Earth Ground And The Grid

The electrical grid transmits power over wires to our houses, and our Bryan Cockfield has covered it very well in his Electrical Grid Demystified series, but what part does the earth ground play? It’s commonly known to be used for safety, but did you know that in some cases it’s also used for power transmission?

Typical House Grounding System

Grounding system normal case
Grounding system normal case

A pretty typical diagram for the grounding system for a house is shown here, along with a few of the current carrying conductors commonly called live and neutral. On the far left is the transformer outside the house and on the far right is an appliance that’s plugged in. In between them is a breaker panel and a wall socket of the style found in North America. The green dashed line shows the normal path for current to flow.

Notice the grounding electrodes for making an electrical connection with the earth ground. To use the US National Electrical Code (NEC) as an example, article 250.52 lists eight types of grounding electrodes. One very good type is an electrode encased in concrete since concrete continues to draw moisture from the ground and makes good physical contact due to its weight. Another is a grounding rod or pipe at least eight feet long and inserted deep enough into the ground. By deep enough, we mean to include factors such as the fact that the frost line doesn’t count as a good ground since it has a high resistance. You have to be careful of using metal water pipes that seemingly go into the ground, as sections of these are often replaced with non-metallic pipes during regular maintenance.

Notice also in the diagram that there are places where the various metal cases are connected to the grounding system. This is called bonding.

Now, how does all this system grounding help us? Let’s start with handling a fault.

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Fixing Faulty But Genuine Apple Power Adapters

apple The standard power adapter for Apple laptops is a work of art. The Magsafe connector has saved more than one laptop owned by the Hackaday crew, and the power brick with interchangeable plugs for different countries is a work of genius. Being a miracle of modern manufacturing doesn’t mean Apple gets it right all the time; the UK adapter doesn’t use the ground plug, leading to the power supplies singing at 50 Hz when plugged in. [Gareth] had had enough of the poor design of his charger and decided to fix it.

The Apple power adapter has two obvious connections, and another shiny metal disk meant for a connection to Earth. In most of the Apple charger ‘extension cords’, this earth connection is provided by the cord. In the smaller plug adapters – even ones where space is not an issue, like the UK plug – this connection is absent.

To fix this glaring oversight, [Gareth] shoved some aluminum foil where the earth terminal on the plug should go. A hole was drilled through the plug to connect this foil to the Earth socket terminal, and everything was covered up with kneadable epoxy.

No, aluminum foil probably won’t do its actual job of preventing horribleness in the event of an insulation failure or short. It will, however, silence the 50 cycle hum emanating from the power adapter, and that’s good enough for [Gareth].

Tube preamp with a dazzling wood case

It’s been a while since we’ve looked in on the world of vacuum tube audio equipment. [Bruce] just finished documenting a tube preamp he built. He actually made a couple of these with slightly different cases but they use the same circuit design. We found his discussion of common errors made when tying into ground quite interesting. It seems that many folks struggle with noise in their circuits because of ground loops. There’s some details about isolating the signal ground from a metal chassis, and also an admonition about not connecting the input or output jacks directly the chassis.
If you like this, don’t miss on of our favorite tube projects, [Bruce’s] Poddwatt.

USB Isolation

[Oleg] over at Circuits@Home has made a USB isolator for his hacking needs. This isolator separates the signal, ground, and power lines of a USB host device, such as a PC, from a USB device like a USB oscilloscope or logic analyzer. This might be useful for Keyboard sniffing, ECG, EEG or diagnosing the control system on the positive ground of your autonomous Ford 8N. What other applications can you come up with for this tool?