Fuses-motor-amps

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G

girl

Member
Location
far away
guys could you try this one:
i got a call that Air Supply Fan is down.
i found 2 burned fuses.

Here are data for motor and disconnect switch:
600 Volts
3 phase
14.3Amps

25 Amp fuses on the disconnect switch for that motor.

Could you please tell me are those fuses of proper amperage
for the motor?

***** one more thing: 2 fuses seem to be more hot than the 3rd one
 
G

girl

Member
Location
far away
buckofdurham ,

600 V is supply voltage to the motor.
i forgot HP but something is telling me
could it be 15HP, i will verify on Monday.
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Two things come to mind. Were any of the fuses non time-delay
and
when you say "warm", I think it's time to check for loose connections, loose clips, etc.
 
G

girl

Member
Location
far away
i see it but didn't your ancestors say; Amerika, Kanada:)

*****sorry i'll make sure it doesn't happen again, thank you for
letting me know.


back to fuses, when i was replacing them oh my my were they hot.



***** smart electricians yes electricians are very smart guys
and i hope one day i will meet right electrician to marry:)
that is my dream!
 
J

john m. caloggero

Senior Member
Hot Fuses

Hot Fuses

Hello GIRL, Based on the amperage and voltage, it appears that you might have a 15 HP motor. Based on the NEC Table 430.250, a 15 HP motor circuit and protection must be based on 17 amps for 575 V.

According to Table 430.52, the maximum TD Fuse permitted is 175 % of 17A or 300 % of 17A for nontime delay fuses. The maximum values allowed would be 30 amperes and 60 amperes respectively.
The size of the branch circuit conductors should be not less than No. 10 Cu or 8 AL.

It appears that the fuses are operating too close to their rating.
 
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G

girl

Member
Location
far away
mdshunk , i am not sure do i interpret the question properly and my
answer might be incorrect but if i understand your Q i am going to say a bit more about myself:

I am a 3rd year Electrical Engineering (female) student @ The University of Toronto and am doing my practical term in Hamilton, Ontario. i am specializing in High Voltage & Communications.

my practical term will end next week and my classes start Sept. 02, 2008.
i will be looking for job again in April 2009.

i am determined to get my Degree in Electrical Engineering and meet some reach electrician to marry and we open our own business.

pls wish me the best,

God Bless You!
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
john m. caloggero said:
Hello GIRL, Based on the amperage and voltage, it appears that you might have a 15 HP motor. Based on the NEC Table 430.250, a 15 HP motor circuit and protection must be based on 17 amps for 575 V.

According to Table 430.52, the maximum TD Fuse permitted is 175 % of 17A or 300 % of 17A for nontime delay fuses. The maximum values allowed would be 30 amperes and 60 amperes respectively.
The size of the branch circuit conductors should be not less than No. 10 Cu or 8 AL.

It appears that the fuses are operating too close to their rating.
Click to expand...

The code does not require that you use the "maximum" permitted fuse size. Some designers specify time delay fuses with a rating that permits them to serve as back up overload protection. With the correct type of fuse, a 25 amp fuse should be fine for this circuit. Also the code would not require #10 copper conductors for this circuit, no matter what size the branch circuit OPCD is. The condutor is only required to have an ampacity of 21.25 amps and a #12 has an ampacity of 25 amps even in the 60?C column.
 
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