🚀 go-pugleaf

In article <4110002@hpiacla.HP.COM> marc@hpiacla.HP.COM (Marc Schwager) writes:
>A friend and I were discussing a connector problem the other day and
>we decided to ask a more informed audience. Sooo.....
>Does anyone know of a connector that meets the following requirements:
>1) three prongs each carrying 50 amps at 5v DC.
>2) (the killer :-) must be able to connect and disconnect hot, with 
>    no arcing.
At this current level, sparking is likely to be inevitable.  You might consider
an air blast arrangement like those found in large circuit breakers or a pyro-
technic driven cable cutter or disconnect.  These would serve to disconnect the
circuit, where arcing is more of a problem.

If you are worried about explosive atmospheres and arcing, you have several
options.  First you need to know the atmospheric composition.  From this data,
there are published curves showing the maximum current that can be broken at
a given voltage without producing an igniting spark.  At five volts, several
amps are possible but certainly not fifty [this is from memory so check the
numbers before trusting me].  Capacitance and inductance must also be taken
into account since they are energy storage mechanisms.  If all of the require-
ments are met such that the available energy is too little to cause ignition,
the system can be considered to be intrinsically safe.

An alternative approach is to use explosion-proof construction in which the
sparking device is contained within an enclosure capable of withstanding an
internal explosive ignition without allowing ignition of the outside
atmosphere.  Companies such as Crouse-Hinds, etc. make such enclosures.  All
cables in and out of the enclosure must be within grouted conduits so this
approach is not good for connectors that have to be dismantled.  Hubbell makes
some connectors that have special mating surfaces and grommets that can be
used in many hazardous locations, but generally it is required that the power
must be disconnected before connections are made or broken.

A final approach is to purge the connector with a non-flammable gas, 
maintaining a positive pressure around the connector such that the connector
is never exposed to a hazardous atmosphere.  Liquid immersion in a material
such as oil might also work in certain circumstances.

The installation of instruments and electrical apparatus in hazardous locations
is a very complicated subject.  While many of the techniques are based on 
experience rather than hard science, the safety record of the chemical industry
shows that they work.  I am sure everyone can point to at least one spectacular
disaster at a chemical plant, but look carefully at the number of deaths or
serious injuries per man hour for all major manufacturing industries.
                                                     Barry
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|  ___  ________  |
| |  / /        | |  Dr. Barry L. Ornitz   UUCP:...!rochester!kodak!ornitz
| | / /         | |  Eastman Kodak Company
| |< < K O D A K| |  Eastman Chemicals Division Research Laboratories
| | \ \         | |  P. O. Box 1972
| |__\ \________| |  Kingsport, TN  37662       615/229-4904
|                 |
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