CPD Gas Piping Systems Design 1

Question 1

According to NFPA 54, what is the minimum required distance between an above-grade outdoor gas meter and a source of ignition such as an electrical panel?

Accepted Answer

3 feet

Answer

NFPA 54 requires gas meters to be located at least 3 feet from sources of ignition, including electrical panels and switches.

Question 2

A sediment trap (drip leg) installed in a gas supply line should be located:

Accepted Answer

Downstream of the appliance shut-off valve, immediately upstream of the appliance inlet

Answer

A sediment trap must be installed immediately upstream of the appliance inlet connection, downstream of the individual appliance shut-off valve, to catch debris before it enters the appliance.

Question 3

When sizing a natural gas piping system, the designer must account for the total connected load in BTU/hr. Which method is commonly used when diversity of gas usage is expected in a large system?

Accepted Answer

Diversity factor method applying a usage factor less than 1.0

Answer

The diversity factor method applies a usage factor less than 1.0 to total connected load because not all appliances operate simultaneously in large systems, resulting in a more economical pipe sizing.

Question 4

What is the maximum allowable pressure drop permitted in a low-pressure natural gas distribution system (under 2 psi) supplying residential and light commercial appliances, per NFPA 54?

Accepted Answer

1.0 in. w.c.

Answer

NFPA 54 limits pressure drop to 0.5 in. w.c. for the supply piping system and an additional 0.5 in. w.c. for the longest run, totaling no more than 1.0 in. w.c. from the meter to the appliance for low-pressure systems.

Question 5

Which gas pipe material is prohibited for use inside a building above ground, per most model codes?

Accepted Answer

Cast iron pipe

Answer

Cast iron pipe is not approved for gas piping systems in any location; approved materials include steel, wrought iron, CSST, copper, and certain PE plastics (for underground only).

(CPD) Certified Plumbing Designer Practice Test

(CPD) Certified Plumbing Designer Practice Test

CPD Gas Piping Systems Design 1