Cable Size

[Carultch]

Note the south wire "commercial mode" calculator allows power factor to be entered and defaults to .9

Even when I enter a power factor of 1, I get significantly larger voltage drop results with Southwire's tool, than I get with Chapter 9 Table 9 data.

You can start with a power factor of 1 at the source, but it will deviate from a perfect 1, due to the fact that the impedance of the wire isn't pure resistance only. I'm inferring that Southwire is likely considering this effect, which increases the amount of vector voltage difference, above what the difference between voltage magnitudes alone would be.

 

[Alwayslearningelec]

Yes the total load is the same per post #16, 79.52 amps. You stated no more than 5% VD, 208*5%=10.4 volts maximum for both sections of the run combined.

Yes the total load is the same per post #16, 79.52 amps. You stated no more than 5% VD, 208*5%=10.4 volts maximum for both sections of the run combined.

Why would the total run be allowed to have 10v voltage drop if the max we are only allowed is 5%? I know its because of the splice but I don't get the logic.

 

[retirede]

Why would the total run be allowed to have 10v voltage drop if the max we are only allowed is 5%? I know it’s because of the splice but I don't get the logic.

Because math. 10 is less than 5% of 208.

 

[ScipioAfricanus]

Interesting, in the SouthWire APP, I get 3/0 @ 478 ft. with a VD of 4.95% on Al conductors. Assuming I have the correct information from some of the posts. It is a bit confusing. It could be my lack of familiarity with 3-phase systems.

He did say at one time that the run is single phase @ 240 Volts, so I assume his transformer feeding the load is a 240 Delta four wire?

That might cause quite an imbalance in the system.

I might suggest doing a load calculation on the neutral wire for this set of feeders, also. Might be able to save a little on the wire size there.

Andy.

 

[infinity]

He did say at one time that the run is single phase @ 240 Volts, so I assume his transformer feeding the load is a 240 Delta four wire?

Actually he stated that the feeder is 1Ø, 208 volts. Nothing in post #16 suggests that the panel is 3Ø.

 

[Seven-Delta-FortyOne]

Interesting, in the SouthWire APP, I get 3/0 @ 478 ft. with a VD of 4.95% on Al conductors. Assuming I have the correct information from some of the posts. It is a bit confusing. It could be my lack of familiarity with 3-phase systems.

He did say at one time that the run is single phase @ 240 Volts, so I assume his transformer feeding the load is a 240 Delta four wire?

That might cause quite an imbalance in the system.

I might suggest doing a load calculation on the neutral wire for this set of feeders, also. Might be able to save a little on the wire size there.

Andy.

He said it’s 208 single phase.

He’s pulling two legs from a 3 phase wye.

 

[Alwayslearningelec]

So again...if info alm the VD calcs and I'm allowed to run 3/0 and 1/0 but the breaker at the main panel feeding the load is 100A I still need 100a SER cable?

 

[infinity]

So again...if info alm the VD calcs and I'm allowed to run 3/0 and 1/0 but the breaker at the main panel feeding the load is 100A I still need 100a SER cable?

If the OCPD is 100 amps then the minimum size SE cable would need to be rated for 100 amps or more. For aluminum that would be #1 AWG.

 

[Alwayslearningelec]

Yes the total load is the same per post #16, 79.52 amps. You stated no more than 5% VD, 208*5%=10.4 volts maximum for both sections of the run combined.

Understood but why does doing a VD calc for 2 sections of the same run change things from doing a VD calc for one continuous run? Because the results ARE different.

 

[infinity]

Understood but why does doing a VD calc for 2 sections of the same run change things from doing a VD calc for one continuous run? Because the results ARE different.

According to what you've stated there is a junction box because there are two sections of the run that have different size conductors. At 5% the maximum VD for the entire feeder is 10.4 volts. For example if section 1 of the run is 4 volts VD then section 2 cannot be more than 6.4 volts.

 

[retirede]

Understood but why does doing a VD calc for 2 sections of the same run change things from doing a VD calc for one continuous run? Because the results ARE different.

I mentioned this in another one of your threads - learn Kirchoff’s laws. This is another case what it would have enhanced your understanding of the situation.