trans atlantic electrical differences

[Alan m]

hi all

i was wonder ing if anyone could expain this

over here in ireland and the uk we use 240volt in our domestic and 110 volt on site .
in the us ye use 110volt domestic and 240 on site.
over here it is 110 for site for safety reasons as the current is less

why is there a difference or does one side not care about their site workers

 

[mastercabman]

in the us ye use 110volt domestic and 240 on site.

On site is 110 v  here in the US.
Some temp. poles have a 240 outlet,but nobody uses it,execpt maybe hardwood floor guys that need the 240 for their sanding machine.

 

[jonny round boy]

over here it is 110 for site for safety reasons as the current is less

Alan,

With 110V the current is MORE. Roughly twice as much.

The reason for 110V on site is that the 110V is centre tapped, which means the voltage alternates from +55V to -55V. Theoretically, that means that in the event of an accident, you're only likely to get a shock of 55V max.

HOWEVER:

Since the widespread use/availability of RCDs, it would be far safer to use 230V with an RCD than 110V without. An RCD will trip before the current reaches 30mA, which is well below the level that will do you any harm. On the other hand, under the right (or wrong, depending on your viewpoint) conditions, you could have several amps running through you from a 110V supply.

As my physics teacher used to say, "the voltage just makes you jump about; it's the current that kills you".

The reason we still use 110V on sites is that a lot of the people who run sites are idiots, who insist on 110V 'because that's how it's always been'. Most site managers will tell you that you're not allowed to use 230V on site, which is completely wrong. They're just trying to enforce regulations that don't exist, because that's what they were taught when they were trained.

That's just one of the reasons I have never, and will never, do site work.

 

[d8b]

the 240V in the US is the equivalent of our 400V 3 phase (I think). In Belgium you almost always find 400V on site. This is for instance used for thos large plaster silos.

I really don't see why you guys have to use 110V for site work. I was always tought that it is the current that will kill you, not the voltage (over simplified but that was the basic point). A 110V machine draws double the current of a 220V machine...

I'm propably totally wrong. My BA4 course (electrical safety for contractors) was a joke and high school is some decades ago.

EDIT: JRB beat me to it and explaines things lovely

 

[d8b]

over here it is 110 for site for safety reasons as the current is less

Since the widespread use/availability of RCDs, it would be far safer to use 230V with an RCD than 110V without. An RCD will trip before the current reaches 30mA, which is well below the level that will do you any harm. On the other hand, under the right (or wrong, depending on your viewpoint) conditions, you could have several amps running through you from a 110V supply.

Are you saying that you don't use a RCD on site? On site as in raining, totally wet excellent conducting conditions. On site as in a place littered with various sharp objects who could slice a cable open and expose a wire...

 

[jonny round boy]

over here it is 110 for site for safety reasons as the current is less

Since the widespread use/availability of RCDs, it would be far safer to use 230V with an RCD than 110V without. An RCD will trip before the current reaches 30mA, which is well below the level that will do you any harm. On the other hand, under the right (or wrong, depending on your viewpoint) conditions, you could have several amps running through you from a 110V supply.

Are you saying that you don't use a RCD on site? On site as in raining, totally wet excellent conducting conditions. On site as in a place littered with various sharp objects who could slice a cable open and expose a wire...

The 110V used on sites in the UK isn't RCD protected, as far as I'm aware. Which is rediculous. But like I said, I've never worked on sites so wouldn't like to say for certain...

 

[Alan m]

ohms law says other wise
the current should be lower

as for the amperage issue
it has got to do with the formula for the current (amps)
this state that the current = voltage / resistance
the resistance is a constant ata known steady  temp
there for if the voltage is changed there is a direct relationship with the current

example
current = 110volts/resistence (just made up no)  2
currnet =55 amps

example 2
current =220/resistance(same as last time ) 2
current =110amps

there for example 2 would be twice as likely to kill you being twice the amps

 

[d8b]

ohms law says other wise
the current should be lower

as for the amperage issue
it has got to do with the formula for the current (amps)
this state that the current = voltage / resistance
the resistance is a constant ata known steady  temp
there for if the voltage is changed there is a direct relationship with the current

example
current = 110volts/resistence (just made up no)  2
currnet =55 amps

example 2
current =220/resistance(same as last time ) 2
current =110amps

there for example 2 would be twice as likely to kill you being twice the amps

your maths are correct, but you make a wrong assumption. The resistance is not a constant.

The 110V machine and the 220V machine have a different motor (and thus a different resistance) If this wouldn't be the case, the 220V machine would spin twice a s fast as his 110V brother (assuming a totally resistive load)

what is important here is that P=U*I

So a 2200W machine draws 10A at 220V and 20A at 110V

That's the reason we changed our net here in EU to 220/400V For the same power conumption we draw half the current of our friends across the pond. Half the current means less wire gauge, means cheaper infrastructure...

greetz,

Philippe

 

[jonny round boy]

Theoretically, yes, but in practice it doesn't work that way.

Let's say you have a 2200W router, such as the OF2200.

I=P/V, so on a 220V supply, the current would be 2200/220, which is 10 Amps.

On a 110V supply, the current would be 2200/110, which is 20 Amps.

Therefore, if you halve the voltage, you need to double the current in order to get the same power.

You are correct in saying that a 220V supply when applied to a fixed resistance will flow at twice the current than 220V - but - the 220V circuit will be designed to handle half the current (since that's all that's needed to provide the same power).

In basic terms, to provide the same power output, a 110V supply will need to be protected by a 26A fuse, compared to the 220V supply on a 13A fuse. So the maximum current that can potentially flow in a 220V circuit is half that of the 110V circuit.

Add an RCD to the 220V circuit however, and in a fault situation the maximum current that can flow is 30mA...

 

[Alan m]

ok i m not a physics buff [blink] so il bow out , i think im wrong [eek].
so a 2200 motor running 110v is uses twice the current that a similar motor on 220v would use.
so why do we use 110 volt on site then. surly its more dangerous

 

[jonny round boy]

ok i m not a physics buff [blink] so il bow out , i think im wrong [eek].
so a 2200 motor running 110v is uses twice the current that a similar motor on 220v would use.
so why do we use 110 volt on site then. surly its more dangerous

I think so, yes.

 

[d8b]

ok i m not a physics buff [blink] so il bow out , i think im wrong [eek].
so a 2200 motor running 110v is uses twice the current that a similar motor on 220v would use.
so why do we use 110 volt on site then. surly its more dangerous

I think so, yes.

You are correct. But all this can be made safe by the correct circuit breakers.

I regulary use 400V 125A connections (you really don't want to handle those cables) I have no fear to use these, because I now all our power distribution boxes are equipped with the correct breakers and RCD's) If we use a genny (often). I personally check wether it is earthed. No earth, I'm not connecting anything.

greetz,

Philippe

 

[d8b]

Just to be clear... What is defined as a 'site' for the UK regulations

 

[GaryLaroff]

the 240V in the US is the equivalent of our 400V 3 phase (I think).

Not quite.  The 400V 3 phase in UK/Continent is three phase.  Here in the U.S. we can have 240V 3 phase but it is an industrial electrical service that must be added to the facility.  The 240V that most American homeowners talk about is single phase and is produced by tapping into two 120 volt supply lines.  Almost any single phase electrical service panel in the U.S. with single phase-only service can can be wired to provide 240V for the kitchen range or in the shop for the table saw, bandsaw, etc.

The primary difference between the 240V in the U.S. and Europe is that UK/Europe have 50 Hz electrical service and the U.S. has 60 Hz AC service.  Many/most motors will not work in both environments.  Looking at the motor plate on a power  tool sometimes shows the motor rating as 120V 50/60Hz or 220V 50/60Hz indicating it will work at either AC frequency and only requires a voltage change, which is easier to do on site than a frequency change.

Gary

 

[tbellemare]

If I'm not mistaken, you gent's keep talking about motors and such when you are referring to electrical safety...

Personnel protection is about the personnel, not the motor.

My body has a fairly constant resistance whether I'm using a 120V tool or a 240V tool. If I get shocked with 110, I get approximately half the current through my body as when I get shocked with 240.

Tom

 

[harry_]

Guys all your theorizing, postulating and formulating is all well and good except you are completely missing the point regarding current.

Regardless of the operating voltage of the tool or the supply it is drawn from , whether it is 1 volt or 1K volt, it is the amount of current available to pass through your body that is the safety factor.

The math may say otherwise, but I know for a fact (heh, please don't ask) that 30V@15A will knock you just as hard as 100V@15A.

Having worked alongside power linemen for a number of years the running joke was 'what do you call a lineman-trainee?........A fuse'

 

[tbellemare]

If I remember correctly, it takes less than a 1/4 amp to kill a human. The smallest breaker that is common is 15 amps.

Tom

 

[Alan m]

iv heard that 0.7 milliamps will kill. iv also heard of 70 mAmps to kill

 

[tbellemare]

I think one factor is how you made the circuit. If it is hand-to-hand, your heart is in between. If it's calf-to-foot, there aren't any vital organs in the path.

Certain voltages cause involuntary muscular movements and can  cause you to "grab on". I'm not certain what range of voltage is the worst for that phenomenon. I think it's worst around 220 but it's here-say from my youth. If I grab a 120 VAC hot wire, there's a lot of stinging and it takes a bit of directed thought to let go.

Tom

EDIT of my EDIT: Grabbing a "hot" wire isn't anything like doesn't have nearly the same effect as touching a hot stove.

 

[AlexThePalex]

If I remember correctly, it takes less than a 1/4 amp to kill a human. The smallest breaker that is common is 15 amps.

It actually can be as low as 30 to 60 milli amps. Fuses that are rated at 15 amps are meant to prevent a short circuit (which can start fires), not an electrocution. To prevent an electrocution you need a RCD or GFCI as it's named in North America. A fuse detects an amp overload, that's why it's rated at a certain threshold. An RCD detects a difference in the current that's send and the current that returns. When you get electrocuted, the return value is different from the sent value because of leakage to the ground (through you).

But it's not the current OR the voltage that kills, it's a combination of both. They are always connected to each other.