question about mounting things in metal box with backplane

Status
Not open for further replies.
Mr. Serious

Mr. Serious

Senior Member
Location
Oklahoma, USA
Occupation
Electrical Contractor
I've done this only once, on my first job after becoming a contractor: purchased a nice NEMA 12 rated box, with a hinged door, and a steel backplane, and I mounted three terminal blocks in it. The part number of the blocks was ALP2P2. They come with four holes around the outside edges for screws or whatever, so what I did was carefully mark center locations for my screws on the metal, and drill and tap 12 holes for machine screws, then mount the things with machine screws and washers.

The metal backplane was thick, and it took hours to drill and tap 12 holes. I know this isn't how the professionals do it. So, what do you do when you have to mount things on a thick peice of steel in the back of a box?

I just saw an ad for terminal blocks, and it mentioned something about "track mountable." So, DIN rails, is that what they're called? I'm not sure if that's a viable option for the blocks I was talking about, because they're big, for up to 350MCM wire or something like that.
 
The spec will state mounting provision, e.g. 35mm DIN rail.
If its DIN rail mountable, much simpler install.
We use bolts and fasteners to secure rail. No drilled/tapped holes. Speeds up the fabrication process.
So check the spec and if it can be mounted to DIN rail, use it!

Sent from my SM-G965U using Tapatalk
 
I have done a lot of making panels up to a 8' wide by 7' high Hoffman double door panels. I always drilled & tapped my holes making sure to use a quality tapping fluid ( speeds up tapping & prolongs life of taps ). Greenlee and at least one other company makes a combination drill bit/ tap that speeds the job up. I liked using gun taps. Din rails the only way to go. Makes quick work and down the road easy changes. Have to be carefully with terminal strips. My boss purchased hundreds of them for the 19 starters that I had to install. He saved money by purchasing terminal strips only rated for 300 volts while every motor was 480 volts. After that made sure to only order & stock 600 volt terminal strips even if we had a lot of 24 or 120 volt control or solenoid wires. Never installed a control transformer over 500 VA inside of any size panel to keep heat inside lower. Liked to install fuse block directly above the starter that it feed rather then all at top or one side if panel. Quicker to troubleshoot if fuse holder or breaker is right above starter. If there was room in panel would always leave at least 6" of slate DIN rails. Great to install plastic wireways to keep wires neat. Lot faster pulling on a wire to see where it terminates to rather then a thick wire bundle with ty rabs every few inches. Good luck.
 
"Did you know that you can chuck a regular tap in a cordless drill and tap holes much faster? You just need realize that you have to run the drill slow depending on the tap size."

And for the original poster (OP), do use tapping fluid, not some old oil you have around.

Mark, center punch, drill, tap; 12 holes in less than 15 minutes. We used 8-32 or 10-32. Screws and nuts are fine when building one, but tapping for any update. We screwed everything but items on rail, whether DIN or one of the older manufacturers block rails.
 
As a gross general rule, it would be hard to find DIN rail mounted terminals capable of holding 350kCMIL cables. There will be a lot of torsional force on those, and they need to be capable of handling any added force from short circuits. If you found DIN rail versions, they are likely only capable of 5kA SCCR, making them all but useless for something that needs 350kCMIL cables.

If you are going to do enough of them in the field, you can buy combo drill and tap units; drill bit followed by tap threads on the same shaft (party in the front, business in the back...). They are too expensive to use every day in a shop, but can be a blessing in the field. The only thing is, you typically can't use them if the panel is mounted in the box already because they would be too deep.

Link example.
 
Unless you're depending on the screws for grounding, couldn't short sheet-metal or self-drilling screws be used?
 
That metal was thick enough that the small self-drilling screws would break off. Larger ones like #12 or #14 probably would work.

I expect to only work with this stuff once in a blue moon, but I may have another job coming up that requires it again. I probably will just use self-tappers, if I'm once again working with a terminal block with a plastic frame that doesn't require grounding.

If I do use machine screws, those combo drill and tap units look nice. Would you use an actual drill, not an impact? And put the drill on high-torque setting and go slowly when you get to the tap part of the bit?
 
Mr. Serious said:
Would you use an actual drill, not an impact? And put the drill on high-torque setting and go slowly when you get to the tap part of the bit?
Click to expand...

Never use an impact! Set the clutch on a regular drill to "drill" and yes, go slow and steady when you get to the tap. You'll figure it out.

Mr. Serious said:
Is tapping fluid the same thing as cutting fluid that comes in a spray can, that I have sometimes used when drilling holes?
Click to expand...

Probably. It should say on the can. But I would think it will work fine. As long as you use a lubricant that isn't old motor oil.

-Hal
 
I use a drill and then follow with self threading machine screws(not self tapping). No issues and super fast. I use anchorlube for drilling.
 
Mr. Serious said:
I've done this only once, on my first job after becoming a contractor: purchased a nice NEMA 12 rated box, with a hinged door, and a steel backplane, and I mounted three terminal blocks in it. The part number of the blocks was ALP2P2. They come with four holes around the outside edges for screws or whatever, so what I did was carefully mark center locations for my screws on the metal, and drill and tap 12 holes for machine screws, then mount the things with machine screws and washers.

The metal backplane was thick, and it took hours to drill and tap 12 holes. I know this isn't how the professionals do it. So, what do you do when you have to mount things on a thick peice of steel in the back of a box?

I just saw an ad for terminal blocks, and it mentioned something about "track mountable." So, DIN rails, is that what they're called? I'm not sure if that's a viable option for the blocks I was talking about, because they're big, for up to 350MCM wire or something like that.
Click to expand...
Was the backplane stainless, or something exotic? Most backplanes are 14ga or 11ga mild steel - a drill bit should go through that like butter. Sounds like you need some better drill bits.

Also, the taps that come with Klein tools are pretty much trash. Get a good spiral flute tap and run in it a cordless drill, and use cutting oil. Drilling and tapping a dozen 10-32 holes should take less than 15 minutes.

Don't through-bolt. If anything ever has to change on the panel, it makes removal / remounting an absolute nightmare since you have to remove the backplane to get to the nuts. If you need to mount heavy components that need fasteners larger than can be tapped into 14ga or 11ga steel, use Riv-nuts and thread you fasteners into them.




SceneryDriver
 
SceneryDriver said:
Was the backplane stainless, or something exotic? Most backplanes are 14ga or 11ga mild steel - a drill bit should go through that like butter. Sounds like you need some better drill bits.

Also, the taps that come with Klein tools are pretty much trash. Get a good spiral flute tap and run in it a cordless drill, and use cutting oil. Drilling and tapping a dozen 10-32 holes should take less than 15 minutes.

Don't through-bolt. If anything ever has to change on the panel, it makes removal / remounting an absolute nightmare since you have to remove the backplane to get to the nuts. If you need to mount heavy components that need fasteners larger than can be tapped into 14ga or 11ga steel, use Riv-nuts and thread you fasteners into them.




SceneryDriver
Click to expand...
or run the bolts in from the back with a lock washer and put the nut on the front.
 
SceneryDriver said:
Was the backplane stainless, or something exotic? Most backplanes are 14ga or 11ga mild steel - a drill bit should go through that like butter. Sounds like you need some better drill bits.

Also, the taps that come with Klein tools are pretty much trash. Get a good spiral flute tap and run in it a cordless drill, and use cutting oil. Drilling and tapping a dozen 10-32 holes should take less than 15 minutes.
Click to expand...
And don't forget to use the proper drill size, such as a #29 for a 8-36 NF which does not have a direct fractional inch equivalent.
 
I think the backplane was just regular steel, my main problem was trying to use the Klein triple-tap. But perhaps I need better drill bits too. I don't think I could have even drilled the holes without tapping within 15 minutes, the way I was doing it. I used the smallest bit 1/16" to drill all the way through the steel, so that the hole placement would be as accurate as possible. Then I used the 9/64 (I think) to drill a little over halfway through, then turned the sheet over and drilled the rest of the way from the other side. I drilled from both sides to avoid burrs of metal sticking out. I probably should have used a bigger drill bit before the tap, because if I recall correctly, I actually tapped them out to 8-32 first, then 10-32. That's an extra step I shouldn't have done.
 
Status
Not open for further replies.
Top