110v or 240v?
I know on most building sites and quarries etc, 110v machinery is used, but.. 110v machinery is just as dangerous as 240v, if you were to use 240v with RCD it would be a million times safer, but, does anyone know, if it is legal?
Answers:
The 110v goes back to the year dot.The transformers used on site have a centre tapped earth and if you ground the impliment you are using the result is a 55v shock which before the advent of RCDs was considered safe.With the comming of RCDs you can limit the tripping current to 30 milli- amps and the speed which the supply is cut off which is a lot safer than the old system.The electricity at work act which regulates what you can and can't do on site and hasn't been updated for a long time but I'm sure in the future 240v with RCD protection will eventually be allowed on sites.
Doesnt it really come down to what the building is wired for?
It is legal to use 240 volt equipment with circuit breaker RCD , but nearly all companies cover their back (and their insurance companies ) by only allowing 120 volt equipment on their sites .
The problem is most industrial equipment IS 110v and it's the current that is the killer, not the voltage.
The UK is one of a very few countries that use 240v.
It is definitely not legal and to have a mass of 240v cables strewn all over the place through puddles etc doesn't sound safe to me RCD or not.
Ever seen a 240V circular saw or reciprocating saw? I never have.
You can legislate any voltage you want, but if they don't make tools like that, you won't get the job done.
Like the other guy said, it's not the voltage that kills you, it's the amps.
RCDs do fail and a 240v electric shock could well be fatal in some wet site conditions.
110v supplies on site are centre tapped earth so you would get a maximum shock of 55v unless you succeeded in connecting to both live and neutral.
If you get caught trying to use 240v on site you may find yourself home rather early. I used to know a chap who reconfigured a transformer to 110v - 240v and to my amazement it was rarely noticed that he was using 240v tools. How the blue plugs went unnoticed says a lot about the competence of site agents.
The reason sites use 110v is that the voltage is dropped via a transformer, therefore isolating you from direct contact with the main system. If a short occurs them the main is not taken out.
If it's the am page that kills then 110v is more dangerous than 240v. Half the voltage, double the current!
Sorry guys, that line about it' s the current not the voltage is just something people say. I am electronics engineer. Ohms law goes I=V/R in this case. Assuming the voltage is 110 the resistance of the human body is about 5000 ohms with wet skin, and can be lower than 5000, the current in this case is 22 milli-Amps .022 amps It takes about 10-20 micro-amps or .0000010 amps across the human heart to kill. Many more are killed by 110 because it is easier to contact. When you are running 110VAC you have a line and a safety ground and common or return ground. When you run 220 you have a 110 line and a second 110 line on the other side of ground. The lines are 110 +110 = 220 plus a safety ground. The biggest reason 220 is used in the U.S. is to push more wattage with smaller wire. If you contact both 110 wires across your body you have doubled the current flow 220/5000 or 44 milli-Amps. However most people get between one line and ground and thus the voltage is only 110 since the scheme is 110-GND-110. The safety RCD scheme goes 55-safety GND-55 and 55+55=110. It is the same scheme as 220 off the pole.
When the voltage rises or the resistance drops the current goes up. Most people getting over 1000 volts across or lengthwise through the body die. But even 20 or 30 volts can kill under the right conditions.
Clive is also correct about the isolating transformer but, the safest scheme with a isolating transformer is to use a non center tapped transformer with neither side connected to earth. That way you contact either line alone with your feet in 3 feet of water without being shocked. This is why OSHA requires isolating transformers. However most still use the center ground in case the line should contact high voltage. This condition would cause the breaker of the HV line to trip.
Gary
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