Wire sizing

[fallguy]

So, I have a simple 30 amp, 125v shore power entry.

i plan to wire it with 10/3 to galvanic isolater

then to a victron multiplus inverter

the inverter is sourced from the battery bank as well at 24v input from a small bank of two 12v in series agm batteries say 100 ah each and 24v

the inverter ac output says 50-67 amps rating

Does the inverter output wire need to be a #6 wire when only a #10 wire sources it?

 

[gonzo]

This should give you the information. For DC you need to calculate the voltage drop from the cable run length, which may make the required size larger.

https://uscgboating.org/regulations/assets/builders-handbook/ELECTRICAL.pdf

 

[fallguy]

The thing is so strange. It is called a 2000w inverter. 120v output is 16 amps. Input current is max 30. But the thing says output current rating is 30 plus the 16 or 46-47 amps. Apparently, it can provide the shore power plus battery power outputs. Thus the AC output current can be higher than input.

@gonzo --would you ever find a problem at survey if the input current wire rating was lower than the output? Or, to rephrase. 10 wire incoming and 10 wire outgoing vs 10 wire in and 6 wire out???

 

[fallguy]

Also, I am having a hard time sourcing a few feet of 6-3 ancor wire. Does AC wiring on a boat require shielding or can I just buy #6 wire by the foot without the xtra shielding?

 

[Rumars]

The name gives it all away: 24/2000/50 means 24V DC battery, 2000VA AC output, 50A DC battery charging.
The victron multiplus has a power assist function, allowing it to combine battery power with ac mains power when the loads exceeds ac mains supply. 1600W is the continuous power it can supply at 77°F, 4000W is peak power. Peak power can only be sustained for a few seconds, it's there to allow for things like starting a motor. Power assist is used for example if your shore power can only deliver 15A, and you need to start a motor, or if the shore power is less then 13A and you use continuous full power. The inverter can not ever deliver 46-47A at 120V AC. It will deliver 50A DC to the batteries in charghing mode.

You wire your AC side with appropriate cable for the VA rating, meaning both AC input and output are ok with 10AWG. The DC side needs to be dimensioned for the maximum expected load and distance to batteries, and it pays to be on the safe side, so you use the inverters peak power rating. 4000W/24V=166.6A, then you measure the circuit lenght to the batteries by adding the lenght of both wires, and use a wire sizing chart to find the size. If you need 10ft of wire from inverter to battery, you look in the chart for 20ft, 166.6A and find the nearest size, wich is 2/0AWG.
Wire size chart Part 1: Choosing the Correct Wire Size for a DC Circuit - Blue Sea Systems https://www.bluesea.com/resources/1437

 

[fallguy]

I have no issue with the DC side.

here is the verbage from them word for word

• AC-out
With its PowerAssist feature the Multi can add up to 2 kVA (that is 2000/120=17A) to the outlut diring periods of peak power requirement. Together with a maximum input current of 50A this means that the output can supply up to 50 + 17 = 67A

NOT a quote...I am limiting input to 30 amps. So I read it as 30 plus 17 or 47A which would require a #6 wire, but so odd. If the device limits inputs to 30amps; doesn't it make sense to not exceed inputs with outputs?

 

[missinginaction]

This thread has me scratching my head. How do you wire this Victron inverter? You guys are figuring out the gauge, I'm going somewhere else. Accepted practice is that the neutral/ground is tied either on the boat (at the inverter or the generator) or at the shore pedestal. The caveat is that this neutral/ground connection can occur only at one source of power AND ONLY when that source is actually producing power.

For instance, if your boat is plugged in to shore power and the pedestal is supplying power, the neutral/ground is tied at the dockside pedestal. If you're running on your inverter the neutral/ground bonds at the inverter. There are typically relays that switch out the dockside neutral/ground pass through when the inverter is activated and the transfer switch is activated.

Confused yet? What I don't understand is how this inverter can be wired and still comply with ABYC rules. If you're running on the inverter and the inverter allows some kind of shorepower (or more likely generator based) boost where is the neutral/ground connection made? You can't make it in two places, even if they are both producing power. Or can you make it in two places if both are producing power? Victron must be using isolation transformers in this application eliminating the physical connection issue when the inverter is operating in tandem with shore/generator power.

That's the only way I can figure it anyway. It's always been an either/or situation. With this Multiplus it's become a "both" inverter and shorepower/generator. Pretty slick these newer technologies.

I wonder how this inverter/charger gets along with ELCI's that are being installed at marinas here in the US as they modernize and adopt the new electrical standards that seek to prevent ESD.

MIA

 

[Rumars]

Now I understand what you mean. Yes the combined output can get up to 67A and you must size the wire and fuse accordingly, at least up to the distribution panel. It's the magic of Victron, allowing you to use more then a common shore power or installed generator can supply, using the batteries. If your boat doesn't have a combined total draw over 30A AC, you don't need to size up the wire, the power assist works on demand, it might kick in if you have weak shore power (you can adjust the level, standard is 30A), but only up to the needed level. You limit the output by the appliances consumption, just like you would do in a house. But, if you plan to expand the AC side in the future by adding more appliances and using them at the same time, install bigger wire and main fuse.

@missinginaction the thing has an automatic relay switching the neutral-ground connection between shore pedestal/generator and its own. It automatically tests for this when synchronizing with the external AC output and adjusts. The inverter generated AC is fully isolated anyway, it is produced by electronic switching. Many generators come with a floating ground from the factory, the multiplus detects this and makes its own connection.

 

[fallguy]

Oh, it requires all series earth ground breakers after the inverter. So an elci or ?gfci must follow it seems. Otherwise, the inverter would theoretically provide power from the batteries.

 

[fallguy]

@Rumars

I don't think I get to decide the wire size. Just seems odd that the thing would ever deliver in excess of incoming limits. Weird science if you ask me.

 

[Rumars]

Weird it might be, but usefull. Many yachts or RV's have enough AC appliances to fully exhaust the 30A of a standard shore power connection, and people want to use them simultaneously. This is designed to allow that, without tripping the breaker. That's why the factory setting is 30A, it only activates if you draw more then that. If you have air conditioning, and a small generator or the marina wiring is not up to standards, you will come to love it, you can heat water, cook or wash without having to upgrade the generator or move to a different berth. If you have an electrically simple boat chances are you will never use the feature.

 

[fallguy]

Weird it might be, but usefull. Many yachts or RV's have enough AC appliances to fully exhaust the 30A of a standard shore power connection, and people want to use them simultaneously. This is designed to allow that, without tripping the breaker. That's why the factory setting is 30A, it only activates if you draw more then that. If you have air conditioning, and a small generator or the marina wiring is not up to standards, you will come to love it, you can heat water, cook or wash without having to upgrade the generator or move to a different berth. If you have an electrically simple boat chances are you will never use the feature.

Kinda what I figured, but I might install a tiny ac unit someday if we move to Texas.