FRCA Paper 04 - Electrical Safety Flashcards
electricity supply to an operating theatre has how many phases?
single phase
electricity supply to theatres consists of what wires?
LINE, neutral and earth wires
NOT live
electricity supply to theatres has what voltage?
approx 240V
Does the electricity supply to an operating theatre have its earth connection at the substation?
The substation earth (star point) creates the ‘Neutral’ wire. The earth connection is a local earth
Is current flow in a wire required for electrostatic interference from a piece of equipement?
no current required
Can an insulating layer stop electrostatic interference?
Insulation will not stop this, it requires a conductive casing as electrostatic fields will not pass through a conductive barrier.
Electrostatic interference from equipment can be reduced by?
- halved by doubling the distance between the signal and power leads.
- Prevented using screened cable.
Electromagnetic interference: must the source be using current flow?
Yes - When an alternating current is flowing an alternating magnetic field is generated around the power wire and this induces current in the signal lead.
Where is the earth connection?
The earth connection is the LOCAL earth and is NOT connected at or to the substation
What are the requirements for an earth connection in terms of:
- resistance?
- current capacity, earth surge test?
- voltage during surge test
- resistance less < 0.1 ohm
- Earth surge test requires that the local earth can carry a current of 25A for 5 seconds.
- Since the resistance of the earth must not exceed 0.1 ohm, the surge test would not require a voltage of more than 2.5 V (from ohms law)
What is the star point?
The earth connection at the substation.
Connecting one side of the 240V supply to earth at the electricity substation creates the neutral connection.
How does the star point protect users?
The substation earth (star point) provides a path for lightening to reach the ground
Why is a star point not used in a three phase electricity supply?
A true three phase supply does not use a neutral connection. Star point is connected to a neutral wire at the substation.
How does an earth free supply increase electrical safety?
The supply is not earth referenced.
The isolating transformer means that the 240 V supply is no longer connected to the Star point.
> > > current can therefore not flow through you, via the ground to complete the circuit.
Increases protection from electric shock.
A line isolation monitor is required for?
Required by an earth free supply to warn if a fault has compromised the safety of the system.
Alarms if the supply has accidentally become earth referenced as the consequence of a fault.
T/F: which ventricle is more sensitive to micro-shock?
The right ventricle.
Can a micro shock induce asystole?
No
In micro shock, what current is sufficient to have an effect?
Anything 50 mA and over
What frequency of electric shock can cause arrhythmias?
> 1000 KHz
T/F: In electric shock, electrons flow through the body.
False, the charge carriers in the body are IONS.