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Double Wire - Double Fuse?

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Kugel8x57

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Want to double up on 8AWG wire to carry 24v-100A to inverter. These are essentially two parallel conductors. Assuming I want 100A total fusing, can I use a 50A Maxi Fuse in each 8AWG wire? Each 8AWG wire will be same length and same connector on each end.

My gut tells me the answer to this question is "yes". However, electricity can do some strange things, and being new to this higher amperage DC stuff, I wanted to double check with you more experienced folks!

Many Thanks and God Bless!!

Kugel
 
You do need a separate fuse for each parallel wire. Look up the rating for your wire. Fuse each wire at it's maximum current capacity. My marine rated wire has capacity of 80 amps for 8awg. I will fuse at 80 amp fuse on each wire, If one wire failed, the other could carry to much more currant than would be safe.
 
If the wires originate from and terminate to common compression lugs then a single fuse is ok.
If they originate from and terminate to separate compression lugs one fuse per wire is a good idea.
@Kugel8x57 sorry that you got three different answers but I call it like I see it.
 
I would say 2.5 different answers...

smoothJoey and I agree; however, he provided the more detailed answer. I only get .5 credit. :)
 
I don't agree. Two wires, parallel for one circuit. One wire fails, not necessary the terminal end. All 100 amps, or even enough to melt the one wire, goes through one of the paired wires. Maybe in a storage area with a mouse nest or whatever. that wire gets hot. Hot causes fire where maybe you do not notice until you and yours are sleeping.
 
smoothJoey said:
If the wires originate from and terminate to common compression lugs then a single fuse is ok.
If they originate from and terminate to separate compression lugs one fuse per wire is a good idea.
@Kugel8x57 sorry that you got three different answers but I call it like I see it.
Click to expand...
NEC says that is not correct, and they are the ruling party....due what you want but 2 fuses is the correct way.
 
This seems to be a topic with many answers. Apparently if you have parallel lines sharing current Both originating auto one lug And terminating at one lug, With fuses on both strands, There’s a possibility of difference in resistance sending more current to one wire than the other, This keeps me away from doubling or tripling up on wiring To prevent from going to a Thicker gauge wire.

EDIT: Misread what was said about the NEC code. I’d go with that. I’d just feel more comfortable if I could get a copy of NEC to check this and more importantly for me to reference the many other questions I have.
 
NEC 310.4

NEC is Us building code. The current book and older ones are available at most libraries. They are hard to read but answer most questions.
 
I think we normally only see multiple parallel at 2/0 and above. Then, fusing to protect individual seems to be common sense but may not be the practice.

8 awg is so skinny I'd just use larger wire.

Parallel runs may not divide current evenly. One fuse might blow, then the other.
I had breakers for separate runs to two inverters, which parallel to share current through their relays. The current was unevenly split 3:1
That turned out to be due to Square-D QO270 breakers differing in resistance. Worked fine with no breaker, and now with 63A Schneider DIN rail supplemental breakers. (originally had 63A at input to inverter, 70A at output, now at both)

If something is in the NEC, then even it not legally applicable to a different location/application, would be good to consider why the rule before consciously not following.
 
Not that Giandel is a shining example but they ship inverter cables with double wires between single compression lugs.
 
Thanks all for the input.

Stationary application:
- Giandel 2000W inverter will be powered by 2s6p 24v-96Ah LFPO battery bank (BB).
- Each 2s 24v pair has a 1C of 16A ==> 6 x 16 = 96. Goal is to not exceed this as a discharge rate.
- Batt Mfg (Miady) says Max Discharge rate is 40A. But I want to minimize stress on BB for longer life. And I plan to limit 1C discharge rate to 15-20 mins per charge cycle. If it's a sunny day, I can run this heavier load for longer periods to utilize excess solar capacity.
- Miady states 10A Charge Current, hence my 1500W Array with 60A MPPT Charge Controller. (Yes I realize this is Max on a clear sunny day.)
- (2000W/24V) x 1.15 ~ 96A.
- I have 750A BB-->Inverter disconnect switch. And, I have some Maxi Blade Fuse Holders and 50A & 60A Fuses and a 500ft reel of 6AWG-19 THHN that I got for a good price ($0.34/ft !!)
- The Maxi Fuse Holders have 8AWG Batt Cable Pigtails, so, even if get some 4AWG wire to go the first 4.5 ft from BB to inverter, it will take two of the Maxi Holders to properly carry the 96A because of the 8AWG pigtails.
- At this point I was planning to run two equal - as identical, as possible - lengths of the 6AWG from BB to inverter with a 50A Maxi Fuse (8AWG fuse holder) in each length.

Hope this helps!

Many Thanks and God Bless!

Kugel
 
I don't care what the f code says. Or whatever code your want quoted. Two parallel wires for on circuit is a bad idea. It is even a worse idea without a separate fuse on each wire. If you want to risk burning your babies go ahead.
 
Zil said:
I don't care what the f code says. Or whatever code your want quoted. Two parallel wires for on circuit is a bad idea. It is even a worse idea without a separate fuse on each wire. If you want to risk burning your babies go ahead.
Click to expand...
Correct.

NEC codes are for homes and commercial buildings... and NEC paralleling rules state 1/0 and larger only with exact cut length conductors.

applying rules written for specific conditions to other situations is unwise.

I vote safety first. Use the correct size wire.

but if you must parallel, use the best quality fuse on each conductor that does not exceed that conductors safe rated capacity.
I personally think the extra fuses and connections for paralleled wires negates any savings over just using the correct wire size.
 
solarsimon said:
Why not tape them both together & keep everyone happy?
Click to expand...
Only if you strip the insulation off first and twist the bare copper together, then re-insulate.
Otherwise, the issue is a poor connection of one diverts all current though the second.
That would be OK if the pair was protected by a single fuse not greater than ampacity of one wire (two paralleled for lower resistance.)
Or, if each wire fused individually. Bad contact, all current goes through other wire, fuse blows.

But poor contact is a bad idea, can dissipates kilowatts and start a fire without blowing fuse.
For PV circuits this is recognized as an issue and arc-fault can help (if poor connection arcs) but not if just resistive and not arcing.

For OP, 8 awg is 80A for 90 degree conductor in free air. 105 degree would be something higher.
But 6 awg is 105A.
Since this is the battery connection, just get a suitable single wire of large enough gauge, fine stranded so flexible, suitable insulation temperature.
If the issue is fitting in terminals, there are ways to deal with that. I would consider necking down, only using as many strands as fit. If you worry, add a split bolt to ensure remaining strands make contact. Or, use split bolt to connect larger wire to smaller at the terminal, but I think using some strands of the larger wire is better.
 
I agree with the safety aspect. When you parallel anything, you can't always ensure the two paths will carry identical current. I am using 2 cables from my battery bank to the main buss bar. I fused both cables separately. But when I added my low power panel, I have it fused at just 30 amps, but I paralleled 2 x #8 cables for voltage drop. The single fuse is fine since the current is easily handled by one of the cables. If I needed over 40 amps, then the 2 wires would need separate fuses to be safe. Always plan for the worst possible case and make sure it will fail in a safe manner.
 
eBay. Seriously, they have everything.

10' of 4 awg welding cable (one color), $18 delivered. 5' red & 5' black, $21

www.ebay.com

4 AWG Gauge AWG Welding Lead & Car Battery Cable Copper Wire MADE IN USA | eBay

4 AWG GAUGE OFC COPPER CAR AUDIO GROUND POWER WIRE SAE J1127 MADE IN USA CHOOSE THE COLOR AND LENGTH PER FT CHOOSE 50/50 TO RECEIVE 50 FT RED AND 50 FT BLACK IF YOU CHOOSE 100 FT AS A EXAMPLE. Features: SAE J1127 TEMPERATURE RATING -50' C TO 105' C ETHYLENE PROPYLENE RUBBER (EPR) JACKET ANNEALED...
www.ebay.com
 
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