One of the plugs in my room did not have any wires attached to the earth pin. Whenever I connect any device that has a metal casing, I get a tingling feeling if I brush my hand against the casing. I shorted the earth and neutral pin in the socket, and that tingling feeling was gone.
My questions here are:
In practice, it's not OK.
It's dangerous for many reasons.
Depending on where you live, it might be against your local electrical code to do so.
And it mighy be against electrical code to do it yourself, especially if you need to ask if it is OK or not.
For example it might have been allowed 20 years ago but not any more due to safety reasons.
Get a licensed electrician to handle the dangerous socket in a safe way.
No it is not okay. Others have mentioned the danger of metalwork becoming live, but there is an additional issue, which an electrician would call a Neutral-Earth fault. Naively, one might think there is no issue as they are at the same voltage. The problem is current. You now have return current from the appliance flowing through the connecting point between Neutral and Earth. To make matters worse, it is not just the current from the appliance itself but it will also act carry some of the current from the rest of the installation (depending on the resistance/impedance of the particular wiring installation) as it's another route back to the transformer. If some other low impedance metalwork- e.g. the case of another appliance- touches the first one you can get significant current flowing and even an arc.
You need to check your installation in general to find out what is earthed, and either connect the Earth at the socket to a proper installation Earth, or (as a kludge) only use insulated appliances with no required Earth connection.
In an old farmhouse that I grew up in, it was possible to measure about 70 volts AC of stray voltage on the metal conduit of the building, relative to a properly installed buried copper ground rod. The building was originally designed to have only two-prong wall outlets without a ground/earth connection for devices.
Conduit, but not intended for earthing/grounding
The building that you are in, most likely has old wiring dating back to the 1940s when it was common to install 2-wire circuits without a ground/earth connection, but the cable was typically installed in rigid conduit or flexible spiral armor-flex.
In this situation the conduit was primarily intended to protect the building wiring from damage, since it was sheathed in a relatively fragile rubber and cloth insulation.
Since the conduit was not really intended to carry power, no particular measures were taken to assure it was thoroughly conductive across its entire length end-to-end, and grounded/earthed properly at the fuse panel or circuit breaker panel.
It may have been painted over, or the lock nuts in electrical boxes are loose, or the conduit was not anchored into the electrical boxes at all. Later reconstruction work, replacing a metal box with a plastic one, would also split the conduit into separate sections that are electrically insulated from each other.
Knob and tube wiring
These old buildings may also still contain a mixed amount of even older wiring known as porcelain knob-and-tube, which ran individual wires on ceramic standoffs nailed into the wood frame of a building.
The ceramic knob has a ring indentation or notch on it, holding wire off the wood frame. Where wire has to pass through a wall or floor, it is inserted into a ceramic tube through the wall or floor.
If the ceramic insulators are still in good condition, knob and tube is still acceptable in the United States, though no new installations are being done with it, and it was not intended to provide grounding/earthing.
Stray voltage induction into poorly earthed/grounded conduit
If you have an exposed knob and tube circuit running parallel to unearthed or poorly earthed conduit, the nearby power conductor can inductively induce electrical current into the conduit, known as stray voltage.
Conduit induction can also occur where there are one-wire circuits nearby where power only flows in one direction next to the conduit through one part of the building to a load, and then returns back to the fuse panel along another path, possibly next to some other conduit.
Conduit induction does not normally occur with modern wiring as the wiring is typically installed in pairs (or for 3-phase, in triplets) through the same conduit, and the opposing current flow in the pair/triplet wires will cancel out any stray voltage induction into the conduit.
Single-wire circuits like this sometimes occurred with knob and tube because it was economical and saved money on always running the circuit wires grouped together in pairs.
Our farmhouse yard light started in the house, through a 2-way switch and up to the roof, to suspended wires out to the dairy barn milkhouse, through another 2-way switch in the milkhouse, and then back to the light pole in the yard, where it was connected to neutral at the pole.
In electrical codes in NA if the wiring does not have ground, the circuit should be protected by GFI breaker or GFCI receptacle should be installed. I believe in Europe that kind of protection called RCD. And connecting neutral and ground at receptacle is bad idea, it may discard some kind of protection.
In a home 3 prong socket the Ground (G) and Neutral (N) are the same wire back in the Main Electrical Breaker Box. A home power wire has 3 wires, Black (L) , White (N) and copper (G). Both N and G are connected together in the Breaker box.
The 3 prongs plug on your apparatus should be connected such that all metal parts would be connected to G. N and L should be connected to the power supply. Many appliances will have a high value resistor between the N and G such that the internal circuit will dissipate any static electricity to ground.
The main reason of using 2 wires for the Neutral:Gound is for security. Just imagine that all appliances would only run on 2 wires N and L. If one of the 2 wires break, 50% of chances are that it could be the Neutral that is broken. Then you ar left with only one wire connected to the appliance, the Live (L) wire. It become a One Appliance connected to the 120VAC of the house. You hold that appliance in one hand (assuming a defective unit with internal connection to some metal ) and with your other hand you happen to touch a grounded part of your house such as a water copper pipe. You would get electrocuted. However if there is a third wire such as the Ground (G) all metal parts of the appliance would have this extra security to discharge any dysfunctional circuitry into the ground, preventing electrocution because your holding hand would be touching metal parts that are already grounded. This is the very reason for the existence of the Gound wire. It is to leak any undesirable current to Earth. In fact the Ground in your electrical box is grounded to a metal pin planted into the Earth ( somewhere).
When you connect such appliance into a non-grounded receptacle the accumulation of static charges could accumulate in the electronic circuit and could slowly become very high to the point of reaching values capable of arcing into a body such as an external piece of metal or your own body. This may be the reason you experience this tingling. It is the accumulated static charges that are discharged onto your own body. A bit like when you rub your feet on a carpet and then reach a door knob, a spark discharge on the door knob.
A well built appliance should have this internal resistance to discharge static charges to the Neutral wire, preventing non compliant connections. Not all appliances have this circuit.
It is not a bad idea to connect your Neutral pin with the the receptacle ground pin but it is not a legal installation. Prevention is always better than fixing the consequences. Your situation imply that your 120VAC receptacle is connected only with a dual wire instead of a triple wire, which is not according to the electrical code. This could have serious legal consequences in case of problems.
My suggestion would be the change that wire, but this could imply a serious endeavor. Rewiring a whole house is a big job.
