How to provide 2 MOPP (Means of Patient Protection) - Heating Rod



Hi Guys,

frequently I am following the treats on this forum and they are very helpful. I am really appreciate it, thank you. I have one question myself. I am developing a device with a heating rod. The heating rod of choice is powered with 240V. The water flowing around the heating rod has a direct contact to patient’s skin. According to the 60601-1 3th edition 8.5.1 the heating rod needs to keep 2 MOPP. The heating rod is earthed according to 8.6. This is 1 MOPP and ok so far. Furthermore the heating rod is tested according to the IEC 60335-1 (safety of household and similar electrical appliances). However unfortunately this standard does not meet the requirements of dielectric strength and clearances and creepage distances of the 60601-1 for 1 MOPP. Beyond that the heating rod provides no further MOP. Unfortunately I have not found any suitable heating rod that would provide the 60601-1 requirements So my question, how to evaluate this situation based on the definition of the 60601-1 3th edition, is this solution acceptable? Or which additional MOP may be implemented to provide 2 MOPP for the heating rod?


Super Moderator
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Peter Selvey

Super Moderator
Just to put some numbers, it is assumed the heater rod passes 1.0kV according to IEC 60335-1, but fails the test at 1.5kV from IEC 60601-1.

(has the 1.5kVac test actually been done? It might be worth to check, the specification sheet might say 1.0kV, but the actual item might still pass 1.5kV)

If it does fail, there does not appear to be any simple solution. The only compliant solution seems to be an isolation transformer, but assuming the heater power is large, an isolation transformer could be huge.

The use of fixed wiring (not plugged into the wall, but direct to building installation), significantly reduces the risk of failure earthing and as a result could justify a reduction in dielectric strength for the heater. This could be written up as equivalent safety as documented in risk management, but might struggle to be accepted by test agencies/regulators.

3dBUnderThe Limit

Starting to get Involved
Unfortunately I have not found any suitable heating rod that would provide the 60601-1 requirements

Based on previous experiens from a similar design, I would say that at least a number of european suppliers of heater rods should be able to supply a heater that would have 1.5kV test voltage between the heater coil and PE.
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