CSLB C-46 Solar ContractorElectrical and Plumbing CodesHard
A solar contractor is installing a new solar thermal system on a commercial building. The system uses a non-potable heat transfer fluid and includes an expansion tank. According to the California Plumbing Code (CPC), an expansion tank for a non-potable closed-loop system must be installed such that it is accessible for inspection and replacement. What is the maximum permitted working pressure of such an expansion tank, relative to the system's working pressure?
- AAt least 2 times the system working pressure
- BAt least 1.5 times the system working pressure
- CEqual to or less than the system working pressure
- DAt least 1.25 times the system working pressure
Show answer & explanationAnswer & explanation
Correct answer: D. At least 1.25 times the system working pressure
CPC Section 1008.3 (UPC 1008.3) specifies that expansion tanks for non-potable closed-loop systems shall be constructed for a maximum working pressure at least 1.25 times the maximum working pressure of the system or water heater, whichever is greater. This ensures the tank can safely accommodate pressure fluctuations.
Why the other options are wrong
- A. 2 times is overly conservative and not the minimum required by code.
- B. 1.5 times is more conservative but not the minimum required by code.
- C. This would not provide a sufficient safety margin for pressure fluctuations.
Non-Potable Expansion Tank Pressure Rating
Expansion tanks for non-potable closed-loop systems must have a maximum working pressure rating of at least 1.25 times the system's maximum working pressure, per CPC 1008.3.
- Ensures tank integrity under pressure spikes.
- Applies to solar thermal space heating or process heat.
- Critical safety requirement.
Memory trick: Expansion Tank: One and a Quarter Times the System's Pressure.