Master Plumber (UPC/IPC) — All Questions

CSST that requires bonding is connected to the grounding electrode system with a bonding jumper. What is the minimum size of that conductor?

• a.14 AWG copper, which is far too small for the bonding jumper
• b.6 AWG copper✓
• c.No bonding conductor is required for corrugated stainless tubing
• d.10 AWG copper, smaller than the code-required minimum size

CSST bonding uses a conductor not smaller than 6 AWG copper, clamped to a rigid metallic gas component and connected to the grounding electrode system, per IFGC 310.1.1 and the manufacturer's instructions. The heavy conductor drains induced lightning energy so a surge cannot arc through and perforate the thin CSST wall.IFGC §310.1.1

A commercial gas train has a component that automatically stops gas flow if the flame is lost. What is that component?

• a.A vacuum breaker installed on the appliance connector
• b.An automatic safety shutoff valve✓
• c.A simple swing check valve on the appliance supply line
• d.A thermal expansion tank connected to the gas manifold

A commercial gas train includes an automatic safety shutoff valve driven by a flame-safeguard/flame-sensing control that closes on flame failure, per NFPA 54. This prevents raw gas from accumulating when ignition is lost. The train also typically includes manual valves, a regulator, and pressure switches in a defined order.NFPA 54

A commercial gas train has switches that shut the appliance down when supply pressure is outside safe limits. What are these devices?

• a.A temperature-only switch mounted on the appliance cabinet
• b.No such devices exist on a commercial appliance gas train
• c.High- and low-gas-pressure switches✓
• d.A flow meter that records the appliance's gas consumption

High- and low-gas-pressure switches on a commercial gas train, per NFPA 54, prevent firing when supply pressure is too high (risking overfire) or too low (risking incomplete combustion). They are interlocked with the burner control so an out-of-range condition locks out ignition until corrected.NFPA 54

A line-pressure regulator has an atmospheric vent connection. How must that vent terminate?

• a.Capped tightly so that no gas can ever escape from the vent
• b.Into the appliance flue so a leak is carried up the chimney
• c.Inside the equipment room near the regulator for easy access
• d.Outdoors, protected by an insect screen✓

A gas regulator's atmospheric vent must terminate outdoors and be screened against insects, per IFGC 410.3, so a ruptured diaphragm releases gas safely outside. A vent-limiting device may be used where permitted. Capping the vent would prevent the regulator from breathing and operating.IFGC §410.3

When downstream piping and appliances could see pressure exceeding their rating, what protection does the code require?

• a.No protection is required if the regulator looks new
• b.A relief valve that is piped down to the building sanitary sewer
• c.Overpressure protection✓
• d.Only a thermal expansion tank on the gas manifold assembly

IFGC 410.1 requires overpressure protection wherever a regulator failure could subject appliances to pressure above their rating, using relief valves, a monitoring regulator, or a series-regulator arrangement. This protects appliance controls not rated for elevated pressure. Elevated-pressure systems always include such protection.IFGC §410.1

An elevated-pressure (2 psi) gas system serves a dwelling. How is appliance pressure managed?

• a.No regulator is needed because appliances accept any inlet pressure
• b.Only commercial buildings are ever allowed to run at 2 psi service
• c.Elevated pressure is never permitted in a dwelling under any code
• d.A line regulator with overpressure protection reduces it near the appliances✓

IFGC 402.6 permits elevated-pressure (for example 2 psi) systems in dwellings when a line-pressure regulator with overpressure protection reduces the pressure to the appliance's rating near the appliances. The higher trunk pressure lets smaller pipe carry the load; the regulator delivers safe appliance pressure downstream.IFGC §402.6

Compared with the standard 0.5 in w.c. low-pressure table, a 2 psi sizing table lets a given pipe carry how much gas?

• a.More gas✓
• b.Less gas than the low-pressure table for the same pipe size
• c.Exactly the same capacity, since pressure does not affect flow
• d.No gas at all, because 2 psi sizing tables are not published

Because a 2 psi system tolerates a much larger pressure drop than a 0.5 in w.c. system, IFGC 402.4 sizing shows the same pipe carrying more gas (or a smaller pipe serving the same load). This is the advantage of elevated-pressure distribution, paired with a downstream regulator to protect appliances.IFGC §402.4

A 250-gallon aboveground ASME propane container is set beside a dwelling. What minimum separation from the building is required?

• a.25 ft
• b.10 ft✓
• c.3 ft, essentially placing the tank against the building wall
• d.5 ft

NFPA 58 requires an aboveground ASME propane container in the 125 to 500 gallon range to be at least 10 ft from a building and from the line of adjoining property that may be built upon. The separation limits fire exposure and allows for relief-valve discharge. Larger tanks require greater distances.NFPA 58

How must portable DOT propane cylinders (such as 20 lb grill cylinders) be stored?

• a.Outdoors or in approved locations, not inside occupied buildings✓
• b.In an attic space above the living area of the dwelling
• c.Anywhere indoors is acceptable as long as it is convenient
• d.In an occupied basement close to the appliance being served

NFPA 58 prohibits storing DOT propane cylinders inside occupied buildings; because propane is heavier than air, a leak in a basement or interior room can pool and reach an ignition source. Cylinders are stored outdoors, upright, and secured. Only very limited quantities are allowed indoors under strict conditions.NFPA 58

How must the relief valve on an aboveground propane container be arranged?

• a.Capped tightly so that pressure can never be released at all
• b.Discharging downward toward grade beneath the storage tank
• c.Venting horizontally into the adjacent building through the wall
• d.Discharging vertically upward and unobstructed✓

NFPA 58 requires a container relief valve to discharge vertically upward and remain unobstructed (with a rain cap that does not restrict flow), so an overpressure release disperses safely away from people and structures. Capping or obstructing the valve defeats the tank's primary safety device and can cause a BLEVE.NFPA 58

After pressure testing, a new gas line must be purged before service. How is purging performed?

• a.Purge with an appliance pilot lit so the air is burned off
• b.No purge is needed once the pressure test has been passed
• c.Purge to the outdoors, away from ignition sources✓
• d.Purge the air into the room to finish the job more quickly

IFGC 406.6 requires purging piping to a safe point of discharge outdoors, away from ignition sources and not into a confined space, when placing gas in service. Purging into a room can create a flammable mixture. No open flame or ignition source is permitted during the operation.IFGC §406.6

Fuel gas is odorized so leaks can be detected. What is added for this purpose?

• a.A visible dye that colors the gas as it leaks from a joint
• b.An odorant such as mercaptan✓
• c.Chlorine, to give it a sharp detectable chemical smell
• d.Nothing; both natural gas and propane are naturally pungent

IFGC 401.6 requires fuel gas to contain an odorant, commonly a mercaptan, giving the characteristic rotten-egg smell so leaks are detectable before reaching a hazardous concentration. Natural gas and propane are otherwise odorless. Odor fade in some soils is why electronic detection is also used underground.IFGC §401.6

What is the maximum support spacing for 3/4 in horizontal steel gas pipe?

• a.4 ft
• b.6 ft
• c.8 ft✓
• d.10 ft

IFGC Table 415.1 lists 8 ft maximum spacing for 3/4 in and 1 in horizontal steel gas pipe (1/2 in is 6 ft; 1-1/4 in and larger is 10 ft). Proper support prevents sag that could trap condensate or stress joints. Vertical piping is supported at each floor level.IFGC §415.1

Underground metallic gas piping is in contact with the soil. What corrosion requirement applies?

• a.No corrosion protection is required for buried metallic gas pipe
• b.Bare steel needs no protection at all when buried underground
• c.It must be protected by coating, wrapping, or cathodic protection✓
• d.Galvanizing alone always suffices with no other corrosion measures

IFGC 404 requires underground metallic gas pipe to be protected from corrosion with coatings, wrapping, or cathodic protection, because soil moisture attacks buried steel. Tracer wire is also installed with nonmetallic pipe for locating. Unprotected buried metal can corrode through and leak.IFGC §404.11

Where fuel-gas piping passes through a masonry or concrete foundation wall, what installation is required?

• a.It must be grouted solidly into the concrete foundation wall
• b.Gas piping is never permitted to pass through a foundation wall
• c.No protection is needed where the pipe crosses the foundation
• d.It must be sleeved and protected from settlement✓

IFGC 404.7 requires gas piping penetrating a foundation to be sleeved and protected so wall movement or settlement does not shear the pipe. Solidly grouting the pipe transfers building movement directly to it. The annular space is sealed to keep out water and gas migration.IFGC §404.7

Fuel-gas piping is prohibited in certain concealed and mechanical locations. Which is a prohibited location?

• a.Exposed along a basement joist with proper support and clearance
• b.Inside an air-supply duct or plenum✓
• c.In an accessible, ventilated mechanical equipment room
• d.In a ventilated attic when it is properly supported and protected

IFGC 404 prohibits gas piping in air-supply ducts, plenums, clothes and dumbwaiter chutes, chimneys, and vents, because a leak into moving air or a flue is extremely hazardous. Piping is routed in accessible or properly protected spaces instead. Piping in solid partitions is likewise restricted.IFGC §404.4

An appliance set up for natural gas is to be connected to a propane supply. What is required?

• a.Convert the appliance (orifices and regulator) for propane first✓
• b.The two fuels are freely interchangeable with no conversion at all
• c.Only the regulator, and never the orifices, needs to be changed out
• d.No change is ever needed when switching between the two fuels

Natural gas and propane have different heating values and pressures, so NFPA 54 requires an appliance to be converted with the manufacturer's orifice and regulator kit before switching fuels. Running a natural-gas appliance on unconverted propane greatly overfires it, producing soot and carbon monoxide.NFPA 54

A sediment trap is required ahead of many appliances but is exempt for certain ones. Which appliances are commonly exempt?

• a.Furnaces, which are the largest gas appliance in the dwelling
• b.Ranges, clothes dryers, and illuminating appliances✓
• c.No appliance is ever exempt from the sediment-trap requirement
• d.Water heaters, because their gas valve is close to the floor

IFGC 408.4 requires a sediment trap ahead of the appliance control but exempts ranges, clothes dryers, outdoor grills, gas lights, and similar illuminating/decorative appliances. Furnaces and water heaters must have the trap. The trap catches moisture and debris before the gas valve and must remain accessible.IFGC §408.4

A residential gas system is pressure tested at 3 psi. What test gauge should be used?

• a.No gauge; a soap-bubble check alone is the acceptance test
• b.Any gauge at all, regardless of its range or the graduations
• c.One fine enough to detect a small pressure drop✓
• d.A gauge reading only in coarse 5 psi increments across its dial

IFGC 406.1 requires a test gauge appropriate to the test pressure so a small leak-induced drop is visible; a coarse gauge could hide a slow leak. For a low-pressure 3 psi test, a gauge reading in fine increments (or a manometer) is used. The reading must hold with no drop for the required duration.IFGC §406.1

A commercial boiler is rated at 400,000 BTU/hr on natural gas at 1,000 BTU per cubic foot. What gas flow must the piping deliver?

• a.400 cfh✓
• b.200 cfh, mistakenly taking half of the rated input
• c.40 cfh, off by a full factor of ten in the division
• d.4,000 cfh, multiplying by ten instead of dividing

cfh = 400,000 / 1,000 = 400 cfh, per IFGC 402.4. Large commercial appliances drive substantial cfh demand that sizes the branch and often the whole service. This cfh is carried into the sizing table at the system's longest length to select the pipe size.IFGC §402.4

A six-outlet gas system is sized. The single longest run from the meter to any outlet is 95 ft. Under the longest-length method, which length governs every section?

• a.The sum of all the individual outlet run lengths added together
• b.Zero, because run length is not used in fuel-gas sizing at all
• c.The length of the run to the nearest outlet on the system
• d.95 ft✓

Under the longest-length method in IFGC 402.4, the single longest run (95 ft) is used to enter the sizing table for every section of the system. This conservative approach avoids undersizing when multiple appliances fire together. Individual section lengths are not summed or averaged in this method.IFGC §402.4

A whole house has appliances totaling 275,000 BTU/hr on natural gas at 1,000 BTU per cubic foot. What total cfh must the meter and main serve?

• a.275 cfh✓
• b.137 cfh, mistakenly taking half of the total connected input
• c.2,750 cfh, multiplying by ten rather than dividing by 1,000
• d.27.5 cfh, off by a full factor of ten in the division

Total demand = 275,000 / 1,000 = 275 cfh, per IFGC 402.4. The whole-house demand sizes the meter and the main from the meter to the first tee. Individual branches downstream are then sized for only the appliances each serves.IFGC §402.4

A new residential gas line is tested with air, not the fuel gas itself. Why is air (or an inert gas) used as the test medium?

• a.Because using fuel gas as the test medium costs more money
• b.Because the fuel gas would damage the test gauge diaphragm
• c.To avoid a flammable mixture during testing✓
• d.Because air is heavier than gas and finds leaks more reliably

IFGC 406 requires the pressure test to use air, nitrogen, carbon dioxide, or another inert gas, never the fuel gas, so no flammable mixture is created in the piping under test. Appliances are isolated because their regulators are not rated for the test pressure. Any pressure drop indicates a leak to repair.IFGC §406.4