Your questions answered: Electrical standards for designing industrial facilities
Questions and comments not addressed during the June 13 webcast are tackled here.
Additional questions from the June 13 webcast "Electrical: New Standards for Designing Industrial Facilities" are answered by Greg Bielowicz, business development manager at Panduit.
Question: Can you also use these to tie my grounds to re-bar for mat grounding?
Bielowicz: I am not sure which products these are referring to, but yes, our GCE connectors are UL listed and comply to IEEE 837-2014 with rebar connections. Please see our product page online or in our catalog for sizing information.
Question: Cleats listed for bonding to cable tray? Cleats used for multi-conductor cable?
Bielowicz: There is no requirement or standards that require the electrical bonding of the cleat to e.g. a cable tray. This is beyond the scope of advice from a cleat manufacturer and should be part of the electrical system design.
Manufacturers are frequently asked for advice on the correct method of securing multi-core power cables. To my knowledge, there is still no independent data that recommends any particular fixing method, but custom and practice suggests that most users presume that any forces on the conductors, which arise in the event of a short circuit, will be restrained within the cable jacket and therefore cable cleats are not required.
The mechanisms within a multi-core cable, which help restrain the conductors in the event of a short circuit include:
- The outer extruded jacket.
- The helical winding of the cores.
- Steel wire or other type of armour if present.
Many short circuit tests using 3/4 core, copper conductor, multi-core cables from various cable manufacturers have been performed. Both armoured and unarmoured cables have been tested across a variety of conductor sizes, but because of the number of manufacturers and the variety of cable types and methods of construction available, it was not feasible to carry out exhaustive tests.
The results of the tests were varied but clearly showed that it is unsafe to presume that the forces between the conductors will always be restrained within the jacket of the cable, whether or not the cable is armoured or tightly helically wound. On some aluminum armored cables, the armour and jacket simply bursts under fairly low peak kA levels.
Our conclusion is that, unless the relevant cable manufacturer can give assurances regarding the performance of their specific cable at the anticipated fault level, fault rated cable cleats provide the safest option for securing multi-core cables.
Question: Panduit can now be used for cable management applications requiring short circuit protection. When is kA protection required for cable runs? Is it called up by a code (i.e. NEC) or is it an optional upgrade?
Bielowicz: You are correct in the use of the NEC reference. However, it is the sole responsibility of the system designer/contractor/consultant to offer a peak and RMS fault level for their system. This information is always available as the system calculations are fundamental to the specification of not only the cleats, but the cable, the switchgear, in fact every other item on the grid/system. Every conductor or cable shall have adequate strength, and be so installed as to withstand the electromagnetic forces that may be caused by any current, including fault current.
Cable restraints should:
- Prevent excessive cable movement due to fault-current magnetic forces.
- Be rated for specific cable size and available current.
- The fifth edition of API/ Recommended Practice 14F (Design, Installation and Maintenance of Electrical Systems for Fixed and Floating Offshore Petroleum Facilities).
Question: Are there concerns with crimps when battery-powered crimping tools are approaching discharge? Is the user alerted? Does the tool lock-out and not perform a defective crimp?
Bielowicz: The control cycle mechanism and audible error feature of Panduit BlackFin tools should help you determine if the crimp was done properly, even when the battery is low. If this audible notification does not go off and you are still unsure that the connection was done properly, you can always use the CT-USB to access the FIN software that keeps data logs of each of the crimps performed and graphically shows the performance of the last crimp.
Question: Can you repeat the pros and cons between exothermic and clamped type grounding?
Bielowicz: Exothermic is unsafe and unreliable. Compression connections are installed safely, conveniently, and have been proven to have an equally acceptable connection quality for the life of the building infrastructure through compliance with IEEE Std 837.
Question: How is a Panduit product clamped at the bus of the switchgear with grounding neutral?
Bielowicz: This will depend on the product you are referring to, but typically the connections are made mechanically with hardware (nuts/bolts or set screws).
Question: Are there any concerns using compression grounding in Ufer ground systems?
Bielowicz: Ufer ground systems are considered direct burial applications and our direct burial rated (UL listed) products should be fine to use in this application.
Question: In either high acidic or high alkaline soils there is a risk of corrosion at the connection point. Presumably exothermic welds avoid this risk. What about compression connections?
Bielowicz: Our compression connections comply to the testing requirements of IEEE standard 837 (2002 and 2014 revisions). If you are unfamiliar with this standard, please ask your sales representative for Panduit’s white paper and have them follow up with you on our latest revision that will be released later this year. The requirements of this standard incorporate an extremely harsh sequential environmental test with salt spray and acid bath type exposure. The standard proves that Panduit’s compression connections are able to withstand these corrosive factors with ease.
Question: How would you compare contact resistance between two methods (exothermic and compression grounding)?
Bielowicz: ECR is sometimes difficult to measure considering it can be measured in as little as microOhms. Resistance is key to the safety of the system, but life-time performance of a system is dependent upon other factors. I would advise comparing reliability or safety testing to qualify/validate the connections and compare one another. Our system is compliant to both the UL 467 safety requirements and IEEE 837 reliability requirements. We would be more than happy to share our test data with you if you are interested. Please contact your Panduit sales representative for more information.
Original content can be found at Oil and Gas Engineering.