Voltage on the protective earth conductor?
As I've said elsewhere, phantom voltage shouldn't bite. 

Yes, the Protective Earth wire will will pick up (via induction or capacitance, like a radio transmission) a very tiny amount of energy from the adjacent hot wire.  However, that should only register on a very sensitive meter, such as a DVM.  

A low impedance meter should instantly exhaust the voltage, leaving no readable figure.  

Alternately, you can put an ammeter across the connection and see how many amps want to flow.  If it's more than microamps, it isn't phantom voltage - and if it's more than 5 milliamps, it is a life safety threat, and at least in America, a GFCI (RCBO) would trip.  

Given that your low-impedance meter still sees the voltage, and it throws a visible spark, this is genuine residual current leakage, and it needs to be dealt with.  You're lucky to catch this one; often, ground faults go through fourth routes that you wouldn't see on the earth wire.  

Now you should begin removing appliances until the leak goes away. That will be the faulty appliance, and it's time to fix or replace it. 

It might happen due to faulty wiring, but that generally happens when someone uses interior wiring in an outdoor location.  This does not sound like an outdoor location.