Conductor sizing 375 foot run

[ActionDave]

So #4's for each hot, (1) #4 for the neutral and (1) #4 for the ECG. Correct.

Yes. Since 20A requires a 12AWG for hot and EGC as you go up in size each conductor goes up to the same size.

 

[Smart $]

So #4's for each hot, a #4 for the neutral and a #4 for the ECG. Correct. Cb on separate phases. I'm not sure but I think both gate openers will operate together. I sized the #4 for starting amps for each motor. Now that I digest this I should size the conductors for running amps at 8.5 each reducing my wire size to #6's.

With both openers operating at same time, #6 for hots, #12 (or any size larger) for neutral, #6 for EGC...

 

[GoldDigger]

With both openers operating at same time, #6 for hots, #12 (or any size larger) for neutral, #6 for EGC...

:thumbsup: The voltage drop calculation will be based on one wire running the distance, not two.

 

[Smart $]

:thumbsup: The voltage drop calculation will be based on one wire running the distance, not two.

...or two wires at twice the voltage.

 

[Smart $]

Another option...

PS: Using direct burial cable would probably save even more on cost.

 

[augie47]

So #4's for each hot, (1) #4 for the neutral and (1) #4 for the ECG. Correct.

That's what I would do and not play the "what if" or "balanced load" game. I would bet there is a decent chance that somewhere along the line, 120v loads will be added (receptacles for tools, lighting, etc). With you (4) #4s you are pretty much covered for most eventualities.

 

[ActionDave]

That's what I would do and not play the "what if" or "balanced load" game. I would bet there is a decent chance that somewhere along the line, 120v loads will be added (receptacles for tools, lighting, etc). With you (4) #4s you are pretty much covered for most eventualities.

High five from me to you augie. Simple is elegant.

 

[American Mike]

Voltage Drop Calculation

Voltage Drop Calculation

2 x K x D x I divided by CM= VD (Single Phase)

 

[bob]

Someone must save us form this absurd code requirement. If the op chooses to put a 60 amp breaker on the feeder, then his proposal as submitted would be correct according to 250.122(B). Just because he uses a 20 amp he must use #4 egc.

 

[GoldDigger]

Someone must save us form this absurd code requirement. If the op chooses to put a 60 amp breaker on the feeder, then his proposal as submitted would be correct according to 250.122(B). Just because he uses a 20 amp he must use #4 egc.

OK, so table 250.122 ( 250.122(A)) allows #10 for this situation. I still do not see a problem with the general requirement, just because it has an apparently paradoxical result in the special case you cite.

 

[bob]

My on going complaint is that there is no scientific reason for the up sizing. If a #10 is good for a 60 amp breaker with #4 cu, why
isn't #10 ok for #4 cu on a 20 amp breaker. There is not engineering reason for the generalized rule. On very long circuit runs
it may be necessary to increase the EGC to reduce the touch potential at the fault. However, there is no reason to make the
size increase mandatory in every case. This paradox occurs many times when upsizing for VD.

GD, Your comment was " I still do not see a problem with the general requirement, just because it has an apparently paradoxical result in the special case you cite. ".
Can you give a more detail explaination of what you mean.

 

[GoldDigger]

Can you give a more detail explaination of what you mean.

Sure.
The rule on proportional upsizing was a very easy rule to write and I think that in a large number of circumstances it will not end up requiring a larger EGC than the table would specify given that you simply put in a bigger breaker.
The table does not linearly scale the EGC size with the circuit amperage and perhaps more importantly the problem it is intended to address deals with the voltage divider effect and the resulting touch potential in the specific case that the hot conductor is larger than the wire size corresponding to the breaker size.

(Not a very coherent statement, sorry, I am listening to the MH streaming video at the moment....)

 

[Smart $]

Sure.
The rule on proportional upsizing was a very easy rule to write and I think that in a large number of circumstances it will not end up requiring a larger EGC than the table would specify given that you simply put in a bigger breaker.
The table does not linearly scale the EGC size with the circuit amperage and perhaps more importantly the problem it is intended to address deals with the voltage divider effect and the resulting touch potential in the specific case that the hot conductor is larger than the wire size corresponding to the breaker size.

IMO, should be removed and the leftmost column heading of Table 250.122 be modified to read:

Circuit Rating?
Not Exceeding
(Amperes)

Then add the footnote:

?Greater of the following:
(a) rating or setting of the overcurrent device in circuit ahead of equipment, conduit, etc.
(b) ampacity of the ungrounded conductors where 800 amperes or less

 

[GoldDigger]

Works for me. But make sure it is clear that it is the ampacity before corrections and adjustments.

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[Smart $]

Works for me. But make sure it is clear that it is the ampacity before corrections and adjustments.

I think I edited after you posted, but pretty much the same meaning.

Why ampacity before???

 

[GoldDigger]

I think I edited after you posted, but pretty much the same meaning.

Why ampacity before???

Because if you enter the table using derated ampacity it would tell you to use a smaller EGC for the same ungrounded conductor if the conditions are harsh.
That seems wrong to me.

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[Smart $]

Because if you enter the table using derated ampacity it would tell you to use a smaller EGC for the same ungrounded conductor if the conditions are harsh.
That seems wrong to me.

But it is debatable whether using a larger size to compensate for adjustments and corrections is actually "increased in size".... and the conditions of use are not all that likely to change if the OCP rating is increased at a later date.

I also believe the conditional footnote would not permit a smaller EGC than "normal"... but please elaborate if you feel I am in error.

 

[GoldDigger]

And I am taking the view that if the size is increased for derating reasons or for voltage drop reasons the EGC size should end up the same.
The EGC will not be subject to the kind of long term overload that derating addresses and so does not need to be upsized for those reasons but should not be made smaller for the same reasons. Just my opinion.

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[Little Bill]

That's what I would do and not play the "what if" or "balanced load" game. I would bet there is a decent chance that somewhere along the line, 120v loads will be added (receptacles for tools, lighting, etc). With you (4) #4s you are pretty much covered for most eventualities.

I agree, just do the simple thing, but I'm not understanding how/why anyone would be adding anything to the OPs circuit if it already is for a designated purpose... the gate openers.

That is unless he is running the circuit to a panel at the gate, which he did not state that.
I was thinking he probably was just running to the required disconnect(s) for the motors that open/close the gates. Especially since he stated MWBC for the motors.

 

[Smart $]

And I am taking the view that if the size is increased for derating reasons or for voltage drop reasons the EGC size should end up the same.
The EGC will not be subject to the kind of long term overload that derating addresses and so does not need to be upsized for those reasons but should not be made smaller for the same reasons. Just my opinion.

I understand... not saying my proposal is an all-satisfying approach, but rather a compromise. It would save having to upsize the EGC proportionately with the ungrounded conductor based on cmil. Instead it would just be upsized to otherwise normal EGC size using a higher rated ocpd.

For example, for a 20A circuit using #4 Cu to compensate for voltage drop, no derating, 75?C terminations, you could use a #8 EGC, opposed to a #4 EGC as it is currently required. This way, the EGC would still be compliant if the ocpd were upsized.