What is the right way to float a home lab?

Question

I just got myself some new toys for my lab at home like 30V DC power supply, KKmoon signal generator and a Rigol DS1052E. I want to float everything, because I don't want to spend any money on stuff like differential probes or isolation transformers. I am doing 100% DC stuff and want to do some probing in my circuits. My questions are:

1. What is the right way to float my home lab?
2. Do I float my three devices separately? For example, somehow removing the ground from the socket coming from the device?
3. Can I plug everything into a mains power strip and remove the ground of the mains power strip before plugging it into the wall?

Please let me know. Thanks.

Answer 1

You can't float everything without an isolation transformer - the neutral will be connected to ground at the entry into the building. For safety any class I equipment does need to remain grounded, in my lab I have an isolation transformer only for the equipment under test, the scope and power supplies still have the case grounds, and are tolerant of the inputs/outputs floating up to 50V from ground (per their manuals). If I need to measure high side DC stuff, I can connect the high side to the scope ground (since the isolation transformer allows that offset) but a differential probe is still needed for measuring small signals with a large offset - it's far cheaper to buy one than smoke an oscilloscope

Answer 2

What is the right way to float my home lab?

If you want to make measurements that are isolated from ground, the only way to do this is with an isolation transformer if your scope is not isolated. There are very few reasons to do this, a high voltage setup would be one reason. Some AC measurements would be another. Differential probes are best.

Do I float my three devices separately? For example, somehow removing the ground from the socket coming from the device?

A reason to do this would for breaking a ground loop on the scope, so that is most likely the only piece of equipment that you'd need to do this on. If you are doing this for AC measurements, the scope could also be floated. It is unsafe to do this on power supplies, where will the fault current go? Not to ground.

There are better ways to eliminate ground loops, one being a differential probe (kind of pricey). Another would be minimizing the grounds between devices, and making sure they are not plugged in on different circuits or plugs. (I've had a few times where this was an issue)

Can I plug everything into a mains power strip and remove the ground of the mains power strip before plugging it into the wall?

No, also very unsafe. No path for a fault current.

Answer 3

There is no right way to float your home lab.

1) No. Right way is not to float equipment that must be grounded.

2) No. Don't float any of them. Equipment that have grounded plugs NEED to be grounded for a reason.

3) No. Because again, equipment with ground pins need to be grounded! Having all lab equipment and the device being examined being connected to single power strip at least makes them being powered from same mains phase and having a single point ground reference.

Answer 4

If everything you do is DC, all you need is a DMM.

Likely what you meant is that it is low voltage but DC to high frequency.

Earth ground is advantageous two good reasons;

1) safety

• the line filter noise currents to the metal frame will go thru you if not earth grounded but your body has stray capacitance to earth
• line transients

2) performance

• EMI reduction with lower CM noise which will be induced into your high impedance circuits.

You may want a consider a static-dissipative work surface, flooring, shoes, wrist strap, soldering iron.

Proper high-frequency DC supply measurements

When it comes to measuring supply ripple, you need an earth grounded low impedance AC coupled coax direct to the scope with an earth ground for a low impedance. A floating ground would inject a high common mode voltage that could get inject noise current into your DUT.

it is always best to measure AC coupled with an external Cap to scope using coax without a probe terminated with cable impedance using an internal option or using a BNC T with 50R inserted.

You don't need a differential probe if you can make one. Most measuremenats can be made with A-B with two matched 10:1 probes. WHen probe ground inductance causes resonance > 20MHz, simply remove clips and use tip and ring.

Answer 5

You certainly do not want to float your equipment if you still have earthed stuff around you, or literally under your feet. That is especially true for (grounded) anti static mats and wristbands. That way lies an early grave.

Answer 6

if you want to float your instruments use battery powered instruments, trying to float mains powered instuments doesn't work well, and is potentially dangerous.

Else power your experiments from batteries or other isolated supplies and then you won't need to float your instruments.

Answer 7

It really doesn't sound like there is any reason for you to float your equipment. Why do you want to float it? You should specify the reason it is a requirement.

I think what you're actually worried about is ground loops? That would only be an issue with the scope. Do know if your scope is not already an isolated variety? Because if it is you don't need to do anything!

Answer 8

First, install GFCI protection

If you don't follow any other advice here, definitely do install 6-8ma GFCI protection. Either a GFCI receptacle or a GFCI device elsewhere that uses its LOAD terminals to protect these outlets.

This is not absolute protection. Not least, if you get between mains hot and mains neutral, the GFCI will perceive you as just another load.

Do ground, just independently

Since you have a really good reason, you can ground yourself independently by driving separate ground rods for the lab. This will amplify the effectiveness of the GFCI devices quite a bit, because dirt can't conduct enough to trip a breaker, but can conduct the 8ma to trip a GFCI.

This too is not complete, but at least these will keep people from laughing at your funeral.