MEIGAN

MEIGaN

MEIGaN

The MEIGaN (Medical Electrical Installation Guidance Notes) document published in September 2007 has given healthcare organisations clear and strict guidance regarding the electrical wiring and installation within new, refurbished or upgraded healthcare establishments. This guidance has been issued for new buildings, refurbished rooms and transportable diagnostic or treatment rooms. The notes stipulate a range of measures to be taken in relation to the electrical mains supply and include new instructions regarding the earthing and equipotential bonding connection of permanently installed medical devices and associated equipment. Developed for healthcare organisations and medical device suppliers, the new MEIGaN guidelines embody the basic principles of the BS7671 IEE Wiring Regulations, but refine this with specific requirements for medical environments.

Topic Contents - theoretical and practical aspects of:

Electrical systems

Mains supplies for Imaging locations

Calculating and measuring mains impedance

Earthing and bonding

Protection against Macro & Micro-shock

Power Quality

Overload Protection

Leakage currents

Isolated Power Supplies

Uninterruptible Power Supplies

MRI installations

Transportable Rooms

Inspection and Testing

Much of the document is concerned with wiring regulations. It has chapters on Mains Supply, Earthing and Equipotential Bonding, Socket-outlets and Bonding, Equipment Wiring Installation, and Transportable Diagnostic and Treatment Rooms. Detail is provided on quality of mains supply, appropriate wiring types and impedances, crimped connections, over current protection and mains monitoring devices. The chapter on Earthing and Equipotential bonding helps clarify this often confusing aspect of the standards. The guidelines include the requirement for a separate earthing terminal box when more than one circuit protective conductor is required for a medical device. Three separate connection bars are needed: the first earth connection bar connects all equipotential conductors from all permanently installed medical device(s) or modules of a system; all equipotential bonding from devices other than the permanently installed equipment connects to the second earth connection bar (a smaller additional connection bar can be connected to this bar to accommodate equipotential bonding conductors from socket outlets) (NHS 1989); the third earth connection bar or isolated earth stud is for the mains supply protective conductor. Managing the earthing in this manner has considerable benefits for testing. For example, with this configuration the origin of leakage currents should be readily identifiable. The bonding impedance threshold was discussed in the question and answer sessions; 0.1 ohm is the limit from a metal part that is protectively earthed back to the earth reference bar; 0.2 ohm is the limit between earthed exposed metal parts of two separate pieces of equipment within the patient area. This is because a star wiring configuration back to the earth reference bars is assumed(IEE 2004): i.e. 0.1 ohm back to the earth reference bar, and a further 0.1 ohm out to the second piece of equipment. In the case of 'plug-in' equipment, electrical safety categories are well defined. However, during questions there was some discussion and disagreement concerning the equivalent definitions for medical electrical installations. Arguably, a clear set of definitions is not fully achieved in the standards. IEE 60364-7-710 specifies three groupings of equipment: Group 0 has no applied parts, Group 1 has applied parts, and Group 2 has applied parts that may be used for intracardiac procedures, and for which a discontinuity of supply may be life threatening.3 IEE Guidance note 7 repeats this definition.4 The Annex to MEIGaN uses the three groups, but focuses the definition on whether discontinuity of supply is life ...