Breaker sizing

[hhsting]

I have jockey pump controller service rated fed from fire pump circuit which is taped ahead of main service disconnect.

The jockey pump is 3/4 hp, 2.5FLA and 27.4A LRC.

The engineer has sized the fuse inside the jockey pump based on LRC and says he is providing the fuse. The fuse size is 30A.

My concern is based on NEC 2017 Section 695 info note jockey pump install need to comply with 430.

So would the jockey pump service rated fuse of 30A oversized or it is acceptable to size it based on LRC? Also would not jockey pump need overload protection?

 

[don_resqcapt19]

While the supply has to be able to supply the locked rotor current of the fire pump and the jockey pump, and the full load currents of any other associated equipment, the jockey pump is installed in accordance with Article 430. What is the voltage and phase rating of the jockey pump, as that does not match up with Table 430.250? You are required to use the table values for sizing the branch circuit short-circuit and ground-fault protective device. Assuming that it is a 3 phase 230 volt motor, the table full load current is 3.2 amps and the maximum time delay fuse permitted would be 6 amps and the maximum one time fuse permitted would be 10 amps. If it was a thermal magnetic breaker, the maximum permitted would be 15 amps.

 

[hhsting]

While the supply has to be able to supply the locked rotor current of the fire pump and the jockey pump, and the full load currents of any other associated equipment, the jockey pump is installed in accordance with Article 430. What is the voltage and phase rating of the jockey pump, as that does not match up with Table 430.250? You are required to use the table values for sizing the branch circuit short-circuit and ground-fault protective device. Assuming that it is a 3 phase 230 volt motor, the table full load current is 3.2 amps and the maximum time delay fuse permitted would be 6 amps and the maximum one time fuse permitted would be 10 amps. If it was a thermal magnetic breaker, the maximum permitted would be 15 amps.

Its 208V three phase. How did you get 6 a or 10 a? 1.50 or 1.75 of full load does not get those?

How can one even fit 10amps fuse in jockey pump service rated controller?

 

[don_resqcapt19]

time delay fuse 3.2 x 1.75 = 5.6 and 6 is a standard size in 240.6
onetime fuse 3.2 x 2 =9.6 and 10 is a standard size

Remember you are required to use the full load currents as found in the code and not on the nameplate for the size of the conductors and branch circuit OCPD...the nameplate value is only used for overload protection.

If the controller fits a 30 amp fuse, it will fit those sizes.. 0-30 are the same physical size.

 

[hhsting]

time delay fuse 3.2 x 1.75 = 5.6 and 6 is a standard size in 240.6
onetime fuse 3.2 x 2 =9.6 and 10 is a standard size

Remember you are required to use the full load currents as found in the code and not on the nameplate for the size of the conductors and branch circuit OCPD...the nameplate value is only used for overload protection.

If the controller fits a 30 amp fuse, it will fit those sizes.. 0-30 are the same physical size.

I dont see one time fuse and x2 in NEC 2017 Table 430.52?

 

[augie47]

Possibly a typo.. the non-time delay should be times 3
Pretty obvious in the Table.
Now that you clarified it's 208, 3/4hp (assuming 3 phase) 3.5 x 3 for nontime delay = 10.5 = 15 amp fuse.

 

[don_resqcapt19]

Possibly a typo.. the non-time delay should be times 3
Pretty obvious in the Table.
Now that you clarified it's 208, 3/4hp (assuming 3 phase) 3.5 x 3 for nontime delay = 10.5 = 15 amp fuse.

Yes, typo..the math shows 3x.

However I did use the 230 volt current of 3.2 amps.
Using a time delay fuse, the maximum size would be 10 and and a nontime delay would be 10 amps as you said.