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IEC 60601-1 cl.15.4.2.1 - Tubular Heating Element (Protection against Overheating)

A

antonoia

#1
Hi All!!
I am working on reviewing the design of a class I device that has a tubular heating element powered with live and neutral trough a relais, the scope is to verify if complies with 60601-1. I found the clause above specified that states: "equipment that incorporates tubular heating elements shall have protection against overheating in both leads where a conductive connection to earth could result in overheating".
I did not fully understand the reason of this requiremnent, from what it is written I believe that if not both leads are disconnected currents can still pass trough the live conductor to earth trough the tubular. If this is the reason why is this requirement of disconnecting both leads applied only to tubular heating element and not also to some other components? Hope someone can help to understand and to verify if this will be applicable also in my case. Many Thanks!!
 

3dBUnderThe Limit

Starting to get Involved
#2
Re: IEC 60601-1 cl.15.4.2.1 - Tubular Heating Element (Protection against Overheating

I think that your analysis is essentially correct.
For a heater this fault would lead to uncontrolled heating. As the heating element could operate with a normal current, any overcurrent protection will not be activated, that would be the difference between this type of component compared with an power supply where the same type of error would trip the fuse.

This is a known failure mode and I would say that disconnecting both leads are necessary
 
A

antonoia

#3
Re: IEC 60601-1 cl.15.4.2.1 - Tubular Heating Element (Protection against Overheating

Thank you 3DBunderthelimit, fortunately in 10 years of working with tubular heating element I did not have occasion of experiencing such failures, perhaps I should try to simulate in a bench test. Are you aware of other devices where this requirement can be still used?
 

3dBUnderThe Limit

Starting to get Involved
#4
Re: IEC 60601-1 cl.15.4.2.1 - Tubular Heating Element (Protection against Overheating

For a heater you would get uncontrolled heating for a device in standby mode. A similar scenario in a motor could lead to uncontrolled movement. If this could lead to a hazardous situation, disconnection of both live and neutral could be an appropriate mitigation.

So I think that it's appropriate to consider this type of failure for other devices in the risk analysis
 
A

antonoia

#5
Re: IEC 60601-1 cl.15.4.2.1 - Tubular Heating Element (Protection against Overheating

Thank you again, I was thinking if a RCD breaker is installed on the building , would not be this enough to mitigate this risk? In case of current on the earth conductor this will disconnect all the poles, or do you think it will be better to have a RCD installed on the device? will this release me from the complying from the requirements of this famous clause? Regards!
 

3dBUnderThe Limit

Starting to get Involved
#6
Re: IEC 60601-1 cl.15.4.2.1 - Tubular Heating Element (Protection against Overheating

I feel that I?m getting in to a grey zone, where I don?t know enough about the system to give a good answer. But I will give you my opinion anyway :)
To me, using an RCD is adding much more complexity in the system than needed. Most likely a requirement of regular testing of the RCD is needed in the documentation. Personally I would opt for a design where I have a switching element in both live and neutral to the heater.
 
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