ECN Forum Forums Code Related Discussion NEC & other Code issues motors

I have a client that moved a bunch of equipment from one shop to another. at this new shop we have 208/120, dont know what the old shops voltage was, but all his motors nameplates voltage are marked 230 volts. can I hook these up to 208 voltage without fear of shortening its motor life?

Thanks,
H2o

Oui [Yes]

You can as long the nameplate stated 208-240 volts yeah it will work but if the motours are rated at 240 volts only some can run on 208 volts but expect to reduce the performace { check the Service Factour rating }

Otherwise B/B transfomer will cure the issue

And check the current drawage on the motours to make sure they are still at the nameplate rated especally if run on 208 volts it may cause some issues with it.

Merci,Marc

Thanks French,
I only saw one name plate with 208-240 listed the rest were all 230/460. So amperage will go up at lower voltage, how shall I calculate my branch circuits? Based on nameplate at 230V*125%? or should I use HP and use Table 430.150 at 208V?

Thanks,
H20

OK, back to 'motor basics' time.

To size your wire, go by the tables in the NEC (430.250 or thereabouts), using the value closest to the actual voltage. For example, the chart might say 16 amps, while the motor is marked 12 amps; size the wire for 16 amps.

To size your breakers and heaters, start with the nameplate FLA, then measure your actual needs, and adjust from there.

For example ... in the nameplate says 12FLA, Start with 20 amp breakers (175% of 12)and size the heaters for 16 amps (140% of 12).

Now, run the motor as intended, and measure. Also see if there are operation problems. It's very possible, in this example, that you'll have to increase the breaker to 25 amps, yet be able reduce the heaters to 10 amps. It's all a matter of starting current, and actual load.

One cannot over-state the importance of the nameplate! I recently came across an installation where the NEC tables said 6.6 amps - yet the motors were marked 10 amps! This is a rare case of the motor maker under-stating the size of his motors. Simply saying "they're 1-1/2 hp motors" isn't enough .... look for the nameplate!

430.6 Tables must be used for amperage of motors Except as per exceptions 1-2-3.
3 phase 208 volt see table 430.250.
Wire size for Mtr. 430.22 amp. off motor table times 125 %.
Breakers or fuses see 430.52 . then 250.52 table.
Overloads 430.32(A)
Everything (except) overloads on most motors calculated from code book (not) nameplate as per 430.6.