120/208 questions about 3 wire and 4 wire systems

Excuse me, you have 208 volt service with a 440 volt machine. Got a transformer between the service and the tool? VERIFY that the motor is dual voltage (208-440) if not your going to be buying a new motor. VERIFY the starter rating at 208v ( inside the cover) . Starter at 440 might not be large enough. My guess the starter will be to small. Changing from 440 to

208 volt will almost double the running current.

Motors are stupid they only care if they get the correct voltages, not much difference to a motor from 208 to 230-240 3 phase. Verify every motor for dual voltage configurations change the ones that require it. There are a few 3 phase motors I have seen that are single voltage only, not many. You will be drawing a bit more current 10-15% you MIGHT have to change the heaters/thermal overloads. Verify the motor current at 208 volt and check the heater value against that rating.

This is a good time to check your grounding of every machine. Run a code gauge ground for each machine and make sure that it is landed at each starter and every motor.

If he is getting 3p center tapped delta that is usually going to be 240 between phases, 120 from A and C to the center tap and 208 from the wild leg (B) to the tap.

Well, that's *one* way to do it. But there are a lot of 3-phase 208 wye services. 208 phase-phase, and 120 phase-neutral. The OP didn't mention center-tapped delta for the new digs, only the place they are leaving.

But he also mentioned '5-wire'. I've seen four-wire, but I can't think what the fifth wire is unless he's counting the grounding conductor as well.

daestrom

Some motors can be dual-voltage. By re-connecting the wiring, they can run on different voltages. But the same horsepower at a lower voltage means more current. At the very least, the motor overloads current setting will need changing. Possibly a larger size starter cabinet as well. (we're talking more than double the current for the same horsepower). If the starter came with the unit, and the whole unit is designed for dual voltage service, then it *probably* is the right size to begin with.

A simple three-winding motor with six leads would be delta-connected for low voltage and star for high-voltage. So your comment about reconnecting the delta motor to star to work on 208 doesn't make a lot of sense to me. And anyway, star-440 connected in delta would be about 254 (okay, 240 would be close enough). But 208 would seem pretty low.

And there may be a control power transformer in the starter unit if it has any relaying and interlocks. If the starter is just a mechanical switch with no relays, this may not be a problem. The control power usually steps down from line to 120. Check to see if this is the case. If so, then the primary side probably has some dual-voltage jumper configuration that needs changing. But too low a voltage to the starter's relaying may prevent it from working at all.

All else fails, look for an installation/setup manual and read the instructions ;-) Or contact the manufacturer.

daestrom

Sorry for the FUD. I missread the post. You are right.

OK...OK, Thanks for the observations...I should have stated that all of the motors are dual voltage and I suppose I had planned to resize the heaters.

Had not considered that the starters might be too small but it makes sense. The starter (and jumpers) appear integral and I had planned on the motors de-rating in hp when lower voltage was utilized. I don't run my tools near their capacity, power-wise, but I am uncertain about the increase current required when starting.

It is 120/208 wye and I was counting the ground (I have heard it called a four wire system but it leads to confusion with outsiders like myself). I was under the impression that the wye configuration was newly (?) required by the NEC (provision of a neutral).

Thanks for the tip about control voltage...I was unaware it commonly was stepped down to 120v...I might have guessed 24v. There are transformers in nearly every machine. Luckily I have the wiring diagrams. All of my machines are quite old as I have collected them over several years from widely disparate sources. I am fairly sure that changing starters and control transformers will cost me more than than I can save by avoiding the purchase of a transformer for my single phase needs for the rest of the building (adequately covered with approximately 200a).

This is closer to the heart of the matter...I have been trying to compare the cost of buying a transformer for my single phase needs with the cost of reducing the voltage on my tools. I had hoped, albeit briefly, to accomplish both with the 120/208 wye configuration.

I can have the higher voltage service if I want it. The power company representative says it doesn't really matter to him (he simply specifies a different set of transformers). I was trying to avoid purchasing an expensive dry transformer myself when I chose the lower voltage because, as I appreciate it, I can get 120v single phase from either of the hot legs to neutral and 208v (or so) single phase between the two hot (stable) legs to neutral and can run my air conditioners without a transformer. There is a "wild leg" (B) that is assumed in our area.

So, now my new question... Can I get single phase 120v out of the higher voltage (220/440v, or so) wye service and is it more likely to be cheaper stepping down or stepping up voltages for my single phase needs. The power company will no longer give two services to a single location.

Thanks again for all observation and opinions. HA Bruce (Hitt Cues)

Not new to the industry, new to some areas of the country. Here in the SW

208 has been around for more than 35 years.

Why, if your getting 208 your getting 3-120 volt legs, 208 between any two legs. Use a single phase panel and run your loads from the panel installed for them.

I doubt that your getting a high leg/wild leg with 208. 208 is a wye system and does not have the high leg like the delta for the 230-240 volt systems. It might be in the area, on existing installations.

As for higher voltages on the incoming. The next step from 208 is going to be 277/480, probably. New service time. Big expense for you if the other is already purchased. Not much point in going to 240 volts from 208 in my opinion. Difference is not that much.

Please check with your power company rep and have him walk you through the electrical system your getting. If it is 208v then you should get

120-120-120-N-G. If the service is 230 or 240v then you will get 120-190-120-N-G. Or something very close. I believe you are confused about the incoming voltages. If your geting the first then your single phase loads are not an issue. If your getting the second then they are. Use suggestion in the body of text.

As a hint the power company charges more for unbalanced services through demand and other charges. As an expample if you draw 10-20-50 amps the meter reads the 50 not a combined total divided by 3. So the more 3 phase loads you have and the less single phase loads you have the better for your monthly bill.

I think I have the picture. Sounds like your best bet is 480 3ph....delta or wye. You will still need a transformer for your 120 volt needs. They are not all that expensive. Many places sell used dry transformer with the same warranty as a new one. Consider: replacing the starters, if you went to 208, would probly cost more than the transformer that you are worried over.

From what you wrote earlier, it sounds like your electrician is 'on track'.

First, I would extend my appreciation to the various persons who replied.

Good suggestion...I checked the starters on the various machines and, as my electrician stated, all but 1 starter on one machine was adequately sized to accomodate lower voltage.

Good suggestion...I have requested that we double check the grounding of each new installation.

Good tip...control voltage is 120 and we will by-pass the step down transformers.

Good suggestion...I am meeting today with the power company representative about power quality and specifications and metering.

I believe this is one of best features of professional groups, such as this one, as I believe two heads are better than one. This group has a exceptionally low signal to noise ratio and commendations are extended.

Regards, HA Bruce

I am not sure what the piece of equipment you are connecting is, but the CNC's that I have done this to required several modifications. The motors, of course need to be configed if they run off line current. The heaters will need to be changed because the current will more than double. If there is an isolation transformer and any control transformers you will have to re-strap those. It may not be a bad idea to have your CNC tech come in and check everything out before you turn on the machine. I have had to repair many machines from incorrect jumpers, heaters and line voltages....One other tip....put in a good ground rod!......Good luck to you in your new shop!.....Ross

One other thing....you may have to change some of you fuse values to reflect the higher current.... Later and good luck, Ross

Zathera,

I have read a number of your posts offering advice to others connected with serious electrical safety issues. My suggestion is that you get off crack or whatever mind enhancing drugs you are using. If it is not drugs then you need to complete high school. Regards,

John Phillips