600 Watts With 10 Gauge Wire

[vashkoproimage]

Im running 6 - 100 watts of panels on my rv. I’m running 10 gauge wire 20 feet for positive and 20 feet for negative. I have them wire in 3 sets of 2 panels series and parallel. Is the 10 gauge wire okay to use?

Also I might be going little over 15 amps though the 10 gauge wire at around 36 volts. I know that if it’s under 15 amps Max series fuse rating I don’t need to use fuses at panels. If I’m a little over is that fine? I will post pictures of specs of the solar panels. Each specs sticker is running in pairs.

Renogy 40 amp charge controller
6- 100 watt Renogy panels

 

[rmaddy]

So they are setup in 2S3P? You need to fuse each of the 3 strings.

The 10AWG wire is fine. The Isc will be close to 18A. 10AWG can handle that just fine. At the voltage and length you have the voltage drop should be just under 3%.

You could wire them in 3S2P and avoid the need for fuses. Just make sure each set of 3 in series are mounted in the same plane.

 

[vashkoproimage]

I was just wired in 3s 2p. I have two panels that have different spec on stickers. It was giving me issues so I swapped to 2s 3p. 1 amp over the 15 amp fuse rating is not okay? So far I hit 15.28 max on the amps. The calculation on the stickers I should get 16.45 max amps out of the panels.

 

[Supervstech]

15A constant can easily become a fire with any weak connection point.
Get fuses.

 

[time2roll]

No fuse needed. 100w panel will not create 15 amps to back feed the other string if there is a fault.

 

[efficientPV]

But, 2 strings will make 10A to a shorted panel. At that current it will burn the connector strips of a shorted panel. 2 strings = no fuse. Three strings = each string has to be fused.

 

[Supervstech]

No fuse needed. 100w panel will not create 15 amps to back feed the other string if there is a fault.

Yeah... you aren't reading all the info before providing advice.

 

[vashkoproimage]

Let say 1 panel fails and I get 16 amps pushed through it and it’s rated for 15 amps max. What will that 1 amp do? If I’m understanding this correctly.

 

[efficientPV]

Panels have a fixed current limit. The idea of a fuse to protect charge controller from panels is ridiculous. The fuse will always be a higher current than the panels can ever supply. A fuse may protect panel wiring from the battery should a controller fail. A fuse is a nice disconnect for testing purposes. The main reason for the fuse is two or more panels ganging up on one panel should it fail. And I've had panels fail from nearby lightning strike which shorted the bypass diodes. Then it burns up internal wiring of the panel. It's your stuff, following codes is optional.

 

[time2roll]

Yeah... you aren't reading all the info before providing advice.

Isc is 5.86

2x 5.86 = 11.72 amps

11.72 amps is less than 15 = no fuse

 

[rmaddy]

Isc is 5.86

2x 5.86 = 11.72 amps

11.72 amps is less than 15 = no fuse

But the OP has 2S3P so it’s 17.58A.

 

[time2roll]

But the OP has 2S3P so it’s 17.58A.

Yes so how does the string with a short also feed current backward?

 

[OzSolar]

Yes so how does the string with a short also feed current backward?

That makes sense but the code doesn't appear to allow for it.

"Article 690.9(A), exception b, states that fusing is not required if the short-circuit currents from all sources do not exceed the ampacity of the conductors or the maximum overcurrent protective device size specified on the PV module nameplate."

Since it doesn't appear to exclude the offending module I'm going to include it in the calculation.

Regardless of my opinion or that it exceeds code it's easy and cheap to install a combiner box plus it makes a lot of sense for initial set up and future trouble shooting so why not just start off that way?

 

[JRH]

I mean, if it’s close enough to debate it , just fuse it and move on..
fuses are sorta fun to mess with anyway…

 

[timselectric]

MC4 Branch connectors and fuse holders are a lot cheaper than a combiner box. And easier to install.

 

[vashkoproimage]

I mean, if it’s close enough to debate it , just fuse it and move on..
fuses are sorta fun to mess with anyway…

I have this type of quick disconnect fuse for my solar panels wires to controller when I work on them. One also for my battery to controller wiring. Also have a full system power off switch for complete shut down to all power sources.

 

[rmaddy]

I have this type of quick disconnect fuse for my solar panels wires to controller when I work on them.

That breaker probably only supports 48.0V at the most, if not not less. What is the Voc of your solar panel array? It's very important that breakers being used as PV disconnects must support enough voltage for the Voc of the panel array (plus a bit of headroom).

I have 3 330W panels in series with a total Voc of about 120V. If I tried to use one of those breakers it would not end well (flames).

 

[JRH]

That breaker probably only supports 48.0V at the most, if not not less. What is the Voc of your solar panel array? It's very important that breakers being used as PV disconnects must support enough voltage for the Voc of the panel array (plus a bit of headroom).

I have 3 330W panels in series with a total Voc of about 120V. If I tried to use one of those breakers it would not end well (flames).

I have found problems with finding reasonably priced DC switch’s that operate in the voltage range you have.. what do you use for your 120v system. I’m only at 80-100v but this does seem to be an Issue taken too lightly.

 

[rmaddy]

I currently have a Midnite Solar MNEPV breaker. It's rated to 150VDC but it is polarized and I only have one on the positive wire. NEC states that both PV wires should be fused.

A 2-pole breaker rated for sufficient DC voltage and amperage should be used. Below is a link to what I believe is a representative example of what some people are using. This is not a specific product endorsement. I have not used this breaker.

https://www.amazon.com/dp/B095YFQWHK

I've seen several threads mention this type of breaker for a PV disconnect.

 

[vashkoproimage]

That breaker probably only supports 48.0V at the most, if not not less. What is the Voc of your solar panel array? It's very important that breakers being used as PV disconnects must support enough voltage for the Voc of the panel array (plus a bit of headroom).

I have 3 330W panels in series with a total Voc of about 120V. If I tried to use one of those breakers it would not end well (flames).

This one is rated at 72v but some people ran more volts without issues. I ran around 60v for a few months without issues.