Fuse size question

[bluedog225]

Good morning

I’ve got a Victron 12/1200 inverter. It’s wired up with 2 AWG fine strand wire. As per the manual. This is the largest wire that can be used with this inverter due to the size of the attachment point.

The surge capacity on this 1200 watt inverter is 2400 watts (approximately 200 amps).

My understanding is that to 2 AWG wire is suitable for loads up to 120 amps. I have the wiring protected by a 300V 125 amp class T fuse in a blue sea fuse holder.

I ran a small refrigerator off this set up for about 12 hours from a warm start. The inverter seemed to handle the load without issue. The refrigerator and freezer got to operating temperature and it seemed to cycle normally. But overnight the fuse blew.

The running load of the refrigerator seems to be between 5 and 10 amps. I don’t have an estimate of the locked rotor amps.

I took apart the fuse and it looks like there was some corrosion in there, but who knows.

My question for you guys is, what’s the appropriate size of a class T fuse on 2 AWG wire in this situation? Am I being too conservative? Note, I need a class T fuse in this application, as this is a lithium iron phosphate battery with a very high discharge rate therefore needing a high amperage interruption capability.

Thanks

 

[walta]

If you used a reducer at the inverter, you could use a larger wire something like this.





Walta

 

[micromind]

Even though it doesn't exactly apply here, the electrical code has #2 fine strand listed at 170 amps at 75C, single conductor in free air.

 

[bluedog225]

Even though it doesn't exactly apply here, the electrical code has #2 fine strand listed at 170 amps at 75C, single conductor in free air.

That is helpful. I think the Blue Sea chart is based on the American Boat and Yacht Council which pretty conservative.

Do you know if there is a published surge rating for 2 AWG (fine) in free air?

I don’t mind a larger fuse but don’t want to risk a fire.

Thanks

 

[fitter30]

Looked at specs for inverter 2200 watts@12 vdc = 183.33 amps
1200 watts 100 amps
T fuse is fast acting
Need to call eaton or buss for fuse recommendation.

 

[dcg9381]

Do you know if there is a published surge rating for 2 AWG (fine) in free air?

Read your wire specs. Fuses protect the wire.

For a Victron 48/3500, I ran 1 gauge copper. I'm fusing it at 100A on 48V batteries which is very conservative. Rule of thumb is 125% of wire rating at rated temp spec.

You're at 12/1200 - so 100A continuous is "possible" (I know Victron rates them at temp) so your actual continuous rating is less.

Surge is tricky.

I've done a lot of DC to AC wiring with inverters, I don't like it when wires get "warm" (even when they are rated for it) - and like you, we've busted 1-2 fuses (I suspect due to improper start up). I definitely over-wire. Class-T fuses are fast acting, I'd say you could step up to:

120A (wire rating) * 1.25% = 150A class-T. What does the Victron manual say?

 

[bluedog225]

I pulled up the Victron manual online but it didn’t seem to speak to external fusing. And I understand that’s not really Victron’s deal.

I did go back and look at the wire seller’s website. I tend to buy quality stuff when I can figure out what that is.

Windy Nation did, in fact, publish a spec for this wire. I guess I got lucky.

My max amps from this inverter at peak surge is about 175 amps.

Looks like the wire is good up to 205 amps. I’m going to order a 200 amp class T fuse. Fingers crossed it will fit my fuse holder. It‘s sometimes a bit of a roll of the dice as the blue sea documentation is not great.

I’ll let the current fuse 125 amp fuse ride and see if it blows. When/if it does, I’ll use the 200.

Thanks all.

 

[micromind]

That is helpful. I think the Blue Sea chart is based on the American Boat and Yacht Council which pretty conservative.

Do you know if there is a published surge rating for 2 AWG (fine) in free air?

I don’t mind a larger fuse but don’t want to risk a fire.

Thanks

Surge current ratings are tricky; it depends on how long the surge lasts.

A #2 would handle 2000 amps but only for a fraction of a second. It would also handle 300 amps for at least a few seconds.