04. Electrical Safety

Question 1

What type of current AC/DC is required to charge a capacitor?

Answer 1

alternating current need to be converted to direct current to charge capacitors

Question 2

How can you calculate the stored energy of a capacitor?

Answer 2

The stored energy of a capacitor is given by the formula: E = 1/2CV2

Question 3

How is a fuse chosen for an electrical apparatus?

Answer 3

Fuse is chosen to allow the apparatus to draw the power it requires to operate

Question 4

For type C(F) equipment the (F) signifies what?

Answer 4

The F suffix states that the patient applied part (the bit of the equipment which is connected to the patient) is

‘FLOATING’,

i.e. is electrically isolated from the rest of the apparatus

Question 5

Type II apparatus requires an earth connection? T/F

Answer 5

False

Double insulated apparatus has TWO physical barriers between the electrically applied part (the part of the apparatus connected to the mains) and the user

Question 6

How can direct current be produced from an alternating current?

Answer 6

Of course by placing a diode (electrical one way valve) in the wire

Question 7

Can electrostatic interference be produced by DC?

Answer 7

No, Electrostatic interference requires a ALTERNATING voltage to be present

Question 8

In an electrical transformer, if the voltage is halved, what happens to the current?

Answer 8

Doubles

If the secondary voltage is half that applied to the primary, then the secondary current is TWICE that drawn by the primary

Question 9

What is the efficiency of a transformer?

Answer 9

> 95%

Question 10

For a single phase mains supply what is the peak voltage?

Answer 10

+/- 339V

Question 11

Why does an earth free supply require a line isolation monitor?

Answer 11

To warn you if a fault has compromised safety of the system

Alarms if the supply has accidentally become earth referenced as the consequence of a fault

Question 12

What is the star point?

Answer 12

Is the Earth connection at the electrical substation

Connecting one side of the 240V supply to earth at the electricity substation creates the neutral connection.

Current flows between LINE and NEUTRAL wires

Is not used in a three phase electricity supply

Question 13

by doubling the separation between signal and power leads, what happens to electromagnetic interference?

Answer 13

Magnetic field strength varies as the reciprocal of the separation SQUARED.