It's not completely obvious what you are trying to do BUT it's almost certainly not safe. You may kill yourself or somebody else.
If you can explain in much more detail and simple words we may be able to help. (Small and simple because language differences mean more complicated words may be misunderstood.)
"Cheater Plugs" = mains power adapters that break the connectivity of the earth circuit, are sometimes used in audio systems to remove ground connections which are causing "hum loops". This is a very dangerous practice which can lead to electric shock.
In the text below "GFCI" = Ground Fault Current Interrupter = device to remove power automatically if even a very small amount of the current is bypassed improperly by eg your finger. If you get a shock then it turns off (almost) instantly. Using GFCIs is a very very good idea.
Lots and lots of references to GFCIs
The following was written with USA installations in mind but also applies in Spain.
(1) Use of Cheater plugs can kill
- ... The cheater plug is also recognized as a safety hazard in laboratory settings. For example, in August 2005, Tarun Mal, an associate professor at Cleveland State University, was electrocuted when he plugged a defective fluorescent lamp into a time switch using a cheater plug. Subsequently, the state of Ohio issued seven citations to the university for unsafe electrical conditions. The Scientist notes that four of the University's seven environmental safety experts agreed that use of the cheater plug "is not uncommon in US university labs". Jim Kaufman, CEO of the Laboratory Safety Institute, says, "When you inspect labs, it's not unusual to find anywhere from one to seven that way."
(2) Alternatives - only one is safe:
There are several alternatives for connecting newer appliances to two-prong receptacles without rewiring the building: removing the grounding pin of the plug, replacing the receptacle with a three-prong outlet, or replacing the receptacle with a GFCI; only the last (GFCI) is safe.
- Removing the grounding pin of the appliance’s plug is unsafe, and leaves the appliance without proper grounding even when relocated and plugged into a properly grounded three-prong receptacle.
2 Additionally, since most NEMA 5-15P plugs have both current-carrying prongs the same width and rely on the ground pin for correct orientation, removing it allows insertion of the plug with hot and neutral wires reversed, creating an additional hazard.
Replacing the receptacle with the three-prong type and leaving the ground screw unconnected is just as unsafe as using a cheater plug, but has the additional disadvantage that subsequent users of the outlet may not be aware that it is not properly grounded. However, if the ground screw of the receptacle is connected to the neutral side, electric shock is possible even if the appliance is properly functioning. This is called a "false" or "bootleg" ground and is a serious safety hazard often undetected by common receptacle testers.
Replacing the receptacle with a GFCI receptacle is the safest alternative. If a GFCI receptacle is properly functioning, then it will shut off the power to a faulty appliance to prevent electric shock. As a safe option that protects all appliances plugged into that receptacle, the National Electrical Code permits such replacement if the installer marks the GFCI as having "No Equipment Ground".