Plastic Nema Boxes...

[Gravitysucks]

Are far more brittle than they appear.
I started building my electric control panel in a plastic Nema enclosure which got set aside for about a month due to a washing machine tragedy and the death of my beloved riding mower. The mower was eventually resurrected but sadly the washer and the floors it flooded not so much. Anyway, I went back to working on my panel this week only to find that there were cracks in the panel radiating from several of the switches to the point I think I'll probably have to scrap the box. I've had quite a bit of experience working with plexiglass, Lexan, etc so I knew that you need to be careful about pressure points and corners in cutouts and was careful so I was really surprised to see cracks had developed after the box had been sitting undisturbed for almost a month. The culprit was clearly the set screws on the back of the switches so it was undoubtedly my fault. I just wanted to let folks know to be aware that those pointy little set screws found on most of the switches that seem to be in general use for panels can be a problem for plastic enclosures if you tighten them a little too much.

 

[Neilyboy]

You talking about the grey carlon boxes? I just finished mounting my hardware last night. If that's the case I'm going to back off some of my screws now lol.
Neil

 

[lschiavo]

I could see that happening with self piercing screws. Try drilling a small hole first. I have always drilled right through and used machine screws/nuts.

 

[Gravitysucks]

You talking about the grey carlon boxes? I just finished mounting my hardware last night. If that's the case I'm going to back off some of my screws now lol.

Not sure of the box material. Here's a couple of pictures of the worse cracks. There are some smaller ones around some other switches.

 

[Sparkncode]

The washing machine problem sucks. My one had a terminal control board failure just before christmas. Luckilly no flood but unwanted expense.

Sucks about those cracks. Maybe using different screws with a flatter point but they only need to be snug, not tight.
Putting a small metal plate between the screw and the plastic would spread the load. I'm guessing thermal expansion at different rates while the box was sitting may have propergated the cracks.

I guess you could remove the hardware and do a fill and paint job on the box if you want to save it. Maybe scrape cracks wider and fill with epoxy then sand.

 

[augiedoggy]

You talking about the grey carlon boxes? I just finished mounting my hardware last night. If that's the case I'm going to back off some of my screws now lol.
Neil

Ive never had an issue with the 4 or so Ive made panels from cracking..

 

[augiedoggy]

I have some of those same switches in mine.. they have pointed screws designed to apply pressure into the mounting plate to hold the switch... I havent had any cause cracks but I Use the softer carlon boxes mentioned above and could see how they could crack.

 

[Neilyboy]

I *think* the carlon box must be of 'softer' less brittle material than the box mentioned. I have another box that I purchased from aliexpress for a different project (CNC controller build) and it is similar material but a bit thinner and feels like it would split if I applied too much pressure while cranking down some screws.
Neil

 

[Gravitysucks]

I checked on the manufacture's web site and the box I have is made from ABS. It actually machined really easily and cleanly, much more so than the polycarbonate type plastics that I'm used to and it seemed to be a much softer material. Obviously I was mistaken. I was just making my OP to give folks a heads up that they might need to be a little careful with these type of boxes so they don't mess them up like I did.
I could probably save this box with some work but I think I'm going to lessen my chances of future problems and purchase a metal enclosure. I've found one that's only $35 more than the plastic box was and it is already drilled out for the design I'm using. Plus, it's bigger so there's room for expansion in the future if needed and with some slight modifications will accept my back plane which is already almost completely wired. Live and learn.