Are there any adverse effects from isolating the AC power supply on my electronics bench?

Question

jw0752 happened to show me an Ebay listing the other day and it was like feeding candy to a baby. My dad, he can be such an enabler! Hehe! So, the long and short of it is that I have acquired this BEAST (a Powervar 12 Power conditioner) and I am planning to modify it so that I can isolate and supply power to my entire bench. The Powervac 12 is capable of supplying 12Amps at 120VAC, so the only thing I was thinking that I needed to be concerned with was possibly exceeding the supply capabilities of the transformer -- however I find the possibility of drawing that much power quite remote. So...

Here are my primary questions:

Is there any reason or side effect that would contradict hooking the entire bench on the isolated secondary side of a transformer?
Are there other things that I should be concerned with safety wise or otherwise plan for?
Modification suggestions?
In general, is this a good or bad idea?

I haven't found too many articles that talk about this, but here are links to a few that I have looked at:

isolation transformer - Electronics Forums

RadiolaGuy.com : Sonny's Tech Tips

http://www.signaltransformer.com/sites/all/pdf/IsolationTransformers%20Increase%20Safety%20of%20Electronic%20Systems.pdf

isolation - Why are we not always isolating the mains supply? - Electrical Engineering Stack Exchange

I have read the following and I take it that I should not connect any of my test equipment to the isolation, only projects that I am working on. What about power supplies? What is the take on this?:

"DO NOT plug your test equipment into the isolation transformer, just the radio. I've seen folks wire their isolation transformer to a plug strip with all their equipment plugged into it and wonder why their "scope's" ground lead went up in smoke when they connected it to the radio chassis. If all your equipment is plugged into the isolation transformer, then nothing is "isolated"! Only the radio (or television) under test should be plugged into the isolation transformer!"

mcb1 · Answer

4ringfan I'm guessing you don't want to listen to your father's advise ... I'm sure he has been able to offer some good advise. Isolating transformers are really only designed to work with double insulated appliances. On a class 1 appliance any fault current is passed through the earth and trips the breaker. If you isolate your bench, then you remove that potential difference and hence the protection. Since this PowerVar maintains the Class 1 by connecting the earth to the sockets, how is the transformer wired? .. does it actually float the secondary or is it just providing a 120v/120v transformer and the neutral is joined both sides.? Also inside the device has a black box which contains ?? The other issue I see if you isolate your bench is the phase voltage (and neutral) can float to anything, rather than it never exceeding the 120/240v. Switchmode type supplies have high harmonics, and its quite likely that the impedance of this device will not remove/smooth that component, which could then pass to other loads. It may also cause the secondary voltage to rise either as an AC or something closer to DC. Bench Isolation If you are trying to ensure you don't get a shock, then I recommend looking at RCD's. (You call them GFCI) A Residual Current Device detects an inbalance between the phase and neutral currents and trips which interrupts the power. Residual-current device - Wikipedia, the free encyclopedia They are available as portable, socket outlet, or switchboard mounted, and the medical/children version will trip at 10mA instead of the normal 30mA. They are mandatory on all NZ homes now. (except for some special circuits). Mark

peterjcs23 · Answer

If this isolated bench were in a corporate lab you would have to do a risk analysis and you would be restricted to who had access to the bench. It is dangerous to run live equipment with no earth and it would be treated as using live equipment. You would be restricted to using safety connections and told to attach connection with the power off unless there was some other protection in place. Earth is your protection and electrocution is painful or/and deadly. Equipment with emc filters will charge up the chassis if it is not earthed and will be ineffective. When you say "run a couple of Variac power supplies without the danger of having direct connection to the mains", what is less dangerous, you should ask yourself? It sounds more dangerous to me as you may be lulling yourself into a false sense of security. Now when you say "I also from time to time like to be able to connect my scope probe ground at a higher potential point in a circuit" you hit on a real issue. The solution is best to use a isolated/differential input scope. These are available from Tektronix eg. Digital Signal / Digital Phosphor Oscilloscopes (DSO/DPO) | Farnell element14 ...these are the scopes you would find in a corporate lab...you can buy second-hand. ...or at lower bandwidth but more affordable from pico scope eg. PICOSCOPE 3425 - PICO TECHNOLOGY - PC OSCILLOSCOPE, DIFFERENTIAL | Farnell element14 ...this is the scope I use at home as I need isolated channels. Floating an ordinary scope off earth is not safe, the isolated scopes come with safety leads. Also you say "In addition to the isolated bench outlets I also have standard outlets that can be used if there is a need." If you mix earthed and non-earthed equipment, you may get paths to earth back through test equipment earth, and potential for smoke! I've seen that happen. What you are suggesting is a step back in time to the 1980s or early 90s when the only way was to use these risky non-earthed methods of working. And re-read what mcb1 has said...@mcb1

Are there any adverse effects from isolating the AC power supply on my electronics bench?

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