Grounding and fuse and wire size

System

I am building a small residential stand-alone system of 4 Kyocera 125 panels, a 60 amp charge controller, 8 Trojan T-105 batteries and a Vector 3000 watt inverter.  The panels will be mounted on a steel cargo storage container and the rest of the system housed inside of the container.  The run from the batteries to the inverter is about 5 ft and would use 4/0 cable. What size cable do I need to use on the battery connections and what size fuse and disconnect between batteries and inverter?  Does the steel container present grounding problems or can it be used as a ground?  Wires form the array would be 8 AWG USE-2 and then go to 6 AWG THHN.  What do I need for equipment grounding and can I use a 6 AWG ground to ground rod or do I need 4/0?  What size ground rod and where do I find one?

Lot's of question, Thanks for your help!

niel

Re: Grounding and fuse and wire size

sunchaser,
you will find on the next page a calculator that uses excel. you need to know the current that has to be passed for a specified distance and plugging in different wire gage numbers will show the voltage drop and the voltage drop percentages. we try to keep it under 3% from the pvs to the charge controller, but some specify under 2%. if you have trouble i can calculate it with knowing the distance and maximum current it is to pass.
the inverter fuse if not specified by the company can roughly be figured by taking the maximum watts of 3000w and divide it by 12volts to come out with 250amps. using a circuit breaker rated for 250amps dc can be both your circuit protection and disconnect to the inverter. i would use no less than the same 4/0 between the batteries for interconnecting them.
now the grounding of the container is seperate from the grounding of your pvs in that the pvs must have a solid run to the ground rod and using #6 will be fine, but if you have #4/0 arround it won't hurt although it is overkill. the container ground shall also go to the ground rod with at least #6. now the rod itself must be 8ft in length and copper clad or coated. this is usually available in electrical supply houses, but you could check with home improvement stores as well for it. if all else fails call an electrician and ask then where you can get one.

Patman3

Re: Grounding and fuse and wire size

I just bought a 1/2" x8' copper ground rod from True Value hardware for about $18. They had marked it up from $14 because of copper price increase. Make sure you get a ground rod clamp for the wire. Here in the desert my dad recommended I pour some water around the rod every 2 weeks or so. He also thought braided wire was better than solid.

niel

Re: Grounding and fuse and wire size

braided wire is good for a ground wire and for radio work, but not underground as this is a definite no no. just be sure of the total equivalent wire gage the braid equals as it should be at least #6. braid underground has more area to decay from corrosion and will break. solid wire is less apt to corrode through and break electrical contact in the soil. you will also find that the braid is much more expensive for the same gage # equivalent. if you're not into radio transmitters then don't bother with the ground wire being braided. i have transmitters, but i just use several smaller wires together to go to ground to give that greater surface area effect they call skin effect. for pvs you just don't need to consider that at all, but you do need to have a low resistance path to the ground.
rather than putting water on the rod try placing a few #14 or #12 radials out from the rod 1 or more feet underground by 4, 5, 6 or more feet in length. even if the smaller wire corrodes through in the soil, the soil would still have higher conductivity due to the copperoxide left behind in the soil and the basic ground rod system would still be intact. if you're in a sandy soil area you can add water occasionally too, but would you remember to always do that and would you want to? it may make a slight difference when a storm is approaching as lightning can lead the rain in a storm. i tend to go on and on at times so i think i'll stop here as you got more than a comment, but an editorial. :-D

Patman3

Re: Grounding and fuse and wire size

I appreciate any comment and especially an editorial - Thanks Niel!! 73's