• The QOTD for 2015.12.27 was addressing the issue of lightning arrestors.  Specifically the use of a Gas Discharge Tube (GDT) and a bi-metal conductor are used to provide a shunt for lightning strikes.

    I'm well aware of GDTs (having designed a few lightning protection cards), but I've never heard of "bi-metal" conductors used as a shunt device.

    Bi-metal conductors are used as series component in lightning protection systems.  Functionally speaking, they allow the mechanical and electrical jointing of aluminum and copper cables while avoiding galvanic (aka corrosion) action between the two metals.  These devices are used when the customer wants to use aluminum cabling (for cost reasons) for the structure rather than copper.  Copper is used for the last few feet to earth ground instead of aluminum because of copper's superior corrosion resistance in wet and/or alkaline environments.

    I'm not aware of any bi-metal conductors that were toasted during a strike.  If that were the case, pretty much the lightning protection system fried by the lightning strike would need to be replaced.

    So what are these "bi-metal" devices the question refers to? 

  • By Howard - edited: December 29, 2015

    I did not see the question, but I assume that the "shunt" refers just to the alternate path that the lightning takes to ground.

    In that case, if you're using aluminum wire for most of the ground line, you should use a bi-metal connector between it and the copper going to the ground rod - as you indicated.

    It is the case that GDT's will require replacement after full strikes or several nearby strikes. 

    Methinks the QOTD is misleading.

    Thanks for posting this.

  • Your use of the term "shunt" in this context is correct.  "Shunt" as you probably know very well is just another word for parallel.  

    The question Howard's comment pertain to was:

    "What component of a wireless network might use a bi-metal conductor or gas discharge tube?

  • By Tom Carpenter - edited: December 29, 2015

    The question, as you stated, asked what component of a wireless network might use a bi-metal conductor (connector may be a more common word here) or gas discharge tube?

    The only correct answer in the list is lightning arrestor. The question is pretty straightforward in that sense. The bi-metal connector (conductor - as it is that too) is used in scenarios where copper cannot be used across the roofing material (or other material) and it connects the aluminum and copper cables together (or vice versa). It is part of the lightning protection system, though not technically part of the lightning arrestor. But it is used "by" the lightning arrestor (or more accurately by the electrical energy [smile]). This would be my further explanation and should explain the inclusion in the question.


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