I've completed the design for my pool timer and now I'm down to designing how this board will actually hold itself inside an enclosure. I already have a box that I'd like to re-use. It looks like the t30004r.

I plan to take out the 2 mechanical timers and insert my 3"x3" PCB in there, but I need to mount it inside the box in a safe way. The PCB itself has external connections coming out on all sides and I'm using many hole-through components. In addition, I also plan to use the 2 switches that are a part of the panel to still allow the control of the light & pump. The board takes in 120VAC so I want it to be secure.

The main option here seems to be adhesive standoffs. Are there better solutions? Any concerns that I should have with adhesive standoffs? I do still want it to be removable.

PCB design



Nothing beats proper screws to secure a PCB within an enclosure. I do not recommend adhesive standoffs, especially if your board has 120VAC on it. The adhesive can break down with time or temperature, and if the board falls into the enclosure it can either short out or cause the enclosure to become live. This is obviously very dangerous.

My recommendation would be to create a "backplate" (using ~16 gauge steel) that screws into the existing mounting holes in the enclosure. Then add holes that line up with mounting holes on your PCB and screw the PCB down to the backplate using, for example, 1/4" diameter standoffs. I have found 6-32 screws/standoffs to be great for mounting most PCBs.

If your PCB doesn't have mounting holes, then the first thing I would recommend is design a new version that has them. That is by far the best option. If for some reason you can't respin the board though, and you must use adhesive standoffs, use some sort of strap (Velcro?) to go over/around the PCB to make absolute certain that even if it becomes detached from the backplate, it still can't fall against the wall of the enclosure. Redundant safety features are a must.

We may be able to provide more specific solutions to your problem if you post an image of your PCB, but based on the information provided in your initial post this is my recommendation.

  • \$\begingroup\$ Thanks for your response. I can still modify my board as needed. That makes sense to me the only tricky piece is how I would be able to create enough space between the enclosure and the back-plate. I'll need to screw the standoffs into the plate and will probably need some nuts to secure it at the bottom. Those nuts are going to live between the enclosure and the plate which means that the existing screws will need some way to add space between the board and the enclosure. Are there plastic tubes that I could insert the screw in to fit it nicely? Other thoughts on that front? \$\endgroup\$
    – ti_chris
    Jul 17 '20 at 10:32
  • \$\begingroup\$ zip ties/ hose clamps could also be used for straps- though you would have to account for the conductivity of hose clamps \$\endgroup\$
    – kp122
    Jul 17 '20 at 10:33
  • \$\begingroup\$ @ti_chris Nylon spacers can be very useful in projects such as this. Check McMaster-Carr or other hardware supply companies for options. \$\endgroup\$
    – DerStrom8
    Jul 17 '20 at 10:54

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