Inherited Job

[eds]

I have inherited a job that will be incorporating up to a 15kw system, largest allowed by our utility. There is a 320 meter socket with (2) 200 ge disconnects, disconnects are single breaker enclosure so no busbars, this is already installed. Meter pedestal is approx 200' away from barn, and 300' away from where we will likely enter the residence. Load calcs have not been done on the house, but I could foresee taking 300 amps to the residence, large residence, multiple dryers, the chance for a electric car or two. My initial plan was to send two feeders to the house ( local ahj has approved with placards posted at service location and house location). One of the 200 disconnects to feed the house and the other 200 to feed a 100 to the house and 100 to the barn, utilizing the outside feeder tap rules and terminating in 100 amp over-current devices at the appropriate structures. Solar panels will be mounted on barn roof and fed into the barn panel, 150 amp bus with 100 amp breaker, this would allow the solar company to feed with the max size of 80. Now to my sticking point, there is already a 200 breaker installed at remote meter pedestal, what rule would come into play since I have no busing in this enclosure, just the breaker lugs? Would I need to remove the 200 amp disconnect and install a 400 to give me the 80 amps for the solar?

 

[ggunn]

Now to my sticking point, there is already a 200 breaker installed at remote meter pedestal, what rule would come into play since I have no busing in this enclosure, just the breaker lugs? Would I need to remove the 200 amp disconnect and install a 400 to give me the 80 amps for the solar?

No.

 

[jaggedben]

I agree with ggunn.

The rules that come into play are:
- 705.12 (A) for the 200A breaker.
- 705.12 (D)(2)(1) for the feeder taps, but your downstream 100A breaker at the house panel has you covered.

2014 or 2017 code.

 

[eds]

2011

 

[shortcircuit2]

2011 was so long ago for me...but I think your feeder tap conductors need to be rated for the 280-amps...the 200-amp breaker at the pedestal and the 80-amp solar breaker. 705.12(D)(2)

 

[eds]

I would like to run down the rules of 705.12 and make sure I am applying them correctly: First 2011

705.12(D)(1) Feeder source will terminate in a 100 amp breaker and breaker hold down, solar source will terminate in a max 80 amp breaker no hold down required
705.12(d)(2) Busbar rating, using a 150 amp main lug panel with 100 amp back fed breaker== 150*120% =180-100=80
705.12(D)(5) Backfed breaker, this I will need to verify. Service disconnect is a 200 ge breaker that might have a line and load
705.12(D)(7) Since I am allowed to use the 100 amp breaker for all calculations on conductor and busbar size upstream from my barn / solar panel, the 2/0 al (sized for vd) and the 200 sevice disconnect would be okay

2014
705.12(D)(1) Dedicated overcurrent will be the 80 amp breaker in panel
705.12(D)(2)(1) Since my feeder stops at this panel and the solar breaker will be installed at this panel also this rule doesn't apply
705.12(D)(2)(2) This barn / solar panel is fed from the 200 amp remotely located service disconnecting means utilizing the outside tap rule and terminating in a 100 amp overcurrent device. I would be allowed to utilize a conductor rated for 100 amps

 

[jaggedben]

Under 2011 both of your outside taps could be subject to the 120 percent rule, requiring them to be rated 233 amps. Of the numerous AHJs I dealt with, only one or two enforced things this way. Best to ask your AHJ before pulling 2/0.

 

[eds]

Under 2011 both of your outside taps could be subject to the 120 percent rule, requiring them to be rated 233 amps. Of the numerous AHJs I dealt with, only one or two enforced things this way. Best to ask your AHJ before pulling 2/0.

What section was cited, and what calculation was used. Secondly, how would you approach terminating the 300kcmil on the 100 amp breaker, any wire reduction would violate the AHJ interpration

 

[shortcircuit2]

705.12(D)(7) Since I am allowed to use the 100 amp breaker for all calculations on conductor and busbar size upstream from my barn / solar panel, the 2/0 al (sized for vd) and the 200 sevice disconnect would be okay

2011 NEC section 705.12(D)(2) says use the sum of the amp rating of OC devices supplying power to the conductor. I see that as the 200-amp breaker at the pedestal and the 80 amp solar breaker.

 

[shortcircuit2]

JB came up with 233-amps. What size is your solar breaker?

 

[shortcircuit2]

It looks like your description of the job has no conduits and wire from the pedestal yet. Just run a separate conduit for the solar back to the pedestal and line side connect the solar.

 

[eds]

80 amp solar breaker, and there is already a 3'' conduit from meter pedestal to barn.

 

[jaggedben]

233 amps is (200+80) divided by 120 percent. 705.12 (D)(2) in the 2011 code applies the 120 percent limit to any busbar or conductor, not clearly exempting a feeder fed from opposite ends. In 2014 705.12(D) was extensively written and the 120 percent rule now applies only to panelboards. The 2011 version also does not explicitly address taps anywhere, which is a problem comparef to 2014 which invokes 240.21(B) and thus effectively legitimizes your outside tap conductors.

 

[shortcircuit2]

OK...got it. Thanks.

 

[eds]

Thanks for the info and help