | N plus one spare unit. |
| 2N | Two independent systems each able to carry the full load. |
| PDU | Power distribution unit. |
| PUE | Power usage effectiveness; total facility power divided by IT power. |
| RPP | Remote power panel; distributes power to racks. |
| Rack | A frame that holds IT equipment. |
| SAT | Site acceptance test. |
| SLD | Single-line diagram. |
| STS | Static transfer switch. |
| Short-circuit current | The current that flows in a fault. |
| Tier | Uptime Institute infrastructure classification, I to IV. |
| TIA-942 | Telecommunications Industry Association data center infrastructure standard. |
| UPS | Uninterruptible power supply. |
| VRLA | Valve-regulated lead-acid battery. |
| White space | The area where IT racks are installed. |
| WUE | Water usage effectiveness; litres of water per kWh of IT energy. |
| Power factor | The ratio of real power to apparent power. |
| Derating | Reducing a rating to allow for conditions such as temperature or grouping. |
| Voltage drop | The reduction in voltage along a conductor under load. |
| Harmonics | Currents or voltages at multiples of the supply frequency. |
| Arc flash | An explosive release of energy from an electrical fault in air. |
| Selectivity | The ability of protection to isolate only the faulted part. |
| Bonding | Connecting metal parts so they stay at the same potential. |
| Commissioning | Testing and proving that systems work as designed. |
| As-built | The record of what was actually installed. |
| Free cooling | Using cool outdoor air or water to reduce mechanical cooling. |
| Economiser | Equipment that enables free cooling. |
| Liquid cooling | Removing heat with a liquid rather than air alone. |
| BESS | Battery energy storage system. |
| PPA | Power purchase agreement. |
| Colocation | A facility renting space, power and cooling to customers. |
For explanations, start with the data center design guide, redundancy explained and what is a data center.
Written by the Vision Matrix Institute editorial team. Worked examples use stated, illustrative assumptions; check them against your project data, the applicable standards and manufacturer datasheets before use.
Frequently Asked Questions
What is the difference between kW and kVA?
kW is real power and kVA is apparent power; they are related by the power factor, so kW equals kVA times power factor.
What does N+1 mean?
N is the capacity needed for the load; N+1 adds one spare unit so a single failure can be tolerated.
What is white space?
The area of a data center where the IT racks are installed.
Where can I read more?
The data center design guide links to detailed articles on each topic.
Want to learn this properly?
This topic is covered in depth in our Electrical Design – Data Center Specialist program.
Ask us on WhatsAppLearn to do this on a full project in the Electrical Design – Data Center Specialist program, or read the data center design guide.