Arc flash studies for Calgary buildings and plants

CCT 01What an arc flash study produces

“Arc flash study” usually means three linked analyses built on one model of the electrical system:

• Short-circuit study. How much fault current each bus can deliver, and whether the installed equipment is rated to interrupt or withstand it.
• Protective device coordination study. Whether breakers and fuses trip in the right order and quickly enough, so a fault is cleared close to where it happens.
• Arc flash assessment. For each piece of equipment, the incident energy a worker could be exposed to at a working distance, the arc flash boundary and the resulting protective equipment requirements.

They answer different questions, and a proposal should say which of the three it includes. The arc flash result depends on the other two: fault current sets how much energy is available, and clearing time sets how long the arc lasts. A slow upstream device can make a modest fault dangerous, which is why a study often ends with recommended setting changes rather than just labels.

The deliverables are an editable system model, a report stating the method, data and assumptions, equipment labels, a list of any equipment found to be under-rated, and recommendations. Ask who owns the model file. Without it, the next change to the building means paying to rebuild the study.

CCT 02Is an arc flash study required in Alberta?

Not by name. Alberta’s OHS Code does not adopt CSA Z462 and does not require arc flash studies. Its hazardous-energy rules are in Part 15, which requires energy to be isolated with a secured energy-isolating device before equipment is serviced, repaired, tested, adjusted or inspected,¹ and requires workers to confirm that equipment is inoperative or otherwise safe before working on it.¹ Part 17 deals with overhead power lines, not electrical work in buildings; it sets approach limits once work comes within 7 m of an overhead line.²

The Z462 link is advisory. A 2009 Alberta government bulletin for property managers recommended keeping CSA Z462 and following it when working on electrical equipment.³ That bulletin cited an edition since replaced; the current one is CSA Z462:24.⁴ Employers remain responsible under Alberta’s OHS legislation for assessing and controlling workplace hazards, and Z462 is the Canadian consensus standard for the electrical hazard, so an owner whose staff or contractors open energized equipment often finds a study is the practical way to meet that responsibility. Insurers, corporate safety programs and client prequalification can make it a contract requirement.

Maintenance has a similar status: CSA describes Z463 as a voluntary guideline.⁵ The arc flash requirements guide covers the legal background in more depth.

CCT 03Who does what in a study

The split matters because every unassigned row becomes an assumption. If nobody confirms protective settings, the model uses defaults, and default settings can produce labels that understate the hazard.

CCT 04Data collection sets accuracy and price

Much of a study’s effort, and many of its errors, come from the field. Drawings are often out of date, and the equipment that matters sits behind closed doors: breaker trip units and their settings, fuse types and ratings, transformer nameplates, and the size and length of the feeders between them.

For services of 600 A and above, Calgary already requires the single-line diagram or shop drawings to show the fault current at every overcurrent device, the service characteristics and ratings, and any series-rated combinations.⁶ Those permit drawings are a good starting point in a building with a recent service change, but they show the design as submitted, not later changes, and they say nothing about clearing times. The commercial permits guide explains when they are required.

Some data can only be read with covers removed or equipment de-energized. That turns data collection into shutdown planning and is a major reason quotes differ. Ask each bidder how they will obtain the settings of each device, and what they will assume where they cannot.

CCT 05What a label tells a worker, and what it does not

An arc flash label summarizes the study result for one piece of equipment: typically the nominal voltage, the arc flash boundary, the incident energy at a stated working distance or a PPE category, and the study date. It tells a qualified worker what the hazard is under the modelled conditions.

It does not say the task is safe, that the equipment is in good condition or that energized work is justified. The label assumes the protective devices operate as modelled, and a poorly maintained breaker can clear slowly and release more energy than the label shows. That is why studies and preventive maintenance belong in the same program, and why infrared thermography is often scheduled alongside them.

Labels also go stale. A label whose study predates a service upgrade, a new transformer or a changed breaker setting describes a system that no longer exists.

CCT 06When to commission or update a study

Commission or update a study when:

• the building has no study, and staff or contractors open energized equipment for testing or troubleshooting;
• the service changes, for example a service upgrade or a change in utility supply;
• distribution equipment is added or replaced, such as switchgear or transformers;
• a generator, UPS system or large new motor changes the available fault current or the operating modes;
• protective device settings change, including after a coordination review;
• an insurer, a corporate safety program or a client asks for it.

Reel 08 · Substation, dusk · illustrative film

CSA Z462 also sets a periodic review interval for studies. Check the interval in the edition your electrical safety program adopts rather than relying on a figure from a website, and keep a change log so the reviewer knows what moved since the last study.

CCT 07What moves the price

No official source publishes arc flash study prices. The price follows effort:

• Equipment count. The number of buses, panels, switchboards, transformers and motor control centres in scope.
• Data availability. Current drawings and recorded settings cut field time; missing ones add it.
• Access and shutdowns. After-hours work and multiple shutdown windows add cost and calendar time.
• Operating modes. Generator operation, tie breakers and multiple utility feeds each add scenarios to model.
• Deliverables. Label printing and installation, the editable model, a coordination study, and a revision after recommendations are implemented.

Ask for those items as separate lines, and compare the equipment list each bidder assumed before comparing totals. The arc flash study and thermography cost guide explains the drivers in more detail.

CCT 08Where studies matter most, and what to keep

Studies matter most where people open energized equipment often and where fault current is high: plants and manufacturing with motor control centres and in-house maintenance, data centres with UPS and generator operating modes, and portfolios where property managers bring in many contractors. Calgary requires an annual electrical permit where a facility employs a full-time journeyman electrician,⁶ and those facilities are where energized-equipment tasks tend to be routine.

At handover, keep the report, the model file and the right to use it, the assumptions list, the drawings the study was based on, the implemented settings and a register of labels. Name who triggers a review when equipment, supply or operating configurations change.