[doremodel]

I have a new air compressor for my hot rod fabrication. The specifications are as follows,
5.5hp 80gal 24amp 240v. My question is, it calls for a 30 amp breaker and time delay fuse, Type "T". I am running 6/2 wire to supply the unit, it is about 90 ft from the main panel so we ran 6/2 for minimal voltage drop and heat distribution. Do I use 30 amp 125v fuses for each leg, or do I need 30 amp 250 fuses for each leg ? Also any recommendations for type "T" fuses at this rating as well as a disconnect box to house the fuses. Need to start grinding! Any info will be GREATLY APPRECIATED. Thanks

[tkrussell]

Where are you located?
Why Class T fuses?
Also you state circuit breaker and fuse. Either or is required.
Where is the unit made?

If located in the US, motors need to be protected by a time delay device due to starting current per Table 430.52 of the NEC 2002 edition, since 5.5 HP is not listed in the code, a fuse can be 175% of nameplate running current, and a breaker can be 250 % higher.

Since the voltage is 240 volt, then Class T fuses are not required, as they are rated for 600 volts. Fuses generally come rated 250 & 600 volt, so Class RK1 should be fine, which is very common.

However, a circuit breaker will be fine also, and only will need a non fused switch at the unit for a service disconnect. And no need to have spare fuses on hand.

So a 5.5 HP motor drawing 24 amps at 240 volts can use a circuit breaker no larger than 60 Amps. If you are certain to use fuses, then a maximum of 50 amp fuse will work. Do not put too small a fuse, I would not use a 30 amp device to protect 24 amps of motor load,since the starting current of 150 to 300 % may cause the fuse/breaker to trip often,esp if the unit starts/stops often.

Oh and good choice on the cable size for the right reasons

[doremodel]

Thank you for your response. Very informative, helped me greatly. One more question, what is the difference between Rk-1 and Rk-5 fuses? Thanks again

[tkrussell]

The Class of fuse is a designation deterimned by Underwriters Laboratories.

The difference between RK1 & RK5 has to do with the time to clear and the maximim peak current let through of each Class.