How to avoid getting zapped by electricity?

Question

I'm going to be doing some experimenting with a small portable ultrasonic welder I am purchasing from asia. I understand that it probably won't comply with local standards so I am going to get an electrical engineer to look over it, to see if its safe to use. However my main concern is the output to the transducer. I've been told that ultrasonic welders can run as high as 3000volts through the output. I am worried that because of this high voltage, it may be dangerous for me to handhold the transducer. I understand that this is a question that I should also put to the engineer and I will ask this. In the short term however, I was wondering if anyone would be able to tell me approximately at what power level/ voltage combination, electricity becomes dangerous?

Answer 1

It is a common misconception people have when they say "it's not voltage that's dangerous, but the current." This is wrong. The fact is that a certain amount of voltage is required to overcome the resistance of the body. Current is a DEPENDANT variable of voltage and resistance. Ohm's Law states that Voltage/Resistance = Current. So voltage and resistance will determine how much current will flow. This is why everything is rated in volts. You don't see utility poles with warnings that say "High Amperage." You could grab jumper cables hooked up to a 12 volt car battery and, as long as your hands are dry, nothing would happen. The voltage is simply too low to overcome the resistance of your body. However, a higher voltage can be dangerous because it will cause more current to flow.

The true danger is the amount of POWER (Watts, or Volt-Amperes) a device is capable of supplying. Some high votlage devices can supply very high voltage but only low current because they draw very little power to begin with - such as the transformer in those plasma globes (lightning balls) you can get at novelty shops. Those are current limited and may draw 10 Watts at most. On the other hand, a large high voltage transformer, such as a microwave oven transformer or neon sign transformer can cause a lethal shock because they are capable of supplying both high voltage and high current. The primary side of those transformers are capable of drawing up to 900 Watts (and sometimes more).

However, note that if the same transformer were stepped down to a voltage of 12 volts, there would be no shock hazard. This is why voltage really is the dermining factor.

So really, the true danger is the voltage and the amount of power available. If what the other commentor said about this being 500 Watts, then yes it can be extremely dangrous. 3,000 Volts at 500 Watts is most likely lethal.

Be careful. And yes, talk with an engineer.

Answer 2

Current is the thing to worry about :
1 mA Barely perceptible
16 mA Maximum current an average man can grasp and "let go"
20 mA Paralysis of respiratory muscles
100 mA Ventricular fibrillation threshold
2 Amps Cardiac standstill and internal organ damage

So 20mA is lethal, in some cases as little as 10mA can be fatal hence some electric guitar safety devices fitted with 10mA fuses.

Answer 3

The key thing is the current. About 35mA is considered to be a reasonable limit. The voltage is not so important but 3,000V is able to jump across gaps. If it is low impedance as a welder would have to be then it is highly dangerous.

However, I don't see any reason why the equipment would expose this voltage and I'm sure that it will be properly insulated. I've handled 25kV without any problems, I'm just glad the insulation worked.

Answer 4

And Ultrasonic welder uses sound waves to weld, about the only way you can get shocked off of it, is to open the electoral panel.
Never try to listen to the sound coming from the welding surface, it could make you go deaf.
The way and ultrasonic welder works, it uses sound to heat the peaces you are welding, and fusing them together.

Answer 5

at 24 V

Answer 6

Legally speaking, according to the electric codes, anything above 24 volts has the possibility of being lethal.

Answer 7

It is not the voltage that kills you, its the amps. Just make sure you are standing on a good and dry conductor when operating the welder, or some thick rubber boots and cloves.

Answer 8

if you're right about 3000 volts they run atleast 500 watts you're talking 166 ma Try to be safe it could kill you if you open it up and touch a open connection.

Answer 9

Don't bend over when the engineer comes:)