As far as I'm aware and I've read in the Web, the spark occurs because the capacitors the ESC filters the input voltage with, have a very low (close to 0 Ohms) resistance. Thus, according to Ohm's law, the current through the input circuit is very high in the first fractions of the second after connecting the battery. This high current causes the spark and melting of the connectors (welding works on the same principle). When we limit the current with a resistor, there is a voltage drop accross it and no the full battery voltage is passed to the ESC. That's why I think Castle recommend placing an 1ohm 5W resistor in the input circuit. If the resistance is any higher, there may be problems with auto-lipo cell detection (please refer to this post). I, however, think that as we mostly use the manual lipo setting for 10S (in case of a 10 S pack), there shouldn't be a problem if using a resistor with higher than 1 ohm resistance.

Some useful links:
http://scriptasylum.com/rc_speed/nospark.html IIRC, there are two 50V capacitors, each 330 uF, in a CC ICE2 HV80, so they form a total of 660uF, 50V capacitor.
http://www.rcuniverse.com/forum/m_39..._2/key_/tm.htm
http://www.rc-network.de/forum/showt...litz-vermeiden
http://mgm-compro.com/index.php?cat=...al-information
http://rc.runryder.com/helicopter/t547501p1/


Nickolay