Powerwall 2 Code/Safety Question

[BIC1]

I'm a bit confused on some PW code issues. I recall seeing on a thread here recently that PW2s now should be installed 3 ft apart. I currently have 1 PW installed in a utility closet in the basement. I plan to add 2 more shortly.

The following is from the NFPA 855, Standard for the Installation of Stationary Energy Storage Systems

Installation of Stationary ESS page 855-18

9.4.2 Size & Separation

9.4.2.1 ESS shall be comprised of groups with a maximum stored energy of 50 kWh each.

9.4.2.2 Each group shall be spaced a minimum of 3 ft (0.9m) from other groups and from walls in the storage room or area.

In a 2-yr old NFPA blog, is states max 40 kWh in a storage space

Residential Energy Storage System Regulations | NFPA | NFPA

I'm planning on adding 2 more PW. I believe that totals 40.5 kWh storage space.

My question is: In a basement storage area, do 3 PW meet the new standards and can they be grouped together or does each PW have to be 3 ft apart? Even if allowable, is having three together a concern? Thanks.

 

[Matt-FL]

The way I read it, is 'each group' could be up to 3 powerwalls (4 goes over 50kWh). So, a 'group' of three would be allowed to be stacked, and if you had more than 3, the second group would need to be 3' away.

But, some local codes are stricter. You may need to research your local codes to see if there are other limitations.

 

[BIC1]

My city is about five years behind on most codes and ignores some, such as the energy codes. To paraphrase Elsa in the movie Casablanca, I have to do the safety thinking for both of us.

 

[BIC1]

Also, it states a group should be 3 ft from walls. That would mean something like a 10x8 dedicated room. Obviously, most are mounted on walls.

 

[jjrandorin]

This question is best asked to your local AHJ, because even if you read something different here or elsewhere, they (your local AHJ) have final jurisdiction on what they will or wont allow.

 

[Vines]

I'm a bit confused on some PW code issues. I recall seeing on a thread here recently that PW2s now should be installed 3 ft apart. I currently have 1 PW installed in a utility closet in the basement. I plan to add 2 more shortly.

The following is from the NFPA 855, Standard for the Installation of Stationary Energy Storage Systems

Installation of Stationary ESS page 855-18

9.4.2 Size & Separation

9.4.2.1 ESS shall be comprised of groups with a maximum stored energy of 50 kWh each.

9.4.2.2 Each group shall be spaced a minimum of 3 ft (0.9m) from other groups and from walls in the storage room or area.

In a 2-yr old NFPA blog, is states max 40 kWh in a storage space

Residential Energy Storage System Regulations | NFPA | NFPA

I'm planning on adding 2 more PW. I believe that totals 40.5 kWh storage space.

My question is: In a basement storage area, do 3 PW meet the new standards and can they be grouped together or does each PW have to be 3 ft apart? Even if allowable, is having three together a concern? Thanks.

I would not overly restrict your powerwall location as Tesla has performed the UL 9540A large scale fire testing and the results show that closer spacing could be allowed based on the AJH.

However the code does restrict installations to just (2) Powerwall 2 AC units due to the kWh quantity maximums being over 40 in a single interior location that isn't a garage or detached group U structure. If your jurisdiction doesnt restrict this, I would not have any issue personally putting 3 in my basement with non-combustible finish.

You want that basement sheetrocked or covered with another fire resistant finish and the code also requires that this be 5/8" type X sheetrock.

 

[BIC1]

You want that basement sheetrocked or covered with another fire resistant finish and the code also requires that this be 5/8" type X sheetrock.

If the batteries burn at 5000 F, will sheetrock make any difference?

 

[Vines]

If the batteries burn at 5000 F, will sheetrock make any difference?

Fire protection design in a residence focuses on the egress of the occupants and alerts to allow time for that egress. Unless the construction is mostly non-flammable this is the best you can do to resist the loss to human life that a fire will cause.

Fires go through an intensity cycle, and also vary in intensity with distance to the point source. The theoretical maximum temperature you quoted is maybe descriptive of the total conflagration temperature at the core of the module. There likely was a significant slow burn that started 20-30 or more minutes before a li-ion ESS was fully engulfed. This is the time to have already alerted the occupants with alarms, sprinklers and smoke.

A small thermal runaway fire that has started in an ess will resist spread of flame somewhat along your sheetrocked wall. If that area is a basement especially with an uncovered wood ceiling and especially if chemical flammables are nearby then you might get to a significant structure or contents fire before a reasonable egress time has elapsed.

Yes, to sheetrock the walls in the area of your ESS is the current code requirement in many areas, and I would do that in my home regardless of code especially in an unfinished basement. Not to fearmonger, but this home in Santa Rosa had only a small damaging Powerwall fire because the fire protection and prevention (sprinklers) worked.
https://www.pressdemocrat.com/artic...to-santa-rosa-home-originated-in-tesla-in-wa/

This is the first Powerwall fire that I have heard of, but they do happen very rarely.

 

[BGbreeder]

If the batteries burn at 5000 F, will sheetrock make any difference?

But generally batteries don't burn at 5,000F, and specifically lithium ion batteries certainly don't. (And yes, I am aware of a non-technical assertion of 5,000F with no data.)

For gases, compressed oxygen and acetylene burns at a maximum of 5,600F.

Oxy-fuel welding and cutting - Wikipedia

en.wikipedia.org

For liquids, nitromethane under ideal conditions gets to 3950F. That is the record holder as far as I am aware.

https://www.sciencedirect.com/topics/physics-and-astronomy/flame-temperature

Pure lithium can burn at up to 3600F, but actual data on studies from batteries is much, much lower;

https://www.sciencedirect.com/science/article/pii/S0378775320308892

which found that the maximum temperature on a burning cell of any type was about 1350F. For perspective, that is about 40% of the flame temperature for natural gas in air.

What Is the Typical Flame Temperature for Different Fuels?

This is a list of flame temperatures for various common fuels. The adiabatic flame temperature for common gases in air and oxygen are given.

www.thoughtco.com

All the best,

BG