cable hookup

[libra]

I was to a local ae shop this morning. I inquired about conduit to protect the cable to and from the battery and was informed that the wires HAD to be run parallel, and strapped together and then enclosed in a pipe for protection.

This is all new to me as I haven't seen anything refering to this in all me searching on the net.

I would appreciate any comments and suggestions.

Libra

[whatsnext]

Libra, Do you live somewhere where this is part of the building code? Otherwise his recomendation seems a bit much. I would think that protecting the terminals from shorts would be a much better use of your time but you can never be too safe with electrical stuff.

John.......

[veewee77]

The wires do not have to be run in conduit unless it is a commercial building, and the reason they need to be run parallel and bound together is to help reduce noise interference.  They actually don't have to be bound together, but if they are, they will stay close together.

Doug

[Vtbsr]

There is a lot of info in the trace manual on battery inductance. You want to keep the cables short and taped. The induced current opposes the applied current(bat curent) which directly causes a loss of inverter performance as reduced efficiency. One scarry thing is flyback effects. That is if the the battery were suddenly removed from the circuit you could get a induced voltage spike in the thousand volt range. There is a table , taped together 3.3 micro-henries inductance, 12 separation 6, and 48" separation 8-9 micro-henries. You might find a lot of info at www.traceengineering.com.

[libra]

This is what I was looking for. It was just that I have never heard of this before.

I am in nw Ontario and have heard that the inspectors are not familiar with dc and prefer to look the other way as long as it is neat.

I would much rather take a little more time, get it right but prefer to know the reasons why things are done rather than they must be done this way because somebody said.

 Appreciate the help guys

Libra

[Ungrounded Lightning Rod]

Running your DC wires close to each other, twisted, or inside a conduit (grounded - drained - at ONE end, though the other may PROVIDE a frame/protective/etc. ground to the inverter or something else if you avoid ground loops) will also help keep down radio interference from the inverter - especially if it has inadequate interference-filtering on its input.

In addition to the interference issue, you NEVER want a loop in your ground or return - especially the protective ground.  Such loops can cause neutral-return, ground-fault, or lightning/surge currents to go places they should not on undersize wiring, increasing the risk of fire.  That's also why neutral is tied to ground in ONE place - typically the main or meter panel - in a utility-fed house's wiring.

Be sure to have a fusable link (i.e. high-current fuse) at the battery end in case the insulation fails somewhere between the battery and the rest of the system.  Otherwise an insulation failure is a fire within seconds.  Do this anyway, but be especially sure to do it if the battery wiring is running close, taped together, twisted together, inside a conduit, etc.

[Ungrounded Lightning Rod]

you NEVER want a loop in your ground or return ...

In this context "loop" means wires connected so that they form a closed circle, allowing currents to split between two conductors.  (You sometimes do that deliberately inside motor windings and transformers, but never on interconnects.)

There's another thing called a "loop" - a j-bend, u-bend or full-circle twist in a single conductor - that you also try to avoid in grounds and returns (though not as religiously) and put in some other things - like antenna cables - in particular ways.  This is because the sudden start/stop of lightning currents corresponds to a high-frequency signal that doesn't like to go through an inductance - and a loop has much more inductance than a straight (or gently curving) run.  So lightning will tend to jump out of a wire just "upstream" of a loop and take some other path.  In wiring you usually want the lightning, once it's in a wire, to STAY in the wire until it gets to the neutral bond, then exit through the house grounding system, rather than jumping over to, say, a water pipe and run along/through (and maybe damage or ignite) some flamible structural material (or body) on the way.

In antenna and satelite/cable-TV wires you do things like put a lightning arrestor or cable ground-bond just upstream of where the wire will enter the wall, and run the line as straight as possible to a ground rod or pipe connection.  Then you put a J-loop (like a J-trap in a drain) in the wire between the arrester and the wall entry - typically right at the entry.  The lightning current goes (mainly) down the ground rather than take the bend.  Also:  Rain runs down the loop and drops off the bottom, rather than trying to run into the wall and rot it.  (That's why it's called a "drip loop", even though its primary purpose is electrical.)

 

[Experimental]

 Libra,  It was mentioned that the neutral lead should be connected to ground !!  

     This is the normal situation in house wireing --BUT !!!  In most of the inverters, commonly sold, this will result in a "burned up", inverter !!

     Read the instruction book that (should) come with your inverter -- most warn you to not hook up to any breaker box, with a grounded neutral !!!!

    Xantrex inverters are very specific to this situation, and I have personal experience, with a "smoked", inverter from this very problem !!

    For a very good fuse block and fuse -- go to your local NAPA auto parts store and ask for the RV fuse block (about $12) and 200 amp fuse --- very good quality and has a rubber cover over the connections !

    I would have included the part numbers, but don,t have them on hand now -- Good luck --- Bill H.....

[bryant wind electric]

 Libra, inductive effects are minimized by taping the cables together. We tape them about every 18 inches or so, and when multiple bundles are being pulled we use color coded tape on each bundle.We also use PVC conduit rather than metal conduit. When wiring your project, if it is to be inspected, arm yourself with the latest issue of the NEC first. It will answer many questions you will undoubtedly have. Remember when wiring, that the current carrying ability or "ampacity" of a wire or cable, will differ drastically depending on whether its installed in "free air" or in protective conduit or raceway. Even the type of insulation and temperature come into play when wiring to meet code. THHN wire, for example, will have a different value than the same guage wire with a different type of insulation. The code book will lay it all out for you, including how many of what size wires are allowed in any size conduit, and what size conduit you need. There is an excellent section in "Home Power" magazine called "Code Corner" by John Wiles, I believe. He does a great job of clarifying a lot of code issues. One last thought.. When using wire and conduit in your system, plan ahead a little. We always use bigger conduit than required, and larger cable than needed.Never settle on the absolute minimum you can get by with. It insures good performance and minimal volt drop over long distances, and later on when you want to add those PV panels, - you can- with minimal system rework. Also, pull an extra "dummy wire" when pulling your main bundles. The " dummy wire" is a small gage ( AWG 10) wire that is capped at both ends and is not installed to carry any power at all. Later on, when you have to try and pull an alarm circuit or communications cable or whatever, you will be glad that you do not have to try and feed a fish tape through that jumble of wire in that nearly full conduit.Just attach your wire bundle to the already threaded wire, and its "like butter" Hope this helps some. Best of luck with your project! Terry Bryant