Hospital Safety Systems

Need for electrical safety in hospital:

The patient`s natural reactions to hazards are reduced or switched-off
The heart muscle is highly sensitive to electric currents (currents > 10 µA)
The insertion of catheters and the like into the body may reduce the electrical resistance of the skin
Body functions are temporarily or continuously supported or substituted by medical electrical devices
Fire and explosion risks through the use of anaesthetics,disinfectants or cleaning.
Even small currents flowing through the human body put the patients life and health at risk.
The availability of the power supply must be guaranteed, even under fault conditions.

Medical IT system in group 2 locations:

In group 2 medical locations, the medical IT system shall be used for circuits supplying

• Medical electrical equipment.
• Systems intended for life support.
• Surgical applications.
• Other electrical equipment located in the “Patient Environment”.

The IT system is supplied by an independent power source, e.g.
Distribution / isolation transformer

• Control-power transformer
• Generating set
• Battery
• Inverter of an UPS

The IT system has no direct connection between live conductors and earth. All exposed conductive parts of the electrical installation are earthed IEC 60364-7-71: A permanent insulation monitoring device must be designed to indicate the first occurrence of a live mass or earth fault; it must trigger an audible or visual signal.

Need for medical IT system :

Insulation fault:

• In the event of an insulation fault RF only a very low current ICe flows
• Fuse does not trip
• In the event of a single-pole earth fault, the power supply is guaranteed
• No interruption of operation
• An Alarm is indicated if an A-ISOMETER is installed

Leakage current:

The IT system is a small local network with low leakage capacitances. The fault current is limited by the body impedance, the earthing resistance and the high impedance of the fault loop. Hazards to persons and equipment arising from high fault currents are reduced.

Fire risk:

A small current flows limited by the high impedance of the fault loop. Considerable less fire risk
Increased protection for persons and equipment.

Requirements for power supply transformer

Protection against dangerous overloads and insulation failure.Requirements for power supply transformers shall be installed in close proximity to, inside or outside, the medical location placed in cabinets or enclosures to prevent unintentional contact with live parts.

Rated voltage Un on the secondary side of transformers = 250 VAC
Transformers according IEC 61558-2-15.

The leakage current of the output winding to earth and the leakage current of the enclosure, when measured in no-load condition and the transformer supplied at rated voltage and rated frequency, = 0.5 mA.

Rated output of the transformers 0.5 kVA … 10 kVA.

For three-phase loads with an IT system a separate three-phase transformer shall be provided for this purpose with output line-to-line voltage not exceeding 250 V.

IEC 61558-2-15 Safety of power transformers, power supply units and similar

Part 2-15: Particular requirements for isolating transformers for the supply of medical locations:
short-circuit voltage = 3%
no-load input current = 3%
inrush current = 12 x rated input current
Single phase transformers
ES0710 series
acc. to IEC 61558-2-15
1…10 kVA
Vertical or horizontal version, or installed in an enclosure

Monitoring of transformer:

Monitoring of overload and high temperature for the medical IT transformer is required. But no circuit breaker for protection against overload and overcurrent should be used (risk: unexpected tripping of the fuse). Overcurrent protective devices (MCB) should only be used for short-circuit protection.

If too many medical electrical devices are in use in an operating room, the information will be displayed on a remote indicator if provided.

Requirements for insulation monitoring device:

For each group of rooms serving the same function, at least one separate medical IT system is necessary.
The medical IT system shall be equipped with an insulation monitoring device in accordance with IEC 61557-8 with the following specific requirements:

• AC internal impedance > 100 kOhm
• The test voltage = 25 V d.c.
• Injected current = 1 mA peak, even under fault conditions
• Indication when insulation resistance = 50kOhm
• A test device shall be provided

The insulation monitoring device (IMD) signals the first fault (RF < 50 kOhm) provides advance information for the medical and technical staff.Hence the essential requirements for Medical IT System are Monitoring of Load, Temperature and Insulation.

Requirements for remote alarm indications:-

For each medical IT system, an acoustic and visual alarm system shall be arranged at a suitable place so that it can be permanently monitored by the medical staff:
A green signal lamp to indicate normal operation
A yellow signal lamp which lights when the minimum value set for the insulation resistance is reached. It shall not be possible for this light to be cancelled or disconnected
An audible alarm which sounds when the minimum value set for the insulation resistance is reached. This audible alarm may be silenced.
The yellow signal shall go out on removal of the fault and when the normal condition is restored
Note: Additionally overload and overtemperature of the IT system transformer must be indicated.

Insulation fault location :

The problem:
In intensive care locations several socket-outlets are arranged at every patient place, sometimes up to 24 socket outlets and more.In an intensive care unit with 4 beds, for example, these are more than 90 socket outlets. In intensive care units usually no technical experts are present, but medical personnel.
If a defective device causes an insulation fault, it will be very difficult to locate the associated socket outlet.In order to guarantee the patient’s safety, the insulation fault must be found as quick as possible.

The solution
Insulation fault location system EDS474

Benefits:

Ungrounded Power Systems according to IEC364-7-710
Fault location systems offer precise and fast localization of defective electrical equipment offer and guarantee a higher protection for patients and staff.
Modern and sophisticated indication panels and visualization possibilities offer precise and fast information to medical and technical staff.
Testing the electrical safety of medical electrical equipment acc. to IEC 62353 / 60601-1.