Shock Protection from DC Energy of Welding Machine

Dear Spades

RCD would not work in this case. Because the working current path and shock current path is same.

That is true for welders with isolated secondaries, but an RCD is effective for auto transformer welders where the shock often occurs between the secondary and the mains earth especially if working in wet/humid conditions where moisture on the gun and the general dampness of the operator's clothing can create a circuit to earth through the operator.

Looking for DC welders ...

Here's a wiring diagram of an auto transformer dual output welder for your interest.

You will note that one of the outputs is DC.

No link found in your post for wiring diagram !

Spades,

GA.

The shop I work at does heavy steel fabrication and welding.

Proper PPE and attire is the best way to prevent welding lead shocks. I've been shocked by a DC generator welder some 30 years ago and will remember that experience for the rest of my life.

PPE is a requirement not a luxury!

Similar to 50V on ac what is the safe voltage and duration in dc.

ELV, or extra low voltage, is below 50v AC or 120v DC. This is considered safe to handle but you can still receive a decent shock from it especially if transients exist.

Many welders use AC secondaries of higher than 50v, the secondary voltage is highest when no arc is being struck, and this is when you will most likely get the shock.

Most welders using MMA welders get their tingles when inadvertently completing the secondary circuit with their body when changing electrodes.

Auto transformer welders present problems of their own particularly if the primary is incorrectly connected to the mains.

Similar to 30mA ac what is the maximum safe dc leakage current.

There is no "safe value", however it does generally take more DC than AC to cause the same level of discomfort.

The degree of danger depends a lot on where the entry and exit points are. If they are such that the current passes through the heart, then the required amplitude to cause possible death will be less than it would otherwise be.

Since the epidermis has a high resistance compared to underlying tissue, if the skin is punctured in the process of receiving a shock, then the current may be higher for the same voltage level. It also depends on the individual as some have a higher tolerance, for instance women tend to have a higher body resistance than men. Humidity or body dampness can also have an effect

Frequency of the AC is also a factor with, coincidentally, the frequencies of mains power supplies being among the most dangerous

Having said all of that, it is generally accepted that an AC of from 0.5 to 1.5mA will be felt as a shock, 3 to 20mA for let-go threshold (the level above which your hands are unable to open) and 30mA at around 50Hz to cause fibrillation. By contrast, a DC of 4mA will be felt as a shock, 15 to 90mA for let-go threshold and 300 to 500mA for fibrillation to occur. A lower level of current sustained for a longer period can skew the above figures considerably

Is any company manufacturing RCD for dc,who.

There are a number of companies such as Siemens, Doepke and ABB producing B type RCDs.

Whilst types A and AC are the standard RCDs in general use, they will not fully protect DC circuits.

AC types are now banned for use in some countries as they fail to recognise DC leakage currents which can be present as a result of PWM controls etc. even in AC circuits .

A types will recognise and react to DC ripple leakage, but B type will respond correctly on a purely DC circuit. They are generally available with varying trip levels up to 500mA

Type B units actually provide better protection for both AC and DC usage than either A or AC types but they are more expensive.

Michael Jackson?

No, another jester in a faraday suit.