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
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
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
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
> 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
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.
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