CCN1 Pipework and Fittings 2

Question 1

What is the purpose of purging a gas installation after completing pipework installation or modification?

Accepted Answer

To remove air from the pipework and replace it with gas, preventing a potentially explosive air-gas mixture

Answer

Purging removes the air from newly installed or modified gas pipework and replaces it with gas. This is essential because a mixture of air and gas within the pipe could form an explosive mixture. Purging must be carried out safely in accordance with IGE/UP/1B, ensuring proper ventilation and that no ignition sources are present.

Question 2

What is the minimum pipe size typically required for a gas meter connection to a domestic boiler with a rated input of 30 kW?

Accepted Answer

22 mm

Answer

A 22 mm pipe is typically the minimum size for supplying a 30 kW domestic boiler from the meter, depending on the pipe run length and the number of fittings. Pipe sizing must be calculated using the appropriate formula or sizing tables to ensure the pressure drop does not exceed 1 mbar from the meter to the appliance.

Question 3

What is the maximum permissible pressure drop between the gas meter outlet and any appliance in a domestic installation?

Accepted Answer

1 mbar

Answer

The maximum permissible pressure drop between the gas meter outlet and any gas appliance in a domestic installation is 1 mbar. This ensures that each appliance receives adequate gas pressure for safe and efficient operation. If the pressure drop exceeds 1 mbar, the pipework may need to be upsized.

Question 4

When sleaving gas pipework through a wall, what must the sleeve extend to on each side?

Accepted Answer

Flush with the wall surface on both sides

Answer

When passing gas pipe through a wall, the sleeve must extend flush with the plaster or wall surface on each side. The gap between the pipe and the sleeve should be sealed at both ends with a suitable fire-resistant sealant to prevent gas migration through the wall cavity. The sleeve protects the pipe from corrosion where it passes through masonry.

Question 5

During a tightness test, what is the stabilisation period required before commencing the 2-minute observation?

Accepted Answer

1 minute

Answer

Before commencing the 2-minute tightness test observation period, a stabilisation period of 1 minute must be allowed. This permits the gas temperature and pressure to equalise throughout the installation after pressurisation. Without this stabilisation period, temperature-related pressure changes could give a false reading.

ACS CCN1 Practice Test

ACS CCN1 Practice Test

CCN1 Pipework and Fittings 2