your MOPPS from your a medical power supply
iEC/EN 60950 is a set of guidelines for the electrical safety of equipment connected to the public power grid, or mains. Now in its 3rd edition, iEC/EN 60601-1 is a further series of technical standards relating to the safety and performance of ‘Medical Electrical Devices’. The regulations are extensive and cofiguremplicated but two things need to be appreciated when selecting a power supply for a medical product:
by philip lechner avnet abacus
As mentioned earlier, IEC/EN 60601-1 3rd edition differentiates between the risk to patients and the risk to operators. A MOP can therefore be classified as Means of Patient Protection (MOPP) or a Means of
1 A power supply that is not ‘medically approved’ but conforms to IEC/ EN 60950 can be entirely suitable for some medical applications.
2 A power supply that’s ‘approved for medical applications’ will not necessarily enable the end product to gain qualification IEC/EN 60601-1.
Two related factors contribute to this apparent anomaly. First, medical products are classed either as medical devices (MD) or in-vitro diagnostic medical devices (IVD). Second, IEC/EN 60601-1 sets out different requirements for the protection of operators and patients. MDs are connected to, or used in close proximity to patients. Examples include respirators, syringe pumps and cardiac monitors. IVDs such as blood glucose analysers, centrifuges and other laboratory equipment will not normally come into contact with patients. It is the responsibility of the medical product manufacturer to determine the likelihood of a patient coming into contact with such devices through a formal risk assessment process (ISO14971). Where there is deemed to be no significant risk of this happening, IEC/EN 60601-1 norms do not apply and a power supply conforming to IEC/EN 60950 can often be used.
means oF protection (mop) Medical devices must incorporate one or more Means of Protection (MOPs) to isolate patients and operators from the risks of electrocution. A MOP can be safety insulation, a protective earth, a defined creepage distance, or an air gap or other protective impedance. These can be used in various combinations.
It’s important to understand that a protective earth is different from a functional earth. The latter is used for EMI suppression. A protective earth is a fail-safe circuit whose only purpose is to protect people from electric shock.
Creepage is the shortest path between two conductive parts (or between a conductive part and the bounding surface of the equipment) measured along the surface of the insulation.
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Operator Protection (MOOP). The isolation, creepage and insulation requirements for each are set out in Figure 1 (below). The main difference between one MOOP and one MOPP is primarily one of permissible creepage distance. Both requirements are satisfied using Basic insulation. To achieve 2 x MOPP qualification the isolation test is particularly demanding at 4000 Vac and the creepage distance of 8mm is twice that required for one MOPP.
3rd EDITION REQUIREMENTS BY CLASSIFICATION Classifications
One MOOP Two MOOP One MOPP Two MOPP
Isolation 1500 V ac 3000 V ac 1500 V ac 4000 V ac
Creepage 2.5mm 5mm 4mm 8mm
Insulation Basic
Double Basic
Double
Figure 1: IEC/EN 60601-1 3rd edition requires differing levels of isolation, insulation, creepage, and leakage current depending on the MOP level.
The withstand test voltages are higher for under IEC/EN 60601-1 than under IEC/EN 60950, as set out in Figure 2 (below).
Isolation type Basic isolation
Complementary isolation Double or stronger isolation
IEC/EN 60601-1 1500V 2500V 4000V
IEC/EN 60950 1500V 1500V 3000V
Figure 2: Test voltage requirements for medical vs. industrial power supplies.
continues p 6 > focus magazine - issue 17
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