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Fish Finder Installation

Grounding Posts/Lugs

What are those little screws in the back of some fish finders?

Many people ask us what the ground screw is for that some electronic equipment has on the back. Here is an explanation of what this is and how to use it.

First, you can generally safely ignore this connection. This is what electronic designers call a chassis ground. It is not directly connected to the ground for the electronics that are inside the device. That connection is generally connected to the negative power line. So, when you run power to the unit, you are “grounding” the electronics inside. The ground of the electronics inside are generally connected to the metal case of the unit via a capacitor, which will pass higher frequencies of noise on the electronics ground to the case, or from the case (hopefully) to power ground.

A Simple Ground Screw Example

Here’s a more simple example: Your Microwave oven. When you’re cooking up last nights Barbecue, you want the microwave power in the food, not on your nose when you peer through the window to watch it explode. (The food, not your microwave). The electronics that creates the microwaves that will cook your dinner gets the same power from the wall outlet as anything else, but in the case of a microwave, the ground pin on the 3 prong plug is connected to the actual metal outside case of the microwave.

In this example, the outside case of the microwave oven protects you from the microwave energy bouncing around inside. It even does this while you can see in through those tiny holes using something called a faraday cage design, which is a fancy way of saying the microwaves are too big to fit through those tiny holes.

In this example, the outside case of the microwave oven protects you from the microwave energy bouncing around inside. It even does this while you can see in through those tiny holes using something called a faraday cage design, which is a fancy way of saying the microwaves are too big to fit through those tiny holes.

Now we can also apply the same rule in the other direction. Say that instead of grounding the outside of the microwave, we ground the outside of a fish finder with this ground screw. What would this do?
Well, it would protect the insides of the fish finder’s electronics from radio waves that might be causing issues with the solar electronics in side the fish finder.
If you are having noise issues of one type or another, and they just started with the most recent electronics addition to your boat, and either something that used to work fine is now doing something strange, or if you can’t get your new fish finder or other electronics gizmo working the way you thought, grounding this ground screw on the newly installed device and/or the other device in your boat that is complaining might help solve the issue.

For More Information

We love to teach fishers and boat owners how to get more out of their investment. So, we have a number of learning resources available for you, our customers.

Our Learning Section on our website

For further information on Marine Electrical DIY Tips, try our YouTube Channel:

Golden Channels on YouTube

These cables come with a two year free, no questions asked replacement warranty.  See our warranty terms section on our website for details.

Finally, we love talking engines, fish finders, and networking.  So, if you need help, please email us and we can help:

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