Sizing of circuit Breaker& supply Cable Fire Pump

[TMMB]

Hi for all

I have 4 fire pumps rating 225KW for each , 3 pumps are working and one standby and there is jockey pump with rating 75KW

i need to know the follwing:

1- sizing of each pump feeder cable & circuit breaker
3- sizing of service transformer , its main circuit breaker and feeder size from transformer to main distribution panel

the distance between transformer and main panel is 50 meter and between main panel to each pump is 30 meter


Please advice how can sizing that

 

[Smart $]

Requires much more detail than what you have provided. Have you even read Article 695???

 

[TMMB]

YES, I have read it, and i tried for calculations as follow:

for fire pump conductor: must be not less than 125% of full load current, it mean
I full load = 225000/(1.732 x 380 x 0.8 x 0.95) = 450 A (PF:0.8 & Efeciency :95%)
then choose conducotr for each fire pump with ampacity not less than 1.25 X 450 A=562 A , 3Cx300mm2 CU/XLPE/PVC

for JOCKEY pump conductor: must be not less than 125% of full load current, it mean
I full load = 75000/(1.732 x 380 x 0.8 x 0.95) = 150 A (PF:0.8 & Efeciency :95%)
then choose conducotr for each fire pump with ampacity not less than 1.25 X 150 A=188 A , 3Cx95mm2 CU/XLPE/PVC

IS THAT CORRECT?

 

[Smart $]

YES, I have read it, and i tried for calculations as follow:

for fire pump conductor: must be not less than 125% of full load current, it mean
I full load = 225000/(1.732 x 380 x 0.8 x 0.95) = 450 A (PF:0.8 & Efeciency :95%)
then choose conducotr for each fire pump with ampacity not less than 1.25 X 450 A=562 A , 3Cx300mm2 CU/XLPE/PVC

for JOCKEY pump conductor: must be not less than 125% of full load current, it mean
I full load = 75000/(1.732 x 380 x 0.8 x 0.95) = 150 A (PF:0.8 & Efeciency :95%)
then choose conducotr for each fire pump with ampacity not less than 1.25 X 150 A=188 A , 3Cx95mm2 CU/XLPE/PVC

IS THAT CORRECT?

You are using "IEC" sizes and ratings. My brain is not currently equipped to verify your conductor sizing, but I don't see any derating. Are the sets run in separate conduits, no more than 3 per.

It appears you are extrapolating the data to align with NEC requirements. That part looks good to me (doesn't really mean much :huh.

What about voltage drop?

Where or is there a controller? If there is a controller, are these conductors between controller and pump motors, or service and controller, or...? Is there any accessory equipment supplied by these conductors? If so, you have to add 100% of that on to the pump motor load at 125%.

 

[TMMB]

derating already applied after choosing the cable , for ambient temp derating & raceway (not touched) and cables on cable trays

the calculated cables between source and controler

and according to NEC , transformer size = 1.25 (fire pumps full load currents + Jockey pump full load current)
= 1.25 (450 x 3 + 150)= 1875 A
Transformer KVA = 1.732 x 380 x 1875 / 1000 = 1234 KVA , the next nearst size : 1250 KVA


PLEASE ADVICE

 

[don_resqcapt19]

Note that for sizing the conductors to a single fire pump that you use 125% of the current as shown in Table 430.250 or one of the other tables in Article 430 if that does not apply to your pump motor. You do not size based on the motor nameplate.

 

[Smart $]

derating already applied after choosing the cable , for ambient temp derating & raceway (not touched) and cables on cable trays

the calculated cables between source and controler

and according to NEC , transformer size = 1.25 (fire pumps full load currents + Jockey pump full load current)
= 1.25 (450 x 3 + 150)= 1875 A
Transformer KVA = 1.732 x 380 x 1875 / 1000 = 1234 KVA , the next nearst size : 1250 KVA


PLEASE ADVICE

That's at a minimum. It'll take some calculation to encertain the chosen xfmr meets the voltage drop requirements...

695.7 Voltage Drop.
(A) Starting. The voltage at the fire pump controller line
terminals shall not drop more than 15 percent below normal
(controller-rated voltage) under motor starting conditions.

Exception: This limitation shall not apply for emergency
run mechanical starting. [20:9.4.2]

(B) Running. The voltage at the motor terminals shall not
drop more than 5 percent below the voltage rating of the
motor when the motor is operating at 115 percent of the fullload
current rating of the motor.

 

[Smart $]

Note that for sizing the conductors to a single fire pump that you use 125% of the current as shown in Table 430.250 or one of the other tables in Article 430 if that does not apply to your pump motor. You do not size based on the motor nameplate.

I don't believe he can use the Tables. His motors' operating voltage appears to be 380V.

 

[TMMB]

that is right, the operating voltage 380V does not appear in that tables, is the calculations correct? please advice

 

[T.M.Haja Sahib]

YES, I have read it, and i tried for calculations as follow:

for fire pump conductor: must be not less than 125% of full load current, it mean
I full load = 225000/(1.732 x 380 x 0.8 x 0.95) = 450 A (PF:0.8 & Efeciency :95%)
then choose conducotr for each fire pump with ampacity not less than 1.25 X 450 A=562 A , 3Cx300mm2 CU/XLPE/PVC

for JOCKEY pump conductor: must be not less than 125% of full load current, it mean
I full load = 75000/(1.732 x 380 x 0.8 x 0.95) = 150 A (PF:0.8 & Efeciency :95%)
then choose conducotr for each fire pump with ampacity not less than 1.25 X 150 A=188 A , 3Cx95mm2 CU/XLPE/PVC

IS THAT CORRECT?

The fire pumps should continue to operate till locked rotor condition. So I think a factor of 250% is better than 125% for sizing up the conductors to the pumps.

 

[dicklaxt]

The fire pumps should continue to operate till locked rotor condition. So I think a factor of 250% is better than 125% for sizing up the conductors to the pumps.

TM this was standard practice for engineering companies I worked for,I don't recall that it was 250% or not but was definitely oversized,,,,,,,I'm not sure that run til burn out is a factor to be considered in all situations,,,,,is it???

dick

 

[T.M.Haja Sahib]

I'm not sure that run til burn out is a factor to be considered in all situations,,,,,is it???

But even fire pumps should be provided with over current protection......

 

[don_resqcapt19]

But even fire pumps should be provided with over current protection......

Yes, but sized to carry the locked rotor current forever.

 

[T.M.Haja Sahib]

Yes, but sized to carry the locked rotor current forever.

But not the short circuit current.

 

[dicklaxt]

Thats probably true but by that time it's probably to late to worry about

 

[Smart $]

But not the short circuit current.

The calculation you quoted earlier was for conductor sizing.

The requirement to carry the locked-rotor currents indefinitely shall not apply to conductors or devices other than overcurrent devices in the fire pump motor circuit(s).

The conductors can be sized to handle greater than 125% of the pump motor's full-load current... 125% is the required minimum.