Electricity is the heart of a data center. Transformers, generators, UPS systems, switchboards and kilometers of cable exist so servers can run without a single second of interruption. But the same energy, when it gets out of control at the wrong moment, can become a life-threatening risk. One of the most dangerous of these risks is arc flash. In this post we explain in plain words what an arc flash study is, how it's done and when a data center or critical facility needs one.
What Is an Arc Flash?
An arc flash is a sudden, very powerful release of energy that happens when electric current jumps through the air between conductors during a short circuit. It lasts from a few milliseconds to a few seconds and produces:
- Temperatures higher than the surface of the sun and heat that causes severe burns
- Extremely intense light that damages the eyes
- A pressure wave that can knock a person down and a blast loud enough to damage hearing
- Flying molten metal and toxic gases
Common causes include touching energized parts during maintenance, a tool dropped into a panel, dust and moisture, worn insulation, using the wrong test equipment and faulty breaker operations. The difference from electric shock: with an arc flash, a person doesn't need to touch the conductor, just being nearby is enough.
What Is an Arc Flash Study?
An arc flash study (arc flash analysis) is an engineering study that calculates how much energy a possible arc flash would release at each point in a facility's electrical system and determines how workers should be protected from that risk. It usually consists of these steps:
| Step | What's done? | Output |
|---|---|---|
| 1. Data collection | Transformer, generator, UPS, cable, breaker and fuse data collected on site | Up-to-date single-line diagram |
| 2. Short-circuit analysis | The highest possible short-circuit current at each point is calculated | Short-circuit levels, equipment rating check |
| 3. Protection coordination | How fast and selectively breakers and relays clear faults is reviewed | Protection setting recommendations |
| 4. Incident energy calculation | Energy released at a given working distance is calculated | cal/cm² values |
| 5. Boundaries and PPE | The arc flash boundary and required protective equipment are determined | PPE requirements |
| 6. Labeling | A label showing the risk information is prepared for each panel | Equipment labels |
| 7. Report and recommendations | Technical and organizational measures to reduce risk are proposed | Detailed report |
| 8. Training | Results and safe work practices are explained to staff | A trained team |
Key Concepts
- Incident energy: The heat energy reaching a surface at a certain distance during an arc flash. Measured in cal/cm².
- Arc flash boundary: The distance at which incident energy drops to 1.2 cal/cm². This is considered the threshold where second-degree burns start on unprotected skin. Anyone crossing the boundary must wear suitable protective equipment.
- Working distance: The typical distance between a worker's face and torso and the possible arc source. Calculations are based on this distance.
Personal protective equipment (PPE) is chosen based on the calculated incident energy. The commonly used category system looks like this:
| PPE category | Minimum arc rating | In general |
|---|---|---|
| 1 | 4 cal/cm² | Arc-rated shirt/pants, face shield |
| 2 | 8 cal/cm² | Arc-rated clothing, face shield and balaclava |
| 3 | 25 cal/cm² | Arc flash suit, hood, gloves |
| 4 | 40 cal/cm² | Heavier arc suit and full protection |
| Above 40 cal/cm² | No category | No energized work, the equipment should be de-energized |
Which Standards Are Used?
- NFPA 70E: The standard for electrical safety in the workplace. It requires the arc flash risk assessment to be done by qualified persons, reviewed at least every 5 years and updated when there's a major change to the system. The current edition is 2024.
- IEEE 1584-2018: The most widely used method for calculating incident energy and arc flash boundaries. It covers AC systems from 208 V to 15 kV.
- IEC 61482: Testing and classification of protective clothing against arc flash.
On top of these, many occupational health and safety regulations require employers to assess electrical risks and protect workers against them. An arc flash study is the most concrete way to meet that obligation on the electrical side.
Why Are Data Centers Especially at Risk?
- High short-circuit currents: Large transformers and generators running in parallel mean very high currents during a fault. The higher the current, the higher the arc energy.
- UPS and battery systems: Battery strings carry arc risk on the DC side too. Since IEEE 1584 doesn't cover DC systems, these parts are assessed with seperate methods (like the DC calculations in the NFPA 70E annex).
- "We can't shut it down" pressure: The expectation of zero downtime creates a tendency to do maintenance energized, which increases exposure to arc flash risk.
- Constantly changing infrastructure: New racks, new PDUs, busway additions and capacity upgrades change the electrical system often; old calculations can quickly become outdated.
- Dense equipment and tight spaces: Electrical rooms have limited working space and short escape distances.
The good news is that a concurrently maintainable design, meaning a dual-path infrastructure where you can shut down one path and keep feeding from the other, greatly reduces the need for energized work. We covered the basics of data center design in our how to build a data center post.
When Is an Arc Flash Study Needed?
| Situation | Why? |
|---|---|
| New facility design and commissioning | Equipment and protection settings are chosen right from the start, labels are ready before opening |
| Capacity expansion (new transformer, generator, UPS, switchboard) | Short-circuit levels and clearing times change |
| Changes on the utility side | A new utility transformer or connection can increase short-circuit current |
| Changes to protection settings | Slower clearing times greatly increase incident energy |
| At least every 5 years | Small changes add up; the standard requires regular review |
| Before an energized maintenance program | Nobody should work without knowing which task needs which PPE |
| After an accident or near miss | Check whether the existing assessment is still valid |
| Insurance, audit or customer request | Enterprise customers and insurers may ask for an up-to-date study and labels |
Ways to Reduce the Risk
The most valuable part of an arc flash study is usually the recommendations section. The most common measures:
- De-energized work: The most effective method. Put the equipment in an electrically safe state with lockout/tagout (LOTO) and work that way.
- Maintenance mode switch (ERMS): Temporarily make the breaker's instantaneous protection more sensitive during maintenance so it clears faults much faster.
- Zone selective interlocking (ZSI): Breakers communicate so the one closest to the fault trips without delay.
- Arc flash detection relays: Detect the light of the arc and send a trip command within milliseconds.
- Current-limiting fuses and optimized protection settings. For large breakers (usually 1200 A and above), a method to reduce arc energy is already mandatory in many electrical codes.
- Remote operation: Opening and closing breakers or racking them in/out remotely keeps the worker outside the arc distance.
- Infrared (IR) windows: Do thermal camera checks without opening the panel cover.
Labels Alone Aren't Enough
At the end of the study a warning label is attached to each panel. The label should show at least the nominal voltage, the arc flash boundary and one of the following: incident energy and working distance, PPE category, minimum arc rating or site-specific PPE level. But a label only works if the person reading it knows what it means. That's why staff training, an energized work permit process and always-available correct PPE are inseparable parts of the study.
Who Should Do the Study?
An arc flash study should be done by qualified engineers experienced in electrical systems and protection. Before working with a firm, we suggest asking:
- Which calculation method and software will be used? (like IEEE 1584-2018)
- Will data be collected on site, or only from old drawings?
- Are UPS and battery systems (the DC side) in scope?
- Does the report include protection coordination and concrete improvement recommendations?
- Will labels be printed and delivered, and is staff training included?
Data Centers and Infrastructure with VECDC
If you're planning your own server room or data center, electrical safety is one of the things to think about at the very start of the design. To assess the power and cooling needs of your server infrastructure, check out our hardware consulting service; as for the arc flash study itself, always have it done by an electrical engineering firm specialized in this area.
If you'd rather not deal with transformers, UPS systems, generators and their maintenance at all, running your servers in professionally operated data centers is a much simpler path. VECDC dedicated servers are delivered within 24 hours, and virtual servers start at $6/month and are ready in about 5 minutes, and you can choose the location when ordering. It saves alot of headache.
Frequently Asked Questions
Is an arc flash study mandatory?
Many occupational health and safety regulations require employers to assess electrical risks, and standards like NFPA 70E require an arc flash risk assessment when work will be done near energized equipment. Since legal obligations vary by jurisdiction and facility, the assessment should be done with a qualified electrical engineer and safety professional.
How often should an arc flash study be updated?
NFPA 70E requires the assessment to be reviewed at least every 5 years and updated without waiting whenever there's a major change to the electrical system (like a new transformer, generator, UPS or a change in protection settings).
Does a small server room need an arc flash study?
The size of the risk depends on short-circuit current and clearing times. In a small server room the risk is usually lower, but the feeding panel and UPS should still be assessed. Having a building-wide study that also covers the server room is a good approach.
What's the difference between arc flash and electric shock?
With electric shock, current passes through the body, which requires touching a conductor. With an arc flash, current jumps through the air; the resulting heat, light and pressure wave can injure people who aren't touching the conductor but are nearby.
In Short
An arc flash study is an engineering study that calculates how dangerous a possible arc flash would be at each point of your electrical system and defines the measures needed to protect workers. Because of high short-circuit currents, UPS systems and zero-downtime pressure, it's especially important for data centers and critical facilities. It should be done for new facilities, after every major change and at least every 5 years, and the best results come when it's combined with a design that makes de-energized work possible and a well-trained team. If you have any questions about your infrastructure, drop us a message, were happy to help.