LJSMITH1
Senior Member
- Location
- Stratford, CT
Interesting debate...
I happen to be in a unique position to work for a fittings manufacturer. Most of our fittings are tested/certified/listed to UL514B. We make both Compression and SetScrew style fittings to this specification. All fittings pass the UL test requirements "WHEN PROPERLY INSTALLED AND USED IN AN APPROPRIATE ENVIRONMENT". That is the caveat which some don't understand. Also, a UL committee develops the 'specs' that manufacturers use to design fittings. How they arrive at the numbers is based on what they feel is appropriate for the application.
There are many factors that can determine the maxiumum ground fault current that a fitting can handle (i.e. contact pressures, metal types, contact surface area, etc.). Assuming set screws are torqued properly and compression nuts are fully tightened, both types can easily pass the ground fault current and electrical resistance (voltage drop) tests specified in UL514B. Is there a type that can perform better in these tests? Yes. The Set Screw version has slightly lower contact resistance due to the destructive nature of the setscrew deforming the plating and relatively high contact pressures exerted on the conduit base metal. However, the improved performance can be considered minor as they have no bearing on the real-world performance requirements. Plus, there are too many other variables to consider (i.e. workmanship, fitting/tubing tolerances, tubing hardness, oxidation, etc.) that would typically negate such an 'edge' in electrical performance.
In addition, in mechanical tests (i.e. bend & pull), both fittings handle the required forces easily. Can these fittings be made to fail these tests? Yes. Let's say the required pull force is 300lbs for 5 minutes, and you apply 450 lbs, odds are the fitting may not pass. Many manufacturers design fittings to meet the UL requirements and nothing more. This makes sense for costs, but sometimes not all field applications are controlled lab environments with people using calibrated torque wrenches or sophisticated current test equipment. Sometimes, it makes sense to slightly 'over-design' to compensate for these differences. A properly designed and produced zinc fitting is every bit as strong and performs as well as a steel fitting. I have seen diecast locknuts that have only a 330 degree cast-in thread, which can't even hold much over the typical torque applied in the field without jumping a thread on the fitting, or cracking. Our company makes locknuts that have two, fully cut threads in each locknut to be able to maximize the amount of torque that can be generated without damaging the locknut.
As for the battle between die cast zinc and steel fittings, I believe zinc is better due to superior dimensional consistency and better assembly performance. Not to mention zinc's inherent corrosion resistance that continues all the way through the fitting.
The main reason why many people switched from zinc to steel in the last 5 years was due to costs. Zinc was at $.65/lb in 2004 and went up to over $2.10/lb in 2006. This caused a great many distributors to flock to steel due to its significantly lower cost. Now steel has risen 45% since the beginning of 2008 and is becoming more in line with Zinc, which has slightly dropped to about $1.30/lb. I am sure many more folks will to return to zinc becuse if price continues to become a mute point, many folks will prefer zinc fittings over steel.
I happen to be in a unique position to work for a fittings manufacturer. Most of our fittings are tested/certified/listed to UL514B. We make both Compression and SetScrew style fittings to this specification. All fittings pass the UL test requirements "WHEN PROPERLY INSTALLED AND USED IN AN APPROPRIATE ENVIRONMENT". That is the caveat which some don't understand. Also, a UL committee develops the 'specs' that manufacturers use to design fittings. How they arrive at the numbers is based on what they feel is appropriate for the application.
There are many factors that can determine the maxiumum ground fault current that a fitting can handle (i.e. contact pressures, metal types, contact surface area, etc.). Assuming set screws are torqued properly and compression nuts are fully tightened, both types can easily pass the ground fault current and electrical resistance (voltage drop) tests specified in UL514B. Is there a type that can perform better in these tests? Yes. The Set Screw version has slightly lower contact resistance due to the destructive nature of the setscrew deforming the plating and relatively high contact pressures exerted on the conduit base metal. However, the improved performance can be considered minor as they have no bearing on the real-world performance requirements. Plus, there are too many other variables to consider (i.e. workmanship, fitting/tubing tolerances, tubing hardness, oxidation, etc.) that would typically negate such an 'edge' in electrical performance.
In addition, in mechanical tests (i.e. bend & pull), both fittings handle the required forces easily. Can these fittings be made to fail these tests? Yes. Let's say the required pull force is 300lbs for 5 minutes, and you apply 450 lbs, odds are the fitting may not pass. Many manufacturers design fittings to meet the UL requirements and nothing more. This makes sense for costs, but sometimes not all field applications are controlled lab environments with people using calibrated torque wrenches or sophisticated current test equipment. Sometimes, it makes sense to slightly 'over-design' to compensate for these differences. A properly designed and produced zinc fitting is every bit as strong and performs as well as a steel fitting. I have seen diecast locknuts that have only a 330 degree cast-in thread, which can't even hold much over the typical torque applied in the field without jumping a thread on the fitting, or cracking. Our company makes locknuts that have two, fully cut threads in each locknut to be able to maximize the amount of torque that can be generated without damaging the locknut.
As for the battle between die cast zinc and steel fittings, I believe zinc is better due to superior dimensional consistency and better assembly performance. Not to mention zinc's inherent corrosion resistance that continues all the way through the fitting.
The main reason why many people switched from zinc to steel in the last 5 years was due to costs. Zinc was at $.65/lb in 2004 and went up to over $2.10/lb in 2006. This caused a great many distributors to flock to steel due to its significantly lower cost. Now steel has risen 45% since the beginning of 2008 and is becoming more in line with Zinc, which has slightly dropped to about $1.30/lb. I am sure many more folks will to return to zinc becuse if price continues to become a mute point, many folks will prefer zinc fittings over steel.
