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NEC 2020 706.15 question

D

dbwildes

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Apr 8, 2024
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Good morning,

I am trying to figure out a solution to article 706.15 Disconnecting means for the battery part of an ESS.
The part I am having trouble with is the section that states...
"For one-family and two-family dwellings, a disconnecting means or its remote control shall be located at a readily accessible location outside the building"

My battery bank currently consists of 3 EG4 Server rack batteries (48v Lifepower4) my inverter(s) are EG4 6000xp.
Is there such a beast that I can remotely activate a disconnect that would be in near my batteries but have the "stop" button outside? I wish I had researched it a little more because I would have bought the batteries with the rapid shutdown feature but here we are.

thanks
Don
 
You can use a Remote Trip DC breaker. Here is an example.

Product - MidNite Solar

MidNite Solar Product Page.
www.midnitesolar.com

Note: This particular breaker uses a 24V Pulse to trip so a momentary push button would be needed, continuous 24V would damage the remote trip coil.
 
BentleyJ said:
Note: This particular breaker uses a 24V Pulse to trip so a momentary push button would be needed, continuous 24V would damage the remote trip coil.
Click to expand...
technically, that device wouldn't qualify. Because it's a "fail secure" and not a "fail safe" design.
(If the power source is lost, it would fail to operate)
But if the inspector doesn't notice, it could sneak by.
 
timselectric said:
technically, that device wouldn't qualify. Because it's a "fail secure" and not a "fail safe" design.
(If the power source is lost, it would fail to operate)
But if the inspector doesn't notice, it could sneak by.
Click to expand...
That is my understanding as well. A normally open contactor powered by a power source via an outside normally closed push button to keep the contactor closed would qualify. Because if the power source failed, the system would fail in what is considered the "safe" state. That's how I have my ESS shutdown system setup as part of my single button all inclusive shutdown system designed. I have one button outside that shuts down the PV RSD system, the inverter AC power connections, and the ESS battery system. You can see some of that in my build thread, but I don't have a lot of details in the build thread. If there is interest, I'd be happy to go into more detail, but I'd do that in my build thread.
 
timselectric said:
technically, that device wouldn't qualify. Because it's a "fail secure" and not a "fail safe" design.
(If the power source is lost, it would fail to operate)
But if the inspector doesn't notice, it could sneak by.
Click to expand...
Just wondering. I have a 24 volt system. If the breaker shutdown circuit is powered directly from the battery, would this satisfy the "fail safe" requirement? If the battery is dead there is nothing to shut down.
 
timselectric said:
technically, that device wouldn't qualify. Because it's a "fail secure" and not a "fail safe" design.
Click to expand...
Where does this requirement come from? Code reference?

The batteries which have external shutdown inputs usually require the contacts to be CLOSED to shut them down, which isn't technically a "fail safe" design. Are they not code compliant?

The MidNite Solar breaker linked above doesn't seem to be remote trip that I can see. What am I missing?

The EG4 Lifepower4 battery lacks a discrete shutdown input that would make this easy. Their larger wall mount batteries have this feature.

Ironically, the Ruixu rack batteries have this feature, but their larger wall mount ones don't.

Mike C.
 
I was wondering about those breakers but had questions about them as well.
I would rather have a fail safe design.
jpwhit, I am curious about your system.
my system has ground mounted arrays so I don't need rapid shutdown on them but I do need a solution for the battery.

Don
 
I haven't found the text.

Does it require "fail safe"?

Obviously series connected cells will still form a high-voltage. They are inside box of battery.
Unlike RSD, not segmenting to < 80V in array.

If battery to inverter are contained within metal, is it OK that the ~56V remains active?
What if it is a UL listed ESS?

For RSD I had hoped inside conduit would be exempt, after all we usually use conduit from array to inverter, but doesn't say that.

Q-Dog said:
Just wondering. I have a 24 volt system. If the breaker shutdown circuit is powered directly from the battery, would this satisfy the "fail safe" requirement? If the battery is dead there is nothing to shut down.
Click to expand...

That is safe extra low voltage, but this code requirement might not care.
 
The Midnite birdhouse was designed for disconnecting PV combininer boxes, has its own battery supply, not sure if that can be used for this purpose. also has a cover so shiny red button out of direct view:

www.solaris-shop.com

MidNite Solar MNBIRDHOUSE1-GRAY Birdhouse

Buy solar panels and complete solar panel kits for home or business. Solaris delivers quality solar energy products at wholesale prices.
www.solaris-shop.com www.solaris-shop.com
 
Q-Dog said:
Just wondering. I have a 24 volt system. If the breaker shutdown circuit is powered directly from the battery, would this satisfy the "fail safe" requirement? If the battery is dead there is nothing to shut down.
Click to expand...
Here's how the Midnite birdhouse seems to work. In conjunction with one of these:

www.solaris-shop.com

MidNite Solar MNBDM-48 Battery Disc Module

Buy solar panels and complete solar panel kits for home or business. Solaris delivers quality solar energy products at wholesale prices.
www.solaris-shop.com www.solaris-shop.com

Amazon/Stellavolta listing details the RT better:

"Remote Trip breaker for use with our Battery Disconnect module ( MNBDM-24 or MNBDM-48 ) and the Rapid Shutdown System. Remote Trip breaker for use with our Battery Disconnect module ( MNBDM-24 or MNBDM-48 ) and the Rapid Shutdown system. All MidNite circuit breakers can be used at 100% rated current when mounted in a MidNite enclosure."


And the birdhouse, it will disconnect the battery breakers (mnedc175 or 250 RT(remote trip), and breakers in any connected PV combiner boxes.

Ironically the RT models aren't UL listed like the regular mnedcs....
 
This would do the trick:

www.currentconnected.com

Tyco Kilovac DC Contactor - 500A Rated | Current Connected

Discover the Tyco Kilovac DC Contactor, the smallest, lightest, and most cost-effective sealed contactor with impressive current ratings.
www.currentconnected.com www.currentconnected.com

1718026904562.png

Has a coil "economizer" which reduces steady state on power to about 1.5 watts.

Your RSD button would have an NC contact that keeps the coil powered by the battery output voltage. Hit the RSD button, coil drops, contactor opens.

All the battery wiring from the battery box terminals, bus bar, to the contactor will remain live, however, so this would only shut off the relatively small wire from the contactor to the inverter. This seems like a lot of work for turning off very little stuff given the inverter is already shutdown under RSD anyway.

Mike C.
 
mciholas said:
This would do the trick:

www.currentconnected.com

Tyco Kilovac DC Contactor - 500A Rated | Current Connected

Discover the Tyco Kilovac DC Contactor, the smallest, lightest, and most cost-effective sealed contactor with impressive current ratings.
www.currentconnected.com www.currentconnected.com

View attachment 221033

Has a coil "economizer" which reduces steady state on power to about 1.5 watts.

Your RSD button would have an NC contact that keeps the coil powered by the battery output voltage. Hit the RSD button, coil drops, contactor opens.

All the battery wiring from the battery box terminals, bus bar, to the contactor will remain live, however, so this would only shut off the relatively small wire from the contactor to the inverter. This seems like a lot of work for turning off very little stuff given the inverter is already shutdown under RSD anyway.

Mike C.
Click to expand...
Can get those 2nd hand for $16 on batteryhookup if you do go in that direction.
 
I always find it interesting that inverters such as Sol-Ark 15K need a closed signal for rapid shutdown.... what if the wires burns through...? Kinda odd if you ask me. But then again, they didn't ask me, so there's that. :ROFLMAO:
 
Cmiller said:
I always find it interesting that inverters such as Sol-Ark 15K need a closed signal for rapid shutdown.... what if the wires burns through...? Kinda odd if you ask me. But then again, they didn't ask me, so there's that. :ROFLMAO:
Click to expand...
A way to (mostly) reverse this is a relay where the NC contacts shut down the inverter. The relay has to stay energized or it drops and closes the shut down signal on the inverter. You can put the relay right next to the inverter (maybe inside it) to minimize the exposure of the closed contact shutdown path.

I hate relays but sometimes they are the best fit for the job. You can get SPST-NC solid state relays, too, though they are not very common.

Mike C.
 
Q-Dog said:
Just wondering. I have a 24 volt system. If the breaker shutdown circuit is powered directly from the battery, would this satisfy the "fail safe" requirement? If the battery is dead there is nothing to shut down.
Click to expand...
There's still the possibility of the shutdown circuit failing, and becoming non functional.
 
Cmiller said:
I always find it interesting that inverters such as Sol-Ark 15K need a closed signal for rapid shutdown.... what if the wires burns through...? Kinda odd if you ask me. But then again, they didn't ask me, so there's that. :ROFLMAO:
Click to expand...
That's the purpose of "fail safe".
There must be a continuous signal to keep the system operational.
If that signal is lost, it shuts down.
No matter why the signal is lost, it should shut down.
If the wiring fails, it's rendered non functional. So, it should shutdown.
 
ok, here is another question. if I use the relay indicated above, it needs a constant voltage to keep the contactor energized so the shut off switch needs normally closed contacts. is there a switch that has multiple poles with NO and NC contacts that would work for the requirements of "the disconnecting means shall be lockable open in accordance with 110.25"

thanks for the answers thus far. you guys are helping me a lot and I hope we are educating others looking for the same information.

Don
 
timselectric said:
If the wiring fails, it's rendered non functional. So, it should shutdown.
Click to expand...
Unless the wiring fails shorted.

And this does happen, though not nearly as often as opens.

There is no absolutely fail safe method, only varying degrees of assurance. This is often measured in "nines", as in "how many nines do you want?". Asking for 3 nines would be 99.9% reliable, 1 in 1000 failures, 6 nines would 1 in a million failures.

Mike C.
 
dbwildes said:
ok, here is another question. if I use the relay indicated above, it needs a constant voltage to keep the contactor energized so the shut off switch needs normally closed contacts. is there a switch that has multiple poles with NO and NC contacts that would work for the requirements of "the disconnecting means shall be lockable open in accordance with 110.25"

thanks for the answers thus far. you guys are helping me a lot and I hope we are educating others looking for the same information.

Don
Click to expand...
Search for lockable E-stop.
Allen Bradley has several options. I have used their stuff for many years.
But, it's not cheap. You can find less expensive options that will be good enough for your needs.
 
timselectric said:
That's the purpose of "fail safe".
There must be a continuous signal to keep the system operational.
If that signal is lost, it shuts down.
No matter why the signal is lost, it should shut down.
If the wiring fails, it's rendered non functional. So, it should shutdown.
Click to expand...
No, you understood my comment wrong. The Sol-Ark inverters receive a signal to tell it to shut down. It's NOT a keep-alive signal! In other words, keeping the RSD contacts open keeps the inverter running. Shorting the 2 RSD terminals out via RSD button shuts down the inverter. Breaking that "shorted out" signal, allows the Sol-Ark to power back up.

As mentioned by @mciholas you can drive a relay via NC contacts on a button, then use the NC terminals as an RSD signal to the Sol-Ark. (When relay loses power because button gets pushed, it goes to "normal" position and triggers RSD.) The problem with this is that unless the relay gets installed inside the inverter, you still have a wire run somewhere that needs to stay connected to keep RSD activated.

Interestingly, IIRC the Tigo tap an CCA setup has an RSD input that is set up the same way. (It can of course just lose power when RSD occurs...)
 
Cmiller said:
No, you understood my comment wrong. The Sol-Ark inverters receive a signal to tell it to shut down. It's NOT a keep-alive signal! In other words, keeping the RSD contacts open keeps the inverter running. Shorting the 2 RSD terminals out via RSD button shuts down the inverter. Breaking that "shorted out" signal, allows the Sol-Ark to power back up.
Click to expand...
I see.
Yeah, that's not the way it should be.
 
Tim, can you quote "fail safe" in the RSD requirement?
 
timselectric said:
Yeah, that's not the way it should be.
Click to expand...
In general, the batteries which have RSD discrete inputs work such that open is on and closed is off, which is backwards of most e-stop and inverter RSD behaviors.

My assumption is that battery makers (the BMS makers really) want the battery to default on and not force every user to make a loopback plug on the RSD input.

Many batteries don't have RSD inputs at all, so they obviously default to on.

Mike C.
 
Hedges said:
Tim, can you quote "fail safe" in the RSD requirement?
Click to expand...
Sorry, I can't.
I don't remember if I read it there. Or if it's just from experience with safety shutdown systems.
I have never installed an engineered safety shutdown system that didn't require fail safe control circuitry.
And any that I have custom designed and built (without any requirements) have always been fail safe.
So, if it's not there (hopefully not the case), you might be able to get away with fail secure. But that kinda defeats the "safety" part of it. If something as simple as a loose connection or blown fuse, renders it non functional.
 
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