What is the purpose of keeping tremie pipe’s tip immersed in freshly-placed concrete for about 1m in underwater concreting?

  What is the purpose of keeping tremie pipe’s tip immersed in freshly-placed concrete for about 1m in underwater concreting? The size of tremie pipe is about 300mm with sections having flange couplings fitted with gasket to prevent water leakage. The tremie pipe should be closed initially to prevent water from entering the pipe. It should be designed with sufficient thickness and weight so that it would not be buoyant when empty inside water. The placement of tremie concrete is commenced by putting the closed pipe underwater to the location for concreting, followed by partial filling of tremie pipe with concrete. In order to have tremie concrete flowed out of the pipe, it is necessary to fill the pipe with concrete of sufficient height to overcome the water pressure and frictional head. After that the tremie pipe is raised about 150mm to allow concrete to flow out. To enhance sufficient bonding, each succeeding layer of concrete should be placed before the preceding layer has rea...
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WHAT IS HOUSE WIRING SYSTEM ?? ISI RULES FOR WIRING

SYSTEMS OF WIRING

• Tree System
• Distribution System

Tree System:

• This system is not used in installation purpose. It is generally used for temporary connections nowadays. In this system branch circuits are tapped from the mains at required places.

• Advantages: Less cost.

• Disadvantages: Appearance is poor.
• Fault location is difficult.
• Large voltage drops.

Distribution System:

• This system is used widely now a days and is used for indoor wiring in buildings. In this system, mains are taken to one or more distribution centres and connected to the distribution boards. From these
distribution boards connections are taken to branch circuits. In this system no joints are required and is
systematic.

• Advantages: Appearance is Good.
• Fault location is easy.
• Each circuit is separately protected by a Fuse or MCB.
• Replacement of Fuse or MCB is easy.
• The system is simple and capable of further extensions.

• Disadvantages: It is costlier than the Tree System.







ISI RULES FOR WIRING

• In AC Supply, the 3 phases should be indicated Red, Yellow, Blue and Neutral should be indicated by Black.
• In DC Supply, +ve should be indicated by Red and -ve should be indicated by Black.
• Earthing should always be indicated by Green.
• In the domestic wiring, 3 pin plug should always be used.
• All metallic appliances should be earthed.
• All switches should be connected through live wire.
• All switches should be fixed at the left side of the entrance door.

IMPORTANT WORDS IN HOUSE WIRING 

• Switch: A manually operated device for closing and opening the circuit. Switches can be 1 way, 2 way, grid switch, push button switch.

• Main Switches:

• ICDP - Iron-Clad Double Pole Main switch is used for single phase supply control. 16/32/63Amps. 250Volt.
• ICTP - Iron-Clad Triple Pole Main Switch for 3 phase supply control.

Fuse: It is the weakest point on the circuit. It is a device used for protecting the installation and cables, & switchgears etc. on
the circuit. 
Types of Fuses:1) Rewireable Fuse (2) HRC Fuse (High Rupturing Capacity Fuse)
MCB: Miniature Circuit Breaker - Used nowadays as a Fuse for protection of the installation. It is very light and requires very less space. Available in Range of 0.5Amps to 63Amps.
MCCB: Moulded Case Circuit Breaker - Used as a protection in the higher range. Available in Range of 50Amps to 1000Amps.
ELCB - Earth Leakage Circuit Breaker - Used as a Protection against earth leakage. Available in Range of 25Amps to 125Amps.

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