306A Gas Piping Systems 2 — Questions and Answers
Question 1: What compound or sealant is approved for use on threaded gas pipe joints?
- Standard plumber's putty
- Pipe joint compound or Teflon tape specifically rated for gas service (Correct answer)
- Regular Teflon tape (white)
- Silicone caulking
Correct answer: Pipe joint compound or Teflon tape specifically rated for gas service
Only pipe joint compound or Teflon tape specifically rated and labelled for gas service may be used on gas pipe threads. Gas-rated Teflon tape is typically yellow and thicker than standard white tape used for water connections.
Question 2: Why is corrugated stainless steel tubing (CSST) sometimes preferred over black steel pipe for gas installations?
- It is less expensive
- It is flexible, faster to install, and requires fewer joints, reducing potential leak points (Correct answer)
- It handles higher pressures
- It is required by code for all new installations
Correct answer: It is flexible, faster to install, and requires fewer joints, reducing potential leak points
CSST is flexible, allowing it to be routed through walls and floors with fewer joints than rigid steel pipe. Fewer joints means fewer potential leak points. It also installs much faster, reducing labour costs.
Question 3: What special requirement applies to CSST gas tubing regarding electrical grounding?
- No grounding is required
- CSST must be bonded to the building's electrical grounding system to protect against lightning-induced damage (Correct answer)
- CSST must be insulated from all metal components
- Only the fitting ends need grounding
Correct answer: CSST must be bonded to the building's electrical grounding system to protect against lightning-induced damage
CSST must be electrically bonded to the building's grounding electrode system to protect against damage from lightning strikes. Without bonding, a nearby lightning strike can induce current in the CSST, potentially burning a hole in the thin tubing and causing a gas leak.
Question 4: What is the purpose of a gas shut-off valve at each appliance?
- To regulate the gas flow rate
- To allow the gas supply to be individually isolated for each appliance for maintenance, repair, or emergency (Correct answer)
- To reduce gas pressure
- To filter the gas supply
Correct answer: To allow the gas supply to be individually isolated for each appliance for maintenance, repair, or emergency
An individual shut-off valve at each gas appliance allows that appliance's gas supply to be isolated without affecting other appliances in the building. This is essential for safe maintenance, repair, or replacement of individual appliances.
Question 5: What is the maximum allowable pressure drop in a residential gas piping system from the meter to the most remote appliance?
- 0.25 kPa (1 inch WC) (Correct answer)
- 0.5 kPa (2 inches WC)
- 1.0 kPa (4 inches WC)
- 1.75 kPa (7 inches WC)
Correct answer: 0.25 kPa (1 inch WC)
The maximum allowable pressure drop is typically 0.25 kPa (1 inch of water column) from the meter to the most remote appliance, ensuring adequate pressure at all appliance connections for proper combustion.
Question 6: What is the function of a gas pressure regulator?
- To increase gas pressure for high-demand appliances
- To reduce and maintain a constant downstream gas pressure regardless of upstream pressure fluctuations or flow rate changes (Correct answer)
- To measure gas consumption
- To filter impurities from the gas
Correct answer: To reduce and maintain a constant downstream gas pressure regardless of upstream pressure fluctuations or flow rate changes
A gas pressure regulator reduces the incoming gas pressure to a safe, consistent downstream pressure. It automatically adjusts to maintain this set pressure despite variations in supply pressure or changes in gas demand from appliances.
306A Gas Piping Systems 2
What compound or sealant is approved for use on threaded gas pipe joints?