Selecting components to meet UL 60601-1

B

blackrooster

#1
Hello All:

I am new to UL60601-1 and could use a little direction on component selection.

We are designing a machine that we want to comply with UL60601-1. In my opinion it is a bit of a stretch to consider it a medical device but some of our customers have indicated that they would like FDA approval. The machine does not have any parts that would be applied to a patient so I think I am just concerned with operator safety.

My question is about selecting components to meet UL60601-1. I see that some things like power supplies are easy to find with a UL60601-1 listing. However there are a lot of component types where I don?t see any options. I don?t know whether I am not looking at the right suppliers or if I am looking for something that doesn?t exist.

As one example, the control of this machine would be well suited for a Programmable Logic Controller (PLC). Unfortunately I don?t see anything similar to this that is intended for a medical electrical device. Are there any off the shelf type controllers that are appropriate for UL60601-1? I would rather not have to design a custom PCB for this machine.

I would appreciate any input that you guys can share with me.
Thanks in advance.
 
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Jaydub

Involved In Discussions
#3
Here is my take:

Only components that form a means of protection or the failure of which would create a hazard, would need to be considered. For example, this most likely includes everything on the primary side of an isolation transformer. These components should meet any relevant safety standards and be used within their ratings. For example most power switches have been evaluated by UL and a myriad of other agencies. They don't need to specifically meet IEC 60601-1, but rather the IEC or ISO standard for power switches. A switching power supply probably does need to meet IEC 60601-1 requirements for your product to pass leakage current and dielectric strength tests.

A PLC probably is not a safety critical component and you could use any one you wish.
 

Peter Selvey

Staff member
Super Moderator
#4
According to UL 60601-1:2003, there is a special clause (3.10DV.1.1) which requires specific components to meet UL standards, and this is limited to wiring, tubing, optocouplers, PWBs, lithium batteries and CRTs.

For other parts, it is the judgment of each engineer whether a part is:

(a) included in the critical component list, and
(b) included in the critical component list with required UL recognition

There are many cases where a part is considered safety critical, but no UL is expected. The part will appear on the component list just so the factory inspector can check if it has changed.

If the engineer insists on UL recognition, usually there is usually some reason. For example, the part itself may be so critical that factory inspection at the part manufacturer is also reasonable. In such a case, choosing a UL recognized part makes things easier (but other routes are also possible).

One problem is the tendency to list UL recognition even if not required. For example, the engineer will often list the maker and material of the rating label (which is reasonable) but then go on to list the UL recognition. However, the recognition is often just for UL 94 (flammability) which has nothing to do with complying with a rating label or UL 60601-1. It then looks as if the UL recognition is required for the rating label, but actually it is not.
 
B

blackrooster

#5
Thanks to both of you for the reply.

My understanding is that the primary criteria for 60601 compliance are dielectric, creepage, clearance, and leakage current. I see how a typical switching power supply is unlikely to meet all of these and so a 60601 power supply is needed.

A few more questions if someone doesn?t mind?

1) Are there other kinds of components besides a switching power supply that you generally would want to look for a UL60601 rating?

2) Is it safe to say that I don?t need to worry about anything low voltage (24V)?

3) As an example, it sounds like a contactor for starting a motor would be a MOP because it carries the mains voltage. I don?t think there are UL60601 contactors so I should just look for one that meets the IEC standard for the device and then verify dielectric, creepage and clearance dimensions. Does this sound right or am I missing something?

Sorry if these are really basic questions. I am obviously very new to 60601 and I?m just trying to get a feel for what is expected.
 

Peter Selvey

Staff member
Super Moderator
#6
Actually UL 60601-1 is not applicable to power supplies. It is kind of an industry quirk which allows power supplies to be certified, strictly against the rules but allowed because it makes the end product evaluation simpler. But it is the exception rather than the rule. Most components have special standards that are written for that component, and the expectation is to use the applicable standard for the component, not UL 60601-1.

If the part is required to be certified, there should be some relevance to the scope of certification. For UL, their certification is based on UL 60601-1 but there is also a disclaimer which limits this to "shock, fire and mechanical hazards" only. So in general the focus is on mains/patient isolation; parts protecting against fire and mechanical hazards. Most of these parts are in the mains circuit.
 
B

blackrooster

#7
That makes sense. I got confused because someone cautioned me against using UL508 components when trying to comply with UL60601 and I assumed that I would be able to find UL60601 equivalents for everything. I didn't understand why power supplies were the only devices I could find.

So my general approach will be to select components that comply with their applicable standards and then verify that the creepage, clearance, and dielectric ratings fall within the limits of 60601. Low voltage components are probably easy to meet the requirements and the danger is low. Mains voltage components have a much higher risk of shock or fire hazards so this will be the focus of any 60601 evaluation.
 
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