Voltage drop calculator

[JerrodGlover]

I keep reading that 2-2-2-4 Mobilhome feeder is the way to go for power to my new shop. I ran a calculator to check my work and I keep coming up with needing 2/0-2/0-1-4. My run is 150' and plan 90 amps to run a mill, lathe and welding equipment.

Am I over thinking this or do I need to step up my wire size?

2-2-2-4 is only good for about 100' of run?

 

[klassenl]

I get #1 or 1/0 aluminum. Still quite large.

Are you sure you need 90 amps. The advice usually given is if it's a one man shop you won't run more than one machine at a time so you kind of calculate to your single heaviest load. Even so it may not save you all that much money.

 

[ard]

http://www.southwire.com/support/voltage-drop-calculator.htm

1/0 Al for 100A at 150 ft.

Recommendations here tend to be colored by many factors..... not just technical. I often hear "its cheap, will save you dollars and who needs 100A anyway?" May all be true, but IMO people can make their own decisions on how much current they need AND how thrifty they need to be. Run the numbers, price the wire...decide

 

[wyliesdiesels]

I do the math manually.

Not hard. I can give u the formula if u want it.

At full 90a load, u will have about 8.62volts voltage drop or 3.6% at the subpanel. Then depending on length of branch circuit wire voltage drop may go beyond the recommended 5%.

So the question is will u ever hit 90a. Doubtful

If u want to keep VD below 3% then go with #1 AL.

 

[wyliesdiesels]

http://www.southwire.com/support/voltage-drop-calculator.htm

1/0 Al for 100A at 150 ft.

Recommendations here tend to be colored by many factors..... not just technical. I often here "its cheap, will save you dollars and who needs 100A anyway?" May all be true, but IMO people can make their own decisions on how much current they need AND how thrifty they need to be. Run the numbers, price the wire...decide

1/0 is way overkill.

I think southwire uses 60* c ratings.

 

[theoldwizard1]

My run is 150' and plan 90 amps to run a mill, lathe and welding equipment.

... but IMO people can make their own decisions on how much current they need AND how thrifty they need to be. Run the numbers, price the wire...decide.

I agree with ard but will add, how many of those are likely to be running SIMULTANEOUSLY ?

Add in a compressor and I will bet you are under 60A (except for start up). You could throw in a lift and a mini-split heat pump and stay below 60A if you are careful not to run more than 1 or 2 at the same time. (Turn off the compressor while welding.)

 

[sberry]

You don't have to turn off the comp. Just don't weld if its running. But I really don't do the math every time I run one of these. A bigger wire wont hurt if its practical but I have done a couple dozen and never had a trip on a 60. Number 2 works great at 150 ft and a breaker HOM is under 10$

 

[sberry]

Recommendations here tend to be colored by many factors..... not just technical. I often here "its cheap, will save you dollars and who needs 100A anyway?" May all be true, but IMO people can make their own decisions on how much current they need AND how thrifty they need to be. Run the numbers, price the wire...decide.

This is the point, they do not know how to calculate load, they cannot determine how much current they need, they are not electricians and do not have decades of experience with dozens of these installations.

 

[ard]

I think southwire uses 60* c ratings.

Just FYI- ...from southwire's calc:

**Note to User:All ampacity values are taken from the Section of 310-15 of the NEC. The conductor characteristics are taken from Table 9 of the NEC. The calculations used to determine the recommended conductor sizes for branch circuits are based on 60°C ampacity ratings for circuits rated 100 amps or less or marked for use with #14 AWG - #1 AWG. Circuits rated over 100 amps or marked for conductors larger than #1 AWG are determined using 75°C ampacity ratings.

 

[manwithtools]

I do the math manually.

Not hard. I can give u the formula if u want it.

At full 90a load, u will have about 8.62volts voltage drop or 3.6% at the subpanel. Then depending on length of branch circuit wire voltage drop may go beyond the recommended 5%.

So the question is will u ever hit 90a. Doubtful

If u want to keep VD below 3% then go with #1 AL.

Why do the math manually today? Are you trying to keep your math skills alive and well? Even if you are doing the math manually, you still need an Ampaciy chart, unless you have it memorized along with all the derating factors....

I'd suggest an app for your phone such as (Electrical Wiring Pro) EWP 2014. Take a look, it's very capable and no need to lug an Ugly's or the NEC around.

 

[wyliesdiesels]

Just FYI- ...from southwire's calc:

Notice the first half of that note?

**Note to User:All ampacity values are taken from the Section of 310-15 of the NEC. The conductor characteristics are taken from Table 9 of the NEC. The calculations used to determine the recommended conductor sizes for branch circuits are based on 60°C ampacity ratings for circuits rated 100 amps or less or marked for use with #14 AWG - #1 AWG. Circuits rated over 100 amps or marked for conductors larger than #1 AWG are determined using 75°C ampacity ratings.

They are basing that off of their misinterpretation of NEC code 110.14c that says u have to use 60* c rating IF under 100a missing the second part of that which allows higher ampacity rating IF the temperature rating of all the termination points is known.

So yeah if the circuit is less than 100a, Southwire calculator will spit out a wire size larger than what 310.15b16 allows.

Why do the math manually today? Are you trying to keep your math skills alive and well? Even if you are doing the math manually, you still need an Ampaciy chart, unless you have it memorized along with all the derating factors....

I'd suggest an app for your phone such as (Electrical Wiring Pro) EWP 2014. Take a look, it's very capable and no need to lug an Ugly's or the NEC around.

I like to stay fresh on my math skills yes, but i have memorized much of the common ampacities and I do have 310.15b16 along with derate chart saved on my phone for quick references.

I do lug ugly's around but rarely use it and one should ALWAYS carry around a copy of NEC which i do most of the time. No telling when someone may question u or the code. Always good to be able to pull it out when needed. Like all the other equipment in our trucks, it is a tool.

Thank you for the app reference. I will check it out.

 

[manwithtools]

I have most of those memorized as well, at least below 1000 amps. I have the benefit of working in our shop everyday and the code book and the internet are but a few steps away....

I still like EWP 2014 when I"m on the floor as it's a quick way to answer a question.

 

[wyliesdiesels]

I have most of those memorized as well, at least below 1000 amps. I have the benefit of working in our shop everyday and the code book and the internet are but a few steps away....

I still like EWP 2014 when I"m on the floor as it's a quick way to answer a question.

i downloaded both paid pro versions as well as the free Lite version on my iPhone. looks like the $3 will be well worth it based on the reviews.

Thanks

 

[manwithtools]

Glad to hear that. Hope you like it. I paid the $3 and didn't look back.