Help w/ sizing motor disco fuses

Status
Not open for further replies.
S

SiddMartin

Senior Member
Location
PA
Motor:

RPM- 1725
HP- 3
Volts- 200 - 3 Phase
Amps -10.3
1.15- Serv factor
Cont. duty
Code H


I have a SQ-D disconnect w/ built in motor starter. My question is sizing the fuses to put in the disco. and also the breaker.

All of the motor starter guts are already installed, I just need to put in the 3 fuses where the line goes in.

Can someone help w/ the calc's , I do not have a lot of motor exp. at all :roll:

thanks
 
Fuse sizing

Fuse sizing

I assume by "200V" you mean a 240V 3-phase you're getting from a center tapped delta transformer. Using a fused disconnect, i think a 30A/3p fuse would be proper for this unit.
 
SiddMartin said:
Motor:

RPM- 1725
HP- 3
Volts- 200 - 3 Phase
Amps -10.3
1.15- Serv factor
Cont. duty
Code H


I have a SQ-D disconnect w/ built in motor starter. My question is sizing the fuses to put in the disco. and also the breaker.

All of the motor starter guts are already installed, I just need to put in the 3 fuses where the line goes in.

Can someone help w/ the calc's , I do not have a lot of motor exp. at all :roll:

thanks
Click to expand...

Are the fuses for overload protection or branch circuit short circuit/ ground fault protection?

Also keep in mind that the nameplate amperage should only be used for overload protection sizing. When sizing branch circuit conductors and branch circuit short circuit/ground fault protection the full load current listed in the Tables in Part XIV should be used.

Table 430.250 lists the full load current value of a 200 volt rated 3 phase 3 HP motor at 11 amps.

Chris
 
We would also need to know which type of fuses you planned on using, time delay or fast blow. Time delay up to 175% FLA, fast blow up to 300% FLA
 
thank you all for the help,

to clarify, I plan on usin Time delay fuses. How do you determine if they protect the motor (overload) or the circuit? I would think that they are protecting the circuit b/c it is before the starter.

and I got the 200 V from the motor itself. I am supplying 208V 3 phase
 
If your starter is providing overload protection, the the fuses are normally sized to provide short-circuit/ground fault protection for the circuit
 
The best infromation on motors is the Bussman Circuit Protection Handbook. Its a must have.
Also Sd D makes a motor data slide chart, you just dial it in.
But Bussman makes fuses and SQ d makes CBs.

If the OLs are set at 115% then I like to size the fuses for backup at 125%, for your motor probably 15amp TD, the branch ckt CB could be 20, 25 or 30 amps.
Don't get hung up on the size conductor, 12 AWG is OK on 30 amp CB
 
Status
Not open for further replies.
Top