Underground Box

A

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
Anyone or familiar with underground boxes that have barriers? Is it uncommon or not practical to bring 120 and 277 into same box? I have light poles that the light is 277 and the receptacle is 120v.

Sorry..just reached out to my quazite guy and he said they do have barriers for them.
 
Alwayslearningelec said:
Because of the different voltages. Usually spec always says that 120/208 and 277/480v entering same box must have barrier. Obviously not a code thing??
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No they can occupy the same box without a barrier unless one is for emergency systems and the other is not. The neutral for each system would require a distinguishable type of identification like white for 120 volts and gray for 277 volts. They're both going in the same light pole which doesn't have a barrier?
 
infinity said:
No they can occupy the same box without a barrier unless one is for emergency systems and the other is not. The neutral for each system would require a distinguishable type of identification like white for 120 volts and gray for 277 volts. They're both going in the same light pole which doesn't have a barrier?
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yea so they want a separate conduit for the light pole light and the receptacle at the pole. So two conduits which is a bit ridiculous but no other way I guess.
 
So I need to run # 8's due to VD and the engineer confirmed this. I would not be able to terminate #8's on the receptacle correct? The junction box on the wall is where we are picking up the feed. Another contractor is running from panel to that foundation wall box. May a box where I peel off to the receptacles with #12?

1741035111875.png
 
That's where I get confused so why is it that at some point you can reduced the upsized wire down to say #12's to feed the load, in this case the receptacle? What dictates that " at this point" you can now go from #8's to #12? why is #12 all of a sudden ok when branching off.

Like this example below. We are picking up from the j-box on the wall from another subcontract who's binging the feed from a panel about 150-200' away. Can I just reduce at that box from #8's to #12'a and feed the receptacles?


1741035985665.png
 
Maybe I should put a box under each light pole. and run the lighting conduit and receptacle conduit to it??

Or maybe a box between the pole( purple dots) like below.

1741037053449.png
 
Alwayslearningelec said:
That's where I get confused so why is it that at some point you can reduced the upsized wire down to say #12's to feed the load, in this case the receptacle? What dictates that " at this point" you can now go from #8's to #12? why is #12 all of a sudden ok when branching off.
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Why are you upsizing in the first place? Voltage drop? Is #12 normally adequate for the load? If yes then if only concern is the voltage drop and to achieve a certain minimum VD then the ability to change back to the smaller conductor could be at any point the the voltage drop would no longer be effected. When you want to maintain a minimum voltage at a given amperage you could even start at a smaller size then go up to the larger one and reduce back down to land in a device.

Your scenario of a #12 assuming 15 or 20 A. Reducing to the #12 protected by appropriately sized OCP device could be done at any point that would no longer create excessive Voltage drop. Depending on your final amperage you need, Southwire app shows about 60ft of #12 without exceeding 3%VD and #8 could be 155ft for the same load requirement. Or a combination of both for lesser distance. but even if you're close the the max of #8 a few inches or ft won't make a significant difference.

I once needed 120V 8A at almost 1200ft out, A #2 can't be landed on a 15A breaker or receptacle so started with a #12 at breaker jumping to the #2 run the distance and drop back to the #12 about 5ft from the receptacle outlet. Final came back with only about 1.5 volts drop.
 
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