# Overload Fuse Type / Class For Sb13 Lathe



## toolman_ar (Jul 8, 2016)

After converting the lathe motor from 440 to 220, I am now checking the fuses for proper size.

I have some confustion on the proper type and class I should use and need advice?

The disconnect on the South Bend 13 is not a motor starter. 
The motor is 1 hp, 3 phase, and has 3 fuses in place. The FLA is 3.2 at 60Hz, and 40c.

The fuse found in the disconnect is a Shawmut, time delay, renewable fuse, RF30, 30 amps, 250v, class H. The fuse is 2" x 9/16". 

This fuse size seems a bit large for this motor. If I use the basic 3.2 amps x 1.25 = 4 amps.

Can I order the same type fuse as found, class H, RF5 and replace the three RF30?

toolman_ar


----------



## JimDawson (Jul 8, 2016)

Normally you want to fuse for the wire size.  If you are feeding with 14ga, then a 15 amp fuse would be correct.   The heaters protect the motor and should be sized correctly.


----------



## toolman_ar (Jul 8, 2016)

Jim,
There is not a motor starter.

Just a disconnect. 

Inside the disconnect are these time delay fuses.

Inside the disconnect are the Frankinstine blade type connectors. 

Power comes in from RPC, to the disconnect, through the fuses. So I guess there is no motor overload protection.

toolman_ar


----------



## JimDawson (Jul 8, 2016)

Oh.  In that case I guess I would try the 5 amp fuses and maybe have some 7.5 amp on hand just in case.


----------



## toolman_ar (Jul 8, 2016)

Eventually the RPC will feed a fuse pannel.

And a proper size breaker will be placed for each machine.

Today I just want to spin this up to see what works or... Does not work.

I will order up some 5's and 7's.

Thank you.

toolman_ar


----------



## talvare (Jul 8, 2016)

Typically when there is no overload protection provided you would want to size your fuses at about 1.25 to 1.5 x FLA and use time delay fuses to prevent  nuisance tripping. Motors typically draw 3 to 5 times FLA on start-up.

Ted


----------



## mksj (Jul 8, 2016)

Motor calculators recommend 6-10 amps depending on the type of fuse at 240V, smaller fuses tend to be high A, larger fuses lower A. The FLA from these tables (1 Hp) is higher than your motor. In a class H fuse at 240V I would use a dual element 6 or 8 amp, same as previously recommended, but have not seen a 7 or 7.5A class H fuse.


----------



## toolman_ar (Jul 9, 2016)

Thank you for the responses.

I have some 5 amp fuses on the way, but might be Monday before I can test the machine.  

If the 5 amp fuses don't survive, I will go with the dual elemen type, 6 to 10 amp.

toolman_ar


----------



## toolman_ar (Jul 23, 2016)

As perdicted the 5 amp fuses did not survive.

I have some 10 amp, dual element fuses on the way.

But I was able to get the lathe to run. Ran very quiet! Only thing I heard was click, clikc, click...

Thank you all for your help.  I have more testing to do once the correct fuses are installed. And lots of cleaning to do.


toolman_ar


----------

