Telescoping safety earth?

[zamproject]

I have some read...
IEC60601 (medical equipment)

-PE connection should accept faulty current without excessive voltage drop

-Impedance between PE and ALL part protected by PE should not exceed 100mΩ

Test condition is 25A or 1.5x the max specified current of the circuits, the greater of both, at 6V 50/60Hz, for 5 to 10s

So in this case, -obviously- daisy chaining connectors will behave less efficiently compared to star connection with bolt and eyelet crimped wire from all sub frame to main frame.

Even if with cascading connector you meet that impedance/voltage drop condition...I suppose this imply that the connector should be specified/rated for the faulty amperage, which put another possible constraint.

Cheers
Zam

 

[sahib]

Thank you for that Zam.

To my defence, I have taken my eyes off the ball and was concentrating more on the use of in-line connectors. So, after all Newmarket was not sitting on this for no reason and my apologies to him if I sounded dismissive.

However, Abbey's brief is that the modules should be removable for servicing. So, even for the star method the options are either spade connector (unless you want to interfere with the earth tab/screw), or in-line connector. I have already mentioned that there are even run of the mill in-line connectors that will perform better than a spade connector.

So, based on the in-line connector method there are three connectors in series. I do not remember the contact resistance of IEC plug/socket mating by heart but I can measure it tomorrow as I have four wire milliohm meter.

The tab/screw contact resistance to first and second module will not have effect on the overall impedance for the second and third module respectively, as you do not have to cut and re-twist the earth wire at each eyelet. Remove the sheathing, twist the wire and then crimp into the eyelet. After crimping I also solder it (though not a common practice).

 

[zamproject]

To my defence,

My comment was absolutely not a review to yours or other comment, but just another brick to the discussion as abbey's question is also interesting me somehow.
I just pass what I read from IEC document I find, that maybe help someone else.

I do not remember the contact resistance of IEC plug/socket mating

Don't remember where I read it, if it's in the previously mentioned IEC60601, or the IEC 60204 (Safety of machinery – Electrical equipment of machines – )
But if the measurement for whatever reason should be made at the other side of the IEC socket (and not at the inside IEC faston or PE bolt) the target is 200mΩ
So from deduction, an extra 100mΩ is allowed from the IEC connector ?!?

After crimping I also solder it (though not a common practice).

From all I read in those IEC publications about wiring/cabling/connecting methods, this is a NO GO
I admit I also do it...have to change my habit...technical/scientifical reasons for NO soldering are more than convincing (obviously)

Cheers
Zam

 

[Newmarket]

Quick note that I have eyes on this but not going to give long reply via mobile phone touch keyboard on weekend
But will quickly say that I was always tempted to add solder to a crimp joint before accepting that it made the connection brittle.snd was unnecessary if the crimp was correctly made as a gas tight connection with the insulation and conductor properly clamped.

 

[sahib]

My comment was absolutely not a review to yours or other comment, but just another brick to the discussion as abbey's question is also interesting me somehow.
I just pass what I read from IEC document I find, that maybe help someone else.

Absolutely. No problems here.

Don't remember where I read it, if it's in the previously mentioned IEC60601, or the IEC 60204 (Safety of machinery – Electrical equipment of machines – )
But if the measurement for whatever reason should be made at the other side of the IEC socket (and not at the inside IEC faston or PE bolt) the target is 200mΩ
So from deduction, an extra 100mΩ is allowed from the IEC connector ?!?

We'll get to this.

From all I read in those IEC publications about wiring/cabling/connecting methods, this is a NO GO
I admit I also do it...have to change my habit...technical/scientifical reasons for NO soldering are more than convincing (obviously)

Cheers
Zam

I have not read the directive in full, but this is not as clear cut as it appears to be. IEC also approves PCB/Solder mount mains inlet. So, it is probably for certain applications and not a blanket cover for all.

The objection to soldering is probably from a point of view that, if the node develops sufficient temperature and the solder melts, the conduction will be compromised. However, (as I also mentioned in another discussion before) this will be the last of your concerns. What happens if your IEC is PCB/Solder mount?

The melting point for a lead free solder is >200 degrees C. To create that level of heat how much current do you need? 25A?, 50?, 100A? For an equipment that draws these sorts of current (high power power amp?) yes, but not for a preamp, let alone a keyboard. Also not to forget that the current into the equipment is limited by its mains fuse, and the fuse is there as the first line of defence.

The safety regulations are there as the bare minimum for compliance. But there can be no objection to go above that, and soldering the node after crimping is an improvement as it reduces the node resistance and we will see this later.

PICTURE NO:1 REMOVED.

Below are some examples from the industry. I m not going to give any names but these are from very well known companies, in some cases global.

In the below image the earth wire is soldered to the IEC. Though, it is wrapped around twice, so even if the solder is melted the connection is still maintained. This is from a broadcast equipment by a global brand.



In the below image the earth wire is soldered both to the IEC and the earth eyelet.



Below IEC is from a test equipment (mains voltage analyser). The earth is soldered as are the live and neutral.



Below has the earth wire soldered to both IEC and the eyelet after crimping.

.

Below is a very interesting one by a very well known pro-audio brand. It is a mains distribution board. IEC is fully PCB mount. The earth connection between the IEC and the earth stud is a PCB track. The earth is distributed to the rest of the equipment including the chassis from the earth stud.




Below are some tests that I carried out using a 4 wire milliohm meter. I could not find the low value calibration resistors but I calibrated the meter using a 100 ohm 0.1% metal film resistor.

I have measured the same node for three-four times and taken the highest reading for the worst case.

Below image shows the contact resistance of an in-line IEC. The right hand side is the mains in. The left hand side is the equipment side. The earth eyelet (black probe) is crimped. I have also added a bit of wire on the mains side so that additional contact resistance on the screw point is introduced.



The below image shows the same set-up except that I have soldered the earth wire to the eyelet from its tip. This halved the contact resistance. Isn't that an improvement?



Below image shows the chassis mount IEC with the earth wire soldered on both the IEC and the eyelet. Note how much the contact resistance has improved.




LAST THREE PICTURES REMOVED

 

[zamproject]

I don't say you can't solder wire !!!

But in this case the wire need to have mechanical constrain, so that the solder point, as the rigidified cable end (by solder sucked) can't move and break.
Crimp connector should not be soldered for the exact reason the wire break at your first picture
For what I read the objection is not about temp and possible melt whit high current fault, but because crimp is mechanically stronger and more reliable.

If conductivity is better with solder, probably the safety balance between lower Ω and connection reliability tend for the second option, also when you consider large gauge, the quality of the soldering structure is probably debatable (heat uniformity etc..)

Safety earth need double crimp connector IIRC

Connection of two or more conductor to one terminal is not allowed for protective conductor (IEC60204, section 13.1.1)
so you last 3 pictures are debatable, at start it's a single conductor, but mechanicillay it's like two ?!?

BUT I can't affirm what I say apply to the present topic.
I read IEC 60204 Safety of machinery – Electrical equipment of machines
and IEC 60601 for medical electrical equipment
Don't know if it's higher standard than consumer electrical product nor if the version I get are up do date.

Cheers
Zam

 

[sahib]

Safety earth need double crimp connector IIRC

In which case the connection in picture no 3 does not comply as it is not crimped to the eyelet.

Connection of two or more conductor to one terminal is not allowed for protective conductor (IEC60204, section 13.1.1)
so you last 3 pictures are debatable, at start it's a single conductor, but mechanically it's like two ?!?

I was not aware of this either. I think it is time to read the directives fully. I had shown it that way for this particular topic.

However, I have removed the images in question but left a note.

 

[Newmarket]

Attempting to cut through this :
Solder connection is okay.
Crimp connection is okay.
(caveat: needs to be correctly made "gas tight" connection.)
Crimp connection with solder applied to the Wire/Crimp interface is not recommended as it introduces a brittle connection.
I admit to being tempted though !
And I only really trust connections made with the appropriate ratchet tool or similar - hopefully in calibration.
Amusingly I used to work at a company manufacturing tensile testing equipment that used a lot of crimp connections in the products - typically for connecting motor drives etc.
Another part of the company - in the USA IIRC - produces kit specifically for testing crimped connections.
Was that used where I worked - no, of course not ! The assembly operator would just give it a good tug to confirm it was okay.

 

[Newmarket]

I read IEC 60204 Safety of machinery – Electrical equipment of machines
and IEC 60601 for medical electrical equipment
Don't know if it's higher standard than consumer electrical product nor if the version I get are up do date.

Medical Equipment has some more stringent requirements . As I recall the main thing is a lower "Earth Leakage Current" spec'.
This can be an issue for mains EMC filters where you might need to use one designed specifically for such use.
For audio kit etc the standards below are directly relevant:

1. EN 62087 – Requirement for audio and video equipment

• EN 62911 – Routine electrical safety testing in production of audio and video equipment

 

[Newmarket]

Newmarket, buddy, you are hanging onto this for no reason. Yes, if one wants to be awkward one can challenge anything. There is nothing stops one from doing it. But the data talks awkward one walks.

Okay. I'll qualify by saying that it might be challenged / rejected by someone who matters. Depending on circumstances it might simply be better to comply and design accordingly eg if it is going to delay "Time to Market" in a commercial environment.

Of course, if you use 0.1" molex header for mains connection and ask me to test it for safety, I'll fail it. But what would be the objection to, say, gold plated fully sealed in-line connector with a couple of thousand insertion life?

Molex KK type ? Now you're talking my type of connector - they were sort of a big part of my working life for a good number of years. Still are but less so atm. But yeah - obv not 2,54mm for mains connection. Meanwhile no objection to your (hypothetical ?) connector if it was rated for mains use by the manufacturer. Obviously cost might be a thing ! But note that I haven't said such connections are impossible. Just that they can be difficult to realise because lots of connectors that look suitable are not rated for mains use and sometimes it's specifically advised that they are unsuitable for mains applications.
This does seem to have changed over the years with things becoming more strict.
I've been round this loop previously and ended up with Neutrik Powercon True
eg
NAC3FX-W

In that particular case the chassis "Earth" connection was made independently of the Earth connection on the connector. But that was simply a function of the mechanics of the equipment and the need for "Direct Earthing" to cope with possible high voltage (kVs) arc events.

There are gazillions of applications out there with 3 way in-line mains connections. I have serviced broadcast equipment where the connection between IEC and the (switching) power supply is made through locking header, or industrial equipment with in-line mains connection. From lighting, to automation the industry uses 3 prong in line connections for mains left-right-centre. There are water proof (if not chemical) 3 prong in-line mains connectors that are designed for outdoor use. Who can object using it inside an equipment. There is in-line male/female IEC. Who can object using it inside an equipment?

Okay. You can use the types of solutions used in automation , lighting etc and I really like those. But due to size/space they are often not wanted internal to moderately sized equipment. No technical objection and I've used eg internal IEC where that has worked out best solution eg powering a "Panel PC" but it's often not practicable mechanically or seen to be commercially justifiable in terms of cost. Yes - ease of service etc I know.
You mentioned somewhere about PCB Header solutions - yes, this can be easier and there a lot more options compared to in line connection.

 

[Newmarket]

Thank you for that Zam.

To my defence, I have taken my eyes off the ball and was concentrating more on the use of in-line connectors. So, after all Newmarket was not sitting on this for no reason and my apologies to him if I sounded dismissive.

No problem. And worth noting that standards often have apparent inconsistencies and disparities both within themselves and in relation to other relevant standards. I know someone involved in drafting rf test standards etc who sometimes "shakes his head" at what finally emerges from the committee.

So, based on the in-line connector method there are three connectors in series. I do not remember the contact resistance of IEC plug/socket mating by heart but I can measure it tomorrow as I have four wire milliohm meter.

Even with the best meter measuring down in single milliohm I'd be doubtful on measurement repeatability due to variables related to the metallic interface - tarnishing, pressure etc.

 

[sahib]

No problem. And worth noting that standards often have apparent inconsistencies and disparities both within themselves and in relation to other relevant standards. I know someone involved in drafting rf test standards etc who sometimes "shakes his head" at what finally emerges from the committee.

Thank you.

Indeed there always is.

Even with the best meter measuring down in single milliohm I'd be doubtful on measurement repeatability due to variables related to the metallic interface - tarnishing, pressure etc.

Absolutely. There is the contact resistance. You remove the probes and put them back on, and the reading changes considerably. That is why I mentioned in my previous post that I used the highest reading for the worst case.

 

[Newmarket]

Thank you.

Indeed there always is.



Absolutely. There is the contact resistance. You remove the probes and put them back on, and the reading changes considerably. That is why I mentioned in my previous post that I used the highest reading for the worst case.

Yes. That sort of thing is my life atm although more related to making capacitance measurements in the picofarad range.
With the IEC connector I was actually thinking more about the repeatability when plugging / unplugging the IEC connection. Since the connection basically involves mating two "rough" (in micro terms) surfaces and so resulting in different actual contact area and cold welds with each repeat.
Might be overthinking it though as the connection should really have a lot of "headroom" before a real problem arises.
But - yeah - low level measurements can be challenging.

 

[sahib]

I have Philips/Fluke PM6304 for those duties (though I have not used it for measuring the IECs). What do you use?

If I am remembering correctly (as it was over 20 years ago), I have seen in-line IEC used in this way inside a large format printer that a friend of mine was discarding. So, I think it would be fine for Abbey's application. I do not think the modules will be plugged/unplugged regularly.

 

[Newmarket]

I have Philips/Fluke PM6304 for those duties (though I have not used it for measuring the IECs). What do you use?

If I am remembering correctly (as it was over 20 years ago), I have seen in-line IEC used in this way inside a large format printer that a friend of mine was discarding. So, I think it would be fine for Abbey's application. I do not think the modules will be plugged/unplugged regularly.

Currently have access to (ie at work)

HAMEG HM8118
MOTECH MT4080A

Additionally Keithley Meters (typically 2000 Series) and a load of Fluke DMMs.

agree I don't see any technical problem with in line IEC connection as described. Even if often unplugged / plugged.
Assuming space isn't a problem.

And if you wanted a more 'configurable' system and the form factor suits then you could look at solutions used in lighting etc as you mentioned

SCOLMORE GROUP | Manufacturer & distributor of electrical Wiring accessories & Lighting

 

[sahib]

That Hameg 8118 looks like a great machine. I have a particular attachment to Hameg brand. My first scope (back in late '70s) was Hameg.

Thank you for the link. Good system. Will come in handy.

 

[warpie]

I found these some time go. Can they be of any help?

https://docplayer.net/53103553-International-standard.html
https://ulstandards.ul.com/wp-content/uploads/2021/02/iec62368-1_draft_4b.pdf