From: David Nelson via EV <[email protected]> >Please note that I am not asking about electrical code here! I know >what the code says. > >What is the actual sustained current carrying ability of the NEMA >L6-30 plug/sockets?
The ACTUAL capacity is determined by the temperature rise. The materials used to make the connector (usually the insulating materials) have a temperature limit. Typical numbers range from 80 deg.C to 130 deg.C. That''s what ACTUALLY sets the maximum sustained current. OK; going by memory since I'm away from home for the holidays... Most L6-30 and -50 receptacles are made from black thermoset plastics (like bakelite) that have a high temperature rating and won't melt. UL says they are good up to 130 deg.C. UL rates them for a 40 deg.C rise. In their testing, the temperature rise at full current did not exceed 40 deg.C. Thus, it can carry full rated current in an ambient as hot as 90 deg.C before the insulation will rise above 130 deg.C. Now a 90 deg.C ambient is pretty hot (194 deg.F)! It's more likely that your maximum ambient will be more like 50 deg.C (122 deg.F). This means you can run at a current that causes TWICE the temperature rise before the insulation's maximum temperature rating is reached. Heating is determined by the SQUARE of the current; so double the temperature rise doesn't mean double the current! But you can run sqrt(2)=1.414 times the rated current. That means the receptacle can handle 50 x 1.4 = 70.7 amps in a 50 amps connector in a 50 deg.C (120 deg.F) ambient. The same logic applies to the cords and plugs. However, they are likely to be made of cheaper soft plastics with a lower maximum temperature rating. They will MELT if you push them this hard! But you can get plugs made of the same high-temperature thermoset plastics as the receptacles. They are bigger, and have to be manually attached to the cord. Likewise, look at the insulation rating of the wire. It's usually printed on it, or there will be a code (like SO, SJO, TTW, etc.) that you can look up online to find its temperature rating. Finally, you could put a temperature sensor on the connector, and use that to determine how much current you can actually draw. Season's greetings! I'll EVing you! :-) -- Excellence does not require perfection. -- Henry James -- Lee A. Hart http://www.sunrise-ev.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
