sub panel wire/breaker question

zozomike

Hi, We currently reside off grid in a sort of temporary 800 ft sq space, but are building a custom 1000 ft house 50' away and will convert the original to its built purpose as a greenhouse. We have honed our power needs with all the normal efficiences, CF/LED lighting plus use a converted freezer for refrigeration, front load cold water wash, solar powered dryer (clothes line) induction cooktops solar oven, 100% solar DHW and passive solar heat with winter wood stove backup at night. So our power needs are of course a fraction of surburban households. Our 1970 watts of pv more than supply our needs plus light construction tools running most of the day. Our Outback VFX 3524 has been fine. Storage was an issue, but I think that is ok now. In the temporary residence we have a 100 amp 120v AC main next to the Inverter and all the equipment is close and fairly tidy. I do not want to relocate all that to the new house although the panels eventual location will be at the new house 130 ft from the CC, ground mount facing a 60x80 pond which should provide some reflection gains. Located at the south of the house.
The 12 panels are in 4 strings currently 80' from other equipment and feed the Flexmax 80 at 90-100 VDC, run in 8/2 with ground UF_B, That then goes to the 804 AH GB Industrial battery a few feet away. At the new house I have built a south south summer shade soffitt above the 8' high direct gain window wall which is designed to carry another future string of PV should we ever require. I have installed a 100 amp sub panel at the new house, planned to feed it from a 60 amp breaker in the first panel and supply it with 6/2 UF-B with ground. Since the Inverter we have can only supply 3500 kv, I believe that wiring (6/2) will be adequate, 3500/120vac=29 amps. If we should however decide to add the extra string, and its own CC I might wish to consider a second inverter, In that case would the 6/2 be inadequate? I cannot find any heavier guage in UF-B so what should I do? I only want to did that ditch one last time! Inspections are not an issue out here BTW, and I have tried several times to connect with professional installers in the region and no one seems to be willing to go near a home built system. I suppose they have their own trust issues about giving paid advice. Don't blame them.

Cariboocoot

Re: sub panel wire/breaker question

So the question is: if you double up on the VFX 3524 will 6 AWG wire handle the combined current?

Well 6 AWG is good for about 70 Amps continuous so yes it would, and if there is a 60 Amp breaker on the line that would trip before the wire would fry.

But why do this? In addition to being able to stack VFX inverters in parallel you can also stack them in series, giving you 240 VAC split between two legs which is much like standard household wiring anyway. Then you would run an adequate (8 AWG) 3 wire conductor to the panels from the inverters and no concerns about >30 Amps on it anywhere. Just another way to achieve the same total power.

With 1970 Watts your FM80 will be putting out a bit over 60 Amps to that 800+ Amp hour battery. If I were you I'd max out that array and controller first before thinking about second controllers or inverters.

vtmaps

Re: sub panel wire/breaker question

As Cariboocoot points out, when you want to push more power through a given conductor, raise the voltage. If you get another inverter and stack it in series to make 240 volts split phase (as Cariboocoot suggested), you can still use your 2 conductor cable, but you lose the split phase and will need a transformer at the house to drop the voltage back down to 120 volts.

In some situations you may be better off with single phase power. 240 volt split phase power likes to have its two 120 volt legs as balanced as possible. The transformer balances the split phase power so that there is only one, single phase leg at the house.

--vtMaps

zozomike

Re: sub panel wire/breaker question

Cariboocoot wrote: »

So the question is: if you double up on the VFX 3524 will 6 AWG wire handle the combined current?

Well 6 AWG is good for about 70 Amps continuous so yes it would, and if there is a 60 Amp breaker on the line that would trip before the wire would fry.

But why do this? In addition to being able to stack VFX inverters in parallel you can also stack them in series, giving you 240 VAC split between two legs which is much like standard household wiring anyway. Then you would run an adequate (8 AWG) 3 wire conductor to the panels from the inverters and no concerns about >30 Amps on it anywhere. Just another way to achieve the same total power.

With 1970 Watts your FM80 will be putting out a bit over 60 Amps to that 800+ Amp hour battery. If I were you I'd max out that array and controller first before thinking about second controllers or inverters.

Cariboocoot I had not thought of that at all AND I LIKE IT! But I did think that I would need to add a second controller for the new string, Is that not correct?

Cariboocoot

Re: sub panel wire/breaker question

zozomike wrote: »

Cariboocoot I had not thought of that at all AND I LIKE IT! But I did think that I would need to add a second controller for the new string, Is that not correct?

An FM 80 can output 80 Amps @ 24 Volts, or basically the power from 2500 Watts of array.

zozomike

Re: sub panel wire/breaker question

Yes, well I made space at the shade soffit for 6 ea 245-250 watt panels, ( thinking Solar Worlds) which puts me beyond reach of the FM 80, but I have a spare FM 60 which I think would handle the extra 1500 watts. So as to construction, if I understand correctly That ditch I have to dig needs a run of 8/2 from each array to controllers, ( 2 runs) and one run of 8/3 with ground between the load center and sub panel. I should add the extra array and controller ASAP, and when the funds allow add a second VFX 3524 in series. Basically now all I have to buy is the wire, the 6 panels and combiner as well as the extra cables to the battery of course. Is that what I'm hearing?

mmag

Re: sub panel wire/breaker question

When I priced uf wire it was similar in price to running conduit with wires in it, and the conduit will give you more options in the future.

zozomike

Re: sub panel wire/breaker question

mmag wrote: »

When I priced uf wire it was similar in price to running conduit with wires in it, and the conduit will give you more options in the future.

I'm sure you are correct about conduit, and a generous size with a string inside makes for much easier additions. Conduit is more labor for sure. and I have basically one run of 70' which then will diverge to three different locations, Hmm Ive seen factory electricians do that sort of thing and much more, not sure I am one of those but my little backhoe will let me run wire anywhere, ( untill I cut into something else.)

mmag

Re: sub panel wire/breaker question

Another thing to consider is if you want to have a battery moniter in your house, or any other gadgets? I was told to put mine in a separate conduit so I didn't get interference from the power wire

zozomike

Re: sub panel wire/breaker question

OH s!!!, I had not thought of that either, but that control wire could lay in a 3/4 pvc conduit in the same ditch? BTW thanks!

mmag

Re: sub panel wire/breaker question

Yeah I put my trimetric wire and cat 5 cable for my inverter remote in a seperate conduit in the same trench