PV Array and 300.3(B)

[eric9822]

We have a third party company installing a 1MW Photovoltaic array on one of our buildings. They are currently wiring the individual strings into a distribution panel that I have posted a picture of below. The white wiring is the -DC, the black wiring is +DC. I believe this is a violation of NFPA 70 2005 section 300.3(B). The electrical subcontractor assures me it does not apply since it is a PV DC system. This does not sound right to me but they are ultimately responsible since the equipment will be owned and maintained by a third party. Opinions?

 

[Volta]

We have a third party company installing a 1MW Photovoltaic array on one of our buildings. They are currently wiring the individual strings into a distribution panel that I have posted a picture of below. The white wiring is the -DC, the black wiring is +DC. I believe this is a violation of NFPA 70 2005 section 300.3(B). The electrical subcontractor assures me it does not apply since it is a PV DC system. This does not sound right to me but they are ultimately responsible since the equipment will be owned and maintained by a third party. Opinions?

Looks like they share a cable tray on the right hand side, so I guess that it is up to the black connectors or bushings. If they are "raceways", like chase nipples, or accessories for a recognized raceway or cable method, you have them for those few inches.

Can't use 320 on them for dc either.

Is the DC- grounded? They need to follow chapters 1 through 7 except for conflicts, where 690 wins. If the wiring is under 50 volts, they may not need the whites to be earthed at all. 200.7(B)>250.20, 250.162, 690.41.

 

[Sierrasparky]

What is the size of the feeder from the distribution panel. looks pretty small

 

[davedottcom]

The colors for DC conductors are no different then AC conductors. Very popular misconception... if you are thinking automotive colors, stop thinking that!

 

[davedottcom]

Oh, sorry... I understand your concern is not the colors but how the conductors are grouped.

My take is... unless article 690 directs you to 300 you don't need to follow it. 690 in itself overides the rest of the NEC... if it doesn't say you can't, you can.

 

[Volta]

My take is... unless article 690 directs you to 300 you don't need to follow it. 690 in itself overides the rest of the NEC... if it doesn't say you can't, you can.

90.3 shows us that chapter 6 only modifies chapters 1 through 4, so you still need to follow 300, 200, 250, and all the rest, unless the other articles differ with 690, then 690 overrides. 690.3

 

[eric9822]

No raceway for the wiring from the string to the combiner boxes. USE wire is used per 690.31(B) a picture is posted from prior to termination.

The -DC is grounded.

The feeder from the combiner box is 1/0 and is adequate.

Article 690 does not say you can ignore 300.3(B)

Thanks for the comments. This forum is an invaluable source of information.

 

[iwire]

My take is... unless article 690 directs you to 300 you don't need to follow it. 690 in itself overides the rest of the NEC...

No, that is not true at all, Chapters 1 through 4 apply generally unless modified by Chapters 5, 6, and 7. See 90.3

The electrical subcontractor assures me it does not apply since it is a PV DC system.

Ask them to show you where that info can be found. The NEC applies to DC as well as AC.

I see nothing in 690 that allows ignoring 300.3(B), IMO the contractor should be following 300.3(B) even though I do not think DC will heat that enclosure wired how it is.

 

[davedottcom]

I had that very wrong!

Let me jump to the other side of the fence!

Ok, now I agree with you Eric9822... unless 690 states an exception, 300.3(B) must be applied.

 

[art82]

why are you looking at 300.3 for first of all we are talking about dc conductors with no load do you understand how it works how much is the voltage once the pnl arrays are combined together

 

[iwire]

why are you looking at 300.3 for first of all we are talking about dc conductors with no load do you understand how it works how much is the voltage once the pnl arrays are combined together

• 300.3 applies to DC conductors.
  
• There is current carried on the conductors
  
• The voltage is irrelevant.

 

[nakulak]

I'm curious (not having done any PV) - do these installs use individual conductors like that (I would have thought they would be using some kind of 2 conductor cable in general). And why all the mess ? (they could have flexed over to the cabinets instead of leaving that mess out in the open)

 

[don_resqcapt19]

I don't see a 300.3(B) violation. The open conductors are a 300.3(B)(3) installation and 300.20 does not apply to DC circuits.

 

[iwire]

I'm curious (not having done any PV) - do these installs use individual conductors like that (I would have thought they would be using some kind of 2 conductor cable in general). And why all the mess ? (they could have flexed over to the cabinets instead of leaving that mess out in the open)

Single conductor USE, keep in mind your wiring panels in series so two conductor cable would not be as helpful as we are used to.

And why all the mess ? (they could have flexed over to the cabinets instead of leaving that mess out in the open)

I agree, the raceway should have run all the way.

I think this installation has some series conductor sizing issues. I all but guaranty that conduit stuffed with all current carrying conductors, across a roof and subject to the double 125% rating required by 690 has undersized conductors.

What is the size of the feeder from the distribution panel. looks pretty small

I wonder about that as well

 

[eric9822]

why are you looking at 300.3 for first of all we are talking about dc conductors with no load do you understand how it works how much is the voltage once the pnl arrays are combined together

I understsand how it works and I agree with Iwire that heating should not be an issue. There is however no exception listed in 300.3(B) for this condition.

 

[iwire]

I don't see a 300.3(B) violation. The open conductors are a 300.3(B)(3) installation and 300.20 does not apply to DC circuits.

Well now I will have to go to my truck and get my NEC.

 

[eric9822]

I'm curious (not having done any PV) - do these installs use individual conductors like that (I would have thought they would be using some kind of 2 conductor cable in general). And why all the mess ? (they could have flexed over to the cabinets instead of leaving that mess out in the open)

Each string is comprised of a row of panels from the top of the rack to the bottom. Using two condutor cable would result in a lot of labor and waste due to the negative and positive terminals being about 10 feet apart.

I agree, the raceway should have run all the way.

I agree it would be a lot prettier but you would still need to transition to free air at some point. It would also significantly increase the cost. These things already take a long time to pay out and thats with incentives from the government and the utility.

I think this installation has some series conductor sizing issues. I all but guaranty that conduit stuffed with all current carrying conductors, across a roof and subject to the double 125% rating required by 690 has undersized conductors.

Conductors are 1/0 or 2/0 depending on the distance from the boxes to the inverter pad. Total load on each conductor is 55 amps. All calcs were done be a licensed PE and signed off by the city building department.

I don't see a 300.3(B) violation. The open conductors are a 300.3(B)(3) installation and 300.20 does not apply to DC circuits.

I had not looked at that. Thanks.

 

[iwire]

Conductors are 1/0 or 2/0 depending on the distance from the boxes to the inverter pad. Total load on each conductor is 55 amps. All calcs were done be a licensed PE and signed off by the city building department.

Regardless it still looks very suspect and I have a bit of experience with this.

By the time you apply 690.(A)(1), 690.(B)(1), 310.15(B)(2)(a), 310.15(B)(2)(c) to the 310.16 ratings those conductors look seriously undersized in the conduit.

No doubt I could be wrong, but if you where to tell us the panel ratings, expected ambient temp, conductor size and number we could figure it out.

 

[eric9822]

No doubt I could be wrong, but if you where to tell us the panel ratings, expected ambient temp, conductor size and number we could figure it out.

Each box is fed by 50 strings. A string is comprised of 6 modules that are rated at 75W, 68.2Vmax, 1.10Amax. Conductors from the strings is 10AWG USE. The conductors from the boxes to the inverters are 1/0 or 2/0 THWN depending on the distance to the pad. A maximum of 6 current carrying conductors are run in each raceway. The annual average high temperature is 70 degrees F, the peak high for this year has been 100 degrees. These temperatures do not take into account the heating effect of being on a roof.

Thanks

 

[Volta]

. . .
By the time you apply 690.(A)(1), 690.(B)(1), 310.15(B)(2)(a), 310.15(B)(2)(c) to the 310.16 ratings those conductors look seriously undersized in the conduit.
. . .

It's hard to tell from the 2nd picture, but the raceway might not be "conduit", but only "tubing", so maybe we don't apply 310.15(B)(2)(c).

IYou've got to be right about 310.15(B)(2)(a), though.

What are the 690 sections that were cut-off again?