Voltage Drop for Generator Shore Power

[twlinddsley]

I am designing a feeder from an empty MCC bucket to an internal 37.5kVA, 480V, 1 Phase transformer in a generator enclosure approximately 800' away. I want to verify if I need to follow the 3% or 5% voltage drop rule in NEC 215.2(A)(1)b IN 2? I am interpreting this as a feeder and branch circuit and can use the 5% for voltage drop...is this correct?

 

[Dennis Alwon]

Informational notes are not a code requirement. Although it is a good idea to prevent VD the NEC only requires us to be concerned about VD when it comes to fire pumps. It may be req. elsewhere but I am not certain.

 

[twlinddsley]

Voltage Drop for Generator Shore Power

Dennis,

Thanks for the reply, and I reposted today before I saw your response.

Just so I understand, the Voltage Drop requirements in the NEC only apply to Fire Pumps...or did I misunderstand you?

 

[charlie b]

There is no limit for voltage drop. It is only addressed in informational notes that are not enforceable. However, it is generally understood that VD should be no more than 3% along feeders, and a total of 5% along the combination of the feeder and branch circuit conductors. So it seems to me that you are describing the situation backwards.

In your installation, can you take credit for voltage taps on the transformer to improve the delivered voltage?

Welcome to the forum.

 

[Dennis Alwon]

The following is for fire pumps but I believe that is the only place that the NEC requires us to follow that rule. The other is guidelines in informational notes which are not enforceable

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 load terminals of the fire
pump controller shall not drop more than 5 percent below
the voltage rating of the motor connected to those terminals
when the motor is operating at 115 percent of the full-load
current rating of the motor.

 

[Dennis Alwon]

I closed the duplicate thread and moved Charlie's post here

 

[fmtjfw]

Sensitive Electrical Equipment

Sensitive Electrical Equipment

also 647.4(D)

 

[Dennis Alwon]

also 647.4(D)

Thanks, I thought there might be another place in the NEC but I could not come up with it. Needless to say it does not affect the OP..

 

[GoldDigger]

For fire pumps, does "the voltage rating of the motor" refer to the NEMA nominal voltage, the bottom end of the voltage range, or something else?
Note also that this rule only specifies the actual final voltage, which is dependent on the incoming service or generator voltage and not a voltage drop (either absolute or percentage).

 

[twlinddsley]

There is no limit for voltage drop. It is only addressed in informational notes that are not enforceable. However, it is generally understood that VD should be no more than 3% along feeders, and a total of 5% along the combination of the feeder and branch circuit conductors. So it seems to me that you are describing the situation backwards.

In your installation, can you take credit for voltage taps on the transformer to improve the delivered voltage?

Welcome to the forum.

I didn't think about the possibility of adjusting the transformer taps, but will definitely look into that. Thanks for the interpretations and suggestions, it has help me determine the next steps.