[RE-wrenches] Rectifier
Ray
ray at solarray.com
Tue Apr 21 10:57:42 EDT 2020
I also don't understand requiring 100 amps for an auxillary dwelling.
230.79 requires a minimum service of 100 amps for a single family
dwelling, but that is a service requirement, not a requirement for a
feeder to another building. Even 230.79(D) says all other buildings
only require a 60 amp service. I think we'd all like to know where
the AHJ is getting these requirements. Is it local amendments that were
added, or is it just a possible misinterpretation?
I suggest possibly reviewing with the AHJ the article 100 definitions of
Service (connection to the Utility) and Feeder. Article 230 covers
Services and does Not apply to feeders. The ADU would only need 100
amps if it had its own service meter.
Ray Walters
Remote Solar
303 505-8760
On 4/21/20 10:05 AM, drake.chamberlin at redwoodalliance.org wrote:
>
> The voltage drop recommendations in the code are actually not
> requirements, but recommendations. Some locations make them
> requirements, but if the AHJ is following the NEC without amendment,
> the 2% and 3% recommended drops are only recommendations.
>
> ---
>
>
> On 2020-04-20 10:56, Mac Lewis wrote:
>
>> This is an example of where some code requirements bump up against
>> logic. I believe the AC voltage will be quite usable at the
>> site, just not for code requirements of the AHJ, and it may get
>> pretty low during high usage times. They make the electrician size
>> it for 100A minimum for an ADU, even though the loads are pretty
>> minimal, and then require <5% VD from the main service entrance.
>> That is the requirement for the certificate of occupancy.
>> Luckily, off-grid buildings don't have these requirements at all.
>> I'm going to size it as an off-grid and probably tie it in at some
>> point in the future.
>> Thanks for the input.
>>
>> On Sun, Apr 19, 2020 at 10:20 AM
>> <drake.chamberlin at redwoodalliance.org
>> <mailto:drake.chamberlin at redwoodalliance.org>> wrote:
>>
>> We had a similar situation, and are now feeding a battery bank
>> with a pair of 48 V Iota chargers. Iota can run on very low
>> voltages. We have one Iota on each leg of the the 120/240 split
>> phase to balance the load. It works.
>>
>> ---
>>
>>
>> On 2020-04-18 21:25, Ray wrote:
>>
>> 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
>> <maclewis1 at gmail.com <mailto:maclewis1 at gmail.com>> 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
>>
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>> --
>> Mac Lewis
>>
>> "Yo solo sé que no sé nada." -Sócrates
>>
>>
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