EN60065 - safety and audio in/out terminals

Following the IEC standard requirements, I have to ensure the dielectric withstanding strength between the ACCESIBLE conductive parts and the mains line terminals. My doubt is whether I have to consider the inpunt/output terminal as accessible conductive parts or not.

As example, thinking on a preamplifier with male XLR output connector: the inner contact of the XLR connector are to be consider as accessible conductive parts? If yes, I have to ensure the dielectric withstanding strength between those and the mains? That means I have to test its withstanding applying 1.5 kV AC (or 2.5 kV AC) to the XLR pins? That would be crazy, in my opinion...

Hello,

You have to insure that in a single fault condition, the equipment is safe. Audio inputs and outputs (cable and connectors) do not provide sufficient protection for the expected overvoltage, so yes you are right, they may carry out High Pot testing between mains and audio input/output.

You will probably have a transformer inside the cabinet. Imagine your transformer has 100pF between Primary live and secondary (that is - j32MOhm). This means that at 1500Vac, the current will be max 47uA. When your input has 100 kOhm to DC ground, about 4.7V will be across the input and DC ground, and 1500V will be across the winding insulation of your transformer.

Probably you will have some form of ESD protection between inputs and your DC ground on the PCB. In case of very high impedance circuits, the ESD protection will take most of the 47uA.

Practically spoken, not everything is tested. When the transformer is OK, many other things can be checked by inspection (clearance/ creepage, what happens when a wire breaks, flammability, etc). This is the reason that many manufacturers use an already approved mains adapter; this eliminates the need for High Pot testing on the low voltage device itself.

When they want to test one input for checking the safety of the mains transformer, you may probably short circuit the inputs. In addition, the voltage is increased gradually so will not get transient effects. Ones I joined a test at 4250Vdc where there was a discharge between Live and PE, so in that case 4kV was between PE and the low voltage input (bad result).

Hopes this takes away some of your worries,

Wim PA3DJS

Imagine the isolation transformer's functional insulation fails - so the full AC supply voltage appears on the secondary windings. Would that event result in dangerous voltages on any of the XLR pins ??

If so, your design does not pass Class 1 requirements.

..... Phil

Values up to 4700 pF are allowed.

.... Phil

Hello Phil,

You are right. When this is that case, and you expect problems, you may use a DC test. I do not have most recent EN 60065, but I think you may use equipotential bonding on circuits not involved in the insulation test (as in EN 60950, par 5.2.2).

Best regards and thanks for the addition,

Wim

Sounds pretty accesible to me.

I think you should.

This is based on memory browsing that standard some years ago..

Why that would be crazy ?

For a testinng make a test adapter that connects together all three XLR pins and gives one output wire. Connect this to your measuring ground. Then make another test adapter that has mains connector where live and neutral pins are wired together and connected to test cable. Connect this to your grounded test AC or DC source (whichever option that standard gives for testing) that has the current measuring to check for any leakage. How you have tested if there is any leakage from any mains carrying wires to any pin on the XLR output connector without risking the audio circuitry wired to that XLR connector. I think this would be the way to go in testing this. Does anybody else have any comment on my testing idea?

what I thought is that carrying out the test applying 2,5 kV AC to an audio input (or output) could damage the device or endanger its reliability

Yes, according to the standard it's possible to connect the pins together and testing them at the same time. I think you're right.

Tom is right. You are only interested in the isolation factor between the mains input and the audio side. Therefore connecting the XLR pins together and then the Mains input pins together and using a suitable Megger or similar instrument up to the appropriate specified voltages (start low and work upwards) and ensure that the insulation resistance stays very high. Do a normal function test afterwards to make sure the unit is still working properly.

If yo do not have a copy of IEC 60065 try:

IEC seems to want it to be pretty accessable. .

"Joseph Krazy Kook"

That link is to a mere 15 page PREVIEW of a 340 page document.

...... Phil

Many thanks, but what you suggest is only a preview of the whole standard. Of course I've got the standard and read it. Now I'm reading it again in deeper, but the reading still has some blank.

• From: wimabctel@xxxxxxxxx * Date: Thu, 12 Mar 2009 13:31:18 -0700 (PDT)

Hello,

You have to insure that in a single fault condition, the equipment is safe. Audio inputs and outputs (cable and connectors) do not provide sufficient protection for the expected overvoltage, so yes you are right, they may carry out High Pot testing between mains and audio input/output.

You will probably have a transformer inside the cabinet. Imagine your transformer has 100pF between Primary live and secondary (that is - j32MOhm). This means that at 1500Vac, the current will be max 47uA. When your input has 100 kOhm to DC ground, about 4.7V will be across the input and DC ground, and 1500V will be across the winding insulation of your transformer.

Probably you will have some form of ESD protection between inputs and your DC ground on the PCB. In case of very high impedance circuits, the ESD protection will take most of the 47uA.

Practically spoken, not everything is tested. When the transformer is OK, many other things can be checked by inspection (clearance/ creepage, what happens when a wire breaks, flammability, etc). This is the reason that many manufacturers use an already approved mains adapter; this eliminates the need for High Pot testing on the low voltage device itself.

When they want to test one input for checking the safety of the mains transformer, you may probably short circuit the inputs. In addition, the voltage is increased gradually so will not get transient effects. Ones I joined a test at 4250Vdc where there was a discharge between Live and PE, so in that case 4kV was between PE and the low voltage input (bad result).

Hopes this takes away some of your worries,

Wim PA3DJS

That's done by the power transformer.

Don't confuse primary and secondary parts.

Graham

You mean I have to test only the insulation of the primary parts, thus I no needing to test accessible in/out terminals if these are connected to the power output transformer?

Alessandro

OK, I will use an already approved power transformer!

Alessandro

I am actually finding that pretty typical of a lot of standards. They end up being set up so that you cannot read just one. For instance, my PPOE purchased the entire ANSI/TIA/EIA-492 series of standards and after studying them some i identified 3 additional standards needed to complete my task. (i hope) .