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Passing 16Arms (ac) through screws.

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alphacat

New Member
Hey,

I have a PCB which is enclosed by a plastic enclosure.
there're 3 metalic male pins - neutral, live & earth - that are coming out of the enclosure and are inserted into a power socket.
The pins are screwed into the plastic enclosure, using metalic screwes.
Since there can be 16A AC current drawn from the power mains, and passing through the metalic pins, the screwes themself should be able to handle such amount of current.

Since i'm new to this field, i'd like to ask for your experience regarding this.
What should be the specifications of the screwes, in order to handle such amount of current - type of metal, surface area, etc?
How can I prevent from the screwes to damage the plastic enclosure and melt the part of it which they have contact with?

Thank you very much.
 

mneary

New Member
The pin vendor may require specific brass mounting hardware in his spec. (Thermal coefficient, etc)

But, what you are proposing is probably illegal, but not for the reason that you ask. I take it that you will be relying on compression between the terminal and the hardware (screw head on one side, nut on the other) to complete the connection. Since most plastic materials will cold-flow, you cannot guarantee this compression over time.
 
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alphacat

New Member
Hey,
Thanks alot!

The structure of this arrangement is such that there is a path for the screw to be screwed into, and as you said, the screw's head presses the pin to the plastics.
I must mention that the screw's head doesnt touch the plastics (as can be seen in the picture below), but only presses the pin to the plastics.

So I understand from you that its illegal to have only the screw's head pressing the pin?
What should be the configuration then?




Hopefully its ok, I wanted to ask another question please regarding what you said about thermal coefficient.
I indirectly contacted a metalic pins manufacturer, told him that my requirement for the pins is that they could conduct 16Arms AC current, and asked him for the required type of metal.
He said that Copper would be fine.
Is there anything else i should be worried about?

Thanks again friend.
 

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mneary

New Member
The copper (or brass) screw touching the terminal looks good electrically and thermally.

To understand what I'm describing you must make a mechanical drawing showing the entire screw end to end. Show the sandwich including the screw head, the terminal, some washers, the plastic, and any other hardware.

All of these items must never cold-flow under the constant pressure of the connection. They must have a thermal coefficient equal to that of the screw. Copper (or brass) hardware meets the requirement.

If your plastic enclosure is part of this sandwich and is under compression, it must also meet this requirement.

[edit] The diagram I added hopefully shows the consequences of using a plastic which cold-flows over time. [/edit]
 

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mneary

New Member
I should clarify that I didn't say anything is illegal, just that if you compress plastic and it makes your connection loose, it would be unsafe (and therefore illegal).
 
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alphacat

New Member
I see,
You really taught me some important things about it.
Thnaks.

Hey Bill,
Thanks for helping out.
I did make contact with the office here who's in charge of passing electrical products compliance with the required standards, and currently i'm trying to gather as much info as i can in order to be prepared for it.
 

alphacat

New Member
The copper (or brass) screw touching the terminal looks good electrically and thermally.

To understand what I'm describing you must make a mechanical drawing showing the entire screw end to end. Show the sandwich including the screw head, the terminal, some washers, the plastic, and any other hardware.

All of these items must never cold-flow under the constant pressure of the connection. They must have a thermal coefficient equal to that of the screw. Copper (or brass) hardware meets the requirement.

If your plastic enclosure is part of this sandwich and is under compression, it must also meet this requirement.

[edit] The diagram I added hopefully shows the consequences of using a plastic which cold-flows over time. [/edit]
Hey,

Thanks alot for the added diagram, its really helpful!

What is then the ideal configuration for the plastics material to not coldflow?
 

tytower

Banned
Don't compress it ,don't heat it and especially don't suck on it
 

eblc1388

Active Member
What was said essentially is there should be two separate forces involved.

One for the cable to make good electrical contact to the metal pin, the other to fix the pin to the plastic enclosure.
 

alphacat

New Member
Alright.

I just dont understand how should the metalic pin should be fixed to the plastic enclosure if not by a screw pressing it only from one side with its head?
 

tytower

Banned
Probably not suitable but a screw through the metal pin , then a washer and nut tightened up then through the plastic with another washer each side locked then by a washer on a nut.

Alternatively drill the plastic with a much larger hole ,glue in a small piece of pipe in say aluminium that can hold the compression loads and run the screw through the center of that
 

mneary

New Member
The products that I have seen are complete without the enclosure. They could be plugged in to the wall as is, (however exposed). The project is placed into the enclosure and the terminals stick out through holes which allow the terminals to emerge from the enclosure.

The project is mounted to the enclosure with insulated hardware. The electrical connection doesn't depend upon the plastic's integrity.
 
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