Electric Guitar Earthing Grounding

Electric Guitar Earthing Grounding:

The subject of electric guitar earthing or grounding, or at least the issues caused when it goes wrong, is a common topic on guitar forums and the Ironstone  inbox. Often shrouded in mystery, its not a difficult concept to grasp, once seen as a whole picture, and that is what this article aims to do. 

To begin with, some definitions. 
The terms grounding and earthing tend to get used interchangeably, but to keep some consistency, this article will stay with the term grounding / ground (or GND). Similarly, two wire signal paths such as those coming from (single coil) guitar pickups, or in a guitar connection lead, will be referred to as comprising a ground (GND) wire and a ‘Hot’ wire. The signal GND wire is electrically known as the negative side (-ve) and the Hot wire known as the positive (+ve). I have used these terms on the diagram that follows in conjunction with some colour coding. This ‘Hot’ is sometimes also called the ‘live’ side of the signal pair, but this article uses ‘Hot’ to differentiate it from the Live part of the mains supply to the amplifier.

So where does the Ground come from?

To understand the whole, its important to start at the beginning, meaning the amplifier rather than the guitar. Mains powered amplifiers have, as part of the electrical plug connection, a ground (in a UK plug its normally called the Earth) connection. That ensures that the amplifier and all of its metal work is solidly connected to the main supply 'ground' – literally via a connection to a metal stake driven into the ground somewhere.
So the amplifiers metal casing always remains safe, as it can never become ‘live’ due to any kind of fault that would result in an electric shock if touched. Depending on the amplifier design (and if its valve or transistor), the GND connection may also be one of the 2 wires that form the feed to the loudspeaker. More importantly for this description, the mains derived amplifier GND connection is then continued along a guitar cable when it is plugged into the amplifier ‘Input’ jack socket(s). Its the larger metal part of a normal ¼” jack plug. The smaller jack ‘tip’ is the ‘Hot’ half of the guitar cable. 
Ground connections inside the guitar.
So far so good, the GND connection from the mains has a route along the guitar cable. So once that is plugged into the guitar, there is now a solid GND route from the guitars jack socket all the way back to the mains (see diagram below based on a 3 pickup Stratocaster layout).
The normal path inside a guitar is then a twin wire connection from the guitar jack socket to the volume potentiometer (pot). The Hot wire goes to the middle (output) pot terminal, the GND to one of the end terminals of the pot and that itself is then normally connected to the metal body of the volume pot.
The output of the 5 (or 3) way switch connects to the other end of the volume pot. So now the volume pots middle terminal (the wiper) can be moved between the full output of the multi way switch and GND, i.e. It acts as a divider (and thus controls the volume).

Electric Guitar Earthing - Grounding PPT JPEG

The important thing now is to ‘share’ that GND connection with all the other guitar elements that need it.
In no particular order that includes;
1) The tremolo claw or similar connection to the guitar bridge. From an electrical safety and noise minimisation perspective, this is probably the most important connection. Simply put, it connects all of the main metal work a player touches (bridge, therefore strings, therefore tuners) to GND all the way back to that amplifier mains plug. So not only is the player safe, but any static electricity etc from him / her just gets dissipated down to ground, not sensed by the pickups, which could end up as ‘crackle and hiss’.
2) The pickups themselves. Any style of pickup has one or more Hot connections, but always a GND side connection. Sometimes is a separate wire from each pickup. In the case of the Ironstones, it's the outer braid or shield wire. Either way, the 3 wires (coming one from each pickup) would normally be soldered back to that volume pot body, the main GND point in the guitar. As mentioned before, pickups use a minimum 2 wire system with one wire being hot (or +ve) and the other GND (or –ve). The same is also normally also true of active pickups.
3) The 5 / 3 way switch and tone pots. As described above, the volume pot body has been the first and most important GND point in the guitar and should act as the distribution (or 'Star') point for all other GND connections. For the best low (electrical) noise performance, the other components (tone pots, multi way switch etc) should also have their metal bodies electrically connected to GND. Many guitar manufacturers choose to do this by a series of small wires looping out from the volume pot body to those other components. On Telecasters with a steel control plate or a Stratocaster with a shielding foil ‘triangle’ the use of these extra GND wires is not strictly needed (or even desirable – see 4 below). This is because the mechanical attachment of the multi way switch, pots etc to the control plate or part shielded scratchplate, makes a perfectly good electrical ‘joint’ to GND.
4) Guitar body shielding. As the Ironstone guitar shielding article (Electric Guitar Shielding) discusses, its desirable to use foil or similar to shield the guitars control and pickup (and jack socket well) areas. But to work correctly, the foil must be a continuous electrical ‘cage’ and it must also be connected to the main guitar GND, i.e. back to the good old volume pot body.  This can, for example, be achieved by using a flying lead from the volume pot body (like the trem claw wire), that is then mechanically connected with a screw etc to the body cavity foil.
And having adhered to all of these rules, 'earthing problems' should be a thing of the past!