HP Limits by Class
Key Takeaways
- Special: 50 HP in charge / 100 HP shift as apprentice under direct supervision; Second Class: 100 / 500; First Class: 500 / unlimited; Chief: unlimited / unlimited.
- Grade C is low-pressure; Grade B is high- and low-pressure boilers; Grade A adds steam engines, turbines, and appurtenances.
- Licensing HP uses DLI rules (10 sq ft = 1 BHP or 67,000 Btu/hr) and totals all header-connected boilers, running or not.
- Experience gates: Special none, Second Class 1 year, First Class 3 years, Chief 5 years with at least 1 year holding First Class.
- All exams require 70% to pass with a 30-day wait after failure; question counts increase with class and grade.
HP Limits by Class
Quick Answer: Minnesota ties plant authority to license class: Special may take charge of 50 BHP (shift to 100 under direct supervision), Second Class 100 / 500, First Class 500 / unlimited, and Chief unlimited / unlimited. Grades A, B, and C decide high-pressure, engines/turbines, and low-pressure scope — not a separate horsepower ladder.
Horsepower limits are the heart of Minnesota's classification statute. The exam will ask whether an engineer may take charge of a plant or only work as a shift engineer, and those two columns are different numbers on DLI's classification chart. Confusing the columns is the most common SIE-style miss in this chapter.
The Four Classes and Three Grades
| Class (low → high) | Typical grade meaning |
|---|---|
| Special | Entry license; all boiler types within small HP caps |
| Second Class | Next step; Grades A / B / C |
| First Class | Mid-senior; Grades A / B / C |
| Chief | Highest; Grades A / B / C |
Grade shorthand used statewide:
- Grade C — low-pressure plants
- Grade B — high- and low-pressure boilers (without the engines/turbines focus of Grade A)
- Grade A — high- and low-pressure plants with steam engines, turbines, and appurtenances
"A" exams include "B" content, so Grade A candidates study the broader plant plus prime-mover material. Low-pressure steam is 15 psi or below; high-pressure steam is above 15 psi. Hot-water boilers are treated as low-pressure when designed at or below 160 psi and 250°F. Matching grade to plant type matters as much as matching horsepower: a Grade C engineer is not the correct in-charge credential for a high-pressure steam plant even if the HP number looks small enough on paper.
Maximum Horsepower — In Charge vs Shift
Use DLI's licensing horsepower (10 sq ft = 1 BHP, or 67,000 Btu/hr input), and remember Minn. R. 5225.1000: total horsepower of all boilers connected to the header counts, whether every boiler is firing or not. Idle boilers still count toward the plant size that drives the required license.
| License | Max HP in charge | Max HP as shift engineer |
|---|---|---|
| Special | 50 | 100* |
| Second Class (A/B/C) | 100 | 500 |
| First Class (A/B/C) | 500 | Unlimited |
| Chief (A/B/C) | Unlimited | Unlimited |
*Special's 100 HP shift role is as an apprentice under direct supervision of the properly licensed engineer — not unsupervised command of a 100 HP plant. Direct supervision means the properly licensed engineer is directing and responsible for the work, not merely "on call across town" in a vague sense.
SIE-style traps:
- Doubling Special's 50 HP in-charge limit to 100 HP in charge (wrong — 100 is the supervised shift/apprentice cap).
- Treating First Class as unlimited in charge (wrong — First Class tops out at 500 HP in charge; unlimited in-charge authority is Chief).
- Ignoring header-connected idle boilers when sizing the plant for the required license.
- Assuming Grade A removes horsepower caps (wrong — grade changes equipment scope, not the class HP ceiling).
Experience Before You Test
| License | Minimum experience (summary) |
|---|---|
| Special | None |
| Second Class | 1 year (low-pressure often 12 months; high-pressure A/B uses 2,000 hours) |
| First Class | 3 years (e.g., 36 months low-pressure or 6,000 high-pressure hours; Grade A also needs turbine hours) |
| Chief | 5 years, and you must have held a Minnesota First Class license for at least 1 year |
Chief Grade A is the top commercial credential: unlimited HP for boilers, engines, and turbines. Qualifying paths stack boiler hours (often 10,000 for high-pressure Chief tracks) plus turbine time for Grade A. Exact hour splits appear on DLI's current classification fee chart — memorize the class HP caps and year gates first; then match grade A/B/C to plant type. Educational offsets may reduce a portion of experience in limited cases, but they never erase the need for an approved application and a passing exam score.
Exam Size and Pass Mark (Classification Chart)
All commercial classes use a 70% minimum and a 30-day wait after failure. Question counts rise with class (Special and many Second Class C exams are 50 items; higher A grades and Chief exams run much longer, with Chief A reaching 140). Application fee remains $50 (includes exam). Two-year license fees differ by class on DLI's published schedule — Special is the lowest ongoing fee band; Chief is higher. Boat Master and Historical credentials exist on the same chart but follow separate HP and experience rules; do not mix them into commercial plant answers.
How Facilities Choose the Required License
Owners must staff the plant with an engineer whose in-charge authority covers the plant's licensing horsepower and whose grade matches pressure and prime-mover scope. A low-pressure 80 HP heating plant can run under Second Class C in charge; a 600 HP high-pressure header needs Chief-level in-charge authority because First Class stops at 500 HP in charge. Shift staffing can use a lower class only within that class's shift column and under the plant's proper supervisory structure.
When in doubt on the exam: identify in charge vs shift, apply the table, then apply grade for high-pressure and turbines. Horsepower without grade — or grade without horsepower — is an incomplete answer.
A Minnesota plant has 600 boiler horsepower connected to one steam header. Which license may take charge of that plant?