3 Phase Electric

[elkangorito]

IS THREE PHASE SAFER than the other options?

NO!!!!

Three-phase is no safer (nor more hazardous) than single phase in a domestic environment.

However, as previously intimated, you really are unlikely to need it

Crossy, what happened to the cart in your avatar? It has disappeared & only the bull remains.

Sorry. Couldn't help myself. Just joking.

[Naam]

When I grew up in the US there were no ground wires on anything and there were no GFI units on anything....anywhere......but.....somehow my generation survived. My house in Thailand is just the same...no ground wires and no GFI's.....I do have a gas water heater though so I have completely avoided the major risk factor.

Chownah

when i grew up in Germany (i was a little baby then) three houses in which basements i spent with my mother were bombed. i don't remember but my mother told me that it took once 14 hours to dig us out... but... somehow i survived. but that does not mean that i am now planning to take a three week long vacation in Baghdad or Fallujah in order to find out that i am indeed bomb-proof.

[elkangorito]

When I grew up in the US there were no ground wires on anything and there were no GFI units on anything....anywhere......but.....somehow my generation survived. My house in Thailand is just the same...no ground wires and no GFI's.....I do have a gas water heater though so I have completely avoided the major risk factor.

Chownah

Chownah, I'm shocked (not literally).

I can't believe that you, of all people, would even say such a thing.

[elkangorito]

If you are going to have any motors over 1kW then 3ph is better for the motor. From a practical standpoint, 3ph doesn't make much sense unless you have over 30kW of load. This is enough for about a 400 m2 home.

You are better off sticking with single phase power. Having 380V power around a house is dangerous. Unfortunately, the electricians working on home installations really aren't qualified to work with higher voltages.

Let's not guess about this...let's talk fact.

First, single phase (neglecting Power Factor);

30kW at 220 volts = about 136 Amps.

So, if you did a maximum demand calculation for your installation (which I can accurately do instead of guessing the load) & it exceeded 100 Amps, it warrants the use of 3 phase.

3 phase (neglecting Power Factor);

30kW at 380 volts = 45.6 Amps per phase.

Cable size & insulation type for 220 volts less than or equal to 100 Amps - 25 to 35mm squared, 0.6/1kV.

Cable size & insulation type for 380 volts less than or equal to 50 Amps - 10 to 16mm squared, 0.6/1kV.

The above sizes are for aerial cables. Length is limited.

380 volts is NOT high voltage. It's still Low Voltage. Medium voltage starts at about 750 volts.

380 volts is marginally more dangerous than 220 volts.

So, how many kilowatts equal 100 Amps at 220 volts? For single phase, 22kW (neglecting Power Factor).

Generally speaking, if you wish to use kilowatts as an "estimate" of maximum demand, anything above about 20kW & it might be wise to think about 3 phase. But don't guess. Get it calculated properly. Your maximum demand CANNOT be equated to the size of your home. This approach can lead to a very significant error & possible extra unnecessary cost or a hazardous installation.

Again, if you want it calculated properly, contact me.

I forgot to mention, the nominal minimum cross-sectional area of aerial conductors according to AS/NZ 3000:2000 is;

Copper - 6 millimetres squared.

Aluminium - 16 millimetres squared.

[chownah]

Any idea why the minimum sizes?...are athese for the slow breakers and you can go smaller with the fast ones?

Edited February 17, 2007 by chownah

[elkangorito]

Any idea why the minimum sizes?...are athese for the slow breakers and you can go smaller with the fast ones?

The minimum sizes relate to a required strength ie birds on wires, wind, tension etc.

[elkangorito]

Any idea why the minimum sizes?...are athese for the slow breakers and you can go smaller with the fast ones?

The minimum sizes relate to a required strength ie birds on wires, wind, tension etc.

Oops! Forgot to mention that Fault Current plays a part in this, particularly if the aerial conductors are Consumers Mains.

[jenkins]

When I grew up in the US there were no ground wires on anything and there were no GFI units on anything....anywhere......but.....somehow my generation survived. My house in Thailand is just the same...no ground wires and no GFI's.....I do have a gas water heater though so I have completely avoided the major risk factor.

Chownah

hi chownah newbie here (jib approved electrician )

in the states the supply is 110volts ? in thaland its 220-- a whole different ball game

110 doesn,t nessesarily need earthing ,220 does

also someone stated that a 12 v car battery could electrocute a person , this is totally untrue, any voltage below 55volts is safe

[jenkins]

I'm building a house with swimmingpool.Do I need 3 phase or will 2 phase be enough.I hear that when you use 3 phase that your electric appliances will use less electric but from the other hand the kilowatt price will be higher.So is it worth to have 3 phase installed.Some advice please.

hello, check the motor/ pump units that are supplyed by the pool people , they may well be 3ph ,

[Crossy]

also someone stated that a 12 v car battery could electrocute a person , this is totally untrue, any voltage below 55volts is safe

Whilst generally true, I'd like to make a couple of points:-

The first sailor to be killed by electrocution in the Royal Navy fell against a 50V DC bus bar, he was unable to free himself and died a slow (and probably very painful) death.

I'll kill you with a car battery (and no electronics). I could drop it on your head, or (more to the point) I could attach it to a couple of acupuncture needles, one in each arm. Once past the skin resistance of several k-ohms (which is what you measure if you get hold on a multimeter probe in each hand) the body's internal resistance is only a few ohms, 12V can easily generate a lethal 100mA or so.

Not a likely scenario I'll agree, but not totally implausible

[Naam]

also someone stated that a 12 v car battery could electrocute a person , this is totally untrue, any voltage below 55volts is safe

Whilst generally true, I'd like to make a couple of points:-

The first sailor to be killed by electrocution in the Royal Navy fell against a 50V DC bus bar, he was unable to free himself and died a slow (and probably very painful) death.

I'll kill you with a car battery (and no electronics). I could drop it on your head, or (more to the point) I could attach it to a couple of acupuncture needles, one in each arm. Once past the skin resistance of several k-ohms (which is what you measure if you get hold on a multimeter probe in each hand) the body's internal resistance is only a few ohms, 12V can easily generate a lethal 100mA or so.

Not a likely scenario I'll agree, but not totally implausible

i repeat: it's the AMPs and NOT the VOLTs that kill. of course not 100mA (milli-amps) but a big car batterie can generate in excess of 100 amps for several minutes. even 10% of this can be lethal.

the info "anything below 55 volts is safe" = rubbish² !

[Naam]

"in the states the supply is 110volts ? in thaland its 220-- a whole different ball game"

*****

rubbish too!

[Pink Mist]

Dont know what sort of a doc you are nam, but 100 milliamps can cause ventricular fibulation, so I hope you are never on my rescue team.

[Naam]

"

Table 1. Estimated Effects of 60 Hz AC Currents

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"

[Naam]

Dont know what sort of a doc you are nam, but 100 milliamps can cause ventricular fibulation, so I hope you are never on my rescue team.

right you are bronco! but in case you need medical advice don't call on me as i am not at all qualified. my doctorate is in physics.

[Pink Mist]

exactly, 100 was the figure I was taught at TAFE, that would be an average figure and I would be interested to know how they can prove it.

The normal RCD's here in Oz are rated at 30 mA and 10 mS, in theory you shouldnt feel it.

I got a heap of boots last week I wasnt wearing proper rubber soled boots, but I reckon we (sparkies) build up a resistance of sorts (sorry for the pun).

[elkangorito]

also someone stated that a 12 v car battery could electrocute a person , this is totally untrue, any voltage below 55volts is safe

Whilst generally true, I'd like to make a couple of points:-

The first sailor to be killed by electrocution in the Royal Navy fell against a 50V DC bus bar, he was unable to free himself and died a slow (and probably very painful) death.

I'll kill you with a car battery (and no electronics). I could drop it on your head, or (more to the point) I could attach it to a couple of acupuncture needles, one in each arm. Once past the skin resistance of several k-ohms (which is what you measure if you get hold on a multimeter probe in each hand) the body's internal resistance is only a few ohms, 12V can easily generate a lethal 100mA or so.

Not a likely scenario I'll agree, but not totally implausible

i repeat: it's the AMPs and NOT the VOLTs that kill. of course not 100mA (milli-amps) but a big car batterie can generate in excess of 100 amps for several minutes. even 10% of this can be lethal.

the info "anything below 55 volts is safe" = rubbish² !

So, is this why that most electrical standards stipulate that a maximum figure of 50 volts RMS AC is safe? Or will you re-write the standards?

It is dangerous to assume that "it's the AMPs and NOT the VOLTs that kill". They work in tandem via Ohms Law. 50 volts AC RMS happens to be the maximum 'safe' "let go" voltage for a human (according to most standards). Of course, electricity can kill a human in a few different ways.

[lopburi3]

The US has had grounded outlets as far back as I can remember (60+) but they were not a requirement until later. Our house built in 1950 had from outlet center faceplate mounting screw to socket mounting screws to steel box to steel conduit to ground. And you made very sure to attach that ground pigtail when using electric power tools (which were metal in those days). Later wire was used to as conduit connections could become detached and remove the link to ground. At present both ground and polarized outlets are used in the US.

[Pink Mist]

also someone stated that a 12 v car battery could electrocute a person , this is totally untrue, any voltage below 55volts is safe

Whilst generally true, I'd like to make a couple of points:-

The first sailor to be killed by electrocution in the Royal Navy fell against a 50V DC bus bar, he was unable to free himself and died a slow (and probably very painful) death.

I'll kill you with a car battery (and no electronics). I could drop it on your head, or (more to the point) I could attach it to a couple of acupuncture needles, one in each arm. Once past the skin resistance of several k-ohms (which is what you measure if you get hold on a multimeter probe in each hand) the body's internal resistance is only a few ohms, 12V can easily generate a lethal 100mA or so.

Not a likely scenario I'll agree, but not totally implausible

i repeat: it's the AMPs and NOT the VOLTs that kill. of course not 100mA (milli-amps) but a big car batterie can generate in excess of 100 amps for several minutes. even 10% of this can be lethal.

the info "anything below 55 volts is safe" = rubbish² !

So, is this why that most electrical standards stipulate that a maximum figure of 50 volts RMS AC is safe? Or will you re-write the standards?

It is dangerous to assume that "it's the AMPs and NOT the VOLTs that kill". They work in tandem via Ohms Law. 50 volts AC RMS happens to be the maximum 'safe' "let go" voltage for a human (according to most standards). Of course, electricity can kill a human in a few different ways.

I'm glad you said most, because the Oz and NZ standards dont define safe voltage.

They do however define voltage ranges, extra low, low, medium and high.

[elkangorito]

Some exerps from AS/NZ 3000:2000, which indirectly indicate a safe 'touch' voltage level;

1.7.2 Protection against both direct and indirect contact by use of extra-low voltage Persons and livestock shall be protected against dangers that may arise from contact with parts which are live in normal service (direct contact) or exposed conductive parts which may become live under

fault conditions (indirect contact).

Protection may be provided by the use of separated extra-low voltage (SELV) or protected extra-low voltage (PELV) as follows:

[a] The nominal voltage shall not be capable of exceeding the limits for extra-low voltage (50 V a.c. or 120 V ripple-free d.c.)

The source of supply shall comply with Clause 7.7.3.

[c] Circuits shall be segregated from other circuits in accordance with Clause 7.7.4.

[d] Unearthed circuits (SELV) shall be arranged in accordance with Clause 7.7.5.

[e] Earthed circuits (PELV) shall be arranged in accordance with Clause 7.7.6.

[f] Other circuit arrangements shall be in accordance with other relevant parts of Clause 7.7.

1.7.4.3.2 Touch-voltage limits.

In the event of a fault between a live part and an exposed conductive part which could give rise to a prospective touch voltage exceeding 50 V a.c. or 120 V ripple-free d.c., a protective device shall automatically disconnect the supply to the circuit or electrical equipment concerned.

NOTE: Lower voltage limits are required for special electrical installations or locations according to the relevant clauses of Section 7.

2.3 DEVICES FOR PROTECTION AGAINST INDIRECT CONTACT

2.3.1 General.

Where protection against indirect contact is to be achieved by automatic disconnection of supply, devices shall be selected and installed to satisfy the requirements of Clause 1.7.4.3.

NOTE: Selection is based on satisfying the prospective touch voltages of 50 V a.c. or 120 V ripple-free d.c. and the disconnection times of 0.4 s for portable equipment and 5 s for fixed and stationary equipment.

Edited February 18, 2007 by elkangorito

[Tywais]

Ohm's law and the body

[Pink Mist]

Some exerps from AS/NZ 3000:2000, which indirectly indicate a safe 'touch' voltage level;

1.7.2 Protection against both direct and indirect contact by use of extra-low voltage Persons and livestock shall be protected against dangers that may arise from contact with parts which are live in normal service (direct contact) or exposed conductive parts which may become live under

fault conditions (indirect contact).

Protection may be provided by the use of separated extra-low voltage (SELV) or protected extra-low voltage (PELV) as follows:

[a] The nominal voltage shall not be capable of exceeding the limits for extra-low voltage (50 V a.c. or 120 V ripple-free d.c.)

The source of supply shall comply with Clause 7.7.3.

[c] Circuits shall be segregated from other circuits in accordance with Clause 7.7.4.

[d] Unearthed circuits (SELV) shall be arranged in accordance with Clause 7.7.5.

[e] Earthed circuits (PELV) shall be arranged in accordance with Clause 7.7.6.

[f] Other circuit arrangements shall be in accordance with other relevant parts of Clause 7.7.

1.7.4.3.2 Touch-voltage limits.

In the event of a fault between a live part and an exposed conductive part which could give rise to a prospective touch voltage exceeding 50 V a.c. or 120 V ripple-free d.c., a protective device shall automatically disconnect the supply to the circuit or electrical equipment concerned.

NOTE: Lower voltage limits are required for special electrical installations or locations according to the relevant clauses of Section 7.

2.3 DEVICES FOR PROTECTION AGAINST INDIRECT CONTACT

2.3.1 General.

Where protection against indirect contact is to be achieved by automatic disconnection of supply, devices shall be selected and installed to satisfy the requirements of Clause 1.7.4.3.

NOTE: Selection is based on satisfying the prospective touch voltages of 50 V a.c. or 120 V ripple-free d.c. and the disconnection times of 0.4 s for portable equipment and 5 s for fixed and stationary equipment.

still doesn't define a safe voltage

[elkangorito]

1.7.2 Protection against both direct and indirect contact by use of extra-low voltage Persons and livestock shall be protected against dangers that may arise from contact with parts which are live in normal service (direct contact) or exposed conductive parts which may become live under

fault conditions (indirect contact).

Protection may be provided by the use of separated extra-low voltage (SELV) or protected extra-low voltage (PELV) as follows:

[a] The nominal voltage shall not be capable of exceeding the limits for extra-low voltage (50 V a.c. or 120 V ripple-free d.c.)

1.7.4.3.2 Touch-voltage limits.

In the event of a fault between a live part and an exposed conductive part which could give rise to a prospective touch voltage exceeding 50 V a.c. or 120 V ripple-free d.c., a protective device shall automatically disconnect the supply to the circuit or electrical equipment concerned.

NOTE: Lower voltage limits are required for special electrical installations or locations according to the relevant clauses of Section 7.

2.3 DEVICES FOR PROTECTION AGAINST INDIRECT CONTACT

2.3.1 General.

Where protection against indirect contact is to be achieved by automatic disconnection of supply, devices shall be selected and installed to satisfy the requirements of Clause 1.7.4.3.

NOTE: Selection is based on satisfying the prospective touch voltages of 50 V a.c. or 120 V ripple-free d.c. and the disconnection times of 0.4 s for portable equipment and 5 s for fixed and stationary equipment.

I think it's self explanatory...unless one can't see the obvious.

[Naam]

"It is dangerous to assume that "it's the AMPs and NOT the VOLTs that kill". They work in tandem via Ohms Law."

-----

i admit that my posting should have read "it's MAINLY amps....". i can't comment on the "electric standards" that <50volts are "safe" and i don't know who these standards established.

read http://www.allaboutcircuits.com/vol_1/chpt_3/4.html posted by "tywais".

Edited February 19, 2007 by Dr. Naam

[chownah]

The way it was explained to me it is infact current flow (amps) that causes death. The explanation was that if you look at the exact physiological mechanism that causes death you will find that a certain current threshold must be crossed for it to occur and whatever voltage is forcing that current is completely immaterial to the process. So from this explanation it is in fact amps that kills.....but....from a practical standpoint a certain voltage is required to create a certain current in a certain situation so in a particular case for practical matters considering the voltage applied can provide good safety advice....but it is a current threshold that must be crossed for death to ensue and having any arbitrarily high voltage will not cause death unless that current threshold is crossed.....i.e. a voltage potential is necessary but not sufficient to cause death, it is necessary to drive the current but it is not sufficient because if it does not cause the necessary current then death will not happen.

[Crossy]

I was always tought "volts jolts, but mills kills", anything over about 20-30mA has the potential to kill if you can't escape or let go.

Consider two sources of 25kV (25,000 volts).

1. The final anode connection of a cathode ray tube (the rubber sucker thing on the back of a TV tube).

2. The incoming bus-bar of your local sub station.

Assuming you're standing on the ground wearing regular shoes then :-

No.1 is capable of a few milliamps, get hold of it and you'll jump around but it's not going to kill you.

No.2 is capable of several hundred amps. Get hold of No2 and you die, no questions asked.

With all these discussions of what's lethal and what isn't it is all down to CIRCUMSTANCES.

Under certain circumstances you can get hold of 25kV and not die, under other (radically different) circumstances (and really, really bad luck) you could get hold of a 12V supply and die.

Generally, I treat any supply above 48V as potentially lethal and avoid getting hold of it.

[Naam]

"Generally, I treat any supply above 48V as potentially lethal and avoid getting hold of it."

*****

wet your fingers, grip with each hand the clean plus and minus poles of a 12v car batterie AND TRY TO HOLD ON. if you are lucky you might be able to tell us about your experience. if unlucky... an obituary in ThaiVisa about a heroic explorer of physics, medicine, amps and volts is assured.

[Crossy]

wet your fingers, grip with each hand the clean plus and minus poles of a 12v car batterie AND TRY TO HOLD ON. if you are lucky you might be able to tell us about your experience. if unlucky... an obituary in ThaiVisa about a heroic explorer of physics, medicine, amps and volts is assured.

Well, I'm glad someone agrees with me that under certain circumstances a vehicle battery can kill.

Since living in the tropics, working on vehicles wearing shorts and being covered in nice salty sweat, I've had a couple of tickles off 12 and 24V vehicle wiring (no NOT the HT leads), usually when leaning into an engine bay with bare legs contacting the chassis, nothing deadly but enough to remind you that it's there!

Edited February 19, 2007 by Crossy

[Tywais]

wet your fingers, grip with each hand the clean plus and minus poles of a 12v car batterie AND TRY TO HOLD ON. if you are lucky you might be able to tell us about your experience. if unlucky... an obituary in ThaiVisa about a heroic explorer of physics, medicine, amps and volts is assured.

Well, I'm glad someone agrees with me that under certain circumstances a vehicle battery can kill.

Since living in the tropics, working on vehicles wearing shorts and being covered in nice salty sweat, I've had a couple of tickles off 12 and 24V vehicle wiring, usually when leaing into an engine bay with bare legs contacting the chassis, nothing deadly but enough to remind you that it's there!

Another tidbit of information. Besides the one hand aproach, it's a good idea to remove rings from the fingers before poking around. Have been cases where rings came in contact with low voltage but very high current sources (car batteries for example) and nearly burned the finger off.

"Rings must never be worn when working with unprotected high current sources. Even quite small nickel cadmium cells have been known to produce enough current to sever a finger when short circuited by a golden ring."

Source: http://www.lboro.ac.uk/admin/hse/policies-...appendix10.html

[Crossy]

Another tidbit of information. Besides the one hand aproach, it's a good idea to remove rings from the fingers before poking around. Have been cases where rings came in contact with low voltage but very high current sources (car batteries for example) and nearly burned the finger off.

Yep good advice.

A similar incident occured many years ago whilst I was working on RADAR equipment. I noticed an 'interesting' smell followed by serious pain in my left ring finger. My wedding ring was acting as a shorted-turn to a high-power high-frequency (900MHz or so) transformer, bloody thing was nearly red hot. Luckily being a Brit. (and therefore having a large mug of tea on the go) serious damage was avoided, I still have the scar.

Edited February 19, 2007 by Crossy