RE- Re: Short circuit/Control Panel

Subject:      RE- Re: Short circuit/Control Panel
       Date:  Sat, 07 Jun 1997 10:26:37 GMT
       From:  robert.michaels-at-online.sme-dot-org (Robert Michaels)
Organization: Society of Manufacturing Engineers
         To:  tesla-at-pupman-dot-com

        Excellent, excellent,  overall posts (no surprise there 
        considering the poster).

 [ ... ]

-> While 1350 watts is only about 11 or 12 amps at 120 volts, it has
-> been my experience that inrush currents can easily be double this and
-> more. You will *not* experience the effects of inrush current if you
  [ ... ]

        Good point.  If someone doggedly and abjectly refuses to
        take Fr. McGahee's advice (or mine - see other post), then
        for catsake and cryin'outloud do get yourself a switch
        which is specificly and clearly rated for inductive loads
        (or for motor-starting which is even more demanding).

-> circuit breakers (not fuses). My main control panel has a bank of
-> circuit breakers of several different values. I just "activate"
-> several in parallel to reflect the maximum current I want to allow.
-> For example, if I want 40 amps, then I activate two 20 amp breakers.
-> Just because my electrical service can supply me with 100 amps is no
-> reason to use a 100 amp breaker! Four 20 amp breakers and one 10 amp
-> breaker and two 5 amp breakers allow me to adjust from 5 to 100
-> amps in 5 amp increments.

        Uh, er, I'm not too sure about this.  It may well suffice
        for casual coiling.  It is assuredly not acceptable in
        in professional practice:

        Paralleling two fuses or two breakers to double the current
        interruption capability is shakey at best.  I'm not at
        liberty to give a lengthy dissertation on why at the moment
        (nor either would most want to read it).  Suffice to say
        it does not automatically give you 20-amps of protection
        to run two 10-amp fuses or breakers in parallel in one
        (or both) sides of the line.

                Fuses and breakers are used for either of two
                ways:  To  =allow=  current or to  =limit=
                current.  In the latter case, there is usually
                some sensitive/expensive/difficult-to-replace
                equipment which must  =never=  be subjected to
                to overcurrents (fast blo fuses usually used
                here).  In this case especially it would be
                exceedingly unwise to parallel fuses.

        If one is going to parallel fuses/breakers for casual coiling
        =at least=  make certain the fuses/breakers are identical in
        type, rating, mfg'r.
 [ ... ]

-> system down from a remote position. This remote panic button is
-> mounted in a box and attached via a cable to the control panel. The
-> panic button is "portable" in the sense that I can move it anywhere I
-> want.

-> PANIC buttons should be a LARGE pushbutton, and preferably
-> illuminated so that you can't miss it in the dark! Place it where you
-> can slam it quickly in case of an emergency.

 [ ... ]

        The idea of a panic button is a super-excellent one.

        I would propose that the panic button  (more professionally
        stated: emergency-stop button or E-Stop as they are widely
        called { =real=  professionals would never actually panic,
        you understand} )  be mounted in a small box at the end of
        a long cable, preferably shielded cable or cable in flexible
        conduit, conduit or shield grounded.

        Cradle the panic button box in your hand at all times when
        operating under power.  That way if you panic (er -- I mean
        experience an untoward event) you can hit the button instantly.

                Dr. Tesla counseled keeping one hand in one's
                pocket at all times.  Taking a page from Fr.
                McGahee's book (or rather post) I'd say: one hand
                in one's pocket and the other on one's panic button.

                                        Calmly coiling, in --
                                        Detroit, USA

                                        Robert Michaels