does absence of a mains Earth lead affect the performance of scopes, AND HOW?

[retrolefty]

Worst case scenario, Whats to stop you walking outside ramming a big earth spike into the ground and wiring it to the socket your scope is plugged in to? Would this work?

 Because the earth ground resistance between the newly spiked ground rod might well have high (as in unsafe) resistance from ground rod resistance/reference at the source of building power service entry. Ground rods and interconnected grounding systems can be very expensive and detailed. I measured open circuit between two ground rods, 10 feet a part, as they were pounded into a rocky substrate.

A couple of ground rods in good ground should provide a low enough resistance path though.

 No it won't. Watch that video a few posts below. Ground resistance from a single point ground rod is non-linear with distance through 'earth'.

 The main point in their 'myth busting' is that round rods must never to be used INSTEAD of a real 'return ground' conductor (copper or alum.) to the voltage source (transformer on pole) or else service panel breakers will never trip on faults but still allow enough current to kill.

 

[Ian.M]

Wrong.  A TT earthing system is exactly that: Separate earth rods at the supply source and at the consumer with no earth conductor provided by the utility company.  For safety, the earth loop resistance must always be low enough for the breaker to trip reliably and the maximum voltage rise at the consumer earth rod musn't be excessive if there  is a fault current less than the tripping current.

It is difficult and usually uneconomic to get the earth loop resistance low enough to reliably trip ordinary over-current breakers, so a TT system almost invariably requires RCD protection.   

See http://electrical.theiet.org/wiring-matters/16/earthing-questions.cfm?type=pdf

[RGB255_0_0]

There are other videos by Mike that go much more into depth.



Basically, the distribution system is earthed to protect their (and your) equipment from transients that naturally occur where these transients want to get to the Earth.

So we have two different meanings for "earth": protective earth (to trip RCD/GFCI for your safety) and systems earth (to protect your/their equipment as much as possible).

Lightning hitting a telephone system outside your home will induce that high voltage into your phone line and it'll look for the lowest impedance and straightest path to the soil. That's what the ground rod is for - to get lightning to the earth with a little damage to you and your equipment.

The entire earthing system is bonded to Neutral so that the current will travel through it and get back onto the Neutral and head back to the utility's transformer/generator.

You only need as many ground rods to conform to local law; and these rod(s) should only connect to ONE point as demonstrated in other videos. Typically, this will be 25 Ohms contact resistance to the soil.



Adding ground rods though can make your electrical supply DANGEROUS if your utility's system IS NOT grounded because if there was a fault in your system where the electricity went to Earth and then the utility suffered the same fault, then the Earth would not be floating, it'd be in circuit. So check with your utility before even thinking about adding ground rods to the property.