PreWired ePanel Inverter DC breaker size.

[mtdoc]

I'm just wondering why the prewired ePanels with Outback GVFX 3648 inverters use 175 amp DC breakers.

The continuous rated capacity is 3600VA and the surge rating of the inverter is 6000 VA.  Outback's installation manual has the table below in it that lists and ampacity of 90 amps and recommended DC breaker size of 125 amps.

Any safety concerns with having the 175 amp DC breaker instead of a lower amp one? Should I have a lower amp breaker or fuse at the battery?

[TomW]

mtdoc;

Do not mistake me for any kind of expert! But...

Breakers / fuses are there to protect the wiring not the equipment.

Just something that old sparkie told me long ago.

You need a high enough rating to allow the equipment to function under all circumstances including short term overloads and it needs to be sized small enough to not vaporize the wires if you have a catastrophic failure.

Tom

[mtdoc]

Understood. But even with that consideration, 175 Amps is too large.  I cannot see any way that the GVFX 3648 would ever approach that much current draw unless it has a short in it.  Why not use a 125 amp breaker as Outback recommends?   

[TomW]

I think you can order them with the breaker you want included?

I am not sure but seems that was an option when I got mine for the FX2524.

I would follow the inverter makers suggestion. I was just trying to clear up a common misconception some folks have on overcurrent protection.

Tom

[mtdoc]

Thanks. Yes - I'm sure you could special order it with a 125 amp breaker. But why choose 175 amp as the default?  There is probably a good reason - just can't think of one....

Interestingly it seems Outback does a similar thing on their Flexpower prewired systems - at least that is what is being reported by an FP1 owner and discussed in THIS NAWS thread.

[TomW]

Interestingly it seems Outback does a similar thing on their Flexpower prewired systems - at least that is what is being reported by an FP1 owner and discussed in THIS NAWS thread.

mtdoc;

Probably more ease of marketing one product for multiple applications in this case a range of inverter sizes?

I am just a customer with no affiliation with Midnite beyond that and helping keep an eye on the this forum.

Tom

[Halfcrazy]

I think the simplest answer to why the 175 is:

The 125 amp breaker has small 1/4 studs and is sorta light duty for 2/0 cable. As you noted Outback uses the 175 as well and that is just how we have done it since we designed and built the Outback inverter. You will notice at Midnight we do offer a lot of 125 amp Epanel options but like I say it is tough wiring and in reality will never make the system safer or any more likely to prevent any damage. When the Outback blows up internally it WILL trip a 175 with ease I have witnessed this 

Ryan

[mtdoc]

OK thanks Ryan.  I knew there had to be a logical explanation! 

[Westbranch]

This has me contemplating another lower rated CB right at (as close as possible) the battery/bus connection rated for the max load from the 1500W inverter. 

I am going to use 2/0 wire from the batt to the E Panel 175A CB... as well as back to the batt.

does this make sense (overkill?) ?

[Halfcrazy]

Well like everyone pointed out the CB is there to protect the wiring and 2/0 and 175 go hand in hand. The real question is if there is an issue say a component failure internally in the inverter does the extra 50 amps on the breaker matter. My thoughts is No it does not if it could trip a 125 before doing damage it should likely trip a 175 as well. Make any sense?

[Westbranch]

Just looked up the specs for my inverter and it calls for

"an inline 100A fuse" using  #4 AWG of less than 6 feet.

So the 2/0 is well above their recommendation, though they do say bigger is better...

ADD: I forgot I was planning to use some #1 AWG for the final connection to the inverter if it will fit the receptacle...

So we are well ' under (over?) fused '  at 175A, I believe. ie there is a deficit in coverage of 75A+-