Re: [PSES] Class 1 appliance

[Scott Xe]

Dear John,

Thanks for your comments.  I have some below results of further
investigation to share with you.

On Mon, 6 Nov 2023 at 22:22, John Woodgate  wrote:

> I put some comments below.
> On 2023-11-06 14:08, Scott Xe wrote:
>
> Last week, we received a sample of an induction hob from a supplier. The
> unit is fitted with a 3-core power card and does not have a class II
> symbol. The earthing core is terminated at a small copper pad on the
> printed circuit board with a protective ground symbol (IEC 60417 - 5019)
> next to the terminal.  It is shocking to note that the copper pad is
> standalone and not connected to the unit circuitry.  We made an inquiry to
> the supplier and replied that the product was designed by the engineer who
> left the company.
>
> *JMW: That alone should indicate that you should have nothing to do with
> the product, unless you are a test house, paid for assessing its safety.*
>

SX: According to the circuit diagram, the PCB missed out a resistor
connecting between 2 capacitors and the isolated earth pad.  The earthing
path is for EMC compliance and the earthing is considered as a functional
earth.  The 2 capacitors must be Y1 class to fulfil safety requirements.

>
> I have two questions regarding the appliance. Firstly, can it be rated as
> a class 1 appliance?
>
> *JMW: If it passes all the safety tests for a Class 1 appliance, it is a
> Class 1 appliance. But it remains a suspect design.*
>

SX: Obviously the appliance does not rely on extra earth protection against
electrical shock.  The live parts must have double or reinforced
insulation in order to meet class II requirements.

>
> Secondly, what are the main purposes of installing a 3-core power cable
> that has no obvious functionality?
>
> *JMW: There is a strong temptation to do that if it's too difficult to
> meet the Class II requirements.*
>

SX: The earth core is used for grounding the interference.

>
>
> Additionally, while examining the PCB layout, I noticed punched holes for
> a resistor and two capacitors connected in series, with the capacitors
> connected in parallel first. Currently, there are no components present in
> those holes. I would like to know if these components are necessary for EMC
> compliance.
>
> *JMW: There is no way anyone can advise you on that, even if we could see
> where the 'missing' components appear in the schematic. You have to test it
> as it is and see whether it meets the EMC requirements.*
>

SX: It is a common practice for oem manufacturers to design a product
embedded with the requirements of many customers.  The actual no of
components is subject to individual customer requirements.  It is likely to
cause confusion and/or miscommunication to the sample preparation team.

>
>
> Your advice is appreciated!
>
>
> Thanks and regards,
>
>
> Scott
>
>
>
>
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Re: [PSES] Class 1 appliance

[John Woodgate]

I put some comments below.

On 2023-11-06 14:08, Scott Xe wrote:
Last week, we received a sample of an induction hob from a supplier. 
The unit is fitted with a 3-core power card and does not have a class 
II symbol. The earthing core is terminated at a small copper pad on 
the printed circuit board with a protective ground symbol (IEC 60417 - 
5019) next to the terminal.  It is shocking to note that the copper 
pad is standalone and not connected to the unit circuitry.  We made an 
inquiry to the supplier and replied that the product was designed by 
the engineer who left the company.
/JMW: That alone should indicate that you should have nothing to do with 
the product, unless you are a test house, paid for assessing its safety./


I have two questions regarding the appliance. Firstly, can it be rated 
as a class 1 appliance?


/JMW: If it passes all the safety tests for a Class 1 appliance, it is a 
Class 1 appliance. But it remains a suspect design./


Secondly, what are the main purposes of installing a 3-core power 
cable that has no obvious functionality?


/JMW: There is a strong temptation to do that if it's too difficult to 
meet the Class II requirements./



Additionally, while examining the PCB layout, I noticed punched holes 
for a resistor and two capacitors connected in series, with the 
capacitors connected in parallel first. Currently, there are no 
components present in those holes. I would like to know if these 
components are necessary for EMC compliance.


/JMW: There is no way anyone can advise you on that, even if we could 
see where the 'missing' components appear in the schematic. You have to 
test it as it is and see whether it meets the EMC requirements./



Your advice is appreciated!


Thanks and regards,


Scott






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[PSES] Class 1 appliance

[Scott Xe]

Last week, we received a sample of an induction hob from a supplier. The
unit is fitted with a 3-core power card and does not have a class II
symbol. The earthing core is terminated at a small copper pad on the
printed circuit board with a protective ground symbol (IEC 60417 - 5019)
next to the terminal.  It is shocking to note that the copper pad is
standalone and not connected to the unit circuitry.  We made an inquiry to
the supplier and replied that the product was designed by the engineer who
left the company.

I have two questions regarding the appliance. Firstly, can it be rated as a
class 1 appliance? Secondly, what are the main purposes of installing a
3-core power cable that has no obvious functionality?


Additionally, while examining the PCB layout, I noticed punched holes for a
resistor and two capacitors connected in series, with the capacitors
connected in parallel first. Currently, there are no components present in
those holes. I would like to know if these components are necessary for EMC
compliance.


Your advice is appreciated!


Thanks and regards,


Scott

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