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Class II type machine , and its compliance with 60601-1

muhammad sadiq

Starting to get Involved
#1
I just started working on a APD dialysis machine as an internee, so I am new to reading through 60601-1 standard.

1) About our APD machine it gets its 24v dc supply, through an external medical grade power supply which is iec 60601-1 compliant(model) and have only two leads (no earth pin), it has been told to me by my seniors that our ME is a Class-II device and hence require double insulation or reinforced insulation, my question is what does this double insulation looks like in practical, my understanding is , if we give the relevant air clearance and creepage distance between electrical board(which works on 12V/5V) and enclosure and the enclosure is made of a non conductive material that gives us 2 MOPP, and hence our machine is class II compliant and have double insulation, so am I right and what if our machine have metal enclosure and we don't have a earth(Class II) how do you give that 2nd MOPP?

2) While going through this forum I came across an argument which said " the classes(class I, class II) are mentioned only for machines that are connected directly to the supply mains (220-240VAC), but if you have a adaptor(24VDC medical grade,60601-1 compliant) in between your ME and mains then these classes do not apply on you " is this correct assessment??
 
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Benjamin Weber

Trusted Information Resource
#2
"Class I" (with PE as means of protection) and "Class II" (no PE) are applicable for devices which are powered by an external power source (see subclause 6.2). This power source may be the supply mains, but it can be an external power supply! All devices are "internally powered". Usually internally powered devices with the opton of an external power supply or a charging function are classified as class II while connected to the power supply/charger, because they normally don't have a PE. The power supply/charger itself maybe class I!

Regarding the metal enclosure: Class I or II are not defined by having a metal enclosure - the only parameter is using a PE or not.

If your device needs a metal enclosure, but you cannot use a PE (e.g. due to IEC 60601-1-11 for home healthcare devices which explicetly allows only class II or internally powered!), you have to implement the creepages, clearances and solid insulation to reach 2 MOP. If you have double or reinforced insulation between the hazardous voltages and accessible parts (the metal enclosure), you don't need to connect the enclosure to the PE - because you already have 2 MOP.
In class I devices you can use the PE as 1 MOP and need only 1 additional MOP by basic insulation (shorter creepages, clearances and lower test voltaged for solid insulation). That is the advantage of class I.
 
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muhammad sadiq

Starting to get Involved
#3
Class I" (with PE as means of protection) and "Class II" (no PE) are applicable for devices whoch are powered by an external power source (see subclause 6.2). This power source may be the supply mains, but it can be an external power supply. Other devices are "internally powered". Usually internally powered devices with a charging function are classified as class II while connected to the charger. They normally don't have a PE.
sir
- does externally powered means mains voltage directly to ME or it means that the power supply unit is outside the ME eg an adaptor like power supply?
-does internally powered means "battery powered " or does it means that the supply unit is inside the ME?
 

muhammad sadiq

Starting to get Involved
#4
my understanding is that the electrical circuit is divided into two parts in this standard
1) Primary (which has mains supply)
2) secondary (which come after a isolation transformer or other isolation devices)

if i use an adaptor like medical grade power supply (which is outside my ME) it already does the isolation and step down of voltage part for us (and provided 2MOP) , so my ME internal circuitry is secondary part and does not require double insulation.

Reasoning for above statement :
- in IEC 60601-1 standard the figure used to show class II device, shows double insulation only around the primary part of the circuit.

is my reasoning correct?
 

Benjamin Weber

Trusted Information Resource
#5
Externally powered means - well, not internally powered ;-) This external power soource cann be a power supply, which itself is connected to the supply mains.

Internally powered means, that hte power source in inside the device (see subclause 3.45 for "internal electrical power source"). This can be a battery, hydrogen fuel cell, nuclear power source or similar.

In my oppinion, you might also need double or reinforced insulation regarding secondary circuits for patient protections. While most secondary circuits may be not hazardous to the operator, you always have to consider the higher degree of protection for the patient required by the standard.
 

muhammad sadiq

Starting to get Involved
#6
just another random ques
in IEC 60601-1 , clause 8.6.9 it talks about "isolated internal screens " for CLASS II ME , what are these screens that they are talking about ?
 

CharlieUK

Quite Involved in Discussions
#7
Class I and Class II refers to how the required two levels of protection are provided between Hazardous Circuits (AC mains) and Accessible Circuits (in this case the 24V output of the PSU)

If the PSU provides 2 MOPP and your 24 V powered device doesn't then generate higher secondary voltages, then I'm not sure why you need a safety earth on the APD machine
 

Benjamin Weber

Trusted Information Resource
#8
Class I and II do not solely relate to devices directly connected to AC mains, but to devices which are powered by an external power source, which the AC mains is only one possibility!

And you always have to consider patient safety, where only patient leakage currents are relevant and as a consequence all usual secondary voltages are considered to be hazardous! While usually the 24V can be considered not hazardous for the operator*, you have to protect the patient from this voltage. This would normally be done by double or reinforced insulation. But a PE might also be helpful for 24V secondary voltages.

This situation (PE for protection against secondary circuits) is also part of the PE impedance test per subclause 8.6.4 b). If you that section carefully, you can see, that higher impedances are allowed for PE connections with relatively low maximum currents (and not the 25 A).

*Very often the additional requirements for this "SELV" (which we actually don't have in ME equipment due to patient safety!) are not considered. According to subcluase 8.4.2 c) you have to take into account the available power and energy as well (less than 240 VA after 60 seconds!).
 

Benjamin Weber

Trusted Information Resource
#10
Yes, of course. That plastic enclosure would be considered "solid insulation" and will have to comply with the relevant requirements:

- Dielectric strength, cl. 8.8.3
- Ball pressure test, cl. 8.8.4
- Mechanical strength tests, cl. 15.3

I strongly recommend to read cl. 8.5 for separation of parts!
 
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