Mounting Blue Seas Class T's in EG4 Indoor Wallmount Battery Conduit Boxes?

[PVGeezer]

I need to add OCPD's to my (indoor) battery system as my EG4 18kPV's are outdoors about 25 feet away. The most straightforward approach seems to be to install class T fuses in the EG4 conduit boxes.

Because the conduit boxes are open at the bottom and assemble to the tops of the batteries I think they meet the Code definition of electrical "enclosure" (where fuses can be installed) rather than "raceway". Also the boxes are pretty big so should meet device and conductor volume requirements.

So I think it ought to be Code compliant to install fuses in them. Anybody tried this or something similar and/or found any Code or other practical issues that would preclude this approach?

Some (planned) details. 4 x EG4 indoor wall mount batteries with indoor conduit boxes mounted. 4, 250a fuses protecting both + and - 4 awg cables to each inverter, one mounted in each conduit box. Two batteries connected in parallel at each fuse using the supplied 2 awg EG4 battery conductors. I'm on NEC 2017.

Thanks!

 

[wpns]

Well, obviously only your AHJ knows for sure, but what are the fuses for? Don't the batteries have breakers like the WallMount OutDoor models? The inverters do, so I'd think breakers at both ends of the wire should meet any OCP requirements, no?

Another problem: 4AWG cables aren't going to handle the 250A peak current required by the inverters, and 25 feet of distance is going to require some pretty hefty DC cables to avoid excess voltage drop. Maybe you meant 4/0 but even that only meets the ampacity, looks like you'd drop about 1.5 volts in the cables at peak inverter power...

 

[PVGeezer]

Yeah sorry 4/0, one set of conductors for each inverter. I get 1.7% (0.8v) V drop @ 250A.

The fuses are needed for each 4/0 because all 4 batteries will be connected in parallel (at the batteries). They have 250A breakers so there's 1000A fault current available.

EG4 gets away with not having additional OCPDs in their standard installation because the inverters and batteries are co-located and they have an ESS listing so the cabling is considered part of the listed system. (No field wiring). I don't have that option. EG4 does note that you may need additional fusing if not installing the batteries and inverters per the manual.

I'm placing 250A fuses in both pos and neg legs because the EG4 battery circuit is ungrounded. OCPDs in all ungrounded conductors are both a Code requirement and good practice.

Sure, I can ask my AHJ but I've found it's preferable to already know the answers before starting those conversations .

So I was just wondering if anyone on here has their EG4 batteries and inverters distant from each other and if so where they placed their OCPDs.

 

[wpns]

I get 1.7% (0.8v) V drop @ 250A.

Per conductor, or for both conductors? And how much drop will you have across the fuses, lugs, and other wiring?

 

[PVGeezer]

Conductor losses per circuit. There will be two circuits (one for each inverter). Four 4/0 conductors total.

I don't have any solid data on what those termination and fuse resistances are. Ive seen numbers tossed about of around a milliohm for high current class T fuses so that would be around half a volt for two fuses in series. Adding termination losses, if I was forced to guess Id toss out a total battery circuit wiring loss of around 3% at peak load, but that's just a guess.

I'm good with around 3%, that's consistent with NEC guidance for branch circuits. Remember that this is at peak inverter load and losses go with the square of the current. I'm rarely going to be more than around 50-60A peak AC demand, so probably much less than 1% energy loss in the battery circuit on average. And this is only during outages, I'm operating grid tied 99% of the time. 1% of 1%....

But it doesn't matter does it? I need the fuses and my inverters and batteries are where they are. So if your point is to try to co-locate batteries and inverters as per EG4's recommendations, I agree. By all means do so if you can. I couldn't in my situation.

I guess no one has tried mounting fuses in the EG4 conduit boxes? I'll give it a try and see how it works out physically and with my AHJ.

 

[littleharbor2]

Please note, The T-class fuse is there to protect the battery cable first. Mounting it in the inverter is defeating the purpose of the fuse. It should be mounted as close as practical, to the battery.

 

[wpns]

Please note, The T-class fuse is there to protect the battery cable first. Mounting it in the inverter is defeating the purpose of the fuse. It should be mounted as close as practical, to the battery.

That's why he wants to install it in the conduit box on top of the battery.

 

[littleharbor2]

That's why he wants to install it in the conduit box on top of the battery.

"Because the conduit boxes are open at the bottom and assemble to the tops of the batteries"

Oops, I missed this part. I saw "conduit box" as being part of the inverters. Sorry for any confusion.

 

[wpns]

Yeah sorry 4/0, one set of conductors for each inverter. I get 1.7% (0.8v) V drop @ 250A.

The fuses are needed for each 4/0 because all 4 batteries will be connected in parallel (at the batteries). They have 250A breakers so there's 1000A fault current available.

EG4 gets away with not having additional OCPDs in their standard installation because the inverters and batteries are co-located and they have an ESS listing so the cabling is considered part of the listed system. (No field wiring). I don't have that option. EG4 does note that you may need additional fusing if not installing the batteries and inverters per the manual.

I'm placing 250A fuses in both pos and neg legs because the EG4 battery circuit is ungrounded. OCPDs in all ungrounded conductors are both a Code requirement and good practice.

Sure, I can ask my AHJ but I've found it's preferable to already know the answers before starting those conversations .

So I was just wondering if anyone on here has their EG4 batteries and inverters distant from each other and if so where they placed their OCPDs.

Sure, not trying to diss your requirements or poke at your constraints, I'd figure if you have that distance to cover it must be for a good reason. Heck, other's AHJs have required battery shutoffs on the outside of the building, which require much more extensive wiring. I'm just brainstorming the solution set.

Just because I like a lot of margin, I'd go with as big a cable size as you can get away with, and if your inverters shut down at high load at night when the batteries are low, you'll know not to do that, as it's (as you say) pretty unlikely.

Should be plenty of room in those conduit boxes for fuses, the one between my Primary inverter and it's battery is pretty full, but the one between the Secondary inverter and it's battery is practically empty, so without an inverter you've got lots of space to work in.

 

[wpns]

"Because the conduit boxes are open at the bottom and assemble to the tops of the batteries"

Oops, I missed this part. I saw "conduit box" as being part of the inverters. Sorry for any confusion.

Yeah, it's non-obvious, I didn't really know what I was getting till I opened the first one. Here it is installed on top of the battery:



Now I just gotta find a use for the four spares I have. 8*)

 

[wpns]

losses go with the square of the current

Power losses go with the square of the current, voltage drop is linear with current.

 

[wpns]

Also, just FYI there's a small gap between the back of the conduit box and the wall, at least when the OutDoor battery is properly mounted to the wall. Just so you know there's a little room for bolt heads or nuts.

 

[Quattrohead]

I used some self-tapping screws, vacuum out the swarf after though.

 

[PVGeezer]

Power losses go with the square of the current, voltage drop is linear with current.

Sure, in that paragraph I was estimating energy losses in the battery wiring. In my (grid tied) case it's really going to be very small, I think probably around 0.01%.

I'm more concerned about SOC management and battery imbalance. I will of course keep wire lengths to all the batteries equal.

I'm also thinking about adding an EG4 chargeverter connected to a 30A generator power inlet so I can transfer energy from my Ford Lightning to the house battery if needed.

The Lightning's capacity is 131kwh. So the equivalent of over $30k of EG4 batteries! Subtract that from cost of the truck and it's a true bargain .

The chargeverter would be right next to the batteries so minimal voltage drop on that circuit. Once in place I can also use the chargeverter for top balancing if needed.

 

[PVGeezer]

Sure, not trying to diss your requirements or poke at your constraints, I'd figure if you have that distance to cover it must be for a good reason. Heck, other's AHJs have required battery shutoffs on the outside of the building, which require much more extensive wiring. I'm just brainstorming the solution set.

Just because I like a lot of margin, I'd go with as big a cable size as you can get away with, and if your inverters shut down at high load at night when the batteries are low, you'll know not to do that, as it's (as

Should be plenty of room in those conduit boxes for fuses, the one between my Primary inverter and it's battery is pretty full, but the one between the Secondary inverter and it's battery is practically empty, so without an inverter you've got lots of space to work in.

Thanks wpns, the photos and suggestions are helpful. The indoor battery conduit box comes broken down, so it might work a bit differently, but I should be able to attach the fuse holders to it one way or another.

Article 480 in NEC 2017 requires a readily accessible disconnecting means in sight of the batteries but only on systems >60V. Didn't see a requirement for discos at the inverter side, unless the AHJ who required that was considering the battery conductors to be service conductors? Even then I would think that the battery breakers in the inverters would qualify.

But of course an AHJ can require whatever he wants. Mine is pretty sensible, he expects me to follow Code but I've never had him require additional arbitrary stuff. So I should be ok on that one.

I'm not looking forward to pulling four 4/0 THWN CU wires through 25 ft of conduit (with a couple 45 degree elbows thrown in just for fun). So I think I'll pass on bumping up to 250mcm, that would probably be pushing things. Gonna buy a gallon of gorilla snot and soak that sucker real good.