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Practice and exam technique

Practice: mechanical and electrical

Compiled by the Sitonce editorial team from the PSI Candidate Information Bulletin, NASCLA's own published material and the federal standards named belowUpdated 2 min readFacts verified 4 September 2026
The short answer

Mechanical carries 4 questions and Electrical 3, so 7 of 125. The questions test what a general contractor coordinates rather than what a trade license would require.

Seven questions between them, and the level of depth is coordination rather than trade.

Four questions

Question 1

Who is generally responsible for coordinating clashes between mechanical, electrical and structural work?

  1. Each trade individually
  2. The general contractor
  3. The design engineer
  4. The building inspector
Answer: B. Coordination between trades is the general contractor's function, and it is why these categories appear on a general building exam at all. The engineer designs and the inspector inspects; neither sequences the work.
Question 2

A drainage system requires venting primarily to achieve what?

  1. Faster drainage
  2. Protection of trap seals from siphoning and back pressure
  3. Removal of sewer gas from the building only
  4. Compliance with fixture unit counts
Answer: B. Venting admits air so the pressure either side of a trap stays balanced and the water seal survives. Without it the seal is pulled or pushed out and sewer gas enters the building, so option C is a consequence rather than the mechanism.
Question 3

What is the purpose of grounding an electrical system?

  1. To reduce energy consumption
  2. To provide a low-impedance path for fault current so overcurrent devices operate
  3. To stabilize voltage under load
  4. To isolate circuits from one another
Answer: B. Grounding gives fault current a path back to the source with low enough impedance that the breaker or fuse opens quickly. A poorly grounded system can leave metal energized without ever tripping anything.
Question 4

Rough-in inspections for mechanical and electrical work generally occur at which point?

  1. After the wall finishes are complete
  2. After installation but before concealment
  3. At the same time as the final inspection
  4. Before any installation begins
Answer: B. Rough-in is inspected while the work is still visible. Closing walls before the inspection means opening them again, and sequencing that correctly is a general contractor's scheduling job.
Do not over-prepare this

Seven questions out of 125, against 31 for Procurement and Contracting. A contractor who spends a fortnight on electrical theory has misallocated their preparation by a wide margin.

What to have tabbed

  • Inspection sequence and what each covers
  • Venting and trap principles
  • Grounding and bonding definitions
  • Clearance requirements around equipment

Common questions

How many mechanical and electrical questions are on the exam?

Four on Mechanical and three on Electrical, so 7 of 125.

What depth is tested?

Coordination knowledge a general contractor needs, not trade license depth.

Why is a drainage system vented?

To protect trap seals from siphoning and back pressure.

What does grounding do?

Provides a low-impedance path for fault current so overcurrent devices operate.

When is rough-in inspected?

After installation but before concealment.

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