Wire recommendation from panel

**Sunking** · 04-29-2016, 02:39 PM

Originally posted by Teocalli

Stranded is easier to work with and for DC applications there is really no difference between both types , what's important is the voltage drop over my 20' and that is why I am using 6/2 instead of 12/2 from the panel, I did follow Sunking's advice and went with marine 6/2 just to be safe.

Good choice and you are welcome. With Low Voltage Systems Voltage drop requirements exceed minimum Current capacity requirements. What I cannot answer is if you needed 6, 12, or 1/0 AWG because you only gave 1 data point of 3 needed. You only gave 1-way distance of 20 feet. To determine wire size I would need to know voltage and current. There is no technical or safety issue in using a larger conductor than needed. Only harm or pain is in the wallet. However it does add additional requirements on Ground Conductors if the system is grounded. If you increase the size of the supply conductors requires you to increase the size of ground conductors which causes more pain in the wallet.

Morro of the story is be careful with over sizing. You want to limit losses to 2-3%. If Codes dictate 12 AWG minimum, but voltage drop calcs determine 10 AWG is required, going to 6 AWG is not gaining you anything meaningful and doubles the cost needlessly. I not only care about your safety and proper operation, I also care about your wallet and keeping the green in it.

**ncs55** · 05-04-2016, 08:47 AM

Sunking, what you say about voltage drop is straight from the code book. However, in real life a 2-3% voltage drop in either the dc or AC side is not even acceptable by most inverter manufacturers standards. In the real world and when you design a system for longevity, the voltage drop should be less than 1% by manufacturer standards. Wire is a small percentage of cost for residential systems and going 1 or 2 sizes larger is not expensive. A 2-3% voltage drop will cause more heat inside of the inverter and is one of the biggest mistakes that cause premature inverter failure. It is more expensive to have to replace an inverter than to simply follow a 1% or less rule. As far as the physics of electron flow and wire nicks. Thank you for your insight, and the only important thing for me, is using the correct size and type for the application, and to strip the covering carefully as to not Nick or cut the strands. Thank all of you for the physics lesson.

**SunEagle** · 05-04-2016, 09:13 AM

Originally posted by ncs55

Sunking, what you say about voltage drop is straight from the code book. However, in real life a 2-3% voltage drop in either the dc or AC side is not even acceptable by most inverter manufacturers standards. In the real world and when you design a system for longevity, the voltage drop should be less than 1% by manufacturer standards. Wire is a small percentage of cost for residential systems and going 1 or 2 sizes larger is not expensive. A 2-3% voltage drop will cause more heat inside of the inverter and is one of the biggest mistakes that cause premature inverter failure. It is more expensive to have to replace an inverter than to simply follow a 1% or less rule. As far as the physics of electron flow and wire nicks. Thank you for your insight, and the only important thing for me, is using the correct size and type for the application, and to strip the covering carefully as to not Nick or cut the strands. Thank all of you for the physics lesson.

As Sunking stated the 2-3% VD is a code requirement and a manufacturer's standards may be higher at 1%, Although a 3% VD should not hurt their equipment, but it will make them run less efficient.

**ncs55** · 05-04-2016, 09:18 AM

Again, you are using code book thinking. In the field it is a different reality. And what I said is exactly what I see and repair on a daily basis. It does not hurt the equipment, it kills it prematurely. You guys need to think beyond code when performing a system design. Code is just a basic minimum guideline and systems installed using only that type of limited thinking will fail before they should.

**SunEagle** · 05-04-2016, 09:21 AM

Originally posted by ncs55

Again, you are using code book thinking. In the field it is a different reality. And what I said is exactly what I see and repair on a daily basis.

If you say so. While I do have field experience concerning electrical hardware I do not repair inverters.

But based on the manufacturer spec sheets that I am familiar with unless the system is considered "critical operation" a 3% VD is not unacceptable for most equipment.

To add most if not all companies that fund a project will not do more than what the NEC requires due to the higher cost and longer payback. Unfortunately that is the normal way most companies run their business.

**ncs55** · 05-04-2016, 09:39 AM

Call up SMA and ask them what is the best voltage drop % for longevity. Schneider Electric will tell you the same thing, as many others. As far as the companies that fund projects go. They only know the costs and have no caring for a proper system design. They only care about how much money they are going to make on each project. In the San Diego area we have seen many contractors go out of business due to the fact that they could not handle fixing the crap that they sold. This is a huge black eye in this industry. In solar, you get what you pay for. A not so good design and crappy installation will be cheap and will fail. A well thought design and a proper installation will harvest more energy, last longer and with fewer problems. I have tons of data to prove this. Price per watt is not the most important thing. A well thought out system with proper installation will cost a few more dollars up front, but saves the customer a lot more in the long run.

**SunEagle** · 05-04-2016, 09:59 AM

Originally posted by ncs55

Call up SMA and ask them what is the best voltage drop % for longevity. Schneider Electric will tell you the same thing, as many others. As far as the companies that fund projects go. They only know the costs and have no caring for a proper system design. They only care about how much money they are going to make on each project. In the San Diego area we have seen many contractors go out of business due to the fact that they could not handle fixing the crap that they sold. This is a huge black eye in this industry. In solar, you get what you pay for. A not so good design and crappy installation will be cheap and will fail. A well thought design and a proper installation will harvest more energy, last longer and with fewer problems. I have tons of data to prove this. Price per watt is not the most important thing. A well thought out system with proper installation will cost a few more dollars up front, but saves the customer a lot more in the long run.

I have no argument with your statements. I have always felt that it is better to spend a little more up front then repairing systems after they broke due to low quality hardware.

**J.P.M.** · 05-04-2016, 10:39 AM

Originally posted by SunEagle

I have no argument with your statements. I have always felt that it is better to spend a little more up front then repairing systems after they broke due to low quality hardware.

The phrase penny wise and pound foolish comes to mind. Probably also applies to planning, design and quality as well. Still, overdesign (or what ignorance may think is overdesign) to cover ignorance is never a substitute for knowledge and experience in practice.

**SunEagle** · 05-04-2016, 10:47 AM

Originally posted by J.P.M.

The phrase penny wise and pound foolish comes to mind. Probably also applies to planning, design and quality as well. Still, overdesign (or what ignorance may think is overdesign) to cover ignorance is never a substitute for knowledge and experience in practice.

I agree with you. It is not worth to over spend when getting a quality installation for less works.

The problem I have run into my 40 some odd years of being a project manager is that the funding for the electrical side seems to take a back seat to the rest of the project. It sometimes takes a project that failed due to penny pinching that helps support my side and allows me to get the funding I needed for my portion.

**J.P.M.** · 05-04-2016, 11:01 AM

Originally posted by SunEagle

I agree with you. It is not worth to over spend when getting a quality installation for less works.

The problem I have run into my 40 some odd years of being a project manager is that the funding for the electrical side seems to take a back seat to the rest of the project. It sometimes takes a project that failed due to penny pinching that helps support my side and allows me to get the funding I needed for my portion.

Couldn't agree more, but I'd apply that to most aspects of a project. Similar to my suspicion that quality suffers as those who pull the purse strings get further, both mentally and physically, from the project or from running a business. As an example, but at the risk of showing my formidable ignorance in such areas, I'd cite the increase in the proportion of MBA's who run hospitals, and note hospital related "accidental" deaths as being reported just now by the whore media. .

**ncs55** · 05-04-2016, 07:02 PM

Originally posted by SunEagle

I agree with you. It is not worth to over spend when getting a quality installation for less works.

The problem I have run into my 40 some odd years of being a project manager is that the funding for the electrical side seems to take a back seat to the rest of the project. It sometimes takes a project that failed due to penny pinching that helps support my side and allows me to get the funding I needed for my portion.

There is a balance in design, quality and budget. I am curious if any of the designers or PM's like yourself even consider if the systems that you put out will make it through say the hundred year storm or the like? If not, then it is a worthy consideration. The problem is, solar is like a gold rush for most companies and it always comes down to How Much Profit will the company make and How Can The Company Make More. This type of thinking always throws the design under the bus, so to speak, and the consumer holding the bag.

**SunEagle** · 05-04-2016, 08:03 PM

Originally posted by ncs55

There is a balance in design, quality and budget. I am curious if any of the designers or PM's like yourself even consider if the systems that you put out will make it through say the hundred year storm or the like? If not, then it is a worthy consideration. The problem is, solar is like a gold rush for most companies and it always comes down to How Much Profit will the company make and How Can The Company Make More. This type of thinking always throws the design under the bus, so to speak, and the consumer holding the bag.

While most capital projects I have worked on either met or slightly exceeded the NEC regulations there were times when "just meeting the code" could have been improved by spending a little more. What I found was that while the design was good and the project succeeded with everything working correctly, sometimes the required maintenance to keep it all working wasn't performed due to budget constraints. So hardware failed earlier than expected.

**ncs55** · 05-04-2016, 08:46 PM

SunEagle, I hear you. I have run across that same situation many times. Usually in smaller commercial systems 30-100kW. They spent everything they had to get the system installed and have no budget for maintenance and are counting on the production without the thought of a failure, to pay them back. It is hard for them to pay for just the materials sometimes. Some of the inverter boards can cost 2-3 thousand dollars and there are usually power supplies etc. that go with the boards that add an extra 3-6 hundred dollars each. The labor cost for repair is nothing compared to the materials. Boards and power supplies also usually fail due to grounding, or lack of, at the array. That can be very costly to repair properly. And in that case the labor is most of the cost. Picture example below of a grounding issue that caused many power supply failures before we got there and examined the array. What you see was not NEC and should have never made it past a final inspection for the time of the install. We had to ground the modules properly along with and before fixing the Xantrex 30-208 permanently. That is why you will see many comments in here from me about the importance of proper grounding of each module with a ground lug and bare copper connecting everything.

**J.P.M.** · 05-04-2016, 10:37 PM

Originally posted by SunEagle

I bet there is also a relationship to the percentage of less nurses at hospitals to rise of "accidental" deaths.

If my wife's opinion in such things counts ( M.S.N., nurse practitioner + prior MBA and CPA), as a matter of common sense, the reduced staffing levels of health care professionals most certainly can contribute to infection rates and less patient care of all kinds. That level of staffing is a direct consequence of management decisions.

**DaveDE2** · 05-04-2016, 10:46 PM

Originally posted by ncs55

A 2-3% voltage drop will cause more heat inside of the inverter and is one of the biggest mistakes that cause premature inverter failure. It is more expensive to have to replace an inverter than to simply follow a 1% or less rule.

Nonsense.

A 2-3% voltage drop results in power/voltage loss in the wires from the panels to the inverter and nothing more. It in no way affects the inverter other than producing slightly less voltage into it.

Wire sizing above and beyond NEC requirements is a tradeoff for the end user, going bigger saves a little power, going smaller wastes a little power.

Wire recommendation from panel

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