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Robbob2112 Answer thread

Fuses, DIsconnects, and breakers on PV lines

Under the 2023 National Electrical Code (NEC), specific requirements exist for the installation and use of photovoltaic (PV) system components such as isolators, fuses, and circuit breakers. Here's a detailed explanation:

### PV Isolator (Disconnects)

A PV isolator, or disconnect switch, is used to safely isolate the PV system for maintenance, emergencies, or other purposes. Key points regarding PV isolators in the NEC 2023 include:

1. **Location Requirements (690.13)**:
- A disconnecting means must be installed for all PV system circuits.
- The disconnect must be located in a readily accessible location and clearly labeled.
- If the disconnect is outside the building, it should be within sight and within 10 feet of the PV system or clearly visible.

2. **Functionality (690.15)**:
- The isolator must be able to open all current-carrying conductors simultaneously.
- It must be rated for the voltage and current requirements of the PV system.
- Must have a visible break or indication of open status.

3. **Marking and Identification (690.14)**:
- Isolators must be permanently marked with their purpose.
- Appropriate signage must indicate the presence and function of the disconnect.

### Fuses

Fuses in PV systems protect against overcurrent conditions, preventing damage to the conductors and components. NEC 2023 stipulates:

1. **Overcurrent Protection (690.9)**:
- Each source circuit, output circuit, and battery circuit must have overcurrent protection.
- Fuses must be rated for the voltage and current expected in the circuit.
- They must be suitable for use in DC circuits if used on the DC side of the system.

2. **Location and Accessibility (690.16)**:
- Fuses must be placed in locations that are accessible for replacement.
- If located in combiners or similar enclosures, the enclosure must be listed for the application.

3. **Temperature Rating (690.8)**:
- Overcurrent protection devices must be rated for the highest temperature they will encounter in service.

### PV Circuit Breakers

Circuit breakers serve a similar overcurrent protection function as fuses but can be reset. NEC 2023 requirements include:

1. **Suitability for PV Systems (690.9)**:
- Circuit breakers must be listed and labeled for the application, including DC ratings if used on the DC side.
- Must have appropriate voltage and current ratings for the PV circuits they protect.

2. **Series and Parallel Applications (690.8)**:
- When used in series or parallel configurations, breakers must handle the combined voltage and current characteristics of the system.

3. **Accessibility and Maintenance (690.15)**:
- Circuit breakers should be installed in readily accessible locations for maintenance and reset.

### Specific Situations

1. **DC to DC Converters (690.71)**:
- Isolators, fuses, and breakers are also required for DC to DC converters, with similar requirements as for other PV system components.

2. **Rapid Shutdown (690.12)**:
- PV systems on buildings must have a rapid shutdown function for the array, which often involves isolators and disconnects to de-energize the system quickly.
 
Attaching the battery negative to ground

Words from Tim
T

Post in thread 'Off Grid Cabin Design - Grounding Question'

In a mobile system (RV, camper, boat) the negative battery is bonded to the vehicle frame. The reason for this is because the vehicle starting system is already done this way. And the two systems (starting and house) are usually connected together at some point.

For a stationary system, it's better to keep the DC system isolated from ground.
So that ground detection devices can function properly.
Only ground the enclosures, frames, racking (exposed metal parts).

Victron is big in the mobile market. And I assume that this is why they still show DC bonding in their diagrams.
  • Like

Other research
robbob2112

Post in thread 'Off Grid Cabin Design - Grounding Question'

@timselectric , can you swing by and provide an answer

A little research -

### Quoting NEC 250.162
>250.162 Direct-Current Circuits.
>
> (A) Two-Wire, Direct-Current Systems. One conductor of a two-wire, direct-current system shall be grounded. Exception: A system equipped with a ground detector and supplying only industrial equipment in limited areas shall not be required to be grounded.
>
> (B) Three-Wire, Direct-Current Systems. The neutral conductor of a three-wire, direct-current system shall be grounded."

### Why It Is Common Practice to Not Ground the Negative Wire of a...
  • Like

T

Post in thread '24V off-grid system - theoretical and practical questions around NG bonding, grounding and earthing.'

GeeGee said:
Hi Tim,

Quick question ---> if the inverter doesn't have a connection between AC and DC, are you still against grounding DC negative to the same ground system as used by AC?
Click to expand...
The inverter itself is a connection between the DC and AC.
  • Like
 
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robbob2112 said:
#3 - My CPAP backup unit

Use this at your own risk just as an idea

This is my cpap backup. Add in a MPPT and a couple of panels for solar charging.

Have to figure the panel count to go from 20% to 100% in 4 hours sun. 4 x 200watt would probably do it.

Fits in a sewing box.

Total probably come in around $1100, basic box is $500

Downside, it will never grow beyond a small system.

I have a Resmed Aircurve 10 ASV unit - when using with heated humidifier and heated hose it consumes 250ish watt hours in 10 hours. With those turned off it consumes around 70wh.

So I have basically 4 nights of use without a recharge, maybe 3 depending.

I have the 20amp LiTime charger plugged into a wall timer so it recharges the battery each day starting around noon. I could also plug a MPPT and some solar panels into the charger plug and recharge that way.

The inverter is not needed for the build - but I have it in case we have a power outage - it will run my full sized fridge for 15hours.
Click to expand...
I don't really understand why you need all that for that Aircurve 10 cpap. I have one. With a cheap 12v adapter you can run it off a 12v @ 100a battery directly without wasting wattage through an inverter.

On the otherhand, if you need to be prepared for a long grid failure and need to be able to reharge it, then a 4 panel solar charger would be good, along with a bigger battery bank and inverter for 120vac. A suitcase generator is good too.

As a DYI type guy, I ran down how to replace the blower motor. The replacement blower motor is about $100 on Alibaba. There are youtubes on the replacement proceedure.
 
I built it because it was cool... thinking about adding racing stripes to the case. 😎

But seriously, it can be trimmed down to the individual user's needs. At the simplest just a battery, fuse, charger, and 12v adapter. I did the connection for the inverter because we frequently have 4+ hour outages. I sized it because both me and the wife need oxygen at night and the portable concentrator draws 270w. The inverter is only to be hooked up if I need to run the fridge. We have around 3 to 4 outages a year, most several hours but at least one is 12+ hours.

And if we camp it serves as a power bank for charging stuff plus my cpap. At 25lbs it is portable.

And I wouldn't hesitate to take apart the machine and clean or replace parts if needed.
 
I don't understand, the image of the components and wiring fell out, just the box pictures were left.
 
robbob2112 said:
I built it because it was cool... thinking about adding racing stripes to the case. 😎

But seriously, it can be trimmed down to the individual user's needs. At the simplest just a battery, fuse, charger, and 12v adapter. I did the connection for the inverter because we frequently have 4+ hour outages. I sized it because both me and the wife need oxygen at night and the portable concentrator draws 270w. The inverter is only to be hooked up if I need to run the fridge. We have around 3 to 4 outages a year, most several hours but at least one is 12+ hours.

And if we camp it serves as a power bank for charging stuff plus my cpap. At 25lbs it is portable.

And I wouldn't hesitate to take apart the machine and clean or replace parts if needed.
Click to expand...
We are on the same page.

I am dependent on power wheelchairs for mobility, and I need to use a cpap.
Hurricane season for the East coast is stalled. It is incubating and will probably start to manifest with a vengence in about a month.

Hence, if you look at my profile you will see the same sort of threads as yours; gathering the best recipe and materials to put together my own emergency solar battery charger.

Flex panels are great, weighing about 5lbs each., they are easy to manage and easy to store. Ideal for my purposes. I wouldn't expect long life with them in a permanent outdoor installation. Maybe 5 years? But I don't need that. I can pull them out of the closet, string them out on a clothesline. and plug ithem into the MPPT that is already plugged into a 24v battery bank.
I then can disconnect and fold it all up and throw it in the closet for the next disaster.

Four 130w Eco-Worthy panels (2S2P) -> Victron 100 30 configred for 24v.
... and then there is the emergency 2kw suitcase generator as a failsafe.

-----

With respect to the Aircurve,

Personally, I am on a fixed income and can't afford the medicare copay for the outrageous prices of durable medical goods.
Our healthcare system is a farce.
So, necessity being a mother I make do with what I have for as long as I can.

So, I replaced the blower motor on mine myself. Not hard.
The trick is finding the replacement blower motor - its a Chinese part that will be found on Alibaba.
Several vendors all selling the same oem part at different prices - around $95 ballpark last I looked.
Its good to know you have that option.

It is a good investment to get a spare blower motor and put it away for the day you need it.
With the world turmoil, who knows if the US and China get into conflict over Tiawan and break trade agreements.
You might need a spare.
 
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Actually amazon has those blower motors for about $120... I am about a year into mine, they provide a new one every 5 years at which point I'll replace this motor and have a spare machine. There are also several places that will overhaul, repair, calibrate, and replace the motor for around $300.

I assume you frequent either or both of these.. lots of good things on them..I am on both under the same username

Apnea Board Forum - CPAP | Sleep Apnea

World's largest and most helpful CPAP and Sleep Apnea forum. Advice, setup manuals, OSCAR software. Make pressure changes and adjustments safely, tips on treatment
www.apneaboard.com www.apneaboard.com

CPAP and Sleep Apnea Message Board | CPAPtalk.com

Get feedback on real CPAP issues from real CPAP users. We have years of feedback on all topics related to Sleep Apnea, including product reviews and the latest releases. Find all the CPAP information you need here.
www.cpaptalk.com
 
robbob2112 said:
Hooking multiple batteries in parallel and where on the bus bar to place the uplink cables.
diysolarforum.com

Calculation of parallel string battery currents

Hi, everybody! I'm a retired EE. I didn't want my EE skills to fade away after retirment, so I exercise them when I can. Whenever I see a non-trivial circuit analysis problem on one of various forums I frequent, I challenge myself to solve it. Recently I watched Will's video about current...
diysolarforum.com diysolarforum.com
Click to expand...

I moved that thread to the General Battery Discussion and pinned it. Make sure your link still works.

robbob2112 said:
You may NEVER exceed the voltage of your MPPT
Click to expand...

It's picky, but I would phrase that as "Never exceed the Maximum PV Input Voltage". "Voltage" by itself could of course refer to the battery voltage or the PV voltage, neither of which should be exceeded. But that warning is usually used in the context of PV input.

I use MidwestSteelSupply for my copper bar as well as some aluminum. I have a local aluminum-only yard that is awesome. It's like a treasure hunt every time I go there.

Otherwise, good summary thread.
 
robbob2112 said:
Actually amazon has those blower motors for about $120... I am about a year into mine, they provide a new one every 5 years at which point I'll replace this motor and have a spare machine. There are also several places that will overhaul, repair, calibrate, and replace the motor for around $300.

I assume you frequent either or both of these.. lots of good things on them..I am on both under the same username

Apnea Board Forum - CPAP | Sleep Apnea

World's largest and most helpful CPAP and Sleep Apnea forum. Advice, setup manuals, OSCAR software. Make pressure changes and adjustments safely, tips on treatment
www.apneaboard.com www.apneaboard.com

CPAP and Sleep Apnea Message Board | CPAPtalk.com

Get feedback on real CPAP issues from real CPAP users. We have years of feedback on all topics related to Sleep Apnea, including product reviews and the latest releases. Find all the CPAP information you need here.
www.cpaptalk.com
Click to expand...
Hmmm. I guess it has been over a year or so since I looked. At that time it wasn't offered anywhere but Alibaba.
Who knew?
 
Paralleling Batteries to bus bars - A practical example without the math



Only parallel the same chemistry, impedance of batteries, BMS rated amps .... to mix different brands you need a YR1035 meter to measure the impedance round trip to the bus bars and adjust the cable length if it is a good bit off, or the position on the bus bar if it is only a bit off.
A bit of a tedious process to get it totally correct.

  • measure the impedance of all batteries and record
  • I would figure my longest round trip and make a set of cables - record impedance per inch
  • measure the impedence of each cable while not connected
  • Bolt empty lug to each bar
  • bolt batteries to the bar one at a time with the set of cables and record.
  • clip the YR-1035 meter to the empty lugs and measure impedance of the round trip through each battery + cables.
Now comes time to figure
Arrange the batteries in order by impedance and connect your cables to the one with the lowest
Make each new set of cables and match total impedance for each battery/cable set by shortening the new ones according to what you measure, if you make a mistake and undershoot rather than remaking the cable just use on the next battery in line

Once you have everything as close as you can get arrange the batteries on the bus bars so the positives start at one end a bus bar, then the negatives start at the other end of the other busbar. Figure where you need to position the cables to the inverter in the line by probing the bus bar with the YR-1035 starting at the same ends until you get the same reading when you switch positions.

These 12 stud bus bars are ideal for this project because you can move the batteries around and get more or less space between them.
signaturesolar.com

600A 12 Stud Busbars | Red & Black Kit

Manage high-current electrical connections efficiently with the 600A 12 Stud Busbars in a Red & Black Kit, ensuring organized and reliable power distribution in your electrical setup.
signaturesolar.com signaturesolar.com

This explains all the math behind it - the above example is doing the same basic thing, but just by probing around with a meter.
S

Thread 'Calculation of parallel string battery currents'

Hi, everybody! I'm a retired EE. I didn't want my EE skills to fade away after retirment, so I exercise them when I can. Whenever I see a non-trivial circuit analysis problem on one of various forums I frequent, I challenge myself to solve it. Recently I watched Will's video about current sharing in a parallel battery string, and it occurred to me that the string is just a circuit. It could be solved using standard circuit analysis techniques giving theoretical values for the battery currents. I wondered if this has been done before and posted on the web. I found a link on this forum...
  • Like

The YR-1035 is an impedance meter that measures using a 1kHz square wave signal verse just a DC reference voltage and a voltage divider like a typical ohm meter.


Was asked this question
"Why would it matter what the impedance is in parallel setup? Would it really matter if one battery gets used a little more than others with LiFePO4 chemistry? In lead-acid chemistry this definitely would matter but I don't see why it would be that critical for LiFePO4 as long as the batteries are of sufficient size."

my answer

If you just run between 20% and 80% doesn't matter much at all.

Same reason we connect cables on parallel batteries in a Z configuration. If you don't you will end up charging and discharging the end with the inverter cables more. With 3 batteries and a Z connect it is still in balance. When you hit 4 batteries the inverter cables go in between battery 1&2 on the positive and 3&4 on the negative. With more than that you can read the link on parralleling more than that. It gets complicated, but if I remember he goes as high as 5 batteries.

With 6 or more batteries it makes sense to either group then in set or 3 or 4 and then uplinking those to another set of bus bars and so on depending on the number of batteries sets of batteries.

This is one of those cases where reality doesn't match what we were all taught about electronics - in electronics the runs on the board are all short enough parallel is equal at all points. This does get wonky a bit as frequency goes up and you have to make the traces wider or deeper and make the runs all curve nice verse squared off corners.

Another example will be with main electrical panel bus bars - if you add a breaker for an AC coupled inverter you put it at the opposite ends of the panel. The AC from the inverter will feed all the loads along the way so no point on the bus bar has more current than it is supposed to. Where if the breaker from the inverter is right next to the main in a 200amp panel you could pull 200amps from the grid and 40amps from the inverter all flowing down to a heavy load. When at the bottom of the panel you will have 200amps from one end and 40 amps from the other and the only place where it is overcurrent is right at the load.

NOTE - the last is a hypothetical example from something @Hedges was discussing in a different thread a few days ago.


On other example would be if you want to parallel a string of 4 x 12.8v batteries with a single 48v battery. Generally a bad idea, but we all know sometimes you have no choice but the best of a bad idea. Get the impedance totally balanced so things look the same from the charger/inverter point of view and it will work reasonably well.
 
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24volt UPS


www.solar-electric.com

Schneider Electric 865-2524 Conext SW 3,000 Watts, 24VDC Inverter/Charger for Split-phase 120/240 VAC

This inverter has been discontinued.
www.solar-electric.com www.solar-electric.com
www.solar-electric.com

Schneider Electric RNW8651016 Conext SW DC Circuit Breaker Panel

Schneider Electric RNW8651016Conext SW DC Circuit Breaker Panel
www.solar-electric.com www.solar-electric.com
www.solar-electric.com

Schneider Electric RNW8651017 Conext SW AC Circuit Breaker Panel for 120/240 VAC

Schneider Electric RNW8651017 Conext SW AC Circuit Breaker Panel for 120/240 VAC
www.solar-electric.com www.solar-electric.com
Victron 250/100
4 - 335w Q cell panels.
Bus bars from Signature solar
Victron Smart Shunt
Class T fuse (150amp)
Class T fuse holder, ignition protected
Blue Sea systems switches for each battery bank
MRBF fuse + holder for each battery bank (also 150amp - each bank can run the inverter with the other off)
4 - LiTime 12v200ah Plus batteries - 200Ah capacity - 200amp BMS
2 - LiTime 48v balancers - using only 2 legs of each for a string
125amp sub panel
10/3 wire to feed the AC in and out of the inverter - 240vac - direct wire from main panel.
10/3 for the well pump 240vac
14/2 for the Server 120vac
14/2 for the furnace 120vac

NOTE - I need to do RSD for the panels of some sort and likely shutdown of some sort for the output - i.e. one button to kill the inverter power out and the PV and disconnect the batteries .... Contactors are my friend for these parts.

NOTE - It is ALWAYS better to buy a battery of the correct voltage verse making a series battery, but if you can't active balancers are the way to keep the batteries in sync. In my case I started with 1 - 12v for a UPS - then I needed more capacity so added another - then I got this equipment free/cheap and needed still more capacity so got 2 more batteries. If I ever get the house on solar it can be put in series to make a 48v200ah battery.


1729610642974.png


1729613760455.png
1729613825007.png
1729613858950.png
1729613891200.png
1729613916246.png
 
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Just because I can never find the chart for the EGC size when I need it, adding it to my answers

1733102007669.jpeg

NEC Table 250.122 specifies the minimum sizes for equipment grounding conductors (EGCs) based on the rating of the overcurrent protection device (OCPD) safeguarding the circuit. Proper sizing of EGCs is crucial to ensure a low-impedance path for fault currents, facilitating the prompt operation of protective devices and enhancing safety.

**Using NEC Table 250.122:**

1. **Identify the OCPD Rating:** Determine the ampere rating or setting of the OCPD (e.g., circuit breaker or fuse) that protects the circuit.

2. **Refer to Table 250.122:** Locate the corresponding row in the table that matches the OCPD's rating. The table provides minimum EGC sizes in American Wire Gauge (AWG) or circular mils for both copper and aluminum (or copper-clad aluminum) conductors.

For example, for a 100-ampere OCPD, Table 250.122 specifies a minimum EGC size of 8 AWG for copper conductors and 6 AWG for aluminum or copper-clad aluminum conductors.

**Special Considerations:**

- **Upsizing Conductors:** If ungrounded (hot) conductors are increased in size to address voltage drop or other factors (excluding adjustments for ambient temperature or conduit fill), the EGC must also be proportionally increased. This ensures the EGC can handle potential fault currents effectively.

- **Multiple Circuits in a Raceway:** When multiple circuits share the same raceway, cable, or trench, a single EGC is permissible. In such cases, size the EGC based on the largest OCPD protecting any circuit within that raceway or cable.

- **Parallel Conductors:** For circuits with conductors installed in parallel, each raceway or cable must contain an EGC sized according to Table 250.122, based on the OCPD rating. Alternatively, a single EGC can be installed if all conductors are in the same raceway or cable tray, sized appropriately for the total OCPD rating.

**Example Calculation:**

Consider a circuit protected by a 250-ampere circuit breaker. According to Table 250.122, the minimum EGC size would be 4 AWG for copper conductors. If the ungrounded conductors are upsized from 250 kcmil to 350 kcmil to mitigate voltage drop, the EGC size must also be increased proportionally. The proportionate increase is calculated as follows:

- Original conductor size: 250 kcmil
- Upsized conductor size: 350 kcmil
- Increase factor: 350 kcmil / 250 kcmil = 1.4
- Original EGC size (from Table 250.122): 4 AWG (41,740 circular mils)
- Upsized EGC size: 41,740 circular mils × 1.4 = 58,436 circular mils

Consulting Chapter 9, Table 8 of the NEC, a conductor with approximately 58,436 circular mils corresponds to between 3 AWG and 2 AWG. Therefore, the next standard size, 2 AWG, should be selected for the EGC.

By adhering to NEC Table 250.122 and considering these factors, electricians can ensure that equipment grounding conductors are appropriately sized, thereby maintaining the safety and integrity of electrical installations.
 
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HRTKD said:
Thanks for attaching the PDF of the poster. I couldn't read the inline image very well.
Click to expand...
yw

I went to amazon and ordered some sheets of vinyl stickers with different bits on it.

For the outside signs to do with RSD and system shutdown I intend to have metal signs with UV proof text made - the winters and summers here are harsh and the stickers won't hold up outside.

I am thinking about getting stencils made for the outside stuff so I can spray paint a red background and then use the stencil to put the text in black or white.

With today's laser cutters stencils are dirt cheap. The metal signs aren't much either.
 
Very nice sum up and collection of basic rules and mentality. (y)

I would like to bring attention to double-info in the list of the very first post.
#1 and #9 are the same. Removing #9? (Unless there is a reason for the double.)
 
MrSparkle said:
Very nice sum up and collection of basic rules and mentality. (y)

I would like to bring attention to double-info in the list of the very first post.
#1 and #9 are the same. Removing #9? (Unless there is a reason for the double.)
Click to expand...
Because I reordered the list
 
Battery charge parameters for LFP

3.55-3.65V/cell for fast charge - 30-60 minutes fixed absorption time (dictated primarily by balancing needs)
3.45V/cell for slow charge (this is the one that maximizes cycle life) - 2-4 hour fixed absorption time (dictated by time needed to get to 100%).
3.375V/cell float.
 
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