Question re 3 Phase.

**Shedhand** · 2nd April 2017, 07:08 PM

Can a sparky help me with some info please.
I have a 17 year old carbatac 12" table saw.
it has a single phase, 2hp motor drawing 11 Amps at max 2850 RPM. The motor has an overload switch which is so sensitive it trips even when ripping radiata pine.
I mostly work with hardwood from bull oak to red gum. So it takes ages to rip, say, a 600mm length.
I had 3 phase connected to my shed last year to run my big dusty. I had a lot of 3 Phase cable and switch gear laying around so it wasnt very expensive to do.
i spent today converting the table saw to 3 Phase.
i had an ASEA Motor in as new condition. 4 Hp, drawing 8amps at max 1450 RPM.
I took the old single phase motor off and mounted the 3 Phase motor in its place.
I removed the old single phase rocker on/off switch and all the wiring.
i wired up the motor and connected it to a rotary 3 phase switch to the correct terninals, Earth, L1, L2, L3. I made a cable to run from the 3 phase power point in my dusty shed to the 3 phase rotary switch. Checked everything was tight and right. Switched the saw on and it worked...except the saw runs backwards. 😕
Have I accidently reversed some wires? 🤷♂️
If so where would i hhave stuffed up and can you tell me how to get the saw cutting in the right direction?
thanks
mike.
INDEMNITY.
I accept all responsibilty for my work. No responsiblity or liability on your part for any advice you may provide.
mike gard

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**Bohdan** · 2nd April 2017, 08:22 PM

Reverse any two of the three active wires.

**Shedhand** · 2nd April 2017, 08:36 PM

Thanks mate! Do you mean any 2 of 3 (L1, L2, L3) in the switch on the saw? Or the plug end?
cheers
mike

**Bohdan** · 2nd April 2017, 08:42 PM

Doesn't matter, any two.

**NCArcher** · 2nd April 2017, 08:48 PM

Switch L1 @ L2 wherever it is easiest to get to.
You should be starting the motor with a 3 phase starter c/w thermal overload. A switch is not a good idea for 4HP.
Something like this
LE1M35U716 | Schneider Electric 4 kW Automatic 3P DOL Starter, 240 V ac, 3 Phase, IP65 | Schneider Electric

**BobL** · 2nd April 2017, 09:20 PM

Originally Posted by Shedhand

it has a single phase, 2hp motor drawing 11 Amps at max 2850 RPM. T

i had an ASEA Motor in as new condition. 4 Hp, drawing 8amps at max 1450 RPM.

Err...... no one spotted the difference in RPM?

At that speed that saw wont cut very fast no matter the HP difference..

**Bohdan** · 2nd April 2017, 11:07 PM

Originally Posted by BobL

Err...... no one spotted the difference in RPM?

At that speed that saw wont cut very fast no matter the HP difference..

Depends on what he used as a drive pulley. If he used one double the size of the original he is back where he started.

**BobL** · 2nd April 2017, 11:21 PM

Originally Posted by Bohdan

Depends on what he used as a drive pulley. If he used one double the size of the original he is back where he started.

Maybe he did but as he didn't say so in his post I'm still surprised no one said anything about it.

**Shedhand** · 2nd April 2017, 11:28 PM

Hi Bob, i did wonder about that too but as the pulley is only a tad under twice the size i dont think it'll be an issue. The speed of the cut is less important than the damn saw cutting out all the time. If its too slow I'll just have to pedal faster. 😬 👍
Cheers

**Shedhand** · 2nd April 2017, 11:33 PM

Thanks Bohdan. Works fine now. If i had 92 bucks to spare...anyway i never run it for more than the time it takes to rip something down. I might only use it a couple of times a week for about 15 - 20 minutes stop start in total.
cheers

**ian** · 3rd April 2017, 06:51 AM

Sheddie

I think that NC Archer was referring to what happens to your circuit (and possibly the saw as well) every time you start the motor.

If I remember the little bit of Elect Engineering I did correctly, it's not a good idea to run a 3 phase motor in the start-up configuration, nor to start the motor in the run configuration.

**Shedhand** · 3rd April 2017, 10:04 AM

Thanks for that Ian. I certainly dont want to fry anything! I'll see if i can pick one up off ePay. 👍 Unless one of our fellow forumites comes up with another solution/suggestion. Who'd be an electrician? 🙄

**Shedhand** · 3rd April 2017, 10:07 AM

I'm looking at one on ePay! 👍

**BobL** · 3rd April 2017, 10:27 AM

Originally Posted by Shedhand

Thanks Bohdan. Works fine now. If i had 92 bucks to spare...anyway i never run it for more than the time it takes to rip something down. I might only use it a couple of times a week for about 15 - 20 minutes stop start in total.

15-20 minutes of ripping bulloak and redgum could still easily overheat a motor, and while its unlikely and hopefully the belt will slip, If the blade gets jammed it will only take about 3 seconds to start cooking the motor. At that point $92 is going to look cheap

**Shedhand** · 3rd April 2017, 10:59 AM

Arghhh😳 Ok Bob! Point taken. Will put it in mothballs until i can get some spare cash together. Thanks for thewarning.👍

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