running 230 volt of a 3 phase 400V power

[Renze]

Hey guys,

I bought a band saw, a machine that costs 1200 Euro new. I bought it for 150 euro, and replaced the missing coolant pump by a 70 W fish pond fountain pump.

Now there's a problem:
The saw is a 400 volt 3 phase machine, and the little coolant pump is a 230 V single phase.

I know that a 4 pole wall plug has 3 phases and a ground, and that a 5 pole wall plug has 3 phases, a ground and a null.
The 230 Volt connection is 1 phase and a null.

Now here comes the question:

Is it safe to get a phase from the 400 Volt main switch (to switch the coolant pump simultaneously with the saw motor) and use an extra 230 volt connection with only 1 wire hooked up, to get the null to split the phase into 230 volt (like any normal 230 volt connection does)

The 230 volt pig nosed wall plug can be mirrored. Would i risk hooking up 2 phases to the coolant pump motor when i turn the 230 v plug upside down ?

Or would i be better off installing a dedicated 5 poled wall plug for the saw ???

How do i determin what the null is in a wire joint box, i do have a voltage meter but how do i measure it ? My brothers and uncles have been messing with the wires for 20 years in my workshop, so i dont think the connections are hooked up according to standardised wire colour codes...

 

[dave_peters]

DONT hook across 2 phases. the voltage will then be 480.
Its best to get professional help with this. but if you are going to DIY then the voltage between any 1 phase and the return on your 5 pin plug is 230. If you only have 4 pin plugs then the voltage between the earth (which is also the return) and any 1 phase is 230. but, if you use this you must have a proper earth cable to the wall socket from your pump and any switch you use ,and you may find that if you have an earth leakage trip it will operate when you switch on the motor.
Definately use a 5 pin plug if you can. the terminals are marked so you should be able to identify them. if the 3 phase motor goes around the wrong way then swap any 2 phase wires around. the 1 phase motor will rotate correctly whatever.
As to how to identify the null, this can be difficult as the earth and the return are joined together at your transformer anyway. you will probably have to find what colour the earth is at the fuse box and track it if its the wrong colour. In UK its always yellow and green coloured

 

[treaney]

Dave P gave good advise.

Do you have a 3 phase supply where you will be using the saw? If you do, your on track otherwise it will cost you mucho euro to get it in.

 

[Renze]

Yes i do have 3 phase 400V, i also run our 7,5 Kw irrigation pump from the workshop.

Using the saw is no problem, but it is rather awkward to swith the saw motor on with the button, then flick another switch to get the 230 V cooling pump running, then open the valve on the drop down cylinder and do it all in opposed direction when you've cut a piece.

I've got the 3 phase plus 1 ground (4 pins) and i also have the 230 Volt 1 phase plus a null and a ground (2 pins one ground)

So i do have what i need: 3 phase, earth and a null. Which means 5 pins.

So how do i determin which one is the null from the 230 V wall connector ??? Is there a difference between the voltage between ground and null, or ground and phase ?

 

[internash]

I know nothing of electrics, but i know if you get many sparks or electric shock........ Its the wrong wire

You could just get a 3 phase cooling pump? that would be more easy???

 

[dave_peters]

You can easily determine which are the 3 phase wires by a process of elimination with a meter. There should be around 480 volts across any 2 of the phase wires, but only 230 volts between any one of the phase wires and the earth ( which is also the null on a 4 pin). Its not a good idea to use the earth as a null to provide 230 volts unless you can provide a seperate earth wire, as any fault in the 230 v appliance will make everything live !!

Its not so easy to tell which is the earth and which is the return on 230 v 1 phase if the wire coding is wrong, since the voltage from the live across either wire will probably read the same because the earth and return are usually joined together at the transformer anyway. you would be safest to look at the fusebox or RCD/earth leakage trip if fitted and trace the wires, the earth will be obvious as it will be fixed to the casing. Sorry I can't be more helpful !!

 

[treaney]

Renze,

Is the problem that the original coolant pump was 3 phase and you are trying to add in a single phase replacement? A digital photo of the wiring/conectors would be of great help .

If you were to pick up 240V from a phase and neutral, you could use this to supply the collant pump. I dodn't think that the load imbalance caused by the coolant pump would cause a major problem (10's of watts vs total load).

 

[Renze]

Tom, you describe exactly what i was trying to ask. I have 3 phase plus an earth, and need another null wire to get a 5 pin connector, so i can switch 3 phases on the saw motor, and mount 1 phase serial to the 220 V cooling pump.

I think i can just measure between the 400V connector and the wires in the 220V joints box, if it reads 400V i know i measure between 2 phases, and if i measure 230V i know one of them is the null, which has to be the one in the 230V wire joint box because a 4 pin 400V connector cant have a null.

I think i'll try tomorrow.

 

[Renze]

I found it:

According to Wikipedia, searching voltmeter, i found that i can measure the electricity with my little screwdriver with built in LED, a.k.a current detector.
If you put your finger on the metal butt of the grip handle, a small current will go through my finger into the earth (so little that the LED will burn on it, but not that i will feel the current, and it wont trigger the ground safety relay either.

Of a normal 220 Volt wall plug, only 1 hole will give light on the current detector, which is the phase.

This answers my question: you can measure a current between ground and phase, but not between null and ground.
I will install the 5 wire cable to the other end of the workshop tomorrow, to feed the saw/coolant pump through a 5 pin connector, and i can install another wall connector to plug in the fan of my workshop heater.

 

[you_know_me_]

hahaha i have no clue what's this posts about no clue at all

 

[diyfarmer]

Why did you write on a post you know nothing about, I read it to but it is over my head too

 

[you_know_me_]

hahaha i wanted you to read it and explain it to me