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Old 01-01-2007, 05:33 PM   #1
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3 phase anyone?


Hi all,

I am new to this so please bear with me. I am writing from Australia so we are talking 240V single phase and 415V 3-phase.

Here comes the problem:

I bought a 3 phase welder off a friend for $150, quite a steal. The cooling fan wasn't working and after checking the wiring I found that it was wired up wrong. I assume that the motor is just a normal single phase fan similar to the ones used in a bathroom. After checking on the net I was surprised to find that it is quite possible to run single phase off a 3 phase supply...so I experimented...

Wikipedia says:
http://en.wikipedia.org/wiki/Three-phase_electric_power

"Single-phase loads
Single-phase loads may be connected to a three-phase system, either by connecting across two live conductors (a phase-to-phase connection), or by connecting between a phase conductor and the system neutral, which is either connected to the center of the Y (star) secondary winding of the supply transformer, or is connected to the center of one winding of a delta transformer (Highleg Delta system). (see Transformer#Polyphase transformers and Split phase ) Single-phase loads should be distributed evenly between the phases of the three-phase system for efficient use of the supply transformer and supply conductors."

I have a 20A 3 phase connector with L1, L2, L3 and Earth (no neutral in the middle) coming into the welder. I had 2 wires and an Earth coming from the fan so I connected L1 to the first and L2 to the second wire and Earth was connected to the case...AND...it worked!

But there is a "however"! I also hooked up 2 240V powerpoints to be able to plug in an angle grinder or something at the front of the welder...just to be fancy.

After using the welder once for a couple of minutes I plugged in the angle grinder and realised that is was running with way too much power...and at the same time I found that the fan had stopped working...probably a while ago.

The fan not working isn't really a problem because the welder is HUGE and for light industrial use and with my couple of welds would probably never overheat but it just buggs me because I have no idea what I did wrong.

Any idea where I went wrong? I am a little confused about the "neutral" or lack there of (http://en.wikipedia.org/wiki/Ground_and_neutral). Was I supposed to connect f.e. 1 fan wire to L1 and the other to Earth? That sounds like a short to me or does it?

Any help is appreciated. I assume I have killed the motor but b4 I get a new one I would like to know how to hook it up properly.

Please help b4 I electrocute myself.

Cheers,

Thomas
Brisbane/Australia


Last edited by Tomkah; 01-01-2007 at 06:44 PM.
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Old 01-02-2007, 01:59 AM   #2
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3 phase anyone?


Tomkah,

As you stated, you are working with a 415V/240V 3-Phase system. State side, this relates to our 480V/277V and 208V/120V systems (we have three, 3-phase systems in use today including the antiquated high-leg system of old). We also have single phase 240V/120V which is not in any way related or to be confused with our 480V/277V and 208V/120V 3-Phase systems.

The specified voltage in a 3-Phase system is the voltage between any pair of legs (phase wires). With 3-phase there are three high-voltage single-phase circuits and three low-voltage single-phase circuits (provided the source transformer has a wye secondary winding as most do today). Because the phase angle between any two phases in a 3-Phase system is 120 degrees (360 degrees divided by 3) the voltage between any phase and neutral (ground potential conductor intended to carry current) equals the high voltage divided by the square root of 3 (1.73).

For example, 415V divided by 1.73 = 240V

Therefore, let's call our phase conductors L1, L2, and L3; let's call our neutral conductor N.

We can now derive seven voltages:

L1 - L2 - L3: 415V 3-Phase

L1 - L2: 415V Single-Phase
L1 - L3: 415V Single-Phase
L2 - L3: 415V Single-Phase

L1 - N: 240V Single-Phase
L2 - N: 240V Single-Phase
L3 - N: 240V Single-Phase

For your 240V loads, a Neutral conductor is required, the current ampacity of this conductor should equal the 3-Phase fuse/circuit-breaker rating.

...Christopher

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Old 01-02-2007, 03:04 AM   #3
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3 phase anyone?


Hi Christopher,

thanks for your detailed explanation .

I was kinda worried that it would have to do with the neutral...which I don't have. I just bought 25m (or something like 75 feet in your "language") of cable (3 conductors, 1 Earth, no neutral)...I guess I better return that if I can.

Cheers,

Thomas
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Old 01-05-2007, 05:18 PM   #4
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3 phase anyone?


hi tomkah, 3 phase is basicly 3 seperate supplys of 240 volts approx. here in scotland. the confusing part is the 4th wire called neutral , so you have red . yellow. blue all each 240volts lets keep it simple / if you have 3 phase supply coming in, there will be to your main fuses before the meter 3 live 1 neutral /now at this point before the consumer breaker box and the meter the neutral is split into neutral and earth by adding a earth to the junction box we then put in an earth rod into the ground also connected to the earth and neutral so now you have 3 live 1 neutral 1 earth
now this gets simply up to your consumer unit / breakers or fuses .. before i go any further imagine i,m building 3 houses so i would bring in say red L1 and a branch from underground or from a pole neutral wire join on an earth before my meter to the neutral put in my earthing rod so i now have single phase 240 only to my first house L1 .N. E. and so on to each house . yellow L2 .N .E 2nd house blue L3 .N. E. 3rd house. back to your welder I had a three phase welder once i ran it on single phase just wired up one L1 bridged L1 L2 L3 remember to increase your wire size 6mm 10mm further you travel from your fusebox do not run anything through coiled cable heats up and melts also the further you travel with lighter cable motors overheat and burn out as to voltage loss you will over heat and burn out a drill quicker allowing the battery to go to low / negative is basicly earth but when on the secondry side after your breakers /fusebox its your safety net you cannot join earth to neg. as to a double consumerbox you cannot put neg. from left set of breakers to right set like 5 sets of breakers neg. must go on the neg. bar above the breakers say your lights to 6 amp breaker neg. goes to that bar above if the neg. when someone was wiring a house and accidently put it to the opposite side . it would trip the breakers. now for your angle grinder imagine its a house your sockets use one of the live any of the three will do red . yellow or blue L1.L2 or L3. now i would use armour core cable say 4mm now connect your earth to metal armour core at your fuse box this give you your live live neg. earth . remember your earth is a must your life depends on it neg. to your earth is wrong it will work as if through an old fuse box it is a neg. earth. but i would buy breaker box and would put the live wires and neg. and earth through a consumer box you could fit it to your welder each live wire will go through a seperate breaker . neg. on to neg. bar earth on to earth bar. then each wire to welder from the box. actually you get a 4 fuse breaker box bridge one live to the fourth breaker and you will connect this to your sockets for your angle grinder your main breaker would be 40amp. 4 off 16amp breakers you could use a bigger consumer box and bridge across to a 6amp breaker for lights you get a bridge bar to connect across from your electrical wholesale supplier for your breakers remember to bridge only to one live... bridge across 2 and doubles your voltage lights will glow very bright and bang. angle grinder goes like mad and is very dangerous / and remember earthing is a must.
regards mike
p.s. sometimes cable comes all the same colour say black i put coloured sleeves or coloured tape on each wire at each end red. yellow. blue.... yellow and green for earth leave the neg. black also a little knowledge is a dangerous thing. you can buy a tester for a few pounds which plugs into your socket this will give you 3 orange lights showing live. neg. earth is ok. if your in doubt you can drive in a metre long copper rod into the ground earth clamp and wire up 10 amp earthing wire will do up to your new box if your welder is in one place. i earth rod all my work areas garden shed , garage , at the end of say a strip of lighting around a farm 240volts lighting up a house or complete a circuit round and back to the mains box instead. i put a seperate consumerbox in my shed .and one in my garage. always remember the wiring can be heavier 4mm. 6mm. 10mm never lighter longer you travel increase your wire size always ask if in doubt. 1mm lights. 2.5mm electric sockets. from the consumerbox input depending on how many appliances sockets lights. etc.and distance.
if you want to go a step further you can always fit a selonoid 3phase switch activated through the neg. you will get a diagram with the unit it costs about 14 pounds uk. ideal for three phase. ideal for isolating a workshop when you leave.



Quote:
Originally Posted by Tomkah View Post
Hi Christopher,

thanks for your detailed explanation .

I was kinda worried that it would have to do with the neutral...which I don't have. I just bought 25m (or something like 75 feet in your "language") of cable (3 conductors, 1 Earth, no neutral)...I guess I better return that if I can.

Cheers,

Thomas
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