Nameplate 430V 3 phase vs. nominal

[pgotseff]

First time posting so please forgive the newbieness.
I've been overlooking our company machine shop 3ph power supply. We have a 480/208 xfrmr (hung from ceiling so couldn't see the nameplate) supplying two panels marked 208 3ph 4W, those panels feed somewhere from 5 to 8 3ph machines (Hardinge lathes, Bridgeport mills, horizontal bandsaw, etc) and some 1ph loads. The nameplate on these machines is all 230V or 240V 3ph. Some are marked "Wired 230V" if they are fed straight to the multitap IM like on a manual Bridgeport mill. A quick check of NEMA motor voltages for "230V" says nominal voltage could be 220V-240V.

I can't find another xfrmr - could these "230V" 3ph machines be fed from 208V 3ph supply?

No opportunity to measure actual ph-ph voltage at machine since machinists were full bore.

Any insight into typical nominal voltages used for small 3ph machines is very much appreciated.

Thanks much
pete g.

 

[Jraef]

Most NEMA design motors are supposed to have a minimum voltage tolerance of +- 10% from nameplate. So if the nameplate says 230V, it can accept anything from 207V to 253V and still maintain torque within rated. More than that and the motor over heats, less and you lose torque, so it might over load.

The problem with "208" is that it may fluctuate +-5% from the utility, so at -5% it gets down to 198V and that is now out of tolerance for a 230V rated motor. However if the motor is over sized for the work at hand, you may never know it; it all depends on loading. If you are not having any issues, I wouldn't sweat it, it's very common.

Besides, in a lot of cases motor mfrs actually design the motors for 220V +15% - 10% and then label them 230V so they are OK with 208, because 208V is actually more common than 230V 3 phase.

 

[cadpoint]

Welcome to the Forum !

Seems like one possible thing to do is a Saturday shout down to look and inspect it and document all the services. Create a line diagram and all the wire sizes that supply power out to each device.

Some thoughts I have is the rate of materail removal or to say, "Multiply the depth of cut by the width of cut and the feed rate to find cubic inches per minute of material removed." It's a machining formula!

Another thing you can look at is the expense ratio of your cutting pieces, bits, tools used, verses production. IE are they burning up tools to get pieces out? If the Torque is not there from the motor then your cutting is taking longer... in Theroy ... the tools might not being worn out but the machine time is not matching the ratio of appliable production!

It's a simple ratio problem and something has to give in this one.

 

[pgotseff]

208

208

Just checked the shops. They are all supplied and run at 3 ph 208. Even though the machines are all nameplate "3ph 230V". Neither the machines or machinists have complained.
Interesting. It would seem 3ph 230/240 is an older voltage.

-pg