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Dealing with DC voltages >100V
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T_guttata:
Hi everyone

I have some questions related to DC voltages >100V.

I'm a mechanical engineer and I also have some background related to electronics, but I just recently started doing eletronics in my spare time. So far I have a 30V 10A power supply and was working with low voltages. But obviously at some point you will need higher voltages for a certain project or encounter high voltage capacitors when trying to repair some circuitry.

Now, I'm familiar with the limits which are considered non-lethal. I know how RCD work and in my home all sockets are protected. However, I don't have experience working in a lab. And obviously I don't want to test the limits of the human body at all. I think that working in the lab is more prone to errors than lets say doing AC (230V) stuff, for example installing a lamp. There are (more) faulty situations which are not protected by the RCD and there are many parts around which are conductive. Maybe someone can give me some input regarding the following questions:

1) What are (the most important) things you must do and must not do related to safety in the lab?
2) What is the maximum voltage when using breadboards? It's clear that high currents over a longer time will dissipate heat which might melt the breadboard.
3) What equipment would you use to charge capacitors to higher voltages? I only found a few (affordable) DC power supplies >60VDC. I'm not really attired to use high voltage converter circuitry from aliexpress (example: https://de.aliexpress.com/item/1005001361171048.html?spm=a2g0o.search0302.0.0.3ebf573cfBp9uU&algo_pvid=38aeedf3-f500-4a4c-8450-1602e2c56aa3&algo_expid=38aeedf3-f500-4a4c-8450-1602e2c56aa3-5&btsid=0b0a556716227504365024617ee323&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_)  because of messing around to set the voltage etc. Is there anything in between a $3 PCB and a DC power supply for several 100 bugs?
4) Insulating gloves; is it recommended? ESD gloves; any safety benefits?
5) Any recommendations regarding literature related to practical safety (prototyping, reparing stuff)?

Thanks for your advice!
bob91343:
You ask good questions.  However, as Louis Armstrong famously said, 'if you have to ask, you'll never know'.

These things become obvious to those who work in the field, in short order.  You will get some tingles and jolts.  You should be especially careful around 240 V mains, although not so much 120 V.  One hand in the pocket is good advice but severely limits your ability to work.  Gloves are a pain and reduce sensitivity too much.

Charging capacitors requires some current limiting resistance, although in most cases the charge period is so short that nothing has time to get hot enough to melt, other than fuses.

You learn early on that when pushing a plug into a socket, you back away from the bench a bit and hold the other hand high if you can.  It's generally accepted that you can't feel anything less than around 10 Volts unless you wet your fingers.  Up to maybe 70 Volts won't distress you too much.  This is for low frequency or dc.  For high frequency, the rules change.  A little rf can cause a burn on the skin.  A lot of rf can do serious damage.

I have been subjected to all of it, even thousands of volts, and I am still here with no permanent damage, at almost age 89.  I still get jolts and they usually give me valuable information.
james_s:
It all depends. Generally speaking, anything under about 48V is considered "low voltage" and is relatively safe. Breadboards are for low voltage and I would never recommend going above 48V in most cases. I did once breadboard most of a ~1kW SMPS with a 340VDC bus on a breadboard but that is definitely a case of "don't try this at home, I'm a professional" and I would never recommend it to anyone.

You can go a very long way in electronics without ever needing to mess with more than about 15V. When it comes to higher voltages standard electrical safety rules apply. Bottom line is if you are not completely sure what you are doing, don't do it. Don't forget that low voltage can be dangerous too if the current is high enough. A car battery is only 12V but it can produce enormous current. My dad had a permanent scar on his finger that happened when he had a wrench on the positive terminal of a car alternator and it short circuited to something else through a ring he was wearing which instantly got red hot. This is why every auto repair manual starts most procedures with "disconnect the negative battery cable"! It is also advisable remove any metal jewelry before working with electricity, even small batteries of certain types can produce a surprising amount of current, enough to cause a serious burn.
David Hess:
For high DC voltages, it is important to use as little capacitance as possible to limit the energy of any discharge through you.  I learned this the hard and painful way.

High voltage circuits also often have large value high voltage current limiting resistors.
Zero999:
The general rule is that DC, carries a lower risk of shock and death, than mains frequency AC. The only additional hazard is, in many cases DC is from a battery, which can't always be isolated.

To be pedantic, high voltage is above 1kV. Mains, is low voltage. The reason for the official definition for high voltage being so high is, below that voltage, you need to actually touch a live conductor to get a shock. High voltages can arc, so you can be shocked, just by going too close.

Extra low voltage is anything below 120VDC, or 50VAC. The reason for this is voltages below those levels are unlikely to deliver a lethal shock, in dry conditions. Of course they can still shock and still carry a small risk of death, but it's unlikely. Appliances using separated (meaning it's separated, i.e. isolated from the mains and earth) extra low voltage, doesn't require an earth connection.

Voltages below 60VDC and 25VAC, don't require all parts to be insulated from the user and are safe to touch, in dry conditions. They carry a very low risk of shock and you probably won't even feel it, unless you have damp skin, or the contact area is large.

In other areas, where there's an increased risk of shock, such as next to a pool, even lower voltages need to be used and in some cases, it's not permissible to have any uninsulated conductors.

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