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Old 25-02-2015, 13:55   #1
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Inverter connection to battery - Fused?

Is there any need (or benefit) to inserting a high amp fuse or circuit breaker in the positive cable from a high capacity inverter to the positive battery terminal?

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Old 25-02-2015, 13:57   #2
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Re: Inverter connection to battery - Fused?

I did. In fact I think the manufacturer recommended it in their install manual. Nothing like an electrical fire at sea to make you wonder if it was worth saving a few bucks. Its never blown in ten years so I figured i've at least saved the cost of replacement fuses...

BTW, depending on it's size your inverter may have a BIG amperage draw from your battery bank, so you may need a BIG fuse. Check your inverter owners manual.
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Old 25-02-2015, 14:02   #3
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Re: Inverter connection to battery - Fused?

My Xantrex 2000 watt inverter stated in the installation instructions to put a breaker or fuse between it and the battery. I don't remember what size it called for, but I'd look on the manufacturer web site or the owner's manual.
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Old 25-02-2015, 14:08   #4
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Re: Inverter connection to battery - Fused?

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Originally Posted by BozSail View Post
Is there any need (or benefit) to inserting a high amp fuse or circuit breaker in the positive cable from a high capacity inverter to the positive battery terminal?

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Yes. First, the ABYC requires circuit protection in all circuits except in the engine starting circuit. Second, I assume your inverter came with instructions and I assume the instructions call for circuit protection. Third, it's good wiring practice and fourth, it's your boat that you are protecting from a possible fire.

A direct short from the battery terminal to ground can carry several hundred amps and melt any reasonably sized wire you might use. If the wire doesn't melt (and possibly set something on fire), the battery could explode.

If you didn't get installation instructions with your inverter, contact the manufacturer and get them. I would also suggest getting a book on boat wiring and studying it before you do any more electrical work on your boat.
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Old 26-02-2015, 08:23   #5
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Re: Inverter connection to battery - Fused?

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Originally Posted by rwidman View Post

A direct short from the battery terminal to ground can carry several hundred amps and melt any reasonably sized wire you might use.
Several thousand short circuit amps actually.

Always fuse the inverter positive cable near the battery post, or directly on the post. For a 2000 watt inverter using 2/0 cable a 250 amp fuse is appropriate. A 2000 watt inverter can pull about 200 amps DC.
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Old 26-02-2015, 08:37   #6
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Re: Inverter connection to battery - Fused?

Yes - as others have said you fuse to protect the wiring. Rating is easy - fuses are not very precise but if you divide the rating of your inverter by 12 (assuming you have a 12v system) and round up to the nearest standard rating AND check that the wiring matches this then that is your fuse rating.

eg. a 300watt inverter requires about 25 amps - say 30amps.

Cable size is likely to be length dependent 4sqmm will do if it is short (<2.5m each cable

a 3kW inverter would want a 300 amp fuse and at least 40sqmm cable.
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Old 26-02-2015, 09:16   #7
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Re: Inverter connection to battery - Fused?

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Originally Posted by rwidman View Post
the ABYC requires circuit protection in all circuits except in the engine starting circuit.
I won't speak to what ABYC requires as this exception for fusing is aimed more at large motors but fusing a starting circuit on a sailboat is something that you should do. The small motors in sailboats do not require many amps to turn over and many boats are set up with banks that are used for both house loads and starting.

Here are a couple things to keep in mind. When you size wires you do so based on the round trip distance (e.g. a 15 foot run from the battery to the engine is sized as a 30 feet, 15 feet of positive wire and 15 feet of negative wire). When you size fuses, you do so based on the wire size, if it is located in the engine room and whether it is a single run or a bundle of wires. If you reduce wire size as you branch off to other connections you need to add a fuse for the smaller wire. It is best practice to get the fuse within 7 inches of the battery; this might not always be possible but you should make all reasonable efforts.

The best resource I have found for sizing wire and fuses is this chart from Blue Sea Systems (warning it is a large pdf). http://assets.bluesea.com/files/reso...ence/20010.pdf

Another great resource for all things marine electric is the Compass Marine website. Compass Marine How To Articles Photo Gallery by Compass Marine How To at pbase.com

The owner of that website posts here as Maine Sail. He also has his own forum section at sailboat owners. Musings With Maine Sail - SailboatOwners.com

For installing inverters specifically, most manufacturers I have seen require the inverter to be installed close to the batteries (typically under 6 feet) and specify the wire size. Based on the specified wire size you can get the fuse size from the Blue Sea Systems chart above. For instance, Xantrex PROwatt SW 2000 watt inverter recommends a 6 foot run of 0 AWG wire and a 250 A fuse. That agrees with the Blue Sea Systems chart for a single wire inside of the engine room. Depending on your application this might vary.

Good luck and fair winds,

Jesse
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Old 26-02-2015, 09:29   #8
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Re: Inverter connection to battery - Fused?

Yes. There should be breakers for both the 120V side and 12V side of the inverter in order to reduce the chances of an electrical fire.
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Old 26-02-2015, 09:46   #9
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Re: Inverter connection to battery - Fused?

Inverter manufacturers almost always specify a Class T fuse. It is bulky and pretty expensive. Any fuse type would help but I tend to go with the recommended fuse type for each application.

Also size the fuse in amps to what the manual says as well. The inverter should be installed as close to the batteries as possible. If is close then you only need the one fuse regardless of whether it is a standalone inverter only or a combined inverter/charger.

If it is an inverter/charger the amps that it puts out in charge mode can be very large. Large enough to cause a fire if the wire is compromised between the charger and the fuse located near the battery. If the charger is a long ways from the battery you should consider putting another fuse close to the charger in addition to the fuse at the batteries.

Some may consider this overkill but it is a safer installation.
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Old 26-02-2015, 17:43   #10
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Re: Inverter connection to battery - Fused?

Yes, fuse it definitely.

One clarification: for direct connection to a sizeable battery bank (like a house bank), ABYC specifies that only fuses or CPD's having at least a 5,000 ampere interrupt capacity (AIC) are to be used.

Only three types of fuses in common use meet this AIC capacity: (1) the aforementioned Class-T; (2) an ANL; or (3) a MRBF terminal fuse. Of these, the Class-T is most often recommended and used.

Bill
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