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I just bought my first oscilloscope. It's a Rigol DHO804. Quite happy with it, but I have 1 question. It is powered by a USB-C adapter and comes with a seperate PE lead. I can plug this in the back of the scope but then there is the other side of the lead. To what should I connect this to? Attached a photo of the scope and the lead. I have very little knowledge about electronics so the answer might be painfully obvious. Please enlighten me.

EDIT: Manual says "Connect the instrument chassis to the ground using the lead.". That's all.

enter image description here

Luuk256
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  • What does the manual say? – Justme Dec 21 '23 at 11:36
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    It says that I should connect it to ground. I quote: "Connect the instrument chassis to the ground using the lead.". But how? I am I this dumb or is this really vague? – Luuk256 Dec 21 '23 at 11:43

2 Answers2

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You connect the protective earth from the oscilloscope to the protective earth of the outlets in your home/laboratory.

The USB port powering the scope doesn't have protective earth. An oscilloscope floating without a protective earth is just waiting to kill you the first time you connect it to anything line powered.

You can probably get away without using the protective earth - as long as you only work with isolated circuits. That means using isolated power supplies or batteries.

It's a bad habit to get into, though, so you should always connect the protective earth. It'll save your hide when someday you forget to think about it and connect your scope to line voltage.

Since you are in the Netherlands, you'll want to clip the protective earth lead to the spring in an outlet.

enter image description here

Image source

All of the springs should be connected to the protective earth of your house.

You can use an alligator clip on the end of the protective earth wire to connect to the spring in the outlet.

I have seen (but cannot locate) Schuko plugs with a banana jack on the back as a ground adapter.

JRE
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  • Thank you JRE for your reply. I definitely want to connect it to PE, for safety reasons. So how do I connect it to my power sockets. I live in the netherlands so we have these kind of wall outlets. Do I need some kind of adapter? https://nlshop.se.com/wcd-compleet-verticaal-2v-kinderbeveiliging-actief-wit-systeem-m – Luuk256 Dec 21 '23 at 11:47
  • I guess one of these would work? https://cem.teleingenieria.es/en/p/earthing-schuko-plug-ebp-eu-for-electrostatic-discharge-esd – Luuk256 Dec 21 '23 at 12:25
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    @Luuk256: Do not use that adapter. It has a resistor that will prevent the protective earth from protecting you. – JRE Dec 21 '23 at 13:08
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    Adding to JRE's excellent response, there are scopes purposely designed to operate in an isolated manner where no earth (safety ground) connection is necessary. They also tend to support battery powered operation (but not necessarily). Scopes of this type also tend to have differently designed BNC connections that reduce the amount of exposed shield conductor on the probe connections, as well as no exposed metal on the probe wire ends. The oscilloscope you show is not one of those and should always be operated with an earth/safety ground connection. – Chris Knudsen Dec 21 '23 at 13:38
  • Thank you for addition Chris, and again thank you JRE for your answer. I'll look into one of these grounding adapters that do not add resistance between the device and earth. If I find any suitbale once I will post them here. – Luuk256 Dec 21 '23 at 14:07
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For safety reasons I would recommend using a ground plug adapter that has a banana plug socket.

enter image description here
Source: https://www.hisco.com/Product/09838-15062

As Lundin said, you have to make sure that it doesn't integrate a MΩ resistor.

Velvet
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    This isn't a correct product. The banana socket has 1Mohm resistor. Intended for ESD wrist straps. – Justme Dec 21 '23 at 11:57
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    While the Desco 09838 product description doesn't explicitly list having a 1Mohm resistor, it does contain Converts a standard outlet into a groundable point for wrist straps and other grounding hardware with banana plugs. Perhaps before using such a product for a safety ground, rather than with a wrist strap, need to confirm with a multi-meter that no resistor is present. – Chester Gillon Dec 21 '23 at 15:03
  • @Justme Don't ESD wrist straps typically have the resistor in the wristband, not in the grounding point? – Hearth Dec 21 '23 at 16:39
  • @Hearth All wrist strap grounding systems I have seen and used (and googled for this answer) have had the 1 Mohm resistor in the mains plug or the terminal block where the straps connect to. The plugs or blocks have the "button stud" interface and they read that they include 1Mohm safety resistors and the strap does not. However, other systems with different interfaces may still exist, with directly grounded terminal blocks or plugs, with the 1Mohm resistors inside the strap plug. But because they allow bypassing the resistor if someone replaces the plug, I wonder if they are safe for use. – Justme Dec 21 '23 at 16:50
  • @Hearth ESD Wrist Strap Testing – What Does High Fail Vs. Low Fail Mean? contains Most wrist strap testers also test for low resistance (typical low fail is less than 750K ohms) , to assure that the 1 megohm resistor is present and performing as intended. ... The 1 megohm resistor is designed to limit the current to 250 microamps at 250 Volts rms AC, which is below the perception level of humans.. I.e. looks like the 1Mohm safety resistor is expected in the strap. – Chester Gillon Dec 21 '23 at 16:58