Help me select some battery terminal fuses please

[hammick]

My 48v Schneider system is fully installed and working great. I have been told by a few here that I need to fuse both the positive and negative battery cables at the terminals even though the positive cable connects to a 250a breaker at the E-panel. Looking for opinions on whether battery terminal fuses are needed and if so what amperage. Pic of my equipment attached. I will fab some terminal covers to protect from dropping a wrench. Battery cables are 10' 4/0.

My batteries are not grounded but my Schneider CC has GFCI protection so essentially they are grounded unless the CC fuse blows. I have read the concerns about GFCI protection on solar CCs but for now I am leaving it that way.

So let's assume something happens and the GFCI fuse in my CC blows lifting the ground. By fusing both the positive and negative cables at the battery terminals I'm eliminating the fire danger, right?

My charge controller is fused in and out with 60a Midnight Solar 100% duty rated breakers.

Specs of my equipment are below. I'm thinking 125a Blue Seas fuses at both positive and negative terminals (next size up is 150a) but thought I would let the experts chime in. Thanks.


p.s: I can't figure out why Schneider requires a 250a breaker for the SW4048 inverter.


Inverter:

SW4048 maximum DC input: 105a
SW4048 maximum DC output: 45a

Charge Controller:

MPPT-60-150 maximum output: 60a
IMG_2562.JPG

[hammick]

I looked closer at the Blue Seas 125a and 150a fuses and the max voltage is 58v. That isn't going to work.

[Logan005]

Your top voltage is 56.7 sounds like the bluesea breakers meet your system requirements?

[Logan005]

oops, 57.6 still within limits,

[Sunking]

My batteries are not grounded

That dictates both polarities must have over current protection on the battery terminal post and any distribution blocks. A floating system is safer and less prone to outages. However a lot more expensive to implement and requires Ground Fault Detection system which adds more onto the cost.

Use the Blue Sea stuff but for Distribution you must use fusses on both polarities. That means instead of using 1 distribution block as pictures below, you must use two of them, one for each polarity. Be careful what you ask for because what you are asking for is very expensive.

[hammick]

oops, 57.6 still within limits,

Where are you getting 57.6v? My bulk charge setting is over 59v and the equalize voltage is 64v.

[hammick]

Sunking I am not sure why you are recommending a DC distribution box. I don't have any DC loads other than my inverter. I am using an SW4048 inverter in an off grid solar application.

[hammick]

This is the fuse I was going to use: http://www.amazon.com/Blue-Sea-Syste...ords=125a+fuse

Until I realized they are only rated to 58v.

[Sunking]

Sunking I am not sure why you are recommending a DC distribution box. I don't have any DC loads other than my inverter. I am using an SW4048 inverter in an off grid solar application.

OK, then you do not need any distrution, but you need Dual Fuse blocks on each battery term post. One pair facing the Inverter, and another pair facing the Controller. 2 units 2151 with 4 MRB fuses.

[hammick]

Sunking which fuses do you recommend? Blue Seas fuses for those blocks are only rated to 58v. Unless they are underrated I'm not sure anyone makes fuses that will work for a 48v application.

My charged controller is wired into my MS E-panel with 60a breakers in and out.

I would hate to use the Blue Seas fuses and go up and find a fuse blown and my batteries discharged.

[Mike90250]

.......p.s: I can't figure out why Schneider requires a 250a breaker for the SW4048 inverter.....

Because the inverter can supply huge AC surge for motor starting, and has to get the power through the breaker.

[Sunking]

Sunking which fuses do you recommend? Blue Seas fuses for those blocks are only rated to 58v. Unless they are underrated I'm not sure anyone makes fuses that will work for a 48v application.

My charged controller is wired into my MS E-panel with 60a breakers in and out.

I would hate to use the Blue Seas fuses and go up and find a fuse blown and my batteries discharged.

OK again your fuses are thermal devices and operate on Current, not voltage. 100 amps through a 58 volt fuse is the exact same current and heat in a 200 volt fuse. There is no difference. We have already been down this road before. Try to keep up, I hate doing things twice and thrice.

As for the sizes you have to determine and should be really easy for you.

Between Charge Controller and Battery should be 1.25 time larger than the current rating of your charge controller. So if you have a 60 amp controller you want a 60 amps x 1.25 = 75 amp fuse. You can round up to 80 or even 100 amps. More on that in a minute.

Next is the fuses between your Battery and Inverter. Your Inverter manual should tell you that.

OK now let us talk about minimum wire sizes and fuses. To prevent over heating of wires, your fuse sizes must be cordinated with wire size. NEC has tables for this and it is not complicated. Assuming you wil use 75 degree rated insulation on the wire rated up to 2000 volts the smallest copper wire you can use on a fuse is:

20 amps on 12 AWG
30 amps on 10 AWG
50 amps on 8 AWG
65 amps on 6 AWG
85 amps on 4 AWG
115 amps on 2 AWG
150 amps on 1/0

You can certainly use a smaller fuse of say 10 amps on a 1/0, but you cannot use anything larger than 150 amps on a 1/0. I use this extreme to make another point. NEC on list maximum limits. But with Low Voltage you can very easily find yourself using much large wire than normal to compensate for voltage drop. Example let's say you will only be running 16 amps between your panels and charge controller. One might think all you need is a 12 AWG wire. You would likely be wrong if say operating at 18 volts on a one way length is say 20 feet, You would need a minimum of #8 AWG to keep you voltage loss to less than 2%. However you need a 20 amp fuse. 20 amp fuse on 8 AWG is no problem. You just cannot use anything larger than a 50 amp fuse on #8 AWG.

[hammick]

Sunking I appreciate the advice but it is clear you don't read the previous posts or if you do you quickly forget. I posted a photo and full specs of my setup above.

My charge controller is not wired to my batteries directly. It goes to my E-panel with 60a breakers on the in and out. So I don't need fuses for the charge controller. My batteries are connected to my E-panel with 4/0 cable and the positive cable has a 250a Midnight Solar breaker at the E-panel (BTW all MS breakers are 100% duty rated).

Schneider's manual says a 250a breaker is required at the E-panel which I have. People have said (maybe even you) that this breaker is way to large. I tend to agree. The Schneider manual says the max DC current is 105a. Schneider also says I don't need to fuse at the battery terminals so I can't just rely on what they say.

Midnight Solar's E-panel manual says to use a 250a breaker for 4/0 wire which I have done.

My choices for Blue Seas terminal fuses are 125a, 150a, 175a, 200a, 225a or 250a (I'm not interested in spending hundreds of dollars on the Schneider breakers you mentioned in another thread).

So I guess my question boils down to this: Shall I fuse the positive and negative terminals at the battery with 250a Blue Seas terminal fuses or go smaller? If smaller what size? 125% of 105a is 131 amps. Should I use a 150a fuse?

There is a possibility the well pump, microwave and refrigerator could all run at the same time and I don't want to be blowing fuses. At $20 a fuse that can get pricey. I want to fuse for a fault that most likely will never occur.

[Sunking]

Sunking I appreciate the advice but it is clear you don't read the previous posts or if you do you quickly forget.

I think we have covered all this in your other thread.

How many pairs of cables do you have going to the Battery? 1 or 2?

[hammick]

Just one pair