[PSES] AW: [PSES] Overvoltage Categories (OVC) and "Reliable" Earthing - 62368-1 vs 60601-1

[Dürrer Bernd]

Hi James,

the citation from clause 5.4.2.3.3 is from EN 623681-1:2014 which is the 
European adoption of IEC 62368-1:2014 (Ed. 2.0). Please note that this 
paragraph has been modified in Edition 3.0 of the standard (IEC 62368-1:2018) 
that has been adopted as EN IEC 62368-1:2020:

"If a circuit isolated from the mains is connected to the main protective 
earthing terminal through a protective bonding conductor, the required 
withstand voltage may be one overvoltage category lower or one AC mains voltage 
lower in Table 12. For an AC mains up to and including 50 V RMS, no adjustments 
are made."

Please note that the reduction of the required withstand voltage is only valid 
for this specific secondary circuit, as Scott already pointed out, i.e. the 
clearances may be reduced in this specific secondary circuit only. You may find 
similar relaxations in other standards, e.g. IEC 61800-5-1, clause 4.3.6.2.3, 
with some examples in Annex B.

The concept of overvoltage categories is explained in clause 4.3 of the generic 
IEC standard for insulation coordination IEC 60664-1. It is a requirement for 
the reliability of equipment in case of overvoltages (e.g. caused by lighting):
"Equipment of overvoltage category IV is for use at the origin of the 
installation.
NOTE 1 Examples of such equipment are electricity meters, primary overcurrent 
protection devices and ripple control units.
- Equipment of overvoltage category III is equipment in fixed installations and 
for cases where the reliability and the availability of the equipment is 
subject to special requirements.
NOTE 2 Examples of such equipment are switches in the fixed installation and 
equipment for industrial use with permanent connection to the fixed 
installation.
- Equipment of overvoltage category II is energy-consuming equipment to be 
supplied from the fixed installation. If such equipment is subjected to special 
requirements with regard to reliability and availability, overvoltage category 
III applies.
NOTE 3 Examples of such equipment are appliances, portable tools and other 
household and similar loads."

Kind regards,

Bernd

Von: Scott Aldous <0220f70c299a-dmarc-requ...@listserv.ieee.org>
Gesendet: Dienstag, 15. Juni 2021 21:21
An: EMC-PSTC@LISTSERV.IEEE.ORG
Betreff: Re: [PSES] Overvoltage Categories (OVC) and "Reliable" Earthing - 
62368-1 vs 60601-1

Hi James,


  *   Do any other safety standards share this reduction in OVC for PE 
connected circuits?

I'm not completely sure what you mean by the reduction in OVC. This is intended 
to refer only to the secondary circuit OVC, not the primary circuit OVC. So in 
the example you gave, the secondary circuit would be classified as OV Cat II, 
but the primary circuit would still be classified as OV Cat III. This is 
clearer in IEC 60950-1...

With regard to other safety standards, IEC 60950-1 has the same provision (see 
clause 2.10.3.6), which is likely the source of the requirement in IEC 62368-1. 
IEC 60065 has something similar but not quite the same in clause 13.3.3. IEC 
62109-1 also has a similar concept in clause 7.3.7.1.2c). This one is 
interesting because it more directly discusses the reduction of OVC across 
galvanic isolation, with 2 energy sources (photovoltaic input and AC mains 
connection). If you happen to have this standard, a read through of the whole 
of clause 7.3.7.1.2 could be helpful. Here's a snippet from 7.3.7.1.2e):

where isolation is provided by means of isolation transformers, optocouplers, 
or similar
galvanic isolation devices, between a considered circuit and an adjacent mains 
or PV
circuit, the impulse withstand voltage rating of the considered circuit is 
reduced by one
level from that of the adjacent circuit; if more than one adjacent circuit is 
involved, the
highest resulting impulse withstand voltage rating applies.

On Tue, Jun 15, 2021 at 10:21 AM Joe Randolph 
mailto:j...@randolph-telecom.com>> wrote:
Hi James:

I cannot provide a detailed answer to your question, but it appears that part 
of the analysis depends on what qualifies as "reliable earthing."

Most safety standards make a distinction between "reliable earthing" (typically 
accompanied by a definition), and what might be called "unreliable earthing", 
which is not a technical term in most standards but can be interpreted to mean 
any earthing that does not qualify as "reliable earthing."

The basic concept is that an earth connection that was permanently installed by 
an electrician is generally considered "reliable," but the earth pin on a 
standard household Type A AC mains plug is generally considered "unreliable."  
These connections are generally considered "unreliable" because it is known 
that some household AC mains sockets have missing ground connections, and it is 
also known that some users will use a "cheater adapter" to put a 3-pin grounded 
plug 

Re: [PSES] Overvoltage Categories (OVC) and "Reliable" Earthing - 62368-1 vs 60601-1

[Scott Aldous]

Hi James,


   - Do any other safety standards share this reduction in OVC for PE
   connected circuits?


I'm not completely sure what you mean by the reduction in OVC. This is
intended to refer only to the secondary circuit OVC, not the primary
circuit OVC. So in the example you gave, the secondary circuit would be
classified as OV Cat II, but the primary circuit would still be classified
as OV Cat III. This is clearer in IEC 60950-1...

With regard to other safety standards, IEC 60950-1 has the same provision
(see clause 2.10.3.6), which is likely the source of the requirement in IEC
62368-1. IEC 60065 has something similar but not quite the same in clause
13.3.3. IEC 62109-1 also has a similar concept in clause 7.3.7.1.2c). This
one is interesting because it more directly discusses the reduction of OVC
across galvanic isolation, with 2 energy sources (photovoltaic input and AC
mains connection). If you happen to have this standard, a read through of
the whole of clause 7.3.7.1.2 could be helpful. Here's a snippet from
7.3.7.1.2e):

*where isolation is provided by means of isolation transformers,
optocouplers, or similar*
*galvanic isolation devices, between a considered circuit and an adjacent
mains or PV*
*circuit, the impulse withstand voltage rating of the considered circuit is
reduced by one*
*level from that of the adjacent circuit; if more than one adjacent circuit
is involved, the*
*highest resulting impulse withstand voltage rating applies.*


On Tue, Jun 15, 2021 at 10:21 AM Joe Randolph 
wrote:

> Hi James:
>
>
>
> I cannot provide a detailed answer to your question, but it appears that
> part of the analysis depends on what qualifies as “reliable earthing.”
>
>
>
> Most safety standards make a distinction between “reliable earthing”
> (typically accompanied by a definition), and what might be called
> “unreliable earthing”, which is not a technical term in most standards but
> can be interpreted to mean any earthing that does not qualify as “reliable
> earthing.”
>
>
>
> The basic concept is that an earth connection that was permanently
> installed by an electrician is generally considered “reliable,” but the
> earth pin on a standard household Type A AC mains plug is generally
> considered “unreliable.”  These connections are generally considered
> “unreliable” because it is known that some household AC mains sockets have
> missing ground connections, and it is also known that some users will use a
> “cheater adapter” to put a 3-pin grounded plug into a 2-pin ungrounded
> outlet.
>
>
>
> If the safety protection method used in the product is very dependent on
> being connected to a reliable earth, the safety standard typically requires
> that the earth connection must be “reliable” as defined elsewhere in the
> standard.
>
>
>
> Note that different standards have different internal definitions for what
> constitutes a “reliable” earthing connection.  So, it’s important to use
> the internal definition that appears in the standard you are actually using.
>
>
>
>
>
> Joe Randolph
>
> Telecom Design Consultant
>
> Randolph Telecom, Inc.
>
> 781-721-2848 <(781)%20721-2848> (USA)
>
> j...@randolph-telecom.com
>
> http://www.randolph-telecom.com
>
>
>
> *From:* James Pawson (U3C) [mailto:ja...@unit3compliance.co.uk]
> *Sent:* Tuesday, June 15, 2021 6:53 AM
> *To:* EMC-PSTC@LISTSERV.IEEE.ORG
> *Subject:* [PSES] Overvoltage Categories (OVC) and "Reliable" Earthing -
> 62368-1 vs 60601-1
>
>
>
> Hello safety experts,
>
>
>
> A question regarding overvoltage categories and “reliable” earthing and
> some differences between standards. I would be interested to hear your
> thoughts.
>
>
>
> *Background:*
>
> When determining the required withstand voltage for insulation, EN 62368-1
> states that:
>
>
>
> *5.4.2.3.3 Determining required withstand voltage*
>
> *…*
>
> *If a circuit isolated from the mains is connected to a main protective
> earthing terminal*
>
> *that complies with 5.6.7, the required withstand voltage may be one
> overvoltage*
>
> *category lower** in Table 13  (JP: Table 13 in this case replicates
> table F.1 from IEC 60664-1 of OVC vs impulse voltage)*
>
>
>
> *5.6.7 Reliable earthing*
>
> *…*
>
> *For permanently connected equipment earthing is considered to be reliable*
>
> *…*
>
>
>
> *Summary:*
>
> A permanently connected piece of equipment with isolated (secondary)
> circuit connected to PE is classed as being one OVC lower than it’s
> installation eg. OVC III becomes OVC II with all of the reductions in
> creepage/clearance/insulation that this results in.
>
>
>
> *Problem:*
>
>- I cannot find an equiva

Re: [PSES] Overvoltage Categories (OVC) and "Reliable" Earthing - 62368-1 vs 60601-1

[Joe Randolph]

Hi James:

 

I cannot provide a detailed answer to your question, but it appears that
part of the analysis depends on what qualifies as "reliable earthing."

 

Most safety standards make a distinction between "reliable earthing"
(typically accompanied by a definition), and what might be called
"unreliable earthing", which is not a technical term in most standards but
can be interpreted to mean any earthing that does not qualify as "reliable
earthing."

 

The basic concept is that an earth connection that was permanently installed
by an electrician is generally considered "reliable," but the earth pin on a
standard household Type A AC mains plug is generally considered
"unreliable."  These connections are generally considered "unreliable"
because it is known that some household AC mains sockets have missing ground
connections, and it is also known that some users will use a "cheater
adapter" to put a 3-pin grounded plug into a 2-pin ungrounded outlet.

 

If the safety protection method used in the product is very dependent on
being connected to a reliable earth, the safety standard typically requires
that the earth connection must be "reliable" as defined elsewhere in the
standard.

 

Note that different standards have different internal definitions for what
constitutes a "reliable" earthing connection.  So, it's important to use the
internal definition that appears in the standard you are actually using.

 

 

Joe Randolph

Telecom Design Consultant

Randolph Telecom, Inc.

781-721-2848 (USA)

 <mailto:j...@randolph-telecom.com> j...@randolph-telecom.com

 <http://www.randolph-telecom.com> http://www.randolph-telecom.com

 

From: James Pawson (U3C) [mailto:ja...@unit3compliance.co.uk] 
Sent: Tuesday, June 15, 2021 6:53 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Overvoltage Categories (OVC) and "Reliable" Earthing -
62368-1 vs 60601-1

 

Hello safety experts,

 

A question regarding overvoltage categories and "reliable" earthing and some
differences between standards. I would be interested to hear your thoughts.

 

Background:

When determining the required withstand voltage for insulation, EN 62368-1
states that:

 

5.4.2.3.3 Determining required withstand voltage

.

If a circuit isolated from the mains is connected to a main protective
earthing terminal

that complies with 5.6.7, the required withstand voltage may be one
overvoltage

category lower in Table 13  (JP: Table 13 in this case replicates table F.1
from IEC 60664-1 of OVC vs impulse voltage)

 

5.6.7 Reliable earthing

.

For permanently connected equipment earthing is considered to be reliable

.

 

Summary:

A permanently connected piece of equipment with isolated (secondary) circuit
connected to PE is classed as being one OVC lower than it's installation eg.
OVC III becomes OVC II with all of the reductions in
creepage/clearance/insulation that this results in. 

 

Problem:

*   I cannot find an equivalent clause regarding overvoltage categories
and reliable earthing in EN 61010-1.
*   Also, I cannot see anything in EN 62368-2 that explains this
decision.
*   It looks like EN 62368-1 is a bit of an outlier in this respect.

 

Questions:

*   Have I missed the clause in EN 61010-1 that covers this? (I've
looked carefully through Clause 6 and Annex K)
*   Do any other safety standards share this reduction in OVC for PE
connected circuits?
*   Have I understood the clauses in EN 62368-1 properly?
*   I've seen (and subsequently unable to find again) a reference that
resistance to transient overvoltages is partly a reliability of equipment
issue. Are the writers of EN 62368-1 less concerned about reliability?  ;-)

 

As always, thanks in advance

James

 

 

 

James Pawson

The EMC Problem Solver

 

Unit 3 Compliance Ltd

EMC : Environmental : Safety : CE + UKCA : Consultancy

 

www.unit3compliance.co.uk <http://www.unit3compliance.co.uk/>   |
+44(0)1274 911747  |  +44(0)7811 139957

2 Wellington Business Park, New Lane, Bradford, BD4 8AL

Registered in England and Wales # 10574298

 

 

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[PSES] Overvoltage Categories (OVC) and "Reliable" Earthing - 62368-1 vs 60601-1

[James Pawson (U3C)]

Hello safety experts,

 

A question regarding overvoltage categories and "reliable" earthing and some
differences between standards. I would be interested to hear your thoughts.

 

Background:

When determining the required withstand voltage for insulation, EN 62368-1
states that:

 

5.4.2.3.3 Determining required withstand voltage

.

If a circuit isolated from the mains is connected to a main protective
earthing terminal

that complies with 5.6.7, the required withstand voltage may be one
overvoltage

category lower in Table 13  (JP: Table 13 in this case replicates table F.1
from IEC 60664-1 of OVC vs impulse voltage)

 

5.6.7 Reliable earthing

.

For permanently connected equipment earthing is considered to be reliable

.

 

Summary:

A permanently connected piece of equipment with isolated (secondary) circuit
connected to PE is classed as being one OVC lower than it's installation eg.
OVC III becomes OVC II with all of the reductions in
creepage/clearance/insulation that this results in. 

 

Problem:

*   I cannot find an equivalent clause regarding overvoltage categories
and reliable earthing in EN 61010-1.
*   Also, I cannot see anything in EN 62368-2 that explains this
decision.
*   It looks like EN 62368-1 is a bit of an outlier in this respect.

 

Questions:

*   Have I missed the clause in EN 61010-1 that covers this? (I've
looked carefully through Clause 6 and Annex K)
*   Do any other safety standards share this reduction in OVC for PE
connected circuits?
*   Have I understood the clauses in EN 62368-1 properly?
*   I've seen (and subsequently unable to find again) a reference that
resistance to transient overvoltages is partly a reliability of equipment
issue. Are the writers of EN 62368-1 less concerned about reliability?  ;-)

 

As always, thanks in advance

James

 

 

 

James Pawson

The EMC Problem Solver

 

Unit 3 Compliance Ltd

EMC : Environmental : Safety : CE + UKCA : Consultancy

 

  www.unit3compliance.co.uk  |
+44(0)1274 911747  |  +44(0)7811 139957

2 Wellington Business Park, New Lane, Bradford, BD4 8AL

Registered in England and Wales # 10574298

 



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