Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulation

P

petruchio

#1
Hi

IEC 60601-1:2005, Clause 8.1 b) requires " ... short circuiting of any constituent part of double insulation ..."

Can anyone explain this to me in plain English? The term "short circuit" applied to insulation just doesn't make sense

I can understand short circuiting creepages and clearances, one literally connects them but that's simply not possible for double insulation.

Standards are like instructions manuals - they only make sense when interpreted by someone else. Kinda makes them useless .... :-(

petruchio
 
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Marcelo

Inactive Registered Visitor
#2
Re: Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulatio

Hi

IEC 60601-1:2005, Clause 8.1 b) requires " ... short circuiting of any constituent part of double insulation ..."

Can anyone explain this to me in plain English? The term "short circuit" applied to insulation just doesn't make sense

I can understand short circuiting creepages and clearances, one literally connects them but that's simply not possible for double insulation.

Standards are like instructions manuals - they only make sense when interpreted by someone else. Kinda makes them useless .... :-(
Double insulation is

insulation comprising both BASIC INSULATION and SUPPLEMENTARY INSULATION
So you need to shot circuit the basic or/and supplementary insulation that are part of the double.

Creepage and clearance are parts of the insulation, so you can short circuit them.
 
P

petruchio

#3
Re: Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulatio

Thanks but you've missed my point ... a short circuit across a creepage or clearance is obvious since these distances separate conductors by air or basic insulation (PCB usually). However, for double insulation, if one constituent is "short circuited" (ie effectively removed) it still leaves the other constituent which is assumed to still provide insulation since the standard only allows for one fault condition at a time. By definition, the fault condition must never create a safety hazard.

What is my argument missing?
 

Marcelo

Inactive Registered Visitor
#4
Re: Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulatio

Thanks but you've missed my point ... a short circuit across a creepage or clearance is obvious since these distances separate conductors by air or basic insulation (PCB usually). However, for double insulation, if one constituent is "short circuited" (ie effectively removed) it still leaves the other constituent which is assumed to still provide insulation since the standard only allows for one fault condition at a time. By definition, the fault condition must never create a safety hazard.

What is my argument missing?
Hum, maybe I´m still note sure what your point is, but...

The other constituent part will only really provide the insulation IF it´s tested to verify that it will. Hence the fault condition of one part being short-circuited - to verify if the other does maintain it´s insulation.
 
P

petruchio

#5
Re: Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulatio

Hi

Thanks for your feedback ...

I'm going through a 60601-1 checklist, hence this particular question. Any insulation, providing that it is qualified (eg via IEC60227..) must be assumed to be good. So if one has to consider a SFC in which one part of the double insulation fails completely leaving only the other part then this remaining part has to be assumed to be good since the standard allows only for single failures.

My thinking suggests that this test must always be passed by definition. Clause 4.8 allows this 'test' to be performed by inspection unless failure is likely to lead to unacceptable risk, in which case 4.9 has to be applied.
 

Marcelo

Inactive Registered Visitor
#6
Re: Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulatio

I'm going through a 60601-1 checklist, hence this particular question. Any insulation, providing that it is qualified (eg via IEC60227..) must be assumed to be good. So if one has to consider a SFC in which one part of the double insulation fails completely leaving only the other part then this remaining part has to be assumed to be good since the standard allows only for single failures.
IEC 60227 is a component standard. I´m not sure why you think that anything in conformity with IEC 60227 or any other means that the insulation is good.

Insulation is good for IEC 60601 only if it passes 8.8 Insulation.

My thinking suggests that this test must always be passed by definition. Clause 4.8 allows this 'test' to be performed by inspection unless failure is likely to lead to unacceptable risk, in which case 4.9 has to be applied.
4.8 is applicable only to components, not to insulation. Although you can use components a part of the insulation, it does not mean that a "certified" component, for example, pass insulation requirements of IEC 60601.
 
P

petruchio

#7
Re: Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulatio

Components includes wiring, PCBs ... so if these parts meet 60601-1 and/or applicable normatives then they have to be assumed to hold up in the event of the failure of the second part of the double insulation.
 

Marcelo

Inactive Registered Visitor
#8
Re: Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulatio

Well, not sure from where you having those conclusions, but let me try again.

Your original question was related to 8.1 b), which says:

SINGLE FAULT CONDITION includes:

1 - short circuit of any one insulation that complies with the requirements for one MEANS OF PROTECTION as specified in 8.8;
NOTE This includes short circuiting of either constituent part of DOUBLE INSULATION that complies with 8.8.
2 – .....
3 – short circuit and open circuit of any component other than a COMPONENT WITH HIGH INTEGRITY CHARACTERISTICS that is connected in parallel with insulation, with an AIR CLEARANCE or with a CREEPAGE DISTANCE unless shorting can be shown not to be a failure mode for the component (see also 4.8 and 4.9);
4.8 and 4.9 apply for the third option.

There´s no link between the first and third option. For the fist option you have to evaluate 8.8 Having a component in conformity with IEC XXXXX means nothing to the first option because it is related to insulation, not components.
 
P

petruchio

#9
Re: Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulatio

OK, thanks. I'll take this up with our notified body, it still makes no sense to me.
 

Peter Selvey

Staff member
Super Moderator
#10
Re: Understanding IEC 60601-1:2005, Clause 8.1 b) - Short Circuiting Double Insulatio

Shorting one part of double insulation is a valid fault condition, but it should result in obvious compliance, provided that each part of the insulation meets dielectric strength / creepage / clearance as per 8.8 and 8.9.

In Clause 8.7 (leakage current), shorting of one part of double insulation is excluded (see 8.7.2 3rd dash). Thus, there is no reason to actually short one part of double insulation in practice.

But it is still necessary to mention it in 8.1 (b) because the requirements in 8.8 and 8.9 are derived from this premise. In other words, dielectric strength, creepage and clearance limits for each part of double insulation are derived from the assumption that one insulation is shorted in SFC.
 
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