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Old 04-26-2021, 01:18 PM   #1
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Can Cable Guage Be Too Large?

Hey!

Can the cables used as the homerun from the panels be too large? Is there any negative effect to the transmission of electrons?

Thanks!

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Old 04-26-2021, 03:01 PM   #2
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Originally Posted by Danjo View Post
Hey!

Can the cables used as the homerun from the panels be too large? Is there any negative effect to the transmission of electrons?

Thanks!
It can certainly be too small. However too large will not hurt conductivity. It will hurt your pocket. as the gauge goes up so will the price. If you get to big it is hard to work with.

Our bus is about 40 feet long. The solar controllers, Junction boxes, inverters, and batteries are in the rear of the bus. We ran #4 THHN copper from the panels in groups of three. Four in the front of the bus, four midway, and four aft. The voltage drop for the longest run was negligible, about 1/10th of a volt.

We might have gotten away with #6 THHN but the price differential wasn't that great.
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Old 04-26-2021, 03:04 PM   #3
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[Edit by moderator - don't give sarcastic advice for stuff like this]

So don't use too large of a gauge. 20,14,12 too big, use a smaller gauge, like 10, 8, 4, even 2.

And if you don't understand this at all, do some research to find out what I'm talking about.
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Old 04-26-2021, 03:14 PM   #4
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Hey!

Can the cables used as the homerun from the panels be too large? Is there any negative effect to the transmission of electrons?

Thanks!
No. Upsize your copper..
Only the physical size of lugs, (which can be changed). Oversize/overated is permitted & encouraged (often required). Less heat/resistance, more ampacity potential, less voltage drop.

[Edit by moderator - don't attack people]
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Old 04-26-2021, 04:59 PM   #5
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The only negative issues are cost and weight, 60' of 4/0 for example would be prohibitive for most.

A DCDC converter or charger can help overcome those.
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Old 04-26-2021, 05:29 PM   #6
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Originally Posted by BeNimble View Post
[Edit by moderator - don't give sarcastic advice for stuff like this]

So don't use too large of a gauge. 20,14,12 too big, use a smaller gauge, like 10, 8, 4, even 2.

And if you don't understand this at all, do some research to find out what I'm talking about.
I am not sure what you are trying to say. But perhaps it would be good to clarify for those who may not know it; when referring to wire gauge size the larger the number the smaller the diameter of the wire.

There is a problem with running too smal a wire for any distance with DC circuits. Internal resistance of the wire causes voltage drops and effective loss of some of your solar power.

Larger diameter wire, smaller gauge number, will reduce the loss. Unless your run is very far, which shouldn't happen in a school bus, #4 should be more than sufficient. If you go with number 2 or less you will find the cost much higher, the flexibility much stiffer and the connections to your devices unlikely to fit. It's just too large in diameter.

If you want to calculate the voltage drop based on wire size, length, and PV voltage this link is to a simple VD calculator.
https://www.jcalc.net/voltage-drop-calculator-nec
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Old 04-26-2021, 07:51 PM   #7
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Cables should be short and fat! If you're aiming for 1% voltage drop under load you'll need fatter cables than the more usual 3% drop. Ampacity charts are all over the internet, but check what voltage drop they're for. Marine systems often are based on 1% drop, but for most things a 3% drop is just fine. If in doubt, go fatter! Besides, in the big scheme of things, the price of cable is a pretty small proportion of the overall conversion cost. Remember that ampacity charts base their quoted cable lengths on the total out-and-back length, not just one way.

Just as important as the cable gauge itself is how you assemble the cables. Use a good circumferential crimper instead of those cheapo hammer crimpers that just give me the willies, use good tinned lugs and heatshrink, then you'll be halfway to keeping voltage drop under control.

John
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Old 04-28-2021, 09:51 AM   #8
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Thanks for the replies

The initial question was asked due to a comment made because someone ran super large cable for the panel homerun. I already knew the answer, but people donít want to listen to me.

So thanks.
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Old 04-28-2021, 09:56 AM   #9
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Originally Posted by Iceni John View Post
Cables should be short and fat! If you're aiming for 1% voltage drop under load you'll need fatter cables than the more usual 3% drop. Ampacity charts are all over the internet, but check what voltage drop they're for. Marine systems often are based on 1% drop, but for most things a 3% drop is just fine. If in doubt, go fatter! Besides, in the big scheme of things, the price of cable is a pretty small proportion of the overall conversion cost. Remember that ampacity charts base their quoted cable lengths on the total out-and-back length, not just one way.

Just as important as the cable gauge itself is how you assemble the cables. Use a good circumferential crimper instead of those cheapo hammer crimpers that just give me the willies, use good tinned lugs and heatshrink, then you'll be halfway to keeping voltage drop under control.

John

When I made my cables all I had was a hammer crimped and could not find anyone locally that had a pneumatic one. So I did the hammer crimps with these stubby lugs supplied by Windy Nation. So far they are holding. I put a big fat wrap of electrical tape over it followed with shrink tube. They seem like they are good, but I know they could be better.

So what about soldering lugs with a torch. Is it possible?
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Old 04-28-2021, 11:28 AM   #10
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If the 'sodder' has an ampacity rating & listed use.
I've used exothermic welding, only on bldg bonding to rebar.
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Old 04-28-2021, 11:35 AM   #11
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You have to think of the wire / cable as a tunnel that the electrons flow through. If you use very large / over sized wire / cable the electrons will be able to social distance.
Sorry I just had to inconvience some electrons for that!
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Old 05-01-2021, 07:26 PM   #12
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Wow, moderators doing the censorship boogy.


I, am , out of, here...
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Old 05-02-2021, 06:52 AM   #13
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Wow, moderators doing the censorship boogy.


I, am , out of, here...
I know, right?

I didnít get to see the original comments. Iím surprised I or my question raised so much vitriol that mods had to edit them out.
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Old 05-02-2021, 07:04 AM   #14
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I ran 4/0 welding cable from the front to the back of the bus for my house batteries.. overkill for 2 AGM batteries but now ill be upgrading to 4,6 or even 8 batteries so im glad i ran the heavy cable when I did as i dont have to re-do it now that im expanding the battery bank a bit.



I spent the $$ to buy a real crimper to put the ends on for a good solid connection to the terminals..
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