Yet another sub-panel wire question / Pulling questions (dual feed)

[dcg9381]

Well, now that the shop is up, gotta power up a house.

My property has a 320 amp feed - to get this, you need to build a panel "bank" to their specifications, as shown..

The panels are Eaton and take BR type breakers. Largest BR breakers are 125A - BR2125. I need to use one of these main panels to feed 2 "sub-panels" at another structure. It's 277' of hard-trench (rock saw needed) to the residence that I'm powering up.


Why am I doing dual feed?
1) Limitations of the Eaton panel
2) I'm going to do an ATS/genset that only covers one panel.

If absolutely necessary, I could replace the Eaton panel - would need a recommendation.


Specs:

• 36" deep x 6" Trench cut by rock saw
• 2 x 2" PVC electrical conduit
• Circuit length: 277'
• Breaker: 2 x BR2125 (Eaton) (accepts #4-2/0 AWG Cu/Al)

I was going to ask "which wire" - the cost of ~500' of copper is prohibitive, even if would allow more amps in the future.

Is it easier to pull SER, individual XHHW-2, or bulk XHHW-2? At this time, I can split the pulls.

• XHHW-2 (copper) - (2/0,2/0,2/0,1) $10.08/ft
• SER (copper) 2/0,2/0,2/0 & #1 - $12.37 / ft
• XHHW-2 (aluminum) - (3/0,3/0,3/0,1/0) $3.14/ft
• SER (aluminum) 3/0,3/0,3/0 & 1/0 - $2.98 / ft

It looks like all of this will fit in 2" Sch 40 conduit.

 

[wyliesdiesels]

Already a problem with your plan.

You CANNOT have more than one feed to a detached structure.

And SER is NOT permitted under ground.

 

[Terry D]

Are you talking about dual feeding the 2 125 amp sub panels. You could just have a 200 amp disconnect outside feeding a 200 amp subpanel to the other structure, and feed a 125 sub off of that. You cannot put a SER cable in conduit. And you can see the cost difference between copper and aluminum. There is nothing wrong with the aluminum. And there is nothing wrong with copper, just cost a lot more. It took me a long time to switch to aluminum, but to be competitive with other contractors, I had to. As far as more amps in the future, the wire size of each conductor, depending on copper of aluminum, is only rated for so many amps. You have to run a larger size of aluminum to get the same amps of copper. I would defiantly consider a few pull boxes for that long of pull, and factor in voltage drops.

 

[pattenp]

….. You cannot put a SER cable in conduit.

SER can be put in conduit, just not below grade.

 

[dcg9381]

You CANNOT have more than one feed to a detached structure.

I hear you. I believe there are two exceptions for this, but would like your opinion.

Exception for grouped disconnects:
While 230.70(A) (comment) requires a service disconnecting means, the term “disconnecting means” is defined in Article 100 and addresses not only a single means, but also multiple means that serve together in a group arrangement as the building service disconnect.....

Section 230.71(A) (paraphrase)
... It can be up to six switches or circuit breakers in a single enclosure or up to six switches or circuit breakers in separate enclosures....

Exception for enhanced reliability, IE ATS/generator:
Additional outside supplies feeders or branch circuits shall comply with 230.2(A). be permitted to supply the following:
225.30(A)6
Systems designed for connection to multiple sources of supply for the purpose of enhanced reliability

SER can be put in conduit, just not below grade.

And SER is NOT permitted under ground.

Thanks, guys. I saw that SER was "wet rated" at 90C - I assume that was OK in conduit, guess not. Can I use SEU? Or is MHF is the only option for PVC conduit? I won't do direct burial here...

 

[dcg9381]

You could just have a 200 amp disconnect outside feeding a 200 amp subpanel to the other structure, and feed a 125 sub off of that.

I think you're talking about replacing one of my panels with a 200A disconnect, correct?

 

[mm08822]

at 277' the wire sizes you've chosen are way too small.

You would need 250kcmil for less than 3% vd for 125a load. Sure it can be argued you'll never see 125a, but the loads aren't known. It's cheaper to do it right the first time.

I would go up 2 wire sizes at that distance without a second thought.


As for 2 feeds, it's still n.g. even if you start another thread.

See if a 200a service is sufficient for your house. If so connect a sub-panel to the main panel. Put a transfer sw in between.

 

[wyliesdiesels]

I hear you. I believe there are two exceptions for this, but would like your opinion.


Thanks, guys. I saw that SER was "wet rated" at 90C - I assume that was OK in conduit, guess not. Can I use SEU? Or is MHF is the only option for PVC conduit? I won't do direct burial here...

Those exceptions dont apply here.

Any service entrance cable is NOT permitted UNDERGROUND. Doesnt matter if its in conduit or not.

You have 2 options- MHF direct buried or in conduit or individual conductors such as AL XHHW in conduit.

 

[brewchief]

How about a 200 amp feed through panel? Has 6 or 8 spots for breakers to feed the seperate buildings and feed through lugs to provide 200 amps to the house.

I wouldn't think twice about replacing the BR panels, one electrician on this board calls them zinsco two or something along those lines, they are not the best quality.

Sent from my SM-G965U using Tapatalk

 

[dcg9381]

Those exceptions dont apply here.

Can you tell me why? Not arguing, request education.

You have 2 options- MHF direct buried or in conduit or individual conductors such as AL XHHW in conduit.

Thank you.

 

[dcg9381]

at 277' the wire sizes you've chosen are way too small.

Thanks. I'm re-calculating. I used the calculator below:

Other calculators say this goes to 4/0 AL or 2/0 copper...

 

[Bert_]

Can you tell me why? Not arguing, request education.



Thank you.

You are allowed one feeder. That one feeder can have up to six disconnects at the building. The only exception that allows more than one feeder is for different voltage or phase.

 

[dcg9381]

Thanks. In that event, I'm going to need to convert the existing panel to something that can supply 200A.

Southwire says 277' is 250 kcmil copper or 500 kcmil aluminum for 200A. 500 kcmil 4 conductors will go through 3" SCH 40 PVC.



Panel:
Everything out there is Eaton, one option is an ECB200RB which seems to be about $300. Up for other options if you guys really don't like Eaton...


Wire Costs:

Copper Cost:
250 MCM Copper (3) + 2 AWG ground = $13.14/ft

AL Cost:
500 MCM AL (3) + 1/0 ground = $6.59/ft

 

[mm08822]

You will need to check the wire size range that the lugs can handle at both ends of the feeder.

The disconnect you listed above is only 250mcm and many 200a dist panels stop at 300mcm. It's easier to buy panels/disconnects that fit the size wire instead of adding extra hardware to get around size mismatch.

The southwire vd app uses conductor resistance at 75C. Southwires app does not adjust resistance based upon direct bury, conduit or free air (even though you get buttons to push!).
The Paige app uses conductor resistance at 53C. This is closer to your situation because you will be in the ground.

You really need a load calc performed. Assuming that results in less than 200a service requirement, I would pull 250mcm. Worst case 300mcm.

 

[dcg9381]

You will need to check the wire size range that the lugs can handle at both ends of the feeder. The disconnect you listed above is only 250mcm and many 200a dist panels stop at 300mcm. It's easier to buy panels/disconnects that fit the size wire instead of adding extra hardware to get around size mismatch.

Thank you. I guess I have to look at the breaker in the catalog to determine allowed wire connection size. I also note that the connectors are rated at 60C or 75C - wire and amp charts go to 90C.

The Paige app uses conductor resistance at 53C. This is closer to your situation because you will be in the ground.

Thanks. I didn't catch that difference in the fine print. Paige app indicates 4/0 copper or 300MCM Aluminum for 200A. At 180 amp, 250MCM (AL), 277'

XHHW-2 3x(300mcm) + 4/0 AL = 5.72/ft (200+ A)
XHHW-2 3x(250mcm) + 3/0 AL = 4.30/ft (180 A)

You really need a load calc performed. Assuming that results in less than 200a service requirement, I would pull 250mcm. Worst case 300mcm.

100-110 amps is the result.

So look for a service disconnect that will support 250/300 mcm AL, 200A, confirm that sub-panel at the residence can handle this conductor size.

Edit: looks like the ECB200RB was replaced with ECCVH200R panel will only support 2.5" knock-outs, which limits to 250mcm.




mm08822, thank you for the detailed help.

 

[wyliesdiesels]

Instead of using wire size calcs, which can and do have errors, I like to do the calcs by hand. Its a lot quicker than searching for a calculator and inputting the numbers.

When i get a chance ill post up the formulas

 

[dcg9381]

Talked to the electrician who told me to run 3" conduit - he said that many municipalities now require it as default...