Help: Please critique my design and input on grounding

[Dzl]

I give up. Done, no more comments about OCP protection and or grounding/bonding on north america mobile systems using inverter chargers with hybrid functions.
Tired of "justifying" following the installation manual.

I'm a little confused, I wasn't asking you to 'justify' anything and no part of my comment was meant to challenge anything you said, simply seeking further clarification on some statements you made but didn't fully explain (or maybe I just didn't fully understand). And I'm certainly not opposed to just following the manual (hence my statement "in my opinion the best approach is buy an inverter from a reputable brand and follow the recommendation in the manual").

I didn't intend to cause offense, and am not really clear what specific thing offended you. I only want to understand your perspective and learn from your experience.

I think if you reread my comment with the assumption that it was made in earnest and not meant to be the least bit hostile, maybe you will interpret it differently, its easy to misinterpret tone on the internet.

If all you had said was "follow the manufacturer recommendations" there wouldn't be much to discuss, but you said a lot more than that and I think some of the things you said deserve further discussion and/or clarification/explanation.

 

[mapguy525]

I'm a little confused, I wasn't asking you to 'justify' anything and no part of my comment was meant to challenge anything you said, simply seeking further clarification on some statements you made but didn't fully explain (or maybe I just didn't fully understand). And I'm certainly not opposed to just following the manual (hence my statement "in my opinion the best approach is buy an inverter from a reputable brand and follow the recommendation in the manual").

I didn't intend to cause offense, and am not really clear what specific thing offended you. I only want to understand your perspective and learn from your experience.

I think if you reread my comment with the assumption that it was made in earnest and not meant to be the least bit hostile, maybe you will interpret it differently, its easy to misinterpret tone on the internet.

If all you had said was "follow the manufacturer recommendations" there wouldn't be much to discuss, but you said a lot more than that and I think some of the things you said deserve further discussion and/or clarification/explanation.

@Dzl
Your post was just the straw that broke the camels back – so to speak. I do understand that you are seeking education regarding system implementation. I also understand that many on this forum will avoid code compliance or think they are exempt from code compliance. Codes although cumbersome at times are very important to identify safe and reliable use methods for the application.

Just giving a “read the manual” response is not really good advice to Beginner/Novice level questions as they are typically struggling with knowing/understanding how AC and/or DC energy functionally work. For individuals without a basis to understand ac/dc systems reading an Owners manual like the Victron 3000 24 70 will be very difficult.

My basis of ac/dc systems comes from a first career of employment in the Equipment Rental business. 25+ years of experience with many different kinds of things. From champagne fountains to 200 class excavators and everything in-between. I will not provide the “easy button” response as I have seen first hand the devastation potential of ac/dc energy. Something as simple as an extension cord end replacement that maintains proper polarity is challenging for many people….

Regarding your comments and questions:

• conditional statements with contradiction:
  
  @tictag
  
  Your fusing selection for any cable should be the LOWER of:
  
  The ampacity rating of the cable
  
  The expected maximum load +25%
  
  In this case, your expected maximum load is 125A + 25% = 156A, the ampacity of 1/0AWG cable is 200A, therefore, your fuse should be 156A or closest standard rating to it. Note: do not consider surge currents when sizing standard fuses - such currents are too brief to activate the fuse.
  
  Of course, if you have professional advice to the contrary e.g. from Victron, then you should follow that - this is just a general guideline.
  
  1. NEC, NFPA and ANSI-RVIA all require consideration of the actual equipment and inter-related equipment when sizing conductors and OCP (fusing).
     
• Question: ”How would this make it potentially unsafe? I get your point about leaving usable capacity on the table, but I don't understand how a potentially slightly undersized breaker is unsafe?”
  
  1. Potential for nuisance fuse tripping and overheated conductors.
     
     1. Nuisance fuse tripping -Typically this issue is dealt with by removing the fuse or up-sizing dramatically such that actual Fuse function is lost. On LFP batteries this is dangerous due to the sudden discharge potential of the battery chemistry.
        
     2. Overheated conductors -short term small over-current events slowly compromise the conductors until failure happens. This could take years of operation.
        
     3. Slightly undersized comment: In this case the difference between the Owners Manual recommended fuse of 300amp @ 24v compared to ~150-180Amp @ 24v is not slight.
        
        1. To me this is not a slight difference. Especially if analyzed mathematically.
           
     4. My point is that leaving capacity on the table due to undersized fusing and conductors is dangerous. NEC agrees if you do a though search of all the related footnotes and sections referenced when researching the sizing of conductors and OCP.
        
        1. See my comments above regarding nuisance tripping and overheated conductors.
           
        2. The undersized wiring becomes a defacto current limiting device because at some point nuisance tripping will be remedied(probably in a poor method) and the slowly compromised conductors will probably be subjected to enough current to melt insulation and short. Fire is very close at hand here.
           
• Question: “One thing you are not mentioning here is that OCP devices also have their own equivalent of 'surge ratings' the trip curve. If this is well matched with the inverter surge, it would seem, that sizing your fuse/breaker on the inverters continuous rating +25% or so, wouldn't be problematic, would it? Am I thinking about this wrong? I'm still trying to wrap my head around the proper logic here. “
  1. Lots of factors here. Yes, they do have specifications. Using the proper OCP for application is the key. My research past and present establishes clearly, to me,the need for a Class T fuse for this type application and any other application that needs a “fast blow” fuse. Automatic resetting devices should not be present here.
     
  2. Battery OCP is your last line of protection. It protects everything including the battery. It must be sized for all the potential simultaneous loads of the battery. Not just one piece of the installed equipment. Again -if you fully research NEC, NFPA, and ANSI-RVIA the sizing requirements are fully outlined.
     
     1. In LFP batteries it is imperative to prevent an uncontrolled sudden discharge of the battery due to the chemistry’s discharge characteristics.
• OCP/wiring used as a current limiting device is poor advice to a beginner/novice due to the potential for not fully understanding the consequences of the decision.
  
  1. Beginners/Novice’s don’t understand that using undersized conductors and OCP requires that the installed device must be de-rated properly and operated in accordance with the de-rating.
     
  2. Goes back to overheated conductors and nuisance fuse tripping, too.
     
• And, to make sure we are on the same page, can you clarify whether we are discussing the inverter circuit OCP, the main battery OCP, or you are thinking of these as one and the same.
  
  1. Battery OCP is for system protection -plain and simple. Properly sizing this fuse protects again nuisance tripping while still allowing things like an inverter to be fully usable without long term risk
     1. In this case Battery OCP and Inverter DC OCP are typically the same fuse.
     2. Inverter AC wiring is a totally different situation.
        

 

[RandyP]

Opinions are like, ....., well you know. Every statement about grounding should be proceeded or followed by a code, standard or listing requirement. There are no opinions that are valid. Just compliance. Codes. Standards and listings have been developed over time to address safety. Safety is number one.

 

[Supervstech]

Opinions are like, ....., well you know. Every statement about grounding should be proceeded or followed by a code, standard or listing requirement. There are no opinions that are valid. Just compliance. Codes. Standards and listings have been developed over time to address safety. Safety is number one.

This is an interesting read... https://www.ecmag.com/section/codes-standards/guardian-ground

By Michael Johnston Published In February 2013
Grounding electrode conductors are essential in the grounding and bonding scheme for services and separately derived systems. They generally must be sized according to Table 250.66 of the National Electrical Code (NEC) and are required to be installed in a continuous length or otherwise spliced in accordance with any alternative in 250.64(C). They must also be protected in accordance with 250.64(B) where subject to physical damage.


In addition to concerns about physical damage, magnetic fields can affect grounding electrode conductors. Section 250.64(E) includes requirements to address such protection. If a grounding electrode conductor is installed in a ferrous metal raceway, the raceway must be electrically continuous from the point of attachment to the cabinet or equipment to the grounding electrode and must be securely fastened to the ground clamp or fitting. Ferrous metal raceways contain iron or steel content, and examples include rigid metal conduit (RMC), intermediate metal conduit (IMC) and electrical metallic tubing (EMT). These conduits and tubing have a magnetic property that reacts to rising and falling magnetic fields present in alternating current (AC) systems.


Varying amounts of current can be present in a grounding electrode conductor during normal operation. During a ground-fault event, the current in a grounding electrode conductor can fluctuate and even be relatively high for the duration of the event.


Ferrous metal raceways must be bonded to the contained grounding electrode conductor to reduce the effects of magnetic fields that are present while the system is energized and in use. The grounding electrode conductor for an AC system or service is an AC-carrying conductor with the current flowing in one direction. This current can rise and fall significantly depending on events such as ground faults, short circuits or line surges. As the current rises and falls, the magnetic field of the contained conductor typically gets larger and smaller accordingly. This means the stresses on the contained grounding electrode conductor increase and decrease as the current goes up or down.


Because the ferrous metal raceway is enclosing this single conductor, there is an inductive reactance between the ferrous metal raceway and the contained grounding electrode conductor. This inductive reactance is one component of impedance and actually impedes current in the contained grounding electrode conductor. The magnetic field and the capacitance results in a coupling effect between the current in the conductor and the surrounding ferrous metal raceway. In actuality, the majority of the current would be present in the ferrous metal raceway rather than the contained grounding electrode conductor.


The magnetic field’s strength increases in proportion to the amount of current in the conductor. In many cases, the magnetic lines of force in the conductor are induced into the conduit enclosing the grounding electrode conductor; they can even surpass the saturation point of the steel raceway. At the point where the grounding electrode conductor exits the conduit, the magnetic lines of force generated by the fault current in the conductor will try to be induced on the end of the conduit, creating a saturation point that exceeds the conduit’s capacity. The steel conduit, in this instance, acts like a steel core of a coil to concentrate the magnetic lines of force. This condition is often referred to as the “choke effect” because it is actually the restriction of a grounding electrode conductor from performing its function. Because of this, specific bonding requirements are necessary for ferrous metal raceways that contain grounding electrode conductors. This is not a concern for grounding electrode conductors that are installed in PVC conduit or other nonferrous metal raceways such as aluminum or brass conduit. Sometimes the type of construction will not permit PVC conduit.


Section 250.64(E) requires ferrous metal enclosures for grounding electrode conductors that are not physically continuous from cabinets or equipment to the grounding electrode, such as sleeves or short lengths of conduit used for physical protection, to be made electrically continuous by bonding each end of the raceway to the contained grounding electrode conductor. This action puts the contained grounding electrode conductor in parallel with the enclosing ferrous metal raceway so the two work together when the current in grounding electrode conductors rises and falls in response to various events occurring on the system. The current will actually divide over both paths, but due to the skin effect, the majority will be present in the surrounding ferrous metal raceway.


The methods required for bonding each end of the raceway are provided in 250.92(B)(2) through (B)(4). These methods apply to all intervening ferrous raceways, boxes and enclosures containing the grounding electrode conductor. If a bonding jumper is used to accomplish this bonding to intervening metal raceways and enclosures, the size of the bonding jumper must not be smaller than the required contained grounding electrode conductor as provided in 250.64(E). Several manufacturers produce grounding and bonding fittings that are specifically designed and listed for this purpose.

 

[RandyP]

This is an interesting read... https://www.ecmag.com/section/codes-standards/guardian-ground

By Michael Johnston Published In February 2013
Grounding electrode conductors are essential in the grounding and bonding scheme for services and separately derived systems. They generally must be sized according to Table 250.66 of the National Electrical Code (NEC) and are required to be installed in a continuous length or otherwise spliced in accordance with any alternative in 250.64(C). They must also be protected in accordance with 250.64(B) where subject to physical damage.


In addition to concerns about physical damage, magnetic fields can affect grounding electrode conductors. Section 250.64(E) includes requirements to address such protection. If a grounding electrode conductor is installed in a ferrous metal raceway, the raceway must be electrically continuous from the point of attachment to the cabinet or equipment to the grounding electrode and must be securely fastened to the ground clamp or fitting. Ferrous metal raceways contain iron or steel content, and examples include rigid metal conduit (RMC), intermediate metal conduit (IMC) and electrical metallic tubing (EMT). These conduits and tubing have a magnetic property that reacts to rising and falling magnetic fields present in alternating current (AC) systems.


Varying amounts of current can be present in a grounding electrode conductor during normal operation. During a ground-fault event, the current in a grounding electrode conductor can fluctuate and even be relatively high for the duration of the event.


Ferrous metal raceways must be bonded to the contained grounding electrode conductor to reduce the effects of magnetic fields that are present while the system is energized and in use. The grounding electrode conductor for an AC system or service is an AC-carrying conductor with the current flowing in one direction. This current can rise and fall significantly depending on events such as ground faults, short circuits or line surges. As the current rises and falls, the magnetic field of the contained conductor typically gets larger and smaller accordingly. This means the stresses on the contained grounding electrode conductor increase and decrease as the current goes up or down.


Because the ferrous metal raceway is enclosing this single conductor, there is an inductive reactance between the ferrous metal raceway and the contained grounding electrode conductor. This inductive reactance is one component of impedance and actually impedes current in the contained grounding electrode conductor. The magnetic field and the capacitance results in a coupling effect between the current in the conductor and the surrounding ferrous metal raceway. In actuality, the majority of the current would be present in the ferrous metal raceway rather than the contained grounding electrode conductor.


The magnetic field’s strength increases in proportion to the amount of current in the conductor. In many cases, the magnetic lines of force in the conductor are induced into the conduit enclosing the grounding electrode conductor; they can even surpass the saturation point of the steel raceway. At the point where the grounding electrode conductor exits the conduit, the magnetic lines of force generated by the fault current in the conductor will try to be induced on the end of the conduit, creating a saturation point that exceeds the conduit’s capacity. The steel conduit, in this instance, acts like a steel core of a coil to concentrate the magnetic lines of force. This condition is often referred to as the “choke effect” because it is actually the restriction of a grounding electrode conductor from performing its function. Because of this, specific bonding requirements are necessary for ferrous metal raceways that contain grounding electrode conductors. This is not a concern for grounding electrode conductors that are installed in PVC conduit or other nonferrous metal raceways such as aluminum or brass conduit. Sometimes the type of construction will not permit PVC conduit.


Section 250.64(E) requires ferrous metal enclosures for grounding electrode conductors that are not physically continuous from cabinets or equipment to the grounding electrode, such as sleeves or short lengths of conduit used for physical protection, to be made electrically continuous by bonding each end of the raceway to the contained grounding electrode conductor. This action puts the contained grounding electrode conductor in parallel with the enclosing ferrous metal raceway so the two work together when the current in grounding electrode conductors rises and falls in response to various events occurring on the system. The current will actually divide over both paths, but due to the skin effect, the majority will be present in the surrounding ferrous metal raceway.


The methods required for bonding each end of the raceway are provided in 250.92(B)(2) through (B)(4). These methods apply to all intervening ferrous raceways, boxes and enclosures containing the grounding electrode conductor. If a bonding jumper is used to accomplish this bonding to intervening metal raceways and enclosures, the size of the bonding jumper must not be smaller than the required contained grounding electrode conductor as provided in 250.64(E). Several manufacturers produce grounding and bonding fittings that are specifically designed and listed for this purpose.

All good info. But ac power systems in a RV are per article 551 of the NFPA/NEC and ANSI RVIA Lv standard. Those two 'codes' give specific direction for grounding in RV's. Read them first, then figure out all the references and referrals to other articles of the code.

 

[RandyP]

This is an interesting read... https://www.ecmag.com/section/codes-standards/guardian-ground

By Michael Johnston Published In February 2013
Grounding electrode conductors are essential in the grounding and bonding scheme for services and separately derived systems. They generally must be sized according to Table 250.66 of the National Electrical Code (NEC) and are required to be installed in a continuous length or otherwise spliced in accordance with any alternative in 250.64(C). They must also be protected in accordance with 250.64(B) where subject to physical damage.


In addition to concerns about physical damage, magnetic fields can affect grounding electrode conductors. Section 250.64(E) includes requirements to address such protection. If a grounding electrode conductor is installed in a ferrous metal raceway, the raceway must be electrically continuous from the point of attachment to the cabinet or equipment to the grounding electrode and must be securely fastened to the ground clamp or fitting. Ferrous metal raceways contain iron or steel content, and examples include rigid metal conduit (RMC), intermediate metal conduit (IMC) and electrical metallic tubing (EMT). These conduits and tubing have a magnetic property that reacts to rising and falling magnetic fields present in alternating current (AC) systems.


Varying amounts of current can be present in a grounding electrode conductor during normal operation. During a ground-fault event, the current in a grounding electrode conductor can fluctuate and even be relatively high for the duration of the event.


Ferrous metal raceways must be bonded to the contained grounding electrode conductor to reduce the effects of magnetic fields that are present while the system is energized and in use. The grounding electrode conductor for an AC system or service is an AC-carrying conductor with the current flowing in one direction. This current can rise and fall significantly depending on events such as ground faults, short circuits or line surges. As the current rises and falls, the magnetic field of the contained conductor typically gets larger and smaller accordingly. This means the stresses on the contained grounding electrode conductor increase and decrease as the current goes up or down.


Because the ferrous metal raceway is enclosing this single conductor, there is an inductive reactance between the ferrous metal raceway and the contained grounding electrode conductor. This inductive reactance is one component of impedance and actually impedes current in the contained grounding electrode conductor. The magnetic field and the capacitance results in a coupling effect between the current in the conductor and the surrounding ferrous metal raceway. In actuality, the majority of the current would be present in the ferrous metal raceway rather than the contained grounding electrode conductor.


The magnetic field’s strength increases in proportion to the amount of current in the conductor. In many cases, the magnetic lines of force in the conductor are induced into the conduit enclosing the grounding electrode conductor; they can even surpass the saturation point of the steel raceway. At the point where the grounding electrode conductor exits the conduit, the magnetic lines of force generated by the fault current in the conductor will try to be induced on the end of the conduit, creating a saturation point that exceeds the conduit’s capacity. The steel conduit, in this instance, acts like a steel core of a coil to concentrate the magnetic lines of force. This condition is often referred to as the “choke effect” because it is actually the restriction of a grounding electrode conductor from performing its function. Because of this, specific bonding requirements are necessary for ferrous metal raceways that contain grounding electrode conductors. This is not a concern for grounding electrode conductors that are installed in PVC conduit or other nonferrous metal raceways such as aluminum or brass conduit. Sometimes the type of construction will not permit PVC conduit.


Section 250.64(E) requires ferrous metal enclosures for grounding electrode conductors that are not physically continuous from cabinets or equipment to the grounding electrode, such as sleeves or short lengths of conduit used for physical protection, to be made electrically continuous by bonding each end of the raceway to the contained grounding electrode conductor. This action puts the contained grounding electrode conductor in parallel with the enclosing ferrous metal raceway so the two work together when the current in grounding electrode conductors rises and falls in response to various events occurring on the system. The current will actually divide over both paths, but due to the skin effect, the majority will be present in the surrounding ferrous metal raceway.


The methods required for bonding each end of the raceway are provided in 250.92(B)(2) through (B)(4). These methods apply to all intervening ferrous raceways, boxes and enclosures containing the grounding electrode conductor. If a bonding jumper is used to accomplish this bonding to intervening metal raceways and enclosures, the size of the bonding jumper must not be smaller than the required contained grounding electrode conductor as provided in 250.64(E). Several manufacturers produce grounding and bonding fittings that are specifically designed and listed for this purpose.

I did not see the words Mobile vehicle or RV anywhere in the article copied above.

 

[Supervstech]

I did not see the words Mobile vehicle or RV anywhere in the article copied above.

True.
The article discusses some reasons for the bonding of metal raceway and explains why ferrous raceway need bonding.

The article is informative about problems associated with ac power in metallic conduit and boxes.

 

[Supervstech]

Basically, the article explains that conduit INDUCES voltage in ferrous raceway, and bonding dissipates it.

Mobile or stationary...

 

[RCinFLA]

Ground of solar panels can be tricky. Regulations call for all panels to be grounded.

Best situation is if your panel grounding is not too far away from you house grounding stake.

Issue is when panels are far away and on a separate ground stakes. Most of the time lightning hits a tree nearby and creates a high ground voltage gradient radiating out through ground from tree. With two separated stakes far apart this ground voltage gradient can be large between the two separated ground stakes and be more likely to blow out some of of your equipment.

Second most common lightning issue is it hitting top ground rail of power poles. This creates a common mode voltage spike relative to your house ground. The utilities common ground cabling from pole to your house helps to reduce this but you still have your house grounding at some distance from power poles grounding system. Good large current surge suppressors in your breaker box can help for this.