Damn Texans...

[SunEagle]

Well I don't see you listed as a mod?

FWIW I can take your ham radio number and get all the info I need on you.

Making threats about finding out personal information about someone usually will get you a vacation from the website.

We are done Sunking I've got you figured out now.

If you have blocked Sunking then why are you still arguing with him?

[SunEagle]

Maybe if I share them, but doing a background check with all the public information on the internet is well within my rights.

Your comment still sounded like a threat to me. Which can mean that you were going to release the information.

[Sunking]

you are arguing with me about a 50$ difference for 500'

Darn right I am as that is a 30 to 50% premium for #10 AWG USE-2 @ 500 ft that either you are absorbing or passing onto the client. That is foolish IMHO. Unless the voltage rating is 2000 volts there is nothing to be gained. 600 volt PV is meaningless for residential installs.

[Sunking]

Well before I go and because no one caught it here is a link explaining why I was asked to use this cable in my install.

Here is what I have been pounding

The success of transformerless inverters may help pave the way for the NEC and the US Solar Industry to adopt 1000V systems, which will further reduce installation costs

Residential systems in the USA are 600 volt or less. A 600 volt USE and PV are the exact same cable, just one is more expensive than the other. That is what the debate is going on within the NEc over PV cable listing. It is meaningless as it comes in 3 voltage ratings of 600, 1000, and 2000 volts. All Building Power Wire is 600 volts. The PV 600 volt rating gains nothing.

[SunEagle]

OK. So it looks like the inverter manufacturer KACO recommends higher voltage rated insulation wire for their equipment which makes sense for ungrounded systems.

This is similar to the VFD manufacturers requiring the wire for the motor leads to be "VFD" rated cable. We found out that "VFD" rated cable was nothing more that standard AWG wire with 1000, 1200 or 2000 volt insulation. You can find these high insulation rated cables that do not have the "VFD" rating but is just as good for less money.

Looks like the "PV" rated cable falls into a similar situation.

[inetdog]

This is similar to the VFD manufacturers requiring the wire for the motor leads to be "VFD" rated cable. We found out that "VFD" rated cable was nothing more that standard AWG wire with 1000, 1200 or 2000 volt insulation. You can find these high insulation rated cables that do not have the "VFD" rating but is just as good for less money.

Yes and no....

The problem with VFD use is that the rise time of the output voltage waveform is very short, leading to high dV/dt exposure in the insulation. With MV wire and cable the insulation is so sensitive to dV/dt that the presence of high levels of even third harmonic voltage can cause insulation deterioration even though both peak and RMS voltages are below the insulation rating. (See http://forums.mikeholt.com/showthread.php?t=155529).
Similar problems can affect wire exposed to the fast edges of VFD output without use of a filter or line reactor.
You can either deal with this by increasing the RMS voltage rating of the insulation and hoping that the degradation will be proportional (and then testing) or you can restrict yourself to particular insulation types which are less vulnerable to these effects or even use enhanced quality control on the formulation of the polymer insulation itself.

So, although VFD wire may have a higher inherent insulation rating, you cannot just assume that any wire with that insulation rating will be suitable for VFD use.
Some might, some might not depending on the formulation that a particular manufacturer uses.

This is very much analogous to the situation with PV wire. The PV wire may also correspond roughly to an existing Building Wire type, possibly with a higher insulation voltage rating, but that is not the only difference.

More on this whole issue in my next post.

[inetdog]

Hold the bus there my friend. Commercial and Industrial installations go well above 1000 volts. No way are you going to make say a 10 Mw array at 600 volts.

But here is to your point. Residential installations are limited to 600 volt max.

1. Following your lead and relying on old data , this reference indicates that even commercial installations do not use voltages higher than 1000V to ground in grounded systems.
They use a maximum of 1000V even in commercial installations. To deal with the high currents needed (~1000A for a 1MW system), multiple string inputs and multiple inverters are used on the DC side. The AC side of the inverters may either produce 480 or 600 volt three phase to be transformed up to meet the utility transmission/interconnect line or in some cases produce MV outputs in the inverters. But that side would not use PV wire.
And a 10MW solar installation is likely going to be composed of ten or more smaller systems with separate DC inputs and combined AC outputs.

However, bi-polar input inverters can use two arrays at +1000V and -1000V, combined in the inverter to get the efficiency of a 2000V array in terms of wire resistance while keeping a maximum 1000VDC to ground. The only use for 2000V rated wire in this environment is to allow the hot leads from the two polarity arrays to be run in a common raceway. Using 1000VDC rated insulation the hot lead and neutral from one array must run in a separate conduit from the hot lead and neutral of the other polarity array.

2. Since the wiring under Article 690 is not Building Wiring under general Article 300 standards, it is also possible to use 1000V DC inputs for residential inverters, using Special Purpose wiring (i.e. PV wiring) instead. Either Article 300 wiring OR PV wiring is allowed by 690.
Now, it would probably be foolish and dangerous as well as expensive in terms of the fuses, circuit breakers, and other wiring odds and ends, to use 1000VDC in a residential installation, but I do not think that it is currently prohibited by NEC 2011. (I admit I may well be wrong on that.)

[inetdog]

Well I don't see you listed as a mod?

What am I missing?

Well, for one thing not all of the named forum moderators from the site are listed at that link with biographies, either for space or privacy reasons.

[SunEagle]

Yes and no....

The problem with VFD use is that the rise time of the output voltage waveform is very short, leading to high dV/dt exposure in the insulation. With MV wire and cable the insulation is so sensitive to dV/dt that the presence of high levels of even third harmonic voltage can cause insulation deterioration even though both peak and RMS voltages are below the insulation rating. (See http://forums.mikeholt.com/showthread.php?t=155529).
Similar problems can affect wire exposed to the fast edges of VFD output without use of a filter or line reactor.
You can either deal with this by increasing the RMS voltage rating of the insulation and hoping that the degradation will be proportional (and then testing) or you can restrict yourself to particular insulation types which are less vulnerable to these effects or even use enhanced quality control on the formulation of the polymer insulation itself.

So, although VFD wire may have a higher inherent insulation rating, you cannot just assume that any wire with that insulation rating will be suitable for VFD use.
Some might, some might not depending on the formulation that a particular manufacturer uses.

This is very much analogous to the situation with PV wire. The PV wire may also correspond roughly to an existing Building Wire type, possibly with a higher insulation voltage rating, but that is not the only difference.

More on this whole issue in my next post.

I agree with your explanation that not all high insulation rated wire is good for VFD's. I am very familiar with the generation of the harmonics and reflective wave issues caused by the VFD and the use of reactors and motor terminators to reduce equipment failures.

Although when it comes to the motor leads, from experience I found that there wasn't a need to pay top dollar for a specific VFD rated wire (manufacturer name not to be disclosed but it was orange in color). You can find a good quality 1000 volt insulated wire for less money. The wire we used did not experience any pin hole or shorting failures and we were able to save a few thousand dollars on the project.

[inetdog]

Although when it comes to the motor leads, from experience I found that there wasn't a need to pay top dollar for a specific VFD rated wire (manufacturer name not to be disclosed but it was orange in color). You can find a good quality 1000 volt insulated wire for less money. The wire we used did not experience any pin hole or shorting failures and we were able to save a few thousand dollars on the project.

I certainly can't argue with experience, I just wanted to make sure that less knowledgeable readers did not draw the incorrect implication that only the insulation voltage rating was important.

BTW, are you comfortable that the manufacturer will not change the insulation composition without re-designating the product? I know that they would at a minimum have to repeat the UL testing for any significant changes, but they would not have to publicize that. Possibly a different file number if you look closely?

[SunEagle]

I certainly can't argue with experience, I just wanted to make sure that less knowledgeable readers did not draw the incorrect implication that only the insulation voltage rating was important.

BTW, are you comfortable that the manufacturer will not change the insulation composition without re-designating the product? I know that they would at a minimum have to repeat the UL testing for any significant changes, but they would not have to publicize that. Possibly a different file number if you look closely?

I am comfortable with this manufacture but again you provided good information concerning identification of product modifications. Thanks.

[Sunking]

Originally Posted by IndianaOHMS

Well I don't see you listed as a mod?

What am I missing?

My username dereckbc. Do not bother to apologize for calling me a liar. I have been a moderator over at Mike Holt longer than you have been in the trade. I am stealth, I do not allow my name to be on the moderator page. Look for yourself at one of my post. What does that TAG under my username say? Check out the Avatar. Anyone who has been here for a while knows it is my Avatar when they were allowed here.

SunKing

[cnttxmdc]

Wow.........

Thanks for the education guys. I'm not sure I can say I have a crystal clear understanding of everything with it going back and forth, but I certainly consider myself enlightened!


(All that discussion over wire.... Just think if I asked where babies came from or what was the best brand of truck!)



As an update, I got my inverter delivered yesterday. It's a SB 5000US, and I paid $1650 including shipping. New in box; it seemed like a good deal to me. I'll be picking up a good amount of steel tomorrow (a Craigslist special, sold as a good sized lot) so that I can build my mounts.


I have two other simple questions (out of plain ignorance on my part): What voltage do you guys have each string wired to put out? I'm assuming that it'd be best to wire each string so that the voltage is as high as the inverter can safely handle, and then of course have the matched strings tied in parallel? I just want some feedback to make sure I'm thinking about that in the right way. Also, would I gain anything by having them isolated from each other with diodes? I seem to remember diodes not being needed in modern panels, but again I just want some feedback and to learn from other's experience & mistakes!

Thanks everyone!
Andrew

[cnttxmdc]

I have two other simple questions (out of plain ignorance on my part): What voltage do you guys have each string wired to put out? I'm assuming that it'd be best to wire each string so that the voltage is as high as the inverter can safely handle, and then of course have the matched strings tied in parallel? I just want some feedback to make sure I'm thinking about that in the right way. Also, would I gain anything by having them isolated from each other with diodes? I seem to remember diodes not being needed in modern panels, but again I just want some feedback and to learn from other's experience & mistakes!

Disregard that first question. I got on the SB website and played with their "Sunny Design" software. For my particular inverter and panels, it appears that having two strings would be the most efficient option.
And after thinking about it, I don't see that adding diodes would be of any benefit.

If anybody disagrees with those two items, please let me know and why that's the case.

Thanks again!