I have read on this Forum some time ago, and can't remember the referance, that the
locknut needs to be spun in order to dig into the metal to assure a good connection. By
just turning the fitting into the locknut, the locknut can not do what it was designed to do.
All locknuts are designed to be tightened with a hammer and a standard blade screwdriver. The body of the fitting should never be grabbed with a channel lock or pliers and turned into the stationary locknut (except when the body has a nut profile provision - such as raintight or compression type).
The recommended assembly sequence would be to insert the conduit, tighten the fitting to the conduit, then insert the fitting into the box, and tighten the locknut last.
There are TWO reasons for this:
1. There is a high chance to distort the ID of the fitting which may prevent the conduit from entering the fitting properly (or at least making it very difficult to seat all the way to the conduit stop). If you don't seat it all the way, it may not be able to be fastened properly and hold the required pull forces.
2. The locknut will not get its "bite" into the metal - especially with teeth or nibs.
The Bridgeport Locknut was one of the first to have serrations and on both sides. They are significant serrations, unlike many other competitors like Steel City or EGS. I also commented in a previous thread that while UL does not have a 'paint removing' requirement for locknuts in UL514B, they did conduct a 'fact finding' study that demonstrated the serrations ability to remove paint and to withstand ground fault current tests without arcing or overheating.
UL reverts to whatever the manufacturer states regarding locknut/fitting assembly. If the nibs are only on one side of the locknut, then the Mfr. would state to the UL test engineers how those locknuts are to be assembled for the current test. With a Zinc locknut like Bridgeport's, the design makes it truly reversible. There are many Steel and Zinc locknuts that are NOT reversible.
As for a previous poster's comment regarding melting point of Zinc vs Steel, it is true that the Steel fitting has a much higher melting point. However, when it comes to performance and functionality, the Zinc fitting meets or exceeds the SAME specification as the Steel fitting does - UL514B.
Let's face it, if ultimate performance was a requirement for these fittings, then we would be making them out of some space-age titanium/platinum alloy with a melting point of 3500 C and tensile strengths 50x of steel or 100x of Zinc. That's not done because nobody wants to pay $100 for a fitting. They would rather pay $.30...:roll: So, the challenge for us manufacturers is how to make a product that meets or exceeds the specification requirements for that low cost...
It really comes down to preference and a quality product.
