General Medical Locations

Question 1

Why should biomedical engineers care about room installation ?

Answer 1

device safety may be compromised which may lead to both business and patient risks.

Question 2

What is the definition of a medical location ?

Answer 2

Room or area where medical devices with applied parts are used.

Question 3

What is an Equipotential Bonding Busbar (EBB) and what principles should be considered when wiring?

Answer 3

An EBB is the reference point for all the electrical groundings in the room and is the only direct connection to the main earthing of the room. It uses a copper bar and where multiple busbars are required the connections between them should be secure.
Should be in both group 1 and group 2 locations.

Question 4

Why is an EBB used in a medical location ?

Answer 4

An EBB is used to provide protective earthing which reduces the risk of microshock. It removes the risk of electro magnetic interference and minimises patient leakage current.

Question 5

What is the difference between disconnection risk and failure risk ?

Answer 5

Disconnection Risk – > Loss of mains supply due to the tripping of an RCD fuse or a circuit breaker. Devices with a disconnection risk use blue medical IT sockets. Disconnection causes patient risk.
Failure Risk –> Mains network supply loss. Uninterruptable power supplies are used to combat this. Failure can cause patient and business risk.

Question 6

What is an applied part ?

Answer 6

Found in IEC 60601 subclause 3.8
Part of medical electrical equipment that in normal use comes into contact with the patient for the medical electrical equipment to function properly.

Question 7

What is the maximum tolerable value of earth resistance in a medical location ?

Answer 7

0.2 ohms.

Question 8

What reasoning is require to decide if a room is a group 1 room or a group 2 room ?

Answer 8

Group 2 is a stricter condition and is chosen if there are applied parts to the circulatory system to be used in the location (e.g. a catheter) or if disconnection to the patient will affect patient safety (transient fault) .
Medical IT is required if a room is a group 2 location and not if it is a group 1 location.

Question 9

What is governance in a hospital setting and what is the guidance document for this ?

Answer 9

Provides direction and strategy for leadership. Involves risk management and assessment. Found in HTM 0601 document.

Question 10

What sort of professionals should be involved in an Electrical Safety Group ?

Answer 10

Radiographers
Radiologists
Electrical Contractors
Electrical Designers
Medical Physicists
Equipment Suppliers
Board Members
Governors

Question 11

What is an EPO ?

Answer 11

Emergency power off switch are able to turn off uninterruptable power supplies remotely in the case of a fire. It has a normally closed contact which opens when pressed and breaks the surface.

Question 12

Describe how voltage is transmitted and distributed by a power station ?

Answer 12

Stepped up to kilovolt range using a 3 phase transformer for transmission to increase efficiency percentage. Stepped down at the local stations to 240 Volts

Question 13

What are the current UK phase colours for mains wiring ?

Answer 13

Earth = Green
Neutral = Blue
3 phases = Brown, grey and black.

Question 14

What is the purpose of a Residual current device (RCD) and what is a downside to an RCD ?

Answer 14

An RCD protects against insulation failure by detecting imbalances in the current flow. They are tripped when there is a current spike.
A downside is that they are sensitive to transient spikes from the mains supply.

Question 15

What is medical IT ?

Answer 15

Blue sockets which have no switch to reduce disconnection risk and an isolated earth system which has its own EBB connection. ONLY USED IN GROUP 2.

Question 16

What is the medical IT earthing system ?

Answer 16

Extraneous dirty earth on the neutral side.
radial clean earth on the live side , which goes back to the EBB.
Plastic link between the two earths and the radial.

Question 17

What current is used when measuring mains resistance ?

Answer 17

1A.

Question 18

What is the easiest way to measure leakage current ?

Answer 18

Use a 4 wire Kelvin meter which injects a 1A current and measures the voltage drop.

Question 19

How do we test for mains resistance ?

Answer 19

Create a circuit using a voltmeter and an ammeter placed around the mains resistance. Use Ohms Law.

Question 20

How do we test the impedance and what is it ?

Answer 20

Z is the impedance which is the phase to phase impedance.
Should ensure the phase synchronisation first.
Can be tested using impedance meter which requires 2 connections so cycle between 1 and 2, 1 and 3 and 2 and 3.

Question 21

How do you test domiciliary device sockets ?

Answer 21

use a socket checker. if doubts use earth loop tests and always ask age/ history of socket.

Question 22

What is micro shock and how is its risks minimised in medical locations ?

Answer 22

Microshock is a term used to describe low frequency currents which have the potential to disrupt the hearts pacemaker (SA node).
Risks are minimised using a radial wiring system with no current loops and using an EBB helps to prevent these loops by ensuring proper grounding. 100 microamps is an unacceptable current.

Question 23

What are the types of supply earth systems ?

Answer 23

TT - (terra) earthing comes from the local earth electrode.
TN - (network) earth connection is supplied by the supply network, either separately as protective earth or combined with the neutral conductor.
IT - (Isolated terra) no point is directly earthed, isolated from earth.

all either connected or separate relating to how neutral and earth are connected.

Question 24

What is a PEC (Potential Equalisation Conductor ) ?

Answer 24

A green cable supplied with a medical device that is plugged in with the mains cable and connects the metal casing on the equipment to a supplementary equipotential bonding connection point. REQUIRED IN GROUP 2.

Question 25

What are the 3 types of applied parts ?

Answer 25

B, BF and CF.

Question 26

What leads may be used to connect to an EBB ?

Answer 26

potential equalisation leads and supplementary equipotential earth bonding connection points. (PE or SEBCP) SEBCP aren’t often needed in group 1 and should be installed close to where the device is.