# tech info

Hi, I need a little bit of info about the wire sizing for upgrading a 10 hp motor to a 15 hp motor. The present system uses a 30 amp protective circuit. The 15 hp motor is rated @ 23.7 max amp. The wiring is 8 gauge. Please tell if a direct swap in motors is likely. nb the voltage is 3 phase 460 volts.
Hope for a speedy response........... Musty
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musty wrote:

Unless very high startup current, sounds fine for the wiring itself. Will need to get starter "heaters" sized for the new motor, probably, though.
Is wiring copper or aluminum? How long a run?
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Insufficient data. <grin>
Starting with your locale. (I'll assume U.S.A.)
Then, if there are _any_ related loads on the same circuit -- e.g. control logic for the piece of equipment involved.
Then, there is a matter of the length of the run from the panel to the motor. 'Long' runs require increasing the wire size.
Now, making a _lot_ of assumptions --
If the equipment is permanently wired (as distinct from plugged in), you are limited, by NEC, to 80% of the rated capacity of the circuit protector.
That's maximum 24A load on a 30A protector. If there's mor-or-less _anything else_ on the circuit -- including control logic -- you're likely to be over the limit.
There's also an open question of the _starting_ draw by the motor. Start-up current draw can be *much* higher than running load. Protective devices need to accomodate _that_ load for the (relatiely short) start-up intervval.
Now, on reasonably short runs, _10_ga_ is sufficent for 30A; with 8 ga. you _could_ -- *UNLESS* the run-length necessitates 'up-sizing' the wire -- go to a (say) 35A (or 40A) protector, which would give some headroom.
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musty wrote: > Hi, > I need a little bit of info about the wire sizing for upgrading a > 10 hp motor to a 15 hp motor. The present system uses a 30 amp > protective circuit. The 15 hp motor is rated @ 23.7 max amp. The wiring > is 8 gauge. Please tell if a direct swap in motors is likely. nb the > voltage is 3 phase 460 volts.
The #8 wire is OK, the 30A protective device is not.
You need a 40A protective device.
If the protective device is a fuse, then you will have to change to a 60A fuse block to accept the 40A fuse.
If the protective device is a c'bkr, then you will have to change the c'bkr.
You will also have to change the motor starter from a NEMA size 1 to a NEMA size 2 complete with the proper overload heaters.
Lew
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