Systems+Engines

Nuts over terminals

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"I am curious why electrical connections that hold a terminal on a threaded post use a stainless-steel post, a nut, and a washer. If you assume that the post can’t be changed—because it comes with the equipment—wouldn’t it be better to use a bronze or brass nut and a copper washer? I’m asking because stainless steel is less conductive than bronze, brass, or copper. If there is room to do so, why not also use a brass nut and put a stainless locking nut on top?"

-- Ken Simpson , Brooklyn, New York


Nigel Calder replies
: You raise a very important point, particularly in view of the plethora of high-current DC circuits that now are being installed on boats. In fact, using stainless-steel bolts, washers, and nuts is not a problem as long as the two terminals being held together are in direct physical contact. If this is the case, the bolts, washers, and nuts aren’t part of the circuit, but just hold the two pieces together.

However, if you accidentally put a stainless-steel washer between the two conducting surfaces and it’s a high-current circuit, the resistance created by the washer could generate enough heat to start a fire. That is why it’s important to make sure that a washer never becomes part of the actual circuit.

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