Medical locations (§710) — Group 2 IT system, isolating transformer and insulation monitoring

Medical locations carry an elevated risk: patients are often weakened, sometimes directly electrically connected to medical equipment (for example via a catheter or an intracardiac probe), and an unexpected power interruption during a procedure can be life-threatening. §710 (based on IEC 60364-7-710) therefore imposes additional requirements on top of the regular NEN 1010 provisions, with the strictest requirements for Group 2 locations.

Group classification

Group 0: locations where medical electrical equipment does not come into contact with the patient (for example a waiting room).
Group 1: locations where equipment comes into contact with the patient externally or via body cavities, but a brief interruption of the supply does not present an immediate danger to life (for example an ordinary examination room).
Group 2: locations where equipment is used for procedures on the heart, the brain or the central nervous system, or where a supply interruption presents an immediate danger to life (operating theatres, intensive care units, cardiac catheterisation rooms).

IT system with isolating transformer in Group 2

In Group 2 locations, the final circuits for medical electrical equipment must be supplied via an IT system with a medical isolating transformer, in accordance with IEC 61558-2-15. This transformer is typically single-phase, with a rated output of 0.5 to 10 kVA. The IT system ensures that a first earth fault does not result in automatic disconnection: treatment can continue while the fault is located and rectified, rather than the supply dropping out mid-procedure as would be the case with a TN or TT system.

Insulation monitoring (MED-IMD)

Because a first earth fault in an IT system is not apparent without active monitoring, a medical insulation monitoring device (MED-IMD), in accordance with IEC 61557-8 (annexes A and B), is mandatory. The MED-IMD continuously monitors the insulation resistance between the live conductors and earth and generates an alarm at an insulation resistance of 50 kΩ — well before an actually dangerous situation can arise, so that staff are warned to fix the fault without the supply having to be interrupted.

Additional equipotential bonding

In both Group 1 and Group 2 locations, additional (supplementary) equipotential bonding is mandatory: all conductive parts within the location — including extraneous conductive parts such as metal pipework and bed frames — are bonded to each other and to the earthing busbar, to minimise the touch voltage between simultaneously accessible parts.

Note: this article covers the core principles of §710. The exact group classification of a specific location is determined by the responsible physician or hospital organisation in consultation with the person responsible for the installation, not by the installer alone — this article does not provide a decision scheme for that classification.

Practical relevance

When (re)building an operating theatre or ICU ward, it is important to establish at the start of the design which locations are classified as Group 2, since this directly determines whether an isolating transformer with MED-IMD is required — adding this retroactively usually requires extensive modifications to the existing distribution board and wiring.

Common mistakes

Treating an ordinary examination room as Group 2 (or vice versa) without consulting the party responsible for care — the group classification follows from medical use, not from an assumption made by the installer.
Applying an IT system without MED-IMD monitoring — without monitoring, a first earth fault remains undetected, turning the advantage of the IT system (continuing to operate through a single fault) into a hidden risk instead.
Limiting additional bonding to only the fixed parts of the installation — extraneous conductive parts such as bed frames and mobile equipment must also be included where relevant.