Wire for 125 amp fuse

[Isetech]

3 KVA inverter (around 13 amps) 16 amp and 1.5 would work however:
A 20 amp combo breaker with a green indicator light using 2.5 mm wire for the input.
32 amp changeover switch.
A 20 amp combo output with a red indicator light using 2.5 mm wire for the output.
16 amp breaker for the 3 socket outlets, wired using 2.5 mm twin+e
10 amp breaker for the light circuit fed from the inverter.
No earth leakage required for the inverter or the circuits (dedicated blue sockets for electronic equipment) and the inverter is mounted next to the main DB.

24 VDC system
2 x 100 amp/hr batteries in series
2 x 125 amp DC fuses (for the battery) mounted in an 8 way DB.

A look on the Alvern website (cable supplied by wholesaler) and a quick scan of the regs = 35 mm, right ?


the 230 VAC rating is 125 amps, does this apply to a 3 m length of 24 VDC
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[Justloadit]

No Earth - Neutral Bond?
No ELU after inverter?
When running of Mains, where is the ELU, before inverter?

[Isetech]

No Earth - Neutral Bond?
No ELU after inverter?
When running of Mains, where is the ELU, before inverter?

Neutral bond after the inverter (axpert inverter)

No earth earth leakage before or after the inverter, not required.

The 20 amp breaker feeding the inverter is in the DB above the inverter.

The light circuit has not fans or anything that required E/L protection.

The socket outlets are dedicated blue socket outlets, used for security system and electronics, all fed from 2 wire cables, no earth. 2 pin plug tops will be replaced with blue plug tops.

[Isetech]

Got prices for a 160 amp fuse holder and 125 amp fuses, eeeish it gets a bit pricey.

So my thoughts: Rather fit a 125 amp DC double pole din rail isolator in an 8 way DB and fit a fuse on the positive terminal of the battery. Looks neater and costs less.

[Isetech]

Working with this "little" 3 KVA unit has got me thinking, smaller unit than the usual 5 KVA units we install, everything must be smaller.

Got so many things going on at the moment, I finally got to sit down today and work on the 3 KVA unit.

My idea that everything for the 3 KVA should be smaller, right out the window, according to the manual, the typical power of the 3 KVA DC is 100 amps compared to the 87 amps of the 5 KVA.

The DC cables must be thicker and the fuses bigger.

The 3 KVA unit has a 142 amp DC input (24 VDC)

the 5 KVA unit has a 117 amp DC input (48 VDC)

The way I see it, the 5 KVA unit should have a 125 amp fuse and the 3 KVA unit a 160 amp fuse.

Reading information shared on the Victron website: A rule of thumb divide the current by 3 to determine the cable size

125/3 = 35 or 50 mm cable.

The 3 KVA unit with a typical current input of 142 amps, would require a 160 amp fuse with 50 mm\2 cable (fuse for protecting the cable).

I see a lot of installer using 2 pole switches for the batteries, I dont see why you would need a 2 pole fuse connector. Only the positive requires a fuse connector or isolator.

The solar DC is a different story.

[Alfred M]

3kva = 2400watts that is 10.5 amps on the 230v ac output side max thus at 24vdc you will only be pulling 111amps from the battery (24v dc) You are using 2x 12v100ah batteries in series 24v using that battery capacity with a 3kva inverter is not very much backup are you using lead acid,gel or lithium ion are you using in conjunction with solar arrays? Inverter 3kva with 100ah not a good combination

[Isetech]

3kva = 2400watts that is 10.5 amps on the 230v ac output side max thus at 24vdc you will only be pulling 111amps from the battery (24v dc) You are using 2x 12v100ah batteries in series 24v using that battery capacity with a 3kva inverter is not very much backup are you using lead acid,gel or lithium ion are you using in conjunction with solar arrays? Inverter 3kva with 100ah not a good combination

Backup only, no solar. Just to keep the lights on (all LED), alarm and computers.

100 amp/hr gel battery.

[Alfred M]

What is your total load in watts? You have 2400wh × 0.5(50%dod)=1200wh if you have a computer in the mix why don't you rather use a ups better protection and switching times

[Isetech]

Finished making the guard to fit below the inverter, it drive me nuts when I see these neatly installed system, then just below the inverter it look crap with all the pipes and cables hanging out the bottom. I decided to laser cut a guard for the space between the invert and DB's. the guard has slots so that it doesnt restrict the air flow.

Collected the 125 amp fuse holder and fuses today. Finished connecting the changeover panel and hooked up my the workshop remote viewing Pi loaded with with solar assistant.

Configured the inverter and plugged in the load box. At 60 % load the battery was already pulling 80 amps, so thank goodness I decided to use the 35 mm cable and 125 amp fuses. Waiting for the batteries to fully charge then I am going to do a 90 % load test and see how low it takes to get to the cutout voltage. I also want to do a thermal scan of the DB, Fuse holders, cables and inverter.

As I mentioned I have done many 5 kva units and thought, it is just a 3 kva unit, the 16mm or 25 mm wire supplied with the unit would be fine. It is going to be interesting to see the thermal scan results, once I start running the higher current tests.

I suppose you have to look at the application, is the inverter going to be loaded past 50 %, highly unlikely, so using 35 mm cable might be a bit of an overkill.

The other way of looking at it, if you load the inverter more than 50 %, you either gonna need a lot of batteries connected in in parallel or the system is only going to backup for a short period of time.

The next 3 KVA unit I will use 25 mm cable with 100 amps fuses, easier to work. Considering the batteries cables are so short (2m) , I can't see it being a problem.

This is the bonus about running these test before we install the unit on site, I can set the load to 4/8/12 or 16 amps and leave it to discharge while monitoring it with solar assistant

[Isetech]

What is your total load in watts? You have 2400wh × 0.5(50%dod)=1200wh if you have a computer in the mix why don't you rather use a ups better protection and switching times

3000VA = 3000 watt which means they say it has a PF of 1

DC = 24 VDC - 142 amps (so even using a 125 amp is lower than spec)

AC = 230 VAC - 13 A

The DOD (depth of discharge) is for the battery, depending on the type, lead acid for example, we set the cutoff voltage not lower than 11.75 VDC. We are moving away from lead acid completely, rather using gel as the cheaper option. It is going to be interesting to see how long they last. Lithium is the way to go, but the customer determines the type of battery by the budget, we all know the common response when quoting.