Allowable Voltage Drop

[mcclary's electrical]

It may be wrong, but I was taught that as a general rule that you need only worry about VD for 120v at 150 ft and 240v at 300 ft. Single phase only.

Use those numbers in the calc. And see how they compare to the 3 & 5 % rules

 

[Jim W in Tampa]

If mostly AC as load i would not worry as most units are 208,240 so a bit low should not hurt any.

 

[jumper]

Use those numbers in the calc. And see how they compare to the 3 & 5 % rules

This is a feeder right? 5%? Correct?

 

[Jim W in Tampa]

One word of caution, the AHJ just might want to see updated engeneering as to this change. Very costly if this hits a problem after conduit and wire

 

[mcclary's electrical]

One word of caution, the AHJ just might want to see updated engeneering as to this change. Very costly if this hits a problem after conduit and wire

In VA, this is not a job that would require an engineers stamp. A master could do this load calc.

 

[mcclary's electrical]

This is a feeder right? 5%? Correct?

3% for feeders OR branch circuit SEPERATELY,,,,,,, and 5% for feeder + branch circuit TOGETHER

 

[weressl]

The only one that can truly provide enough info to make that determination is the POCO... because it all depends on what voltage they will be supplying you with, actual based on your calculated load... not the nominal... you already know that.

In summary, if you don't know what you are starting with, how can you plan for voltage drop % and stay above nominal tolerance.

Correct.

Upper and lower limits of acceptable voltage to be delivered by the Utilities or Service Company at the service point is defined based on ANSI Standard and enforced by the rules of the regulating authority of the State or area.

Brownouts are also allowed by the PUC or Public Utility Commission(in this State), that will allow the power distributor to lower the voltage even further. During that period you may be outside of the ANSI limit of +15/-10% acceptable voltage tolerance of the individual equipment. Accordingly you can't log performance complaints to the equipment manufacturer, although the equipment may still work, just not to well or even trips/self protects.

 

[weressl]

Suppose I have
Generator
1- Main Distribution Panel (MDP)
2-Panel Board
3-Equipment

From Generator to Main Distribution panel for feeder voltage drop is 0.5%
From Main Distribution panel to panel board ( which is located in building) for feeder is 2.2% drop
From panel Board to equipment ( which is branch ) is 2%

Now,
The total voltage drop for feeder becomes 2.7%
The total voltage drop for branch becomes 2%

The total voltage drop for branch + feeder becomes 4.7%

Now any comment?

Yes, there is. You STILL have not defined the VOLTAGE in numerical values. You need to define the voltage, the specific ANSI limit parameters and so on.

A generator maybe outside of the discussion since the ASNI limitations are only applicable to generating facilities under (de)regulatory control.

 

[Jim W in Tampa]

It is not the POCO problem if the voltage drop is on the lines you installed from transformer secondary. This is where either the electrician or engineer needs to do the math. Problem begins when we start adding loads without knowing what the new load will do to voltage drop. If we see 2 panels with 200 amp mains we can not assume that if fully loaded that we ok.
As in the OP case you have a somewhat easy load calculation for the public side of building. As to what equipment is in the prep room i do not know.

 

[raberding]

voltage drop

voltage drop

Beware that some jurisdictions - Los Angeles, for example - have local amendments that restrict VD to 3% on feeders

 

[Hameedulla-Ekhlas]

Yes, there is. You STILL have not defined the VOLTAGE in numerical values. You need to define the voltage, the specific ANSI limit parameters and so on.

A generator maybe outside of the discussion since the ASNI limitations are only applicable to generating facilities under (de)regulatory control.

oh, I see
do you want to know the voltage in numberical value
very good question.
three phase voltage is 380 volt
one phase voltage is 220 volt

Is that what you need?
by the way, one more question NEC states that 5% voltage drop is reasonable operation. This is for 208 3Ph and 120 1Ph

how about the 380 3Ph and 220 1Ph percentage amount changes as voltage changes.

 

[weressl]

oh, I see
do you want to know the voltage in numberical value
very good question.
three phase voltage is 380 volt
one phase voltage is 220 volt

Is that what you need?
by the way, one more question NEC states that 5% voltage drop is reasonable operation. This is for 208 3Ph and 120 1Ph

how about the 380 3Ph and 220 1Ph percentage amount changes as voltage changes.

380/220V System is not an ANSI standard value so the ANSI rules are not applicable.

Look at the Red Book(141) for voltage values and acceptable tolerances to define what is an acceptable range at each pojnt of the distribution system. That will define nominal and utilization values.

Another point I was trying to lead you to is that you have to define the voltage value for each segment. From Utility delivery point to the utilization point you need to use the same voltage. Eg. from the generator to the panel you use (probably) 400V and calculate 2% that will give you 392V at the panel. From the panel to the utilization point you have to use the 400V again NOT the 392V to calculate the 2.7% and that will give you 381.2V that is still above the motors nominal voltage.