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I'm dealing with an equipment which has a lot of internal wiring. The system is powered in 12V but the wires carry a good amount of current (in excess of 10A). I need to connect different units with screws terminals (power supply, relays, potentiometers etc..) and for this purpose I am using insulating ring terminals which are crimped to the wire and then secured (for reliability issues) with an extra heat shrinking tube. The ring itself of the terminal is not insulated and a single fault condition could cause the terminal to touch any of other electronics inside the panel. In order to increase the reliability level which kind of insulation can I put on top of the screws of the ring terminals? Is hot melt adhesive a good option? Or is there a specific solution? I usually dont rely much on insulation that melts at low temperatures since high currents can cause quite an increase of temperature which can in its turn melt down the insulation and start a negative cycle which in the end destroys the lead.

example image

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  • \$\begingroup\$ Let me see if I've got this straight. To connect two wires, you crimp each one to a ring terminal, then use a nut and bolt to connect the two? And you're worried about the unsecured junctions flopping around inside your box? If that's not true, please give a more detailed description. \$\endgroup\$ – WhatRoughBeast Jun 17 '14 at 9:59
  • \$\begingroup\$ Look at the example in the picture. A crimp terminal is used to connect a wire to a power transistor through a screw. If the transistor falls of and reaches the metal casing or if another lead is detached this could cause a failure. How can I insulate the screw to provide a higher level of reliability? Cover with a cap? Use some kind of hot-melt adhesive? Silicone rubber? \$\endgroup\$ – Francesco Jun 17 '14 at 10:17
  • \$\begingroup\$ @Francesco Some terminal blocks have a transparent covering over them like this one computerweb.com.tw/rimages/269/terminal-block-TB-2503L-B.jpg Maybe they have a power transistor with a similar protective cover. \$\endgroup\$ – Sohail Jun 17 '14 at 10:28
  • \$\begingroup\$ Thanks! but the transistor in the picture is just an example! I am not using any transistor in my system ;) I am looking for a general solution for crimp terminals secured with screws. Just think about any kind of barrier strip, how do I insulate the conductive parts? \$\endgroup\$ – Francesco Jun 17 '14 at 10:35
  • \$\begingroup\$ @Francesco Well, then potting the terminal seems to be the only solution. \$\endgroup\$ – Sohail Jun 17 '14 at 11:05
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If you do the mechanical part of your job right, then there's no way that anything can be flopping around inside your box, just inviting disaster.

Here are a couple of examples of equipment laid out properly:

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Notice how everything is laid out neatly, as if it were planned, and harnessed and secured properly in order to completely eliminate the possibility of an inadvertent mis-connection/short in the box.

Also, in the topmost photo, notice the use of crimp terminals and a Jones-type barrier strip secured to the chassis in order to make connections to a cable leading to the outside world, and a terminal board used to secure - and provide connections to - the resistor array.

This method of construction can be used universally where wiring by hand is required, will yield very reliable equipment, and eliminates the need for hot glue. ;)

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  • \$\begingroup\$ Isn't there a problem with running wires carrying different currents right next to each other like those boxes show? After all, we didn't know about the spinners and other electronic physics junk until was it the 50s or 70s, but even when two wires are insulated, when they run next to each other they an affect each other due to field disruption or something. I dunno. Some joe rogan podcast with Eric Weinstein was talking about it. \$\endgroup\$ – comeatmebro Nov 19 '18 at 22:33
  • \$\begingroup\$ Anyway, when you have two metals separated by an insulator, that's a capacitance. So why isn't this capacitance between all those wires and why wouldn't that affect the integrity of the system? \$\endgroup\$ – comeatmebro Nov 19 '18 at 22:33
  • \$\begingroup\$ From what I've learned about signal wiring, its better that if they must be near each other at some point, its best they cross at 90 degree but realistically you just want them to have as little run distance as possible, within reason, where they are the same length away from each other. Its why I see rats nests of wiring in high power amplifiers more than "neat" wiring where everything is bound together, running one direction, tucked and angled sharply to follow chassis bodies, etc. \$\endgroup\$ – comeatmebro Nov 19 '18 at 22:33
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If your design may lead to loose components or terminals, consider changing your mechanical design. Secure the components and connections with fasteners suited to the job - whether it's nuts and bolts with locking washers, or double bolts, or a particular adhesive. Make sure all ring connections are not only mechanically and electrically sound to each other, but to the enclosure as well. You shouldn't have "floating" ring connections, they should be terminated to a terminal block or otherwise mechanically attached to the enclosure so they do not move inside the enclosure.

If you feel the need to also protect any exposed conductors, select a suitable silicone conformal coating. These can be UV or heat cured, and once cured can withstand a great deal of heat, vibration, and other typical environments without falling off. Be sure to use the minimum necessary to coat the conductors, too much will add unnecessary weight, and under some conditions, such as strong vibrations, the additional mass may allow it to fall off the protected component.

Further, silicone conformal coatings are easily removable and replaceable without chemicals, unlike some epoxy compounds.

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