Help: Please critique my design and input on grounding

[Tularosa]

Hi All - Attached are my plans. Please critique any elements of my design I have purchased all components except fuses and wires. Could use some help understanding if I need to ground my solar panels themselves. I haven't installed anything except for the generator (which has been powering my cabin for a while by itself). Thank you!! Lorenzo

 

[Capt Bill]

I also wonder I need to ground my solar panels. The first thing I noticed is only your generator is grounded. My thoughts go to: that service panel need your # 1 ground wire going to it, and any other ground could connect to that ground. I am not an expert in solar; that is my perspective from wiring up a couple of house.

 

[Dzl]

Will your batteries / DC system have a ground connection (at the negative battery terminal or busbar probably) or will this be an ungrounded/floating system?

 

[Tularosa]

@Capt Bill - Thank you.
@Dzl - That's exactly what i'm asking. I could easily ground the negative bus if that's required.

 

[mapguy525]

@Capt Bill - Thank you.
@Dzl - That's exactly what i'm asking. I could easily ground the negative bus if that's required.

Is the power panel "existing"? If so and was installed with a permit -grounding will be in place for existing circuit loads.

If an electrical permit is involved -seek out the opinion of the inspector for what they expect for a ground system. Some electrical inspectors are fanatical about "how" the grounding(continuous cable) is done and ohm values.

 

[Dzl]

@Dzl - That's exactly what i'm asking. I could easily ground the negative bus if that's required.

I plan to with my system, but both options are acceptable in certain contexts. My context is mobile, so I am bonding the negative busbar to the vehicle chassis, I'm not sure how the situation differs with a residential off-grid system, but I bet there are more resources available for your situation. My guess is that in a stationary off-grid system, you would want your battery negative bonded to earth-ground.

On the DC side of things, I think you should look into grounding your inverter, your PV array, and possibly the SCC to your negative busbar or a separate ground busbar (this is called 'equipment grounding', i.e. connecting the not-normally-energized metal chassis' of your electrical components to the grounding system see here).

Some resources you might find helpful:
The NEC sections on Grounding and Bonding, and on PV systems
Mike Holt's videos on grounding (particular this one on system and equipment grounding, and this one on the fundamentals of grounding)

 

[Capt Bill]

Re: Service Panel Grounding: IMO: that service panel would be the #1 place to ground, and then connect all other grounds to that. If you are not familiar with wiring a service panel, study up and get help when needed. Re Ground wires in a service panel: This part might be confusing at first to a newbie/ initially looking at inner part 120vac service panel. Unless some unknowledgable person wired stuff up before you got there; the Black (or Red) colored (sheated) wires are for the Hot 120 ac current going to a circuit breaker matching to that wire size; and all the White 120vac neutral wires (in my panels) are all connected to same gound bars as the ground wire. The ground wire are usually bare copper while the 120 vac white neutral wire are sheeted and usually colored White. That bus bars inside your service panels, that clamp white wires, and bare ground wires together ( via wires inserted through holes and tighten down via screws) all get connected to a right gauge size ground wire often sheeted in green, stretched out and connected to a good ground via a nearby cooper rod in ground. If this sounds like Greek and/ore new lessons, study harder to understand more specifics. I have seen some sunset book explain all about it with basic diagrams and good basic language explanations. I also see someone left ya a web info link. I am wondering if you are wiring an off grid cabin, or RV, and not connected to grid power , or will be connecting to grid.

IF you are connecting to the grid, and/or planning to wire any 220 - 240vac circuits from your service panel circuit breakers, and considering wiring your own service panel, you will have study hard / to understand how the two biggest Hot wires and one Ground coming into your service panel, connect to 2 different hot 120 ac current bars in panel / w an incoming ground also going to the ground bus bar or bars; and how all the white wires and bare wire connect up with to each other and ground, via those same grounding bus bars. ... From the looks of your diagram, I recommend you seek more hands on type /experienced help (like an experience friend to double check before your service panel gets energized. If grid tied, best done with a permit, and get the inspection. If you are off grid, and only planning for only one 120vac Inverter line in, and possible a generator line in to service panel, and 120vac lines out through circuit breakers matched to wire size, ...your wiring might be simpler, but you have to feel confident about handling All the Details before flipping on the power. Study up and get answers to all your curious questions answered. If this sound like Greek, study harder and get some help. Best Wishes in All Ways form not claiming to be expert ... :+) Bill

 

[Tularosa]

I plan to with my system, but both options are acceptable in certain contexts. My context is mobile, so I am bonding the negative busbar to the vehicle chassis, I'm not sure how the situation differs with a residential off-grid system, but I bet there are more resources available for your situation. My guess is that in a stationary off-grid system, you would want your battery negative bonded to earth-ground.

On the DC side of things, I think you should look into grounding your inverter, your PV array, and possibly the SCC to your negative busbar or a separate ground busbar (this is called 'equipment grounding', i.e. connecting the not-normally-energized metal chassis' of your electrical components to the grounding system see here).

Some resources you might find helpful
The NEC sections on Grounding and Bonding, and on PV systems
Mike Holt's videos on grounding (particular this one on system and equipment grounding, and this one on the fundamentals of grounding)

Thank you. This is a stationary off-grid system. I really appreciate all this info.

 

[Tularosa]

Re: Service Panel Grounding: IMO: that service panel would be the #1 place to ground, and then connect all other grounds to that. If you are not familiar with wiring a service panel, study up and get help when needed. Re Ground wires in a service panel: This part might be confusing at first to a newbie/ initially looking at inner part 120vac service panel. Unless some unknowledgable person wired stuff up before you got there; the Black (or Red) colored (sheated) wires are for the Hot 120 ac current going to a circuit breaker matching to that wire size; and all the White 120vac neutral wires (in my panels) are all connected to same gound bars as the ground wire. The ground wire are usually bare copper while the 120 vac white neutral wire are sheeted and usually colored White. That bus bars inside your service panels, that clamp white wires, and bare ground wires together ( via wires inserted through holes and tighten down via screws) all get connected to a right gauge size ground wire often sheeted in green, stretched out and connected to a good ground via a nearby cooper rod in ground. If this sounds like Greek and/ore new lessons, study harder to understand more specifics. I have seen some sunset book explain all about it with basic diagrams and good basic language explanations. I also see someone left ya a web info link. I am wondering if you are wiring an off grid cabin, or RV, and not connected to grid power , or will be connecting to grid.

IF you are connecting to the grid, and/or planning to wire any 220 - 240vac circuits from your service panel circuit breakers, and considering wiring your own service panel, you will have study hard / to understand how the two biggest Hot wires and one Ground coming into your service panel, connect to 2 different hot 120 ac current bars in panel / w an incoming ground also going to the ground bus bar or bars; and how all the white wires and bare wire connect up with to each other and ground, via those same grounding bus bars. ... From the looks of your diagram, I recommend you seek more hands on type /experienced help (like an experience friend to double check before your service panel gets energized. If grid tied, best done with a permit, and get the inspection. If you are off grid, and only planning for only one 120vac Inverter line in, and possible a generator line in to service panel, and 120vac lines out through circuit breakers matched to wire size, ...your wiring might be simpler, but you have to feel confident about handling All the Details before flipping on the power. Study up and get answers to all your curious questions answered. If this sound like Greek, study harder and get some help. Best Wishes in All Ways form not claiming to be expert ... :+) Bill

Excellent! This is an off-grid cabin. I have the generator wired up currently. Now incorporating the solar plans. Thanks for all this info.

 

[mapguy525]

Please study the links @Dzl posted. The Mike Holt links are very good professional information. Proper grounding and bonding requires some though so all the needed pieces of the puzzle are identified and included in the grounding/bonding system design. I would look at the videos before venturing into the NEC sections due to the way code language is structured.

@Dzl
Some resources you might find helpful:
The NEC sections on Grounding and Bonding, and on PV systems
Mike Holt's videos on grounding (particular this one on system and equipment grounding, and this one on the fundamentals of grounding)

 

[Tularosa]

Please study the links @Dzl posted. The Mike Holt links are very good professional information. Proper grounding and bonding requires some though so all the needed pieces of the puzzle are identified and included in the grounding/bonding system design. I would look at the videos before venturing into the NEC sections due to the way code language is structured.

Thank you!

 

[Supervstech]

Remember, there are several types of grounding.

1. Lightning EMF dissipation.

2. Equipment safety bonding.

3. Service ground return path.

1 is obvious. Metal things need a ground point to prevent destructive static emf.

2. All devices with ground fault protection need a ground path to function.

3. Electrical generating services need a neutral bonded to ground to give spike etc. A path for safety.

 

[tictag]

A few other considerations:

1. Your 1/0AWG cable from your DC distribution to MultiPlus is only rated for 200A but you have fused that line with a 300A fuse.
2. You 2/0AWG cable will be conducting the same current as your inverter, why use two different size cables?
3. Your inverter is rated for 3kW, which is a 125A current draw from you battery. Anything above 2AWG cable will be sufficient. 2/0AWG is overkill and adds nothing but additional cost and weight to your project with no additional benefit.
4. Your PV cable run will only ever carry around 30A (assuming Imp = 7.5A) in normal operation, why include a 70A breaker? This is an unnecessary cost where a simple switch will do to isolate the array.
5. Your array is configured as 1S4P with Voc = 48V, but your SCC supports up to 150V. This is a sub-optimal configuration. By configuring your array as 2S2P you will be halving the current and thereby quartering your losses (P(loss) = I²R), which means that you can use a radically smaller cable than 2/0 even considering the 160' distance. Assuming Isc = 19.66A and Voc = 96V, you can achieve a <3% voltage drop using anything above 6AWG cable. 320' of 6AWG would cost around $1,085, whereas the same quantity of 2/0AWG would cost $2,592 (price quoted from WindyNation via Amazon.com)
6. Check the specs of your genset, you may need to manually earth the genset's neutral line.
7. Check your energy / consumption audit, your 2,520Wh battery bank would only deliver your inverter's rated output for less than one hour.

 

[mapguy525]

From Victron Multiplus 24 3000 70 manual
https://www.victronenergy.com/upload/documents/Manual-MultiPlus-3k-120V-(firmware-xxxx4xx)-EN.pdf

4.2 Connection of battery cables


In order to utilize the full capacity of the product, batteries with sufficient capacity and battery cables with sufficient cross section should


be used. See table.


12/3000/120 24/3000/70


Recommended battery capacity (Ah) 400–1200 200–700


Recommended DC fuse 400A 300A


Recommended cross section (mm2)


per + and - connection terminal


0 – 5m 2x 50mm2 50mm2


5 – 10m 2x 70mm2 2x 50mm2


* ‘2x’ means two positive and two negative cables.


Remark: Internal resistance is the important factor when working with low capacity batteries. Please consult your supplier or the relevant


sections of our book “Energy Unlimited”, downloadable from our website.


Procedure


Proceed as follows to connect the battery cables:

 

[Tularosa]

A few other considerations:

1. Your 1/0AWG cable from your DC distribution to MultiPlus is only rated for 200A but you have fused that line with a 300A fuse.
2. You 2/0AWG cable will be conducting the same current as your inverter, why use two different size cables?
3. Your inverter is rated for 3kW, which is a 125A current draw from you battery. Anything above 2AWG cable will be sufficient. 2/0AWG is overkill and adds nothing but additional cost and weight to your project with no additional benefit.
4. Your PV cable run will only ever carry around 30A (assuming Imp = 7.5A) in normal operation, why include a 70A breaker? This is an unnecessary cost where a simple switch will do to isolate the array.
5. Your array is configured as 1S4P with Voc = 48V, but your SCC supports up to 150V. This is a sub-optimal configuration. By configuring your array as 2S2P you will be halving the current and thereby quartering your losses (P(loss) = I²R), which means that you can use a radically smaller cable than 2/0 even considering the 160' distance. Assuming Isc = 19.66A and Voc = 96V, you can achieve a <3% voltage drop using anything above 6AWG cable. 320' of 6AWG would cost around $1,085, whereas the same quantity of 2/0AWG would cost $2,592 (price quoted from WindyNation via Amazon.com)
6. Check the specs of your genset, you may need to manually earth the genset's neutral line.
7. Check your energy / consumption audit, your 2,520Wh battery bank would only deliver your inverter's rated output for less than one hour.

Thank you sir. I made some of the sizing decisions (i.e., Victron 1/0) given that's what it calls for, but I could have read it wrong. Perhaps it meant max size? This is all very good feedback. I appreciate it so much.

 

[Tularosa]

From Victron Multiplus 24 3000 70 manual
https://www.victronenergy.com/upload/documents/Manual-MultiPlus-3k-120V-(firmware-xxxx4xx)-EN.pdf

Thank you!

 

[tictag]

I made some of the sizing decisions (i.e., Victron 1/0) given that's what it calls for, but I could have read it wrong.

Your fusing selection for any cable should be the LOWER of:

1. The ampacity rating of the cable
2. 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.

 

[mapguy525]

Your fusing selection for any cable should be the LOWER of:

1. The ampacity rating of the cable
2. 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.

I don't understand why people keep applying branch circuit wiring and OCP on these type installs. Installing it at less than full capability doesn't make sense for several reasons. At some point in time a user will try to use the maximum ability of the equipment. Then bad crap happens.

 

[Dzl]

I don't understand why people keep applying branch circuit wiring and OCP on these type installs.

Can you clarify/explain what you mean by this, to those of us (cough cough me) too slow to understand you are saying, specifically with regards to 'branch circuit wiring'.

 

[mapguy525]

Can you clarify/explain what you mean by this, to those of us (cough cough me) too slow to understand you are saying, specifically with regards to 'branch circuit wiring'.

Maybe my terminology could have been better.....

My frustration/concern is regarding blanket advice from experienced and or professional users regarding OCP/wiring that doesn't consider the planned/installed devices(system) actual capability for determining the needed protection. The overwhelming volume of users on this forum is the beginner/novice group. This group need clear safe guidance in all steps of the process to embrace the technology potential.

Using the common if/when logic of OCP and wiring sizing on the DC input side of inverter/chargers leaves usable capacity available and a potentially unsafe to use system. These devices -depending on brand can short term surge 2x of rating, Some can even run at a power boost level above the nominal rating for 30 minutes. These capabilities must be considered and accounted for in the install. This is why there are multiple layers of OCP protection. 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.

Most of these type devices can use multiple power sources at one time, provide load support/sharing between sources, and charge battery simultaneously.
Personally, i always use the term catastrophic fuse for battery fuses in the realm of use. This keeps me focused on what that particular fuse is for. This fuse is to protect your wiring, devices, and the battery itself in an unexpected over-discharge event. Yes, this event should never happen in a well planned install, but personally I am unwilling to take that risk on any install i perform.