Can enclosure of semiconductor or electrolytic capacitor provides basic insulation?

S

sankui

#1
Dear all,

Our products mainly employ switching power supply (SPS) to power the equipment. In SPS, there are several semiconductors and electrolytic capacitors. some of these components are close to the transformer and may influence the safety spacings between primary and secondary. However, if the enclosure of semiconductor or electrolytic capacitor (sheet) is regarded as basic insulation, additional sleeve may not be necessary.

Can anyone tell me that whether the enclosure of semiconductor or electrolytic capacitor (sheet) provides basic insulation?

Thanks and regards.
 
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Stijloor

Staff member
Super Moderator
#2
Re: Can enclosure of semiconductor or electrolytic capacitor provides basic insulatio

Dear all,

Our products mainly employ switching power supply (SPS) to power the equipment. In SPS, there are several semiconductors and electrolytic capacitors. some of these components are close to the transformer and may influence the safety spacings between primary and secondary. However, if the enclosure of semiconductor or electrolytic capacitor (sheet) is regarded as basic insulation, additional sleeve may not be necessary.

Can anyone tell me that whether the enclosure of semiconductor or electrolytic capacitor (sheet) provides basic insulation?

Thanks and regards.
Any electronics folks that can help?

Thank you!!

Stijloor.
 

Al Rosen

Staff member
Super Moderator
#3
Re: Can enclosure of semiconductor or electrolytic capacitor provides basic insulatio

Dear all,

Our products mainly employ switching power supply (SPS) to power the equipment. In SPS, there are several semiconductors and electrolytic capacitors. some of these components are close to the transformer and may influence the safety spacings between primary and secondary. However, if the enclosure of semiconductor or electrolytic capacitor (sheet) is regarded as basic insulation, additional sleeve may not be necessary.

Can anyone tell me that whether the enclosure of semiconductor or electrolytic capacitor (sheet) provides basic insulation?

Thanks and regards.
That's what basic insulation is. Supplementary insulation would be the additional sleeve and two sleeves would be reinforced insulation.
 

Peter Selvey

Staff member
Super Moderator
#4
Re: Can enclosure of semiconductor or electrolytic capacitor provides basic insulatio

Generally this is not a good idea.

Components which provide safety insulation (with respect to electric shock) should be specifically designed for that purpose, and with the design either directly controlled by yourself (such as a custom transformer design) or a recognised component (e.g. capacitor approved by a 3rd party agency).

The main reason for this is production control: your obligation covers all products not just the sample that underwent IEC 60601-1 testing. If you are using a non-safety recognised component for a safety purpose, the only option would be test every item on the production line which is not economically feasible.

So, best to just put the insulation sheet in.

Now, there is an issue in IEC 60601-1 that the required spacings are in general higher than what is really needed. If the spacing is, say, 0.5mm less than the limit, you might reasonably argue that the insulation on the capacitor or semiconductor is enough to get you over the line. But keep in mind the real story is that the spacing alone is enough for safety (e.g. by inspecting requirements IEC 60664-1). And if it is a component, you need to be confident of the relative positions in regular production. Again, the insulation sheet may be a simpler option.
 
S

sankui

#5
Re: Can enclosure of semiconductor or electrolytic capacitor provides basic insulatio

Generally this is not a good idea.

Components which provide safety insulation (with respect to electric shock) should be specifically designed for that purpose, and with the design either directly controlled by yourself (such as a custom transformer design) or a recognised component (e.g. capacitor approved by a 3rd party agency).

The main reason for this is production control: your obligation covers all products not just the sample that underwent IEC 60601-1 testing. If you are using a non-safety recognised component for a safety purpose, the only option would be test every item on the production line which is not economically feasible.

So, best to just put the insulation sheet in.

Now, there is an issue in IEC 60601-1 that the required spacings are in general higher than what is really needed. If the spacing is, say, 0.5mm less than the limit, you might reasonably argue that the insulation on the capacitor or semiconductor is enough to get you over the line. But keep in mind the real story is that the spacing alone is enough for safety (e.g. by inspecting requirements IEC 60664-1). And if it is a component, you need to be confident of the relative positions in regular production. Again, the insulation sheet may be a simpler option.
Hi Peter,

I am sorry that my question seems to confuse you. Actually, I am not talking about the components which used to bridge the primary and secondary, e.g. Y1 capacitor, transformer, optocoupler.

My question relates to the plastic enclosure of non-safety relevant semiconductors or electrolytic capacitors. Since the small size of the switching power supply, the components which do not provide any safety insulation also adjacent to the safety relevant components, e.g. the bulk capacitor closes to transformer core. This may reduce the insulation distance (assumed that primary winding to core is BI and secondary winding to core is SI, the body of bulk capacitor may bypass the distance from primary winding to core). As we know, for electrolytic capacitor, there is no certification program existing. So the electrolytic capacitor belongs to non-approved component.

What should be considered for the plastic enclosure of semiconductors or electrolytic capacitors?
 

Peter Selvey

Staff member
Super Moderator
#6
Re: Can enclosure of semiconductor or electrolytic capacitor provides basic insulatio

I expect we are talking about the same thing. The cases that I have seen before are (values for example only):

Pri-core internal creepage = 3.2mm (creepage)
Core is conductive ferrite material
Core to secondary electrolytic capacitor 1.0mm (clearance)

Total clearance pri - sec = 3.2 + 1.0 = 4.2 mm < 5.0 limit for 2nd edition.

Then, the applicant may say that plastic covering on secondary capacitor helps to comply. Although in the test sample, 4.2mm is perfectly safe, we should reject it for DI as explained above, since there is no production control over the construction of the secondary capacitor, and there may be a question over the exact positioning of the capacitor with respect to the core (in regular production).

Safety isolation should be planned, intentional, consistent in regular production, and tending towards a bit of overkill to keep things simple.
 
Last edited:
S

sankui

#7
Re: Can enclosure of semiconductor or electrolytic capacitor provides basic insulatio

Thanks, Peter. I just found an OSM/EE DECISION SHEET about the insulation of plastic enclosure of semiconductor component, see below.
Standard:

EN 60950:2000

EN 60950-1 :2001
Sub clause:

2.10.5
Sheet no. :
95/17

Page: 1 of 1
Subject:
Insulation of plastic enclosure of semiconductor component
Key words:
Semiconductor insulation
Meeting:
OSM/EE - 1995
Item 9.14

Question:
Type of insulation of plastic enclosure of semiconductor component

Decision:
The plastic enclosure of a semiconductor can be considered as basic insulation. These components including alternatives must be listed in the list of critical components and there must be a remark in the service documentation.

Explanatory Notes: -
From above decision sheet, it seems that the plastic enclosure of electrolytic capacitor also can be considered as basic insulation.
 
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