off grid setup questions related to grounding and awg

[sensij]

6ga wire, 100a fuse is a safety mismatch. 6ga is only rated for 40a power transmission. But it is rated 101a for "chassis wiring" So it will take the load for a few minutes, but then the insulation is likely to flambe.

Mixing up power transmission guidelines (based on the 700 circular mils per amp rule) and NEC ratings for specific wire types is asking for trouble. Properly insulated and terminated, 6ga can safely carry more than 40 amp continuously. I think we all agree that the 100 A fuse in this situation is not properly protecting the conductor, does not have a basis in expected load, and seems to be some sort of catastrophic failsafe recommended by the manufacturer without a clear engineering basis.

[Mike90250]

6ga wire, 100a fuse is a safety mismatch. 6ga is only rated for 40a power transmission. But it is rated 101a for "chassis wiring" So it will take the load for a few minutes, but then the insulation is likely to flambe.

[claydbal]

I apologize for any confusion with my posts. I "thought" that inverter had 120volt receptacle outlets where you would plug in an extension cord. Based on what Mike stated and some research on my part I see that the AC output needs to be wired to a "distribution" CB or fuse panel similar to what you have shown.

What can be an issue with a large CB panel is that you may end up connecting too much load and over drive that 300Watt inverter. You just have to understand what you are connecting and how many continuous amps the total load will draw at the same time.

Conductors have a maximum current rating the yare allowed to safely handle without over heating, and the minimum size conductor is determined by the breaker or fuse being used so as to prevent to high of a current from flowing over heating the wiring and connections. On a 20 amp breaker the smallest conductor you can use is #12 AWG conductor. A 12 AWg conductor can safely handle 30 amps if the insulation is rated for 90 degrees. So 20 amps of current flowing on a #12 AWG conductor is no problem

As to the rest of your question a 300 watt inverter is not even enough for one single AC circuit let alone a breaker box which is why this is so odd.

thanks guys!

[Sunking]

Although the result is usually the same, the design practice I was trained to is slightly different. I will size the conductor to safely carry the designed load, and then size the breaker to protect the conductor (not breaker first, then conductor).

That is the way it is suppose to be done. But a manufacture cannot specify their product to be used in a non compliant manner as in the case of this product.

[sensij]

Conductors have a maximum current rating the yare allowed to safely handle without over heating, and the minimum size conductor is determined by the breaker or fuse being used so as to prevent to high of a current from flowing over heating the wiring and connections. On a 20 amp breaker the smallest conductor you can use is #12 AWG conductor. A 12 AWg conductor can safely handle 30 amps if the insulation is rated for 90 degrees. So 20 amps of current flowing on a #12 AWG conductor is no problem

As to the rest of your question a 300 watt inverter is not even enough for one single AC circuit let alone a breaker box which is why this is so odd.

Although the result is usually the same, the design practice I was trained to is slightly different. I will size the conductor to safely carry the designed load, and then size the breaker to protect the conductor (not breaker first, then conductor). When a manufacturer requires an OCPD to protect their specific equipment, it adds another constraint, but does not allow NEC / NFPA / UL requirements to be dismissed. Many times for some types of equipemnt this additional constraint shows up in the specification of current vs blow time for the fuse (fast-acting vs time delay, for example)

In a 12 awg example, 20 amps is usually the max breaker size allowed due to the rating of the terminals. The 30 amp rating of 90 deg wire is mostly helpful to give a higher current from which to derate due to other design considerations (ambient temp, conduit fill, etc). It is very rare that 12 awg wire would be designed properly with a 30 amp breaker.

In any case, I agree that conductor overheating is the condition that is to be protected against.

[Sunking]

I believe morningstar has a 6ga wire, because that's the largest that fits the terminals. And they spec a 100A fuse in case of catastrophe .

Mike you are aware a 100 fuse requires a minimum #2 AWG copper conductor right? This is one of those times the manufacture does not comply with any known electrical codes. Look at the wiring diagram closely, then ask yourself is there any way it can be integrated into a premises wiring systems.

Fist thing I noticed is on the output only 2-wires which is OK assuming you add the 3rd wire inside the breaker panel, but notice it tells you to earth ground the grounded circuit conductor. You cannot do that because it will now force normal load currents to flow on your ground conductors. That is forbidden for obvious reasons. The neutral is already grounded in the breaker panel. You cannot bond it again

As mentioned a 100 amp fuse requires a #2 AWG copper or #1 AWG aluminum wire. Now if it were a 1000 watt inverter I could see that as that is what they use at 12 volts

As for the 3-amp fuse on the output you can certainly add, but it serves no purpose as the minimum size wire you can use inside on premises wiring is #14 AWG which is good for 15 amps all day long. 600 watts @ 120 volts is around 5 amps which should blow that 3 amp fuse in a minute or two.

Does any of that strike you as odd? Why would a manufacture suggest hardware and configurations that don't work or safe?

[Sunking]

would you clarify please? is there a drop or draw through the cb panel or do you mean that there may be too many draws connected to the cb panel that would cause the overload?

thanks and pardon my ignorance.

Conductors have a maximum current rating the yare allowed to safely handle without over heating, and the minimum size conductor is determined by the breaker or fuse being used so as to prevent to high of a current from flowing over heating the wiring and connections. On a 20 amp breaker the smallest conductor you can use is #12 AWG conductor. A 12 AWg conductor can safely handle 30 amps if the insulation is rated for 90 degrees. So 20 amps of current flowing on a #12 AWG conductor is no problem

As to the rest of your question a 300 watt inverter is not even enough for one single AC circuit let alone a breaker box which is why this is so odd.

[SunEagle]

would you clarify please? is there a drop or draw through the cb panel or do you mean that there may be too many draws connected to the cb panel that would cause the overload?

thanks and pardon my ignorance.

I apologize for any confusion with my posts. I "thought" that inverter had 120volt receptacle outlets where you would plug in an extension cord. Based on what Mike stated and some research on my part I see that the AC output needs to be wired to a "distribution" CB or fuse panel similar to what you have shown.

What can be an issue with a large CB panel is that you may end up connecting too much load and over drive that 300Watt inverter. You just have to understand what you are connecting and how many continuous amps the total load will draw at the same time.

[SunEagle]

The 300W morningstar sure sine (600w surge for 10 minutes) is not a portable inverter. It is made for hardwire on site, there are no outlets on it. Nice and efficient, and has a remote off switch. Just not enough oomph to start a fridge.

I believe morningstar has a 6ga wire, because that's the largest that fits the terminals. And they spec a 100A fuse in case of catastrophe . The Blue Seas fuse block fuse holder Sunking showed is a great item.

Mike. You are correct.

I need to look at equipment make and model data before I make any comments. The specs shows that the maximum DC wire size could go to #2 awg which would require that 100A fuse.

[claydbal]

Didn't let me answer.

You are correct even 20amps would do nothing more than heat up that #12 wire.

I was also curious to why the inverter was hooked up to a CB panel instead of just using an extension cord. A CB panel (even for small dedicated loads) could easily overload that 300watts.

would you clarify please? is there a drop or draw through the cb panel or do you mean that there may be too many draws connected to the cb panel that would cause the overload?

thanks and pardon my ignorance.

[Mike90250]

The 300W morningstar sure sine (600w surge for 10 minutes) is not a portable inverter. It is made for hardwire on site, there are no outlets on it. Nice and efficient, and has a remote off switch. Just not enough oomph to start a fridge.

I believe morningstar has a 6ga wire, because that's the largest that fits the terminals. And they spec a 100A fuse in case of catastrophe . The Blue Seas fuse block fuse holder Sunking showed is a great item.

[Sunking]

Didn't let me answer.

Really was not directed at you, I Knew you knew the answer, it was to make a point. No chance in hell that inverter could even generate 5 amps for any meaningful length of time. Point is the Inverter is a very Soft Source not capable of operating any OCPD unless very small of an amp or less. Not like a utility transformer that can produce thousands of amps.

[SunEagle]

Maybe after 30 minutes depending of the fuse type. However that is a moot point, no FUSE IS REQUIRED or needed. It is just useless hardware. The inverter being a mobile inverter has the protection built in.

Riddle me this. What happens to a 12 AWG wire with say, 3, 5, 10, or even 20 amps flowing through it continuously?

Answer: Nothing as it can safe handle up to 30 amps in free air all day long. To feed it into a breaker panel would require you to use a 20 amp breaker in the breaker panel. Now ask yourself this. What good does it do to have a 300 watt inverter supplying a AC breaker panel? A 300 watt inverter is made to have one very small AC circuit like your laptop power brick plugged into it. Not wired into a premises wiring system.

Didn't let me answer.

You are correct even 20amps would do nothing more than heat up that #12 wire.

I was also curious to why the inverter was hooked up to a CB panel instead of just using an extension cord. A CB panel (even for small dedicated loads) could easily overload that 300watts.

[Sunking]

OK let see how it can be done safely and work. Not sure about the charge controller and inverter with respect to if they bonded the chassis to the negative polarity or not. If they did forces you to use a Grounded System. If no tit can be Floated and here is how it is done correctly.



If the chassis is bonded to the frame, then you must Ground the system and here is how it is done.



Here is the Battery Fuse Block available from Blue Marine

BLU_Terminal_Fuse_Blocks.gif

[Sunking]

But if that 300w inverter has a surge rating of 600 watts then at 120v it could see a jump of 5 amps which may eventually blow that 3 amp fuse. Just a thought.

Maybe after 30 minutes depending of the fuse type. However that is a moot point, no FUSE IS REQUIRED or needed. It is just useless hardware. The inverter being a mobile inverter has the protection built in.

Riddle me this. What happens to a 12 AWG wire with say, 3, 5, 10, or even 20 amps flowing through it continuously?

Answer: Nothing as it can safe handle up to 30 amps in free air all day long. To feed it into a breaker panel would require you to use a 20 amp breaker in the breaker panel. Now ask yourself this. What good does it do to have a 300 watt inverter supplying a AC breaker panel? A 300 watt inverter is made to have one very small AC circuit like your laptop power brick plugged into it. Not wired into a premises wiring system.