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Sub transient reactance X”d worshiper.
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Discussion Starter · #1 ·
I searched the site a bit, but never saw a discussion on the repair of the Class 1 division 2 Ex enclosures for switching equipment.

I run in to this a lot, where someone mistakes the threading as the NC Corse standard and decides to try to fit the selected bolt in to it. Resulting in a broken bolt or one that now cannot be removed with out drilling and re-taping the bolt hole.

I have never seen a enclosure that was not, a Quad lead threading. I'm sure there are a few.

For the apprentices that are getting in to this area. The study of the different machine threading and how to properly tap and die material is a good study.

Below is the differences of the types of bolt threading that is available.

Line Font Parallel Electric blue Diagram


The application of the right lubricant and threading lubricant to prevent electrolysis of the material is also important.

So How many of you run in to this with the Ex enclosures?

Do you have other repair procedures that you can share?
 

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I've seen a few too in similar shape. Luckily enough, I've been able to drill it out and retap the holes. Whenever I put almost any screw or bolt into an XP enclosure it get a day of STL. And the first guy I see using an impact to put them in gets an ear full. They rank up there with those that take the globes on XP lights and tighten the crap out of them.
 

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Sub transient reactance X”d worshiper.
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Discussion Starter · #3 ·
I've seen a few too in similar shape. Luckily enough, I've been able to drill it out and retap the holes. Whenever I put almost any screw or bolt into an XP enclosure it get a day of STL. And the first guy I see using an impact to put them in gets an ear full. They rank up there with those that take the globes on XP lights and tighten the crap out of them.
Do you re-tap to the same. Quad lead? or go to the standardization of the single lead available?

Those quad lead taps, are very hard to come by. And super expensive.
 

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Do you re-tap to the same. Quad lead? or go to the standardization of the single lead available?

Those quad lead taps, are very hard to come by. And super expensive.
The few I've retapped I've used the closest standard tap to the bolts at hand. I don't recall ever seeing a quad lead bolt, or having any difficulties in chasing the threads.
 

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Sub transient reactance X”d worshiper.
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Discussion Starter · #7 ·
One more.
If one full thread, of a Bolt, is showing past the Nut, it's just as strong as 20 threads showing past the nut.
Under a Tensile Strength test (straight pulling) done according to ASTM standards, the Nut never strips off, the Bolt breaks just under the head.
ASTM = American Standards and Testings Methods
To complete the trivia:

Hex cap screws
  • Flat washer facing under the head that meet specific tolerances as described under ASME B18.2.1-1996.
  • They will usually be manufactured by a cold-heading process (large runs of standard sizes) or turned CNC operation.
  • A radius under the head at the shank.
  • Body diameter of plus nothing, minus .011″ for an 1-1/4″ diameter fastener.
  • Some common fastener specifications unless otherwise specified: ASTM A449 and SAE J429 Grade 2, 5, and 8.
Hex bolts
  • A die seam across the bearing surface is permissible.
  • The typical bolt is manufactured by hot-forging process.
  • Allows a reduced body diameter to be not less than the minimum pitch diameter of the thread.
  • Some common fastener specifications unless otherwise specified: ASTM A307A, A354, and F1554.
 

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Chief Flunky
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The tensile strength of the bolt is taken into consideration. It’s called a flame path or flame gap. In the event of an internal explosion the bolt stretches and the tiny gap it forms between the cover and the box cools the escaping gas so that it cannot propagate s flame outside the box. You are kidding yourself if you think it will hold the pressure. The metal housing in most boxes ruptures at 10-20 PSI. It’s supposed to be a controlled failure. So switching bolt grades, not using a torque wrench, or messing with the threads and geometry compromises the box.

Surprised by what you are seeing. You can theoretically use ANY bolt but there is a ton of publicly available data on 1/4-20 Grade 5 bolts so that’s what is normally used on everything in underground mines in North America. If they use a different fastener you need to put everything back exactly the same way.
 

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If you can not find a tap or your helper got hold of it and broke it then take a disk grinder and cut 3 slots up the threads and wack it in with a impact if the captured nut or sheet metal is buggered up.
 

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Discussion Starter · #12 ·
The tensile strength of the bolt is taken into consideration. It’s called a flame path or flame gap. In the event of an internal explosion the bolt stretches and the tiny gap it forms between the cover and the box cools the escaping gas so that it cannot propagate s flame outside the box. You are kidding yourself if you think it will hold the pressure. The metal housing in most boxes ruptures at 10-20 PSI. It’s supposed to be a controlled failure. So switching bolt grades, not using a torque wrench, or messing with the threads and geometry compromises the box.

Surprised by what you are seeing. You can theoretically use ANY bolt but there is a ton of publicly available data on 1/4-20 Grade 5 bolts so that’s what is normally used on everything in underground mines in North America. If they use a different fastener you need to put everything back exactly the same way.
Yes the enclosure is suppose to breathe. This is why the installation of breather and drains are installed with desiccant packs inside the enclosure.

BREATHER-DRAINS.pdf (adalet.com)

The more thread leads on the (Cap screw/bolt) the less holding force/ clamping force it can maintain.

Yes, if the OEM uses specific lead design in the fasteners, use it.

This gives me a idea on another string: the maintenance of the Ex enclosures for 4x/IP66 for class 1,2 areas

especially the aluminum enclosures that are old and not maintained well with the internal corrosion.
 

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Chief Flunky
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Yes the enclosure is suppose to breathe. This is why the installation of breather and drains are installed with desiccant packs inside the enclosure.

BREATHER-DRAINS.pdf (adalet.com)

The more thread leads on the (Cap screw/bolt) the less holding force/ clamping force it can maintain.

Yes, if the OEM uses specific lead design in the fasteners, use it.

This gives me a idea on another string: the maintenance of the Ex enclosures for 4x/IP66 for class 1,2 areas

especially the aluminum enclosures that are old and not maintained well with the internal corrosion.


Sent from my iPhone using Tapatalk
 

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Install, troubleshoot, maintain, and upgrade electrical systems, plant utilities, PLC's, mechanical
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One more.
If one full thread, of a Bolt, is showing past the Nut, it's just as strong as 20 threads showing past the nut.
Under a Tensile Strength test (straight pulling) done according to ASTM standards, the Nut never strips off, the Bolt breaks just under the head.
ASTM = American Standards and Testings Methods
When taking a "how to bolt things together" class at a nuclear power house, STNP,
having at least two full threads past the nut was required to have the "full thread engagement" required.
 
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