Wires for Class II Medical Device

Dear Community,

I am choosing wires for our medical ventilator design, and am very confused. Since our device would have to be classified as a Class II medical electrical equipment, I figure that the wires used in the ventilator need to satisfy certain certifications. However, the only info about the electrical requirements for Class II equipments is listed below: (https://www.ebme.co.uk/articles/electrical-safety/classes-and-types-of-medical-electrical-equipment#:~:text=Class%20II%20medical%20electrical%20equipment,double%20insulation%20as%20shown%20below.):

The method of protection against electric shock in the case of class II equipment is either double insulation or reinforced insulation. In double insulated equipment the basic protection is afforded by the first layer of insulation. If the basic protection fails then supplementary protection is provided by a second layer of insulation preventing contact with live parts.

In practice, the basic insulation may be afforded by physical separation of live conductors from the equipment enclosure, so that the basic insulation material is air. The enclosure material then forms the supplementary insulation.

Reinforced insulation is defined in standards as being a single layer of insulation offering the same degree of protection against electric shock as double insulation.

Can anyone familiar with the medical device industry suggest how I can find qualified wires/cables on digikey?

Thanks so much ><
-Yumeka

Hi Yumeka,

Class II refers to how the isolation between the AC power source (wall outlet power) and the patient is handled. In Class II, the power supply accomplishes this isolation with its internal double insulation or single reinforced insulation. For medical devices used around patients, Class II power supplies are typically required.

Regarding wires used in medical devices, I think it primarily depends on whether they are within an enclosure or are potentially exposed to the patient. Within an enclosure, the there probably no specific requirements other than that they are capable of handling the electrical and environmental conditions they may be exposed to. This would be covered by the appropriate UL or IEC specifications.

I think there may be a few different topics that are getting confused here. Many regulations and standards commonly classify the things they’re regulating into different groups or “classes,” so simply stating that something needs to be “Class II” is not sufficient to communicate requirements without also mentioning which standard or regulation is being referenced.

The information referenced above discusses one approach for protecting a patient against accidental shock or contact with a live electrical circuit. Issues relating to which wire types are considered suitable for use inside a device is a separate question, as Dave mentions. “UL wire styles” might be a useful search term.

Additionally, devices intended for medical use are subject to regulations regarding leakage currents. While insulation systems may prevent direct contact with a power source, there is always some degree of capacitive coupling across an insulation barrier through which AC current can flow and potentially deliver a harmful shock to a patient. A “medical” power supply typically will have a lower level of leakage current than non-medical types.

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