Monday, April 20, 2009
health and safety
(a) exposed conductive parts
(b) high voltage over 1000 volts, overheadlines and poor use of portable equipment
(c) R.C.D
(d) designed constructed installed maintained protected used
(e) ingress
(f) safely and securely de energised and isolated
(g) automatic disconnection of the supply of electricity
(h)
1 work activity
2 made dead
3 becoming live
4 inadvertly
5 unreasonable
6 reasonable
7 precautions
8 protective equipment
9 suitable
10 maintained
11 properly
(b) high voltage over 1000 volts, overheadlines and poor use of portable equipment
(c) R.C.D
(d) designed constructed installed maintained protected used
(e) ingress
(f) safely and securely de energised and isolated
(g) automatic disconnection of the supply of electricity
(h)
1 work activity
2 made dead
3 becoming live
4 inadvertly
5 unreasonable
6 reasonable
7 precautions
8 protective equipment
9 suitable
10 maintained
11 properly
Wednesday, April 15, 2009
RCD (Residual Current Device)
Electric shock occurs from two types of contact, direct and indirect.
Direct contact is when a person exposes the live and neutral wires and touches them directly resulting in electrocution.
While indirect contact is when by some fault the live wire is touching the casing of whatever it is contained in so when the casing is touched, and not the wire directly, that person is electrocuted…. unfortunately.
RCD’s are designed to prevent electrocution. The device does this by automatically shutting off the power or tripping as it is known whenever leakage current is detected. Leakage current is detected when the RCD notices an imbalance in the energised live wire and the return neutral wire. The RCD prevents electric shock by disconnecting the circuit within milliseconds of detecting an imbalance this prevents a person becoming an accidental ground for the leakage current and resulting in a lethal shock.
The supply is connected to terminals for live and neutral, the earth wire runs the length of the device uninterrupted, the load is also connected to terminals.
When the reset button is pressed the contacts close and this allows current to pass, it is the solenoid which keeps the contacts closed after the reset switch is released.
The sense coil also known as a differential current transformer surrounds the live and neutral and normally there is no current detected as they are equal and opposite but when there is a fault there is an imbalance in the two conductors.
The current is picked up by the sense coil, this is transferred to the circuitry, the circuitry then removes power from the solenoid which can no longer hold the contacts down which are forced apart by a spring this cuts off the electricity to the appliance thus preventing electric shock.
The test button passes a small amount of current through the device purposely causing an imbalance so as to verify the RCD will trip. If it does not trip it should be replaced.
An understanding of Faraday’s law would greatly help you understand the operation of an RCD because Faraday’s law says that current through a coil induces an emf and an equal but opposite current will cause the induced emf to equal zero so therefore whenever current is forced to take a different route an emf is induced tripping the RCD.
Electric shock occurs from two types of contact, direct and indirect.
Direct contact is when a person exposes the live and neutral wires and touches them directly resulting in electrocution.
While indirect contact is when by some fault the live wire is touching the casing of whatever it is contained in so when the casing is touched, and not the wire directly, that person is electrocuted…. unfortunately.
RCD’s are designed to prevent electrocution. The device does this by automatically shutting off the power or tripping as it is known whenever leakage current is detected. Leakage current is detected when the RCD notices an imbalance in the energised live wire and the return neutral wire. The RCD prevents electric shock by disconnecting the circuit within milliseconds of detecting an imbalance this prevents a person becoming an accidental ground for the leakage current and resulting in a lethal shock.
The supply is connected to terminals for live and neutral, the earth wire runs the length of the device uninterrupted, the load is also connected to terminals.
When the reset button is pressed the contacts close and this allows current to pass, it is the solenoid which keeps the contacts closed after the reset switch is released.
The sense coil also known as a differential current transformer surrounds the live and neutral and normally there is no current detected as they are equal and opposite but when there is a fault there is an imbalance in the two conductors.
The current is picked up by the sense coil, this is transferred to the circuitry, the circuitry then removes power from the solenoid which can no longer hold the contacts down which are forced apart by a spring this cuts off the electricity to the appliance thus preventing electric shock.
The test button passes a small amount of current through the device purposely causing an imbalance so as to verify the RCD will trip. If it does not trip it should be replaced.
An understanding of Faraday’s law would greatly help you understand the operation of an RCD because Faraday’s law says that current through a coil induces an emf and an equal but opposite current will cause the induced emf to equal zero so therefore whenever current is forced to take a different route an emf is induced tripping the RCD.
Tuesday, March 31, 2009
Monday, March 30, 2009
Friday, March 27, 2009
RE:Chraistian Bale
I, as the well learned dragon that i am, find it is quite apparent that Ste Conway is THE best Batman to ever have graced our existence!
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