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Re: Power Cords, and the like

Hi All,

	I will second Jim's notes here!  At work, I deal with hundreds of
different high current/voltage AC connectors.  Get the nice (and not cheap)
ones from Hubbell or some real industrial type AC plug.  ANY of the "good
ones" are an order of magnitude better than what you will find in the
consumer section of the hardware store for hooking up your oven or dryer.
Don't exceed their current ratings!  When they say 30 amps, they "really"
mean it!!  ;-))

Cheers,

	Terry


At 11:35 AM 5/26/00 -0700, you wrote:
>With the recent series of posts talking about power cords, I'd like to
>mention that I have a web page with the NEC ampacities for various flexible
>cords at http://home.earthlink-dot-net/~jimlux/hv/cordamp.htm
>
>My experience has been that the cord itself usually isn't the problem, but
>rather the connectors, and specifically, the connection of the wire to the
>prongs or pins in the connector.  For instance, when a stress is applied to
>the cord, it pulls the wires out of the screw clamps.  Or, the blades of the
>plug are inserted into a couple of springs in the receptacle.  Everytime the
>cord gets yanked, the springs get bent a little more.  Most of us have
>encountered 115VAC receptacles where the springs are weak and the plugs
>don't stay in or make good contact.
>
>Thermal fluctuations also cause problems.  As the connector changes
>temperature, the various components expand and contract, often at different
>rates, and connections can loosen, etc.
>
>
>How do you make good cables and connectors?
>
>Using good quality connectors.  When you are designing for cost, you want to
>save all you can on manufacturing costs and materials, so you make the
>springs out of the least expensive alloys, or, you use the thinnest wire
>that will carry the current and/or meet code.  More expensive connectors
>tend to have better quality components.
>
>Using locking connectors (like the Twist lock series from Hubbell and
>others).  The mechanical design of these tends to reduce the side forces on
>the blades and pins when the plug gets bumped or pulled.  The really nice
>connectors are the big plastic housing (or aluminum housing) multi pin ones
>that have round pins, are weatherproof, and are quite durable. They're also
>$100 each or more.  For high currents, the "cam lok" type are really nice,
>except for the fact that they are only single conductor, so connection
>sequence is important for safety.
>
>Using good strain relief on the connectors. The cable is usually fairly
>strong, as is the connector, so you want the loads from one or the other to
>be transmitted cleanly, without being coupled into the conductors, or worst
>of all the connection from pin/blade to wire.  A decent strain relief helps
>a lot.  Companies like Kellems and Woodbury(?) make stuff that works real
>well.  Just using a physically large connector helps, because there is more
>slack wire inside the connector, and the contact area between cable and
>connector is larger.
>
>
>
>