Battery Cable Size for 2000W Inverter

[MikeP]

"Using 2 smaller cables that when added together will give you the capacity of the required larger cable is a no no. If at some point in the future you get a poor connection on one of the 2 cables the remaining good cable will try to carry the load and can overheat."

Good point and you are right, it cannot possibly meet safety requirements for that reason.

It was a bad suggestion on my part; DON"T do it.

 

[Avenger]

You can get tinned welding cable. I believe the problem with it is that the insulation doesn't meet requirements for oil resistance, which makes it a no-no in machinery or bilge spaces.

 

[Pascal]

soldering battery cable is a no no on boats because of vibration. only crimping will do.

i was going to mention somethign like your diagrams.

when using multiple batteries in parralel in a bank, the best way to connect them is to connect the + on one end and the - on the other one. it spreads the load on the batteries. so if you have bank used for inverter and house, i don't see why you woudn't be able to connect them at each end.

ex. connect the inverter + and the house/start - at the battery at one end, then the inverter - and the house/start + at the battery at the other end.

 

[sgharford]

Outside of finding 500 MCM marine grade wire for the negative side, I think the better choice is two grounds. I am sure there is a better way, just not sure what that is.

 

[Sonny]

"Out of curiosity - If your inverter is wired to 12 volt house bank, how was it done on your boat?"

My inverter is mounted a few inches away from the battery bank. It's a 2kw
Heart/Xantrex with an intermittant transfer switch issue.

 

[sgharford]

So I read the bible this morning ("Boatowner's Mechanical and Electrical Manual" by Nigel Calder) for further enlightenment. He specifically calls out in inverter installation using a (very) large negative ground from battery to bus bar. The bus bar then ties to all other items like starter, DC Panels, and Inverter. I think I can use single lug on starter as my bus bar since I believe only one wire on it thus far directly from battery (I think DC panels grounds are taken off somewhere else down line). If not, I’ll add bus bar if too many cables off starter lug already.

So I will have new 500 MCM (bigger than 0000 cable) negative side battery cable made and attach to starter. Then I will have 0000 ground cable go from starter to inverter. Below is DC wiring game plan.

Note that manual calls for 300 amp Class T fuse using 250 MCM wire (next biggest size to 0000), but 0000 wire is only rated to 260 amps so I am going to use 250 amp Class T fuse instead? Rob – thanks for pointing out that manual calls for specific fuse type.

Per Keith, I will try cabletech.com to see if they carry appropriate 500 MCM tinned wire with proper marine rated insulation and follow up with this post where one can have cables this large made. I will order 0000 cable and connectors from Genuine Dealz as this is largest size they carry. If anyone thinks they see problem with design, please chime in.

 

[Silverado6x6]

http://www.cableyard.com/catalog/product_info.php?cPath=21&products_id=35

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My footnote: I live in Alaska and this cable type is used in really severe conditions, hope it helps.

 

[sgharford]

Here's a place for really big cable - Apparently wire this size is called "Diesel Locomative Cable".

http://gencable.com/index.shtml?cables/dlo.htm

 

[34Hatt]

We use 500 MCM here in work it is HUGE don't even think about something that big it is not needed. The 0/0 is fine fror 2000 watt. I used 2/0 on my 1500 watt system.

Also you made a comment in the very beginning about using 390 amp/hrs max.
You are putting in two 275 for a max of 550 amp hr so you do not want to use more then 50% so 225 amp hr is all you should pull out so that the batteries will have a longer life.

 

[sgharford]

I was talking to Mike from Genuine Dealz who appears to be very well versed in the world of cables. He spent about 40 minutes on the phone with me - would not expect this kind of service from a web driven storefront.

Basically we (well, really Mike - who walked me over the phone thru NEC tables via internet he was looking at) came to deduction that Xantrex based their wire sizes on NEC table 310.16, which list wire sizes for buildings in Conduit, which is completely inappropriate for a marine/rv application. Since wire in conduit, it has to be further de-rated because of additional heat in conduit that causes additional resistence.

The correct NEC table to reference would be 400-5b, which is for single conductor open air cable. Much higher amp ratings for wires. ABYC 25 ( Pertains to inverter wiring http://74.125.45.104/search?q=cache:tA41GNYgheMJ:192.82.104.224/documents/standards/abyc/A-25.pdf+ ) has even more liberal ratings then 400-5B. He also found another listing on how to install marine inverters which appears to be a written by reputable person at http://www.jtbmarine.com/installing.pdf which I am going to read.

Xantrex does not give any other options in their wiring specifications - only as I stated - 250 MCM for 0 to 6 feet, 350 MCM for 6 to 12 feet. Apparently this is beyind overkill by ABYC standards. Basically, from what I have read - NEC 310.16 has 0000 wire rated for 260 amps at 90 degrees F while ABYC has it rated for 378 continous amps inside engine spaces at 105 degrees and 445 amps outside engine spaces at 105 degrees.

I think we all agree Xantrex needs to modify their owners manual for marine installation. I am going with 0000 for entire installtion. Thanks everyone - what a pain in the rear this was.

 

[sgharford]

I promise to let this thread die after this. I checked Magnum’s 2000 W inverter installation manual and they too recommend 4/0 (0000) wire for installation. Looking at ABYC E-11 Table IV (http://www.pkys.com/Reference.htm )which is apparently applicable to inverter installations they list the following “Allowable Amperages” for wires run inside engine rooms:

1/0 – 242 amps
2/0 – 280 amps
3/0 – 327 amps
4/0 – 378 amps

The appendix of Xantrex Prosine 2.0 manual says nominal current at full load is 200 amps. You think they would have listed the Full Load Amps when the thing starts up if they are telling you to use 250 to 350 MCM wire. FLA not listed anywhere. With info they provided, 1/0 wire should be fine if not for mandate that 300 amp breaker be used in which case I guess you have to size wire at 3/0 which is still a big difference from 250 MCM.

I think the problem with both Xantrex and Magnum installation manual is that they took worse case installation scenario – even though that scenario not explicitly stated ( appears they assume permenant mount in building that requires wire run in conduit) - and give wire size for ONLY that type of installation. If this the case, then they should also give Full Load Amps so installer can apply proper codes based on particular installation (ABYC for marine) or, better yet – give an extra paragraph in their 50+ page manuals that gives wire size for buildings, boats, and RV installations based on applicable codes and save the user the trouble.

 

[Boatsb]

I have a 2k watt inverter and the instructions required 2/0 for short runs ( I forget how long) and up to 4/0 for long ones. Mine ran 8 foot so I was safe with the shorter one. I almost never use it so I can not speak of the durability of the wiring but it did not seem to get hot when I tested it at the largest load I could.

 

[Beckytek]

On the 2 diagrams you posted one had a negative ground. On the other it looks like you have a positive ground. On my starter, the + positive is connected. Better check that polarity.

 

[Pascal]

i think you're making this more complicated that it needs to be. 2000w inverter, 6 to 10' wire run, use 4/0 marine cable. simple. that's what is recommened in the Xantrex Freedom and Magnum Inverter I've used. Run that straight from your battery bank, don't mess with the starter system, with a 300amp fuse and heavy duty battery swtich.

i like the KISS method... (Keep it Simple Stupid)

 

[sgharford]

I replaced the starter over the summer and thought the battery was ground to starter, probably was + like you said. I'll be back to boat over weekend and see what I really have. If inverter (really) needs 4/0, then one would think that you would need single point ground to battery larger the 4/0 if it's going to handle the inverter and rest of DC load (starter and DC panels). I'm going to get actual amps off starter nameplate and estimate all current DC loads plus measure actual wire already in place to see if jiving with ABYC E-11 Table IV. I'll post new "planned install" diagram on Monday based on findings. I'm hoping this thread will help anyone in future that intends on installing a 2000W inverter on a 43 DC in particular, although thinking I would start a new one when I get the AC side done to so it all can be reference in one place. In retrospect, should have laid out existing DC wiring configuration before posting – got ahead of myself.

As an aside, per a prior post on 43 inverter post that someone suggested, I was going to split the current AC panel so one side is fed directly from inverter. The other side will be fed directly from either shore power or generator. The water heater, stove and battery charger will be on that side, while the lights and refrigerator will be on inverter side. If you run both sides through inverter there is a potential to run 50 amps through the inverter automatic switchover relay that detects when external AC is present which is only rated for 30 amps. This can cause relay to weld shut (Xantrex put a notice out about this on their web-site). Interesting that stock AC panel design can blow 30 amp fuse for shore power by having everything on, but the generator can handle the whole thing (has a 50 amp breaker).