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Wednesday, May 17, 2017
Question:
Good morning Charlie,
I am a bit mystified that Aluminum is still allowed as a service supply or even as cables to lights/switches/outlets? This is based on my experience from the original World Trade center incoming services being aluminum and were the cause of several fires due to Ali-corrosion from the “brass Allen keyed bolts” into the “cad/zinc plated receptacles” and then holding the “Ali conductors”- not a solid conductor but multi-wired, were squeezed with several strands fractured. Even some of the service Buses were Ali [Dissimilar materials causing cathodic corrosion]. Lots of white Ali powders around and on the bottom of the main cabinets. An 800 Amp service is nearly always found in industrial/office type situations and probably very rarely check for Impedances/Corrosions!
Seems strange the NEC still allows/recommends Ali conductors and some are even copper coated (still corrode if the copper is broken by the knurl on the securing Allen Bolt or screw. What are your thoughts on the uses [none of the Ali conductors we have seen were “tinned” or “tinned then ferruled”] We only use copper conductors and Brass Buss Bars for incoming service distribution busses and conductors (yes, we do put some electrical corrosion greases over these terminations to stop the copper Verdigris forming)?
Look forward to your response. Sincerely yours, Geoff
A
Answer:
Hey Geof thanks for your question. Splicing and termination devices must be identified for the specific conductor material as stated in 110.14. I suspect some of the problems you mention are related to incorrect termination devices or methods including the lack of torqueing as now specifically required by 110.14(D). In general conductors can be copper or aluminum as stated in 110.5. Notice that the word aluminum was added here in the2017 NEC but it was previously included in other parts of the NEC. Aluminum conductors must be made of an AA-8000 series electrical grade aluminum alloy conductor material as stated in 310.106(B). Both Aluminum and copper have advantages and disadvantages so it is the designer or engineer's choice. Aluminum conductors are often used for feeders and services.