This can be caused by a number of things, none of them good. Current leaking or going to ground is a short circuit. If the supply 3 phase breaker isn't tripping, it sounds like current is "leaking" to ground. This is likely a connection problem in the device which the plug is powering, or if the device is employing a 3 phase motor, the motor may be going bad. This can be checked by "ohming out" the motor windings. If this problem is occurring in more than one three phase plug supplied from the same panel, it's possible that the earth ground from the panel is inadequate. This is tested with a megger with the entire panel shut down. Again if it's occurring with just one plug, the problem is likely in the device being powered.
bad ground
yes
No, but burning oil will give you bad spark plugs.
Fuel burning is the burning of fuel. In an automobile engine it is called combustion. The gasoline mixed with oxygen and ignited by the spark plugs explodes.
Every gas burning internal combustion engine has spark plugs. Diesel engines do not. Your Impala is not a diesel, so it has plugs.
oily deposit on the spark plugs electrodes
yes, there's a huge sticker on your engine that says "use twin ground plugs retard"
yes you can. for example in a 380V 3 wire system the 4th wire or neutral gives 220 volts against each of the 3 phases so you can have 3phase 380 volt plugs as well as 220 V single phase plugs. ah and by the way you can have as many 3 phase plugs as you like or as the power supply can support ampere wise.
You do not need to gap double ground spark plugs. Just put them in right out of the box, but note how they are gapped. As the plugs wear out, the gap increases, so when you notice the gap increasing, change the plugs.
Spark plugs are a critical part to most modern engines, and are a part that you can replace yourself. Older types of spark plugs (pictured) can be replaced with platinum-tipped or multi-ground plugs, which have 2 or more bottom ground electrodes (hooks) and, typically, do not need gapping of the hook spacing. Although multi-ground plugs cost 2x or 3x times more, they can last years longer, avoiding replacement of hard-to-reach plugs, or in harsh climates, wilderness or sandy areas.
If they are burning white they are OK it could be your core pack or your rotor button, if this don't take care of it than it could be out of time just a hair.
spark plugs fouled with oil. blue smoke from tail pipe.