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power switch connections.

Question asked by fixbear on Nov 6, 2018

It seems that the blog has been slow lately.  And that a old question on connectors has resurfaced.  I think I should explain the resulting problems we all seem to get into with crimp connectors.  Specifically female dissconects like a .250 or .187 blade.

 

First we need to know that when you flip a switch to the on position, It does not make a positive connection. but bounces from on to off for several milliseconds.  Each bounce (up to a hundred) causes a arc between the contacts and shortend's the life of the switch.  It also oxidizes and carbonizes the contacts which in turn create resistance and heat.  One of the contacts is directly connected to the output terminal of the switch and the .250 blade that you slide a disconnect on. Now if you use a disconnect that has already gone though a overheat, and has the related oxidation from the heat,  or the weak tension from loss of temper from the heat.  Your just setting yourself up for a premature failure of the new switch. 

 

What about the 7 grades of disconnection terminals. Each case has to be evaluated as for temperature, current, and vibration..Basically the 2 we would keep on a truck are the solid tube, copper sleeve, nylon insulated.  And the 900 degree high temp steel nickle plated. It just doesn't pay to carry all 7. There is no application that we need a lower temp vinyl. Butt and brazed tubes are ok, but will not meet the high amp requirements.  Why insulated and copper or tin sleeve tube. Vibration and wire movement. They are designed to clamp and restrict the insulator to prevent wire movement.

 

Crimpers are another story. There are a lot of cheap crimpers designed for home market and often used in the automotive field.  But not for major equipment power crimping. If your crimper does not have changeable dies, Locking stork, Adjustable lock tension.  It probably is not meant for our trade. There are a few dedicated high end crimpers out there for just one type of crimp.  All good ones will have a cam over design and a ratchet to force crimp to completion. Expect to spend $75 or more for a good one. I have one Square D that cost $500 thirty five years ago for #8 and up to 500 MCM.  Hate to think what it would cost today.

 

Resistance makes heat.  Heat makes oxidation.  Oxidation makes resistance.  All are a vicious cycle with electrical current.

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