Page 48 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Limitations of wheastone bridge

• Not suitable for very high Resistance measurement due to overheating of arms, leakage over insulation of
bridge arms by the application of high EMF. So inaccurate
• Not suitable for the low resistance measurement due to contact resistance drop. so inaccurate

Short and open circuit in series circuit
Short circuit (Fig 21)
A short circuit is a path of zero or very low resistance compared to the normal circuit resistance in series circuit
short circuit may partial or full.
Short circuit causes an increase in high current passes through the circuit

Fig 21

Open circuit in a series circuit (Fig 22)
An open circuit result whenever a circuit is broken or is incomplete and there is incomplete and there is no current
flows through the circuit. Any ammeter in the circuit will indicate no current.

Fig 22

Causes for open circuit
Improper contact of switches, burnt out resistors.

Effects of open in series circuit
1 No current flows in the circuit
2 No device in circuit
3 Total supply voltage appear across the open
Short and open in parallel circuit
Short circuit (Fig 23)

Shows a parallel circuit with short between point ‘a’ and ‘b’. This causes reduction of circuit resistance almost
‘zero’. There for the voltage drop will be almost ‘zero’. Then the result is that a very high current passes through
the short circuit. Short circuit may causes burning of the circuit elements like cables, switches etc. To avoid
burning of circuit components safety devices like fuse.

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CITS : Power - Electrician & Wireman - Lesson 5 - 12