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dgibson
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Voltage Concerns for a New Machine

06/28/2011 3:50 PM

I am making preparations to receive a new CNC lathe. The manufacturer's spec sheet stated:

Voltage: 220 volts, 3 phase

Amps: 92 Amps (36 KVA)

I let the manufacturer know that I had 208 volts, 3 phase and was initially planning on using a 100 amp breaker and #3 wire for just less than a 100 ft. run.

They replied: "Should work"

My question is; Will it really work or will the voltage differences make a difference on the wire size and breaker size? I know that the machine will run on 208V.

Thanks,
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JRaef
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#1

Re: Voltage Concerns for a New Machine

06/28/2011 4:45 PM

Your breaker is too small even if it was 220V. You cannot load the circuit to more than 80% of the rating. So if your machine draws 92A FLC at 220V, the current draw at 208V will be roughly 97A, you will need a minimum of a 125A circuit; conductors and breaker. Without knowing the length and voltage drop it's impossible to determine your conductor size, but it won't be any less than 1AWG.

Most machines with AC motors will have a voltage tolerance of +- 10%, but your CNC machine has lots of other stuff in it. If the mfr says 208V is OK, he's the authority, but I would get it in writing in case there is a warranty issue later.

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dgibson
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#3
In reply to #1

Re: Voltage Concerns for a New Machine

06/28/2011 5:14 PM

Thanks, I was mostly wondering how much it was going to cost when the electricians come in.
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KJK/USA
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#2

Re: Voltage Concerns for a New Machine

06/28/2011 5:13 PM

dgibson,

To re-enforce what JRaef stated, I am in total agreement.

Get it in writing from the manufacturer, specifically that this equipment will work on your voltage of 208V and beef up your CB and feeder conductors.

Personally, I think you may have problems operating this at 208V.

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dgibson
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#4
In reply to #2

Re: Voltage Concerns for a New Machine

06/28/2011 5:18 PM

Thanks, the machine specs are 200 to 22o volts. They just gave me the 220 volt information on the order confirmation form.
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Dammit
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#5

Re: Voltage Concerns for a New Machine

06/28/2011 7:26 PM

Also insure that if you have any control transformers that the primary is tapped on the 208 volt terminals....
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dvmdsc
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#6

Re: Voltage Concerns for a New Machine

06/28/2011 10:06 PM

220 Volts "smells" European and 50Hz, When 3 phase motors are used, it will run faster.

If tacho controlled no problem. Make sure this is no issue too.

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Fredski
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#7

Re: Voltage Concerns for a New Machine

06/29/2011 9:24 AM

I just read the entire thread. You have red flags everywhere. You didn't mention if this was 50 or 60 hertz. I'd check that. And yes it's true that a machine designed for 208V "will run" on 220V, 230V too. My strong suggestion to you is either get a machine to match your voltage or get your service to match your machine. If you Mickey Mouse something when you begin you should expect problems down the road. It's far easier to get it right now then deal with issues after you've paid to install it wrong.

good luck
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dkwarner
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#8

Re: Voltage Concerns for a New Machine

06/29/2011 11:44 AM

We recently installed a somewhat smaller CNC Lathe (rated 60 Amp @208V). It is running on a somewhat shorter length of #6 wires (our 'electrician' is trying to get by using the existing wires that used to feed a 480V machine), and the supply voltage during working hours tends to be closer to 204V. It ran fine at low RPMs, but stopped with a low voltage alarm at higher speeds. Many of the machines in that section are powered by a 75KVA 480-208V transformer. The input tends to be just under 470V, so moving the inputs down one notch on the transformer brought the output up to 210V, and seems to have solved the problem, without causing any undesirable side effects on the other machines.

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perry
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#9

Re: Voltage Concerns for a New Machine

06/29/2011 11:48 AM

dgibson: most of the machines i wired had a auto transformer shipped/or built in with the machine that could be reconnected for different voltages found around the world.perry
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dgibson
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#10
In reply to #9

Re: Voltage Concerns for a New Machine

06/29/2011 12:07 PM

That has been my experience also. Thanks,
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chrisg288
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#11

Re: Voltage Concerns for a New Machine

06/29/2011 8:00 PM

We are getting some new (to us) equipment too. (small kitchen mfgr)

a cnc and a new dust tower. my boss is working on the problems. he told me today that the 30hp motor is drawing over 400amps on startup, and is having a very slow time starting. He went out on the tower, turned the fan shaft by hand, and then ran back to the starter, turned it on, and away it went...

Someone suggested to him to use a time delay breaker, that will give a few extra seconds of current befor breaking. (there is a few hundred feet of exhaust ducting attached.

What is the right way to approach this problem? What about having a manual or gravity damper that can unload any static pressure at startup time?

any suggestions are appreciated. (sorry if this is OT) I don't mean to divert the thread. we are installing a new cnc too.. but that is next weeks project.

chris
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dkwarner
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#12
In reply to #11

Re: Voltage Concerns for a New Machine

06/29/2011 8:40 PM

Sounds to me like you have a broken connection on one phase. A three phase motor is not self-starting if one phase is missing, but under light load, many will run in either direction when manually started.

Check the voltage on all three phases at the motor (motor temporarily disconnected, or motor running if that is safe). all three should be within one or two percent of the same value. Then check all three line to ground voltages; same thing.

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Fredski
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#13
In reply to #11

Re: Voltage Concerns for a New Machine

06/29/2011 8:45 PM

I think DK might be right. Start it and put an amp meter on it. If it's drawing 150% of rated amperage you have a leg down. You know what to do from there.
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chrisg288
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#14
In reply to #13

Re: Voltage Concerns for a New Machine

06/29/2011 10:12 PM

thank you both!!
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chrisg288 (2); Dammit (1); dgibson (3); dkwarner (2); dvmdsc (1); Fredski (2); JRaef (1); KJK/USA (1); perry (1)

Previous in Forum: Ferranti High Voltage Test Equipment   Next in Forum: Standard Medium Voltage Systems in Morocco and KSA

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