When doing the volt drop calculation, be sure to correct for
temperature, per the note after table 8, chapter 9 of the NEC. The table
values default at 167 deg F (75 C). An underground cable will be
operating closer to earth temperature. When I run volt drop for a 4/0
copper cable at 60 deg F, I'm seeing that you could go over 60 amps and
maintain a volt drop of 3%.
Not sure what the requirements for the building are, but that exceeds
most of my off grid systems. 60+ amps at a final voltage of 232 v is
almost 14kW. Is there air conditioning? What are the calculated loads
for this building? Is the inspector actually calling this a problem?
I would do a proof of concept: turn every light on in the place, along
with some typical appliances (hair dryer, microwave) hit a circular saw
to really make the point, with a DMM plugged in. I found long ago that
actual measured volt drop was not as bad as Chapter 9 first predicts.
Ray Walters
Remote Solar
303 505-8760
On 4/18/20 3:41 PM, Darryl Thayer wrote:
Hi Mac, There are a few questions like is it Al or Cu wire, What makes
it unusable?
for Voltage drop, I use Vd=2KIL/CMA for your case the unknown is the
current. The installation of an inverter with grid support. Many
inverters have this, you want a multimode inverter such as a
Schneider, Outback, SolArk and I could name at least 4 more. A normal
house will run on 30 amps. So assume 30 amps,
Vd=2x21.6x30x1100/211600 =6.7 volts
So if the main house is at 240 Volts the remote house is at 233
Volts. The multimode inverter could be set at grid support beyond 30
Amps. For higher house loads the inverter can support up to 30 to 50
amps additional. (SolArk is 50 amp) I would add a balancing
transformer at the end of the line to make the 120 loads balance. (an
Autotransformer) such that 120 volts loads are balanced and the load
is shared between 240-Volt conductors. Based on my customers'
experiences I would use AGM LA batteries, as I expect low usage of the
battery and quick recharge, but that is the customer's choice. I had
one customer that had 10 years on the float-AGM battery set.
On Fri, Apr 17, 2020 at 8:15 AM Mac Lewis <[email protected]
<mailto:[email protected]>> wrote:
Hi wrenches,
I've got a architect client with a sub-optimal power situation on
one of the projects he is working on. I'm running through a
couple of scenarios that may work. Its a ADU (accessory dwelling
unit) that is about 1100' from power. The farmer had taken it
upon himself to bury some 4/0 a few years ago to run power out
there. Voltage drop is the big issue and its not going to pass
the AHJ inspection. We could just ditch the grid and go off-grid,
but it seems like a shame to not tap into the grid resource.
Instead of dealing with the voltage drop, I was thinking it may
make sense to rectify that low AC voltage input and parallel a
smallish battery bank (size is yet to be determined), then use an
off-grid inverter to serve the loads at good voltage.
I am looking for feedback on this concept. What do you think?
Also, are there any recommendations for good quality rectifiers
with wide input voltage window?
Thanks in advance for your help
--
Mac Lewis
*
"Yo solo sé que no sé nada." -Sócrates
*
_______________________________________________
List sponsored by Redwood Alliance
List Address: [email protected]
<mailto:[email protected]>
Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive:
http://www.mail-archive.com/[email protected]/maillist.html
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
<http://www.re-wrenches.org/etiquette.htm>
Check out or update participant bios:
www.members.re-wrenches.org <http://www.members.re-wrenches.org>
_______________________________________________
List sponsored by Redwood Alliance
List Address: [email protected]
Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive:
http://www.mail-archive.com/[email protected]/maillist.html
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out or update participant bios:
www.members.re-wrenches.org
_______________________________________________
List sponsored by Redwood Alliance
List Address: [email protected]
Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive:
http://www.mail-archive.com/[email protected]/maillist.html
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out or update participant bios:
www.members.re-wrenches.org
