Does 2xMOOP / 2xMOPP require two separate converters / layers of isolation?

Also see: Why do medical devices need 2xMOPP?

Developers working on medical devices are frequently faced with the challenge of designing according to the stringent electrical safety requirements of IEC60601-1.

One question is whether you need two separate levels of isolation in order to fulfil the 2xMOOP and/or 2xMOPP requirements.

For example, you could design your device like this in order to achieve 2xMOPP isolation:

This is expensive and often unneccessary!

First, you have to understand that IEC60601 does not specify how many converters you have to use, it mandates that you have a minimum isolation voltage! 2xMOPP does not neccessarily mean that you have 1xMOPP plus an additional 1xMOPP converter, it just means that you have to fulfil more stringent isolation requirements than for many non-medical products.

The isolation requirements are:

• 2xMOOP: 3kV isolation
• 2xMOPP: 4kV isolation

IEC60601-1 allows two methods of achieving MOOP and MOPP:

• Either you use two separate layers of isolation, like the two converters shown above
• Alternatively, you can use reinforced isolation, i.e. a single converter that has additional isolation.

In most cases, IEC60601 products use reinforced isolation instead of having two separate converters.

Some arguments for preferring reinforced isolation as opposed to using two separate converters are:

• Two converters are typically more expensive than using a single, reinforced isolation converter
• You have additional risk of one of the components not being available for purchase any more, which could lead to expensive re-certification of your device
• If you have two converters, you will have approximately two times the risk of one of them being defective (for example, because of aging capacitors after operating your device for a couple of years.)
• Your device will have lower efficiency since more power is wasted in the two converters than would be wasted in a single converter.

Source & more reading: Johner Institute