Power
Extra considerations for products designed for “medical in the home applications”
When designing medical equipment, the power supply should be fairly simple: find a medical grade unit and away you go. However as usual things aren’t always that simple. Here, the power specialists at Luso Electronic Products discuss the extra considerations required
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are in the patient home is becoming more prevalent. With people having long term illness and medical conditions, they can sometimes be more easily cared for in their home, rather than having to make regular hospital or clinic visits. This usually means the patient has their own medical equipment that has been specifically designed for use in a domestic setting.
In general, for a medical power supply ensure that the unit selected meets the required levels of protection. They should be certified to the globally recognised standard, 60601-1, which defines the safety requirements for equipment that is connected to a power supply and used to diagnose, treat or monitor a patient in a medical application; be that in a medical, dental or lab environment.
But where the end equipment is intended to be used in a home or domestic environment then there are extra considerations to take into account, to deal with the uncontrolled environment and the fact that users might be untrained. This means that the equipment must also meet the IEC 60601-1-11 standard which covers the extra safety considerations for equipment used in a home healthcare environment.
One of the major issues is because the power source in a domestic environment isn’t considered to be as stable as that in a laboratory or hospital. To compensate you need to take extra care regarding input voltage and earthing.
Input voltage
The power in domestic homes is more variable than you may think. In the UK the voltage is nominally 240V AC, however to compensate for variations you need to allow for a power supply taking up to 264V input, a 10 per
44 February 2023
cent variance. Also, as you would want your product to be usable elsewhere round the world, the same applies so the lower limit of your input range needs to be 85V. So, look for a power supply offering an extra wide input range of 85V to 264V.
Earthing
In a domestic environment you need to ensure that the power supply is earthed. This is achieved by the power supply having extra insulation so it is an earthed supply. You can find the unit you need by checking if it’s a Class II supply.
What’s the difference, between a Class I or Class II supply? On a Class I unit the power supply provides a protective earth in case there is an insulation failure, by using a 3-pronged AC plug. Class II units rely upon the insulation in the power supply to provide the protection. For medical in the home applications, you need a Class II unit.
To ensure compliance to IEC 60601-1-11 the power supply used needs to be Class II as its assumed that the electrical environment has a poor protective earth conductor or maybe none at all. Class II power supplies provide this proper level of protection by having double or reinforced insulation and doesn’t rely on protective earth grounding. Not all medical power supplies in the market cover these extra requirements.
IEC protection classes - a brief overview
There are three protection classes defined by the IEC, depending upon the need/ requirement for a protective earth to be connected. Or how the user is protected from electric shock when the insulation in the equipment doesn’t work for some reason.
Class I – standard power supplies where the protection is provided by insulation and
Components in Electronics
the use of a connection to earth. Class II – required for medical in the home requirements. The protection is provided by using two levels of insulation in the power supply, be that double or reinforced. There is no need for earthing. Class III – this is for SELV (Safety Extra- Low Voltage) circuits where no further protection or earthing is required, not something to consider as these are not under consideration for medical applications.
MOPP qualification the isolation test is particularly demanding at 4000 Vac and the creepage distance of 8mm is twice that required for one MOPP. Creepage is the distance measured along the surface of insulating material between two points, and clearance is the direct distance through air between them.
Most medical units are 2 x MOPP and that is what we would suggest for most applications.
IEC PROTECTION CLASSES Class I Class II Class III
Users are protected from electric shock by insulation and the use of a protective earth/grounding
Users are protected from electric shock by two levels of insulation (either double or reinforced) no earthing required
Input is connected to a SELV circuit where no earthling is needed
Fig 1: Overview of the IEC Protection Classes for Power Supplies
MOPPS & MOOPS – what does this mean?
MOOP is “means of operator protection,” MOPP is “means of patient protection” - the latter is a higher level of protection and the highest level being 2 x MOPP. The main difference between one MOOP and one MOPP is the creepage distance. Both requirements are satisfied using basic insulation. To achieve 2 x
Patient connected devices Another consideration is to what level of contact does the end equipment come into contact with the patient. This is called “applied parts,” and depending on what parts of the equipment come into direct contact to enable it to function. There are 3 classifications, B (Body), BF (Body Floating) and CF (Cardiac Floating). Type B: The least stringent of the three
Classification 1 x MOOP 2 x MOOP 1 x MOPP 2 x MOPP
MOOP V MOOP - the differences Isolation 1500 V ac 3000 V ac 1500 V ac 4000 V ac
Creepage 2.5 mm 5 mm 4 mm 8 mm
Fig 2: The differences between the various MOOPs and MOPPs
www.cieonline.co.uk
Insulation Basic
Double Basic
Double
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