Proper grounding metal parts

Hymie

Joined Mar 30, 2018
1,277
For the purposes of electrical safety of the pin ball machine – the only parts required to be earthed are those that are only separated from the mains supply by Basic insulation. Therefore it is likely that only the input/chassis of the Meanwell PSU would be required to have an earth connection. All other metal/conductive parts being separated from the mains/live parts by double/reinforced insulation (a minimum distance of 5mm).
 

Thread Starter

Raymond175

Joined May 28, 2019
57
For the purposes of electrical safety of the pin ball machine – the only parts required to be earthed are those that are only separated from the mains supply by Basic insulation. Therefore it is likely that only the input/chassis of the Meanwell PSU would be required to have an earth connection. All other metal/conductive parts being separated from the mains/live parts by double/reinforced insulation (a minimum distance of 5mm).
Can you explain what you mean here?

The metal parts that I want to earth are the parts that are not connected to any electrical circuit (e.g. the cabinet legs), and are insulated by wood with quite enough distance. But it is possible that they might get connected to an electical circuit in case of any issues (e.g. broken wire dangling against the leg brackets or side rails, etc.).

The pinball machine operates on high voltage underneath the playfield with a possible maximum of almost 7 amps.
 

Hymie

Joined Mar 30, 2018
1,277
The reason that conductive (metal) parts of a product that are separated from mains parts by Double/Reinforced insulation are not required to be earthed, is that this level of insulation is deemed not to fail.
Where only Basic insulation is provided (between mains and accessible conductive metal parts), then they are required to be earthed. Should this Basic level of insulation fail, then the earthing will prevent an electric shock hazard being present.
 

Thread Starter

Raymond175

Joined May 28, 2019
57
The reason that conductive (metal) parts of a product that are separated from mains parts by Double/Reinforced insulation are not required to be earthed, is that this level of insulation is deemed not to fail.
Where only Basic insulation is provided (between mains and accessible conductive metal parts), then they are required to be earthed. Should this Basic level of insulation fail, then the earthing will prevent an electric shock hazard being present.
I'm really confused now... Are you saying that for example the cabinet legs don't need to be earthed? And if that is indeed what you are saying, then why are these in actual pinball machines earthed?
 

Hymie

Joined Mar 30, 2018
1,277
The pinball machine legs may very well be earthed by virtue of the fact that they are attached to the chassis of the machine – but there would be no possible insulation failure that could result in the legs becoming live, and therefore are not required to be earthed for safety reasons.
 

Lo_volt

Joined Apr 3, 2014
316
If there is any possibility that line voltage or any high voltage can reach the metal legs then they need to be grounded. This is also required for any metal frame or other external parts that a user may come in contact with. If there is any possibility of it becoming live through a loose wire or other fault it must be grounded.

To comply with IEC and UL safety standards, the ground from the incoming power cord must be bolted to a metal part with a ring terminal and a star washer. Typically this metal part is the box holding the electronics. To make things simple, I usually use a stud pressed into sheet metal. There should be no chance the terminal can vibrate or wiggle loose.

I don't have the relevant standards at the moment nor do I recall what document numbers they are, but they are all consistent with that grounding scheme.

You don't need to use the uninsulated braid but it won't hurt to do so. It is nice to use because it can carry lots of current and is a very low resistance connection. If you use any insulated wire for grounding make sure it can carry at least the current of your AC line fuse. Color code for ground is either Green or Green with a Yellow stripe.
 

Thread Starter

Raymond175

Joined May 28, 2019
57
If you use any insulated wire for grounding make sure it can carry at least the current of your AC line fuse.
Do you actually mean the incoming household AC line which is fused at 16A, or the incoming AC for the power supply at 5A or the outgoing DC for the power supply at 6.7A?
 

Lo_volt

Joined Apr 3, 2014
316
Do you actually mean the incoming household AC line which is fused at 16A, or the incoming AC for the power supply at 5A or the outgoing DC for the power supply at 6.7A?
You should have a fuse or circuit breaker on the incoming AC line inside the pinball machine. Your HOT lead should go first through a fuse, then through a switch then to your power supply. Since that fuse is what is protecting the wiring inside the machine, the ground wire should be able to handle at least the current specified by that fuse.
 

Thread Starter

Raymond175

Joined May 28, 2019
57
You should have a fuse or circuit breaker on the incoming AC line inside the pinball machine. Your HOT lead should go first through a fuse, then through a switch then to your power supply. Since that fuse is what is protecting the wiring inside the machine, the ground wire should be able to handle at least the current specified by that fuse.
I'm not aware that in an actual pinball machine there is a fuse or circuit breaker before the power supply... Currently my AC power cord goes from the wall socket into an 5A line filter with IEC connector, to the AC power switch to my power supply.

I only know that there are a bunch of 4A fuses on the power driver board (PCB):
1612297967609.png
 

Hymie

Joined Mar 30, 2018
1,277
It is likely that the Meanwell PSU has integral overcurrent fault protection (based on supply from a 20A branch circuit), and no additional input fusing/overcurrent protection is required.
The 48Vdc output of the PSU is within SELV limits, although I would not want to grab hold of 48V, the voltage is not considered to present a hazardous potential.
 

Lo_volt

Joined Apr 3, 2014
316
@Hymie, If the Meanwell supply is the only thing running off of incoming the AC, then you are correct, it's protected by its internal fuse. If anything else uses mains AC, then it will need fuse protection as well.
 

Thread Starter

Raymond175

Joined May 28, 2019
57
You should have a fuse or circuit breaker on the incoming AC line inside the pinball machine. Your HOT lead should go first through a fuse, then through a switch then to your power supply. Since that fuse is what is protecting the wiring inside the machine, the ground wire should be able to handle at least the current specified by that fuse.
I've opened up my official pinball machine again and checked whether or not the incoming AC has a fuse, and actually it does: A slow-blow 5A fuse.
 
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