john12ax7
Well-known member
One (often overlooked) standard for the chassis earth ground is that it shouldn't be able to be loosened from the outside world. This eliminates standard screws and bolts. What is a good DIY solution?
Bonding Chassis to Earth Ground - Physical Connection
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Monte McGuire
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If you have IO connectors that electrically attach to the chassis as a result of their mechanical attachment and also have chassis solder tabs, you can bond your PCB to the chassis quite effectively. Most XLR connectors can do this.
The reason why I like this approach is that it bonds the chassis to the PCB at the outside edges, and allows you to end up with a ground and chassis configuration that follows the "pin 1" recommendations - to encourage pin 1 currents between connectors to flow in the chassis metal or the outer edge of the PCB, and not get injected into the middle of the PCB. It also allows robust RFI filtering from signal pins to the chassis, also keeping RFI out of the actual circuitry, constrained to the connector area.
The reason why I like this approach is that it bonds the chassis to the PCB at the outside edges, and allows you to end up with a ground and chassis configuration that follows the "pin 1" recommendations - to encourage pin 1 currents between connectors to flow in the chassis metal or the outer edge of the PCB, and not get injected into the middle of the PCB. It also allows robust RFI filtering from signal pins to the chassis, also keeping RFI out of the actual circuitry, constrained to the connector area.
john12ax7
Well-known member
I think that is a good approach for the PCB and Pin 1.
But what about the safety earth connection which should be on its own post and inaccessible from the outside world. (I should have been more clear in that I was asking about safety earth)
But what about the safety earth connection which should be on its own post and inaccessible from the outside world. (I should have been more clear in that I was asking about safety earth)
Audio1Man
Well-known member
Hi John
I must assume that you are talking about the AC Power Safety Ground (Green Wire).
The main thing is that upon servicing the system the SAFETY GROUND is not accidently removed.
PEM stud, Welded stud, Special head screw with KEP Nut (built in star washer) or GREEN screw will work and pass UL, CSA, VDE, CE. Other ways can be used that I have not mentioned.
System internal grounding will and can be buggered during service, however it will not KILL PEOPLE, only make the product not work as well.
The best DIY is a 3/4' long Allen, Hex head or other special type not a Slot or Phillips screw through chassis with KEP NUT. This is a fixed stud to the chassis. Now add star washer, then the ground lug to the Green AC incoming cord, then another flat washer and KEP NUT. This then gives you the fixed safety ground. Now add additional grounds to the other circuity as needed.
Duke
I must assume that you are talking about the AC Power Safety Ground (Green Wire).
The main thing is that upon servicing the system the SAFETY GROUND is not accidently removed.
PEM stud, Welded stud, Special head screw with KEP Nut (built in star washer) or GREEN screw will work and pass UL, CSA, VDE, CE. Other ways can be used that I have not mentioned.
System internal grounding will and can be buggered during service, however it will not KILL PEOPLE, only make the product not work as well.
The best DIY is a 3/4' long Allen, Hex head or other special type not a Slot or Phillips screw through chassis with KEP NUT. This is a fixed stud to the chassis. Now add star washer, then the ground lug to the Green AC incoming cord, then another flat washer and KEP NUT. This then gives you the fixed safety ground. Now add additional grounds to the other circuity as needed.
Duke
john12ax7
Well-known member
Yes was referring to the green wire AC safety ground, basically for alternatives to a typical Phillips screw.
Thank you Duke.
Thank you Duke.
screws and nuts are used most often, Fender used to solder the grn wire,
one tripped out thing i learned was to make the grn wire longer than the wht and black.
why? if someone yanks the power cord out and the strain relief pops, then the blk and wht wire will be ripped loose before the grn wire, thus, the chassis loses power before the grn wire is ripped, or better yet, the wht and blkget ripped and the grn wire stays till the cops show up and arrest the drunken biker who ripped your amp up because you refused to play Born to Be Wild.
plenty of code correct diagrams online, stick stuff, like where to put the internal lock and stuff,
one tripped out thing i learned was to make the grn wire longer than the wht and black.
why? if someone yanks the power cord out and the strain relief pops, then the blk and wht wire will be ripped loose before the grn wire, thus, the chassis loses power before the grn wire is ripped, or better yet, the wht and blkget ripped and the grn wire stays till the cops show up and arrest the drunken biker who ripped your amp up because you refused to play Born to Be Wild.
plenty of code correct diagrams online, stick stuff, like where to put the internal lock and stuff,
Rob Flinn
Well-known member
CJ said:
My dear old Dad told me this for wiring up mains plugs etc when I was about 10. I have always done it ever since. It has an advantage in that if the Brown (insert you countries colour for live here) or live wire touches the chassis it will blow a fuse because the chassis is still Earthed rendering the unit safe.
Use a stout nut and bolt , toothed and flat washers , torque it down very good till the toothed washers bite into metal , you want a gas tight seal thats never going to loosen . Remove any paint/passivation/rust on the surfaces where the bolt goes through also.
One mistake often made in DIY is to use the fixing from the IEC socket to secure your Ground , never use a fixing that goes through plastic for your safety ground ,plastic creeps and will loosen over time . The bigger the bolt the better the contact ,the lower the resistance ,the better your electrical safety equipment can function under fault condition .
Most often you find nuts with toothed washer attached on commercial gear , often it will be thread-locked too . bringing a few small hand tools when you visit electronics recycling and you can easily find loads of bit you need .
One mistake often made in DIY is to use the fixing from the IEC socket to secure your Ground , never use a fixing that goes through plastic for your safety ground ,plastic creeps and will loosen over time . The bigger the bolt the better the contact ,the lower the resistance ,the better your electrical safety equipment can function under fault condition .
Most often you find nuts with toothed washer attached on commercial gear , often it will be thread-locked too . bringing a few small hand tools when you visit electronics recycling and you can easily find loads of bit you need .
Rob Flinn
Well-known member
warpie said:
I do that but I also use a locking washer on the outside of the case as well as the inside.
Rob Flinn
Well-known member
warpie said:
Not normally, but it is a good idea.
Double nuts are common but I am not in position to cite code...
JR
JR
john12ax7
Well-known member
warpie said:
The problem with that picture is the metal thread screw. You shouldn't use a regular flat head or Phillips screw. It should be something than cannot be easily unscrewed from outside the chassis.
ruffrecords
Well-known member
I rememeber that was the preferred UL way of doing back in the 80s.warpie said:
Cheers
Ian
john12ax7
Well-known member
warpie said:
Yes, self-clinching type stud probably best. Are those doable without a machine shop?
iampoor1
Well-known member
What about a small metal tab, divided through the chassis?
A screw or bolt with toothed washers both sides followed by a nut ,securely torqued down there wont be any real chance of undoing it by mistake , if its visible on the back panel and you wanted to be extra sure you could use a 'security'torx head bolt ,and make sure its clearly labeled or stamped ground to prevent tampering .
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