how much battery cable in conduit?

[solarvic]

I am ready to start running conduit for my inverter cables. Going to have 2 sets of 4/0 cable. Should I have 2 runs of conduet so each set of cables would have its own conduit or is it ok to have all 4 cables in 1 conduet. Conduit is 2 1/2 inch inside dia.I tryed putting all 4 cables thru a piece of conduet I have and I kind of think 4 cables in 1 conduie seemed kind of tight. solarvic

[BB.]

For AC power circuits--They MUST be in the same conduit and go through the same, single, panel opening into the power box. If you "split" the cable run for AC cables, the current is actually AC coupled into the sheet metal (if going through separate openings in the side of a main panel as an example), and cause the sheet metal to overheat.

With DC power cables, there is some ripple current on the input power cables--but you could run them separately (you will not get the circulating currents like AC would create).

However, it is a good idea to run +/- cables bunched together (same conduit, etc.) and not make any "loops" between them.

Basically, looping/separate +/- runs makes the cables a "better antenna"... Both for transmitting (inverter noise getting onto AM/FM radio bands) and for receiving energy (lightning strikes, nearby transmitters, etc. which can damage/interfere with inverter operation or bring noise into AC electronics).

So, if you can keep them bundled together and in the same conduit, you should be much happier with the results.

-Bill

[solarvic]

It just seemed that having 2-+ and 2- - cables going thru one 2 1/2 conduit seemed preety tight so I just went and bought another piece of conduit for for 2 separate runs. This is DC 24 volt inverter cables. 4/0 size copper. solarvic

[RCinFLA]

You should have battery +/- cables in pairing together. This help cancel out their magnetic fields. From a single phase AC inverter there will be varying current in the battery lines that can cause a magnetic buzz to any loose metal nearby like a lid on a breaker box. For sinewave inverter the current profile is like a full wave rectified shape yielding a 120 Hz ripple. For a MSW inverter there will square box current pulses with near zero current gaps.

Pairing + and - battery cables also cuts down on their net series inductance which is helpful to reduce the battery line impedance as seen by the inverter. Lots of cabling inductance will cause extra ringing of the inverter DC input voltage.

As to putting more then one pair per conduit, it depends on heating IR loss in the confined space. Generally for low voltage battery linesyou should not have enough IR loss to be a problem since you are striving for low resistance lines to avoid voltage drop to inverter.

[john p]

If you twist each pair the + and - cables together. you will get even less problems.

Easiest way to do this is lay the lengths of the + and - cables together in a straight line.tie the two ends together to something solid.ie a post ,about 3 ft above the ground,get a short length of "fencing wire" and use it to tie the other ends of the cables together tightly ,then make a tight loop that extends past the cable ends . put that end in an electric drill chuck hold the drill and the cables reasonably tightly above the ground and parallel to the ground then power up the drill and keep going until you have a nice twisted pair. NOT too tight a twist. just until it looks "nice" They will stay like that after yoiu have finished then feed them through the conduit.
I patented this idea about 45 years ago, but the patent is only valid on Christmas day if it falls on an even number year and there is a lunar eclipse.So it ok to use other times.

[Solar Guppy]

Please post a picture of this technique in action utilizing the OP's 4/0 wiring

[solarvic]

I was thinking of putting all 4 of the 4/0 cables thru 1 2 1/2 "conduit. Layed a piece of 10 ft straight on floor. First of all the terminals altogether wouldn,t fit. So tryed stagering them in length. Wasn,t very successful and the cables were tight. Then I decided two separate conduits were better. I am having 1 inverter for household use and another one to run my 240 vac pump. I don,t know how well it will work till I try it. If the 2 4000 watt inverters don,t get enough power from my battery, then I have an 1100 watt exeltech inverter to go with one of the 4000 watt inverters. I know I won,t overload the inverter cables, but might overload the battery. Only testing will tell.
solarvic

[john p]

I am at home and dont have some lengths of #4 cable to demonstrate but have a look at this #6 cable and how the wire end is made to tie the ends together and how the loop is made to go in the drill chuck..
it works very well on up to #2 cables.
After having a look at the photo make the loop so it just long enough to go in the chuck and tie the wire around the cable ends a bit more securely than in the photo. but it will give you the idea how its done..

[DavidOH]

I learned a few things reading the National Electric Code.

I had a couple of questions:
Q: Can I run AC and DC lines together?
A: NO! The AC will "bleed" into the DC line.

The twisting pairs ( + and - ) together will "negate" each other from causing electromagnetic interference.

The NEC found here was useful in answering some of my questions:
http://www.nfpa.org/index.asp

If you sign up as a member ( no charge ) you can access the on-line document to read it.

[Vic]

johnP,

The cable in question is 4/0 or 0000 cable, or four ought.
The recommended twisting in a drill will make it fatter, and the drill would probably need to have a five HP gas motor. Kids, do not try this at home!

vic, I ran four 4/0 cables in two inch EMT, but the thickness of insulation is critical. Recently ran four 4/0 cables in 2.5 inch conduit, as it is closer to code. These cables were standard UL listed 105 degree insulated battery cable wiring, with lugs on the end. Altho, if was fine stranded cable, perhaps about 200-ish wires per cable.

In pulling into two inch EMT, did stagger the lugs, and the cables were only five and one half feet in length X four cables.

In my case, the derating may have been fudged for two inch EMT, as the two negative cables are in parallel. Whatta I know? Vic