Electrical Inspection — Is AC inspected independent of DC?

[OrdinaryBeauty]

My question in brief: Is DC wiring in a residence subject to electrical inspection? I've been told that it is not, but I cannot find anything in writing which supports or refutes this. And I am referring to wiring for power, not low voltage communication or landscape wiring.

My circumstances: off-grid, new construction of a future home with solar power, someday. I've wired redundantly, AC & DC, because I had a sudden opportunity to do so without cost, and because there was so much advice recommending using DC wherever possible for greater efficiency. I figured I could sort it all out later.

I am still a long way from actually installing a solar power system, but I want to pass my electrical inspection as soon as possible so I can 'close up' and get to finishing the interior.

My AC breakers, panel, and ground rods are in, and I think I am ready to call for an inspection even though I have done absolutely nothing with my DC wiring except to pull it to boxes.

Or am I off my rocker? If I am off base, what am I lacking?

And thank you all for being so generous with sharing your experiences and for taking the trouble to do so.

—Leila

[CA_Tom]

My question in brief: Is DC wiring in a residence subject to electrical inspection? I've been told that it is not, but I cannot find anything in writing which supports or refutes this. And I am referring to wiring for power, not low voltage communication or landscape wiring.

My circumstances: off-grid, new construction of a future home with solar power, someday. I've wired redundantly, AC & DC, because I had a sudden opportunity to do so without cost, and because there was so much advice recommending using DC wherever possible for greater efficiency. I figured I could sort it all out later.

I am still a long way from actually installing a solar power system, but I want to pass my electrical inspection as soon as possible so I can 'close up' and get to finishing the interior.

My AC breakers, panel, and ground rods are in, and I think I am ready to call for an inspection even though I have done absolutely nothing with my DC wiring except to pull it to boxes.

Or am I off my rocker? If I am off base, what am I lacking?

And thank you all for being so generous with sharing your experiences and for taking the trouble to do so.

—Leila

Are you planning to do anything further at this point with the "DC" wiring?
Or just put face-plates on the boxes after you've documented exactly where all the wires go and which one is which.

Because if you're just putting face-plates on them, then it seems you *are* done with your DC wiring. And I'd think you're ready for the rough-in electrical inspection. And the final electrical inspection will be once all your fixtures are in place - which is after drywall anyhow.

BTW - what are you using for "DC wiring"? Is it the same wiring used for the AC wiring just everything goes to one central wiring closet? If so, it seems it's redundant to have that as well as the AC wiring - so can't see how it would be "without cost"

[Sunking]

My question in brief: Is DC wiring in a residence subject to electrical inspection?

Yes, no different than AC, its all power and lighting circuits in the eyes of NEC. The DC and Ac wiring cannot occupy the same space and has to be completely isolated from one another like CATV, Fiber, and Phone. The DC wiring will have to use different color codes to distinguish it from AC and polarity.

Who ever told you it is not inspected needs to be ignored. All wiring in a home is subject to inspection even Class 1 and 2 low voltage under Article 725 like a door bell transformer or low voltage lighting. It all falls under building Power and Lighting.

[russ]

Spokane or thereabouts? Lots of good sun but a tad cool right about now I believe.

[Mike90250]

.... there was so much advice recommending using DC wherever possible for greater efficiency. I figured I could sort it all out later

........

Or am I off my rocker? If I am off base, what am I lacking?

I can assure you that you have NOT gotten reliable advice about running DC as a low loss alternative to AC. Unless you are using 50KV DC buss to power substations.

The only commonly available DC gadgets are 12V for boating and truckers. They consume the same watts as AC versions, but because of their low voltage, they use large amounts of amps. That high amperage means voltage loss in even 8ga wire, is enormous.

The inspector should not care about AC or DC labels on the wires, he should be looking for safety issues, such as proper breakers to protect the wires (DC rated breakers cost more than AC breakers) and safe connection points (outlets) switches and lighting fixture installation that won't cause a fire. (DC switches are also expensive)

The generally accepted thing is to wire in a sub-panel (AC) with a transfer switch, that powers your critical loads, and use a small, efficient inverter to power loads, off your batteries.

If you have a 12v battery, and run a LED light and cell phone charger next to it, you are fine, but trying to distribute DC at low voltages, is not very practical.

Now, if you are doing something with 96V DC gear, that lowers the amps enough that DC is a viable alternative.

[Sunking]

They consume the same amps as AC versions,

Mike that appears to be a typo.

[Mike90250]

Mike that appears to be a typo.[/COLOR]

It was, and I corrected it in about 90 seconds. Man, I am so busted.

[Sunking]

It was, and I corrected it in about 90 seconds. Man, I am so busted.

Sorry, I read it almost as soon as you posted. Fell free to delete my post.

[CA_Tom]

The only commonly available DC gadgets are 12V for boating and truckers. They consume the same watts as AC versions, but because of their low voltage, they use large amounts of amps. That high amperage means voltage loss in even 8ga wire, is enormous.

I believe there are a number of things intended for RVs as well.

Lighting *might* be more efficient, since typical AC light is often incandescent still - while typical DC light is probably LED and lower amount of lumens.
You'd have to sit down and figure it out I think.

I'd agree that a dedicated subpanel and transfer switch is probably a better investment than any DC wiring.

[OrdinaryBeauty]

Okay, well all y'all have at least confirmed that validity of my nagging sense of "I've got a bad feeling about this". At least now's a good place to start with making things right.

So, I understand most of what all y'all have told me, and I have no argument. I still don't know how to proceed, and will have to ponder what you've said and possibly ask more questions.

I was able to wire the DC at no cost, because I didn't have to pay for wire, and the added $50 for hired help seems like nothing in the grand scheme of things. So I went ahead and did it. Especially because if I didn't do it in the moment, it would cost me to do it later. So there's that.

My AC wiring is typical, connected to my panel, all normal, allegedly to code (I hope to find out soon). My DC wiring is just there, running in the walls to boxes for outlets, lights, and switches. The main thing that I had intended to do with DC was lighting, having been told that using LED lights direct to DC (rather than AC converted to DC) is the direction that things are headed. The argument seemed good, given that large factories are busy converting to such a setup for the cost-savings. Plus, I would have a ready source of DC power.

Of course, all usual measures of "cost-savings" should not be assumed to be applicable for solar power, right.

I have come across some DC things such as ceiling fans that would be useful, although right now it does seem that most everything that is powered by DC is designed for marine or RV use (and butt ugly or mighty expensive).

Sunking, when you say, ". . . DC and Ac wiring cannot occupy the same space and has to be completely isolated from one another . . .", I don't know enough to know what this means. I think that "isolated" means that there are no bare wires in contact and no chance to combine DC with AC. But I am quite possibly wrong, and I do not know how "same space" in this case would be defined. (I do know that when AC and DC outlets are in the same space, the outlets must be different.)

FWIW, the only thing I've purchased in anticipation of solar power is a used 3-way fridge, and I can always sell that for what I paid. In other words, I'm not tied to making this work based upon something I have already dumped money into.

I actually never desired to try and figure out all of this. What I'd love is to have someone I could turn all this over to and have them make it happen. But so far I haven't encountered anyone near me who seems up-to-date and trust-worthy.

(russ, I'm not far from the Canadian the border, where indeed it is usually sunny and is currently only 0ºF.)

Thank you all again. Even though I am still miles from having something set up, I've learned a lot from reading these forums over the last few months.

[russ]

For nearby Spokane from PV Watts - is for grid tied but the insolation numbers should be good.

RESULTS

1.94	53	3
2.53	61	3
3.86	100	6
5.10	126	7
5.97	148	8
6.28	148	8
7.57	176	10
6.74	158	9
5.21	121	7
3.75	94	5
1.84	47	3
1.54	42	2
4.36	1,274	$ 71

Find A Local Installer Download Results: Monthly | Hourly
* Caution: Photovoltaic system performance predictions calculated by PVWatts® include many inherent assumptions and uncertainties and do not reflect variations between PV technologies nor site-specific characteristics except as represented by PVWatts® inputs. For example, PV modules with better performance are not differentiated within PVWatts® from lesser performing modules. Similarly, the “Energy Value” column simply multiplies the utility-average electricity price by production. Complex utility rates and financing can significantly impact the energy value. See Help for additional guidance.

Requested Location	spokane, wa
Weather Data Source	(TMY2) SPOKANE, WA 14 mi
Latitude	47.63° N
Longitude	117.53° W
DC System Size	1 kW
Module Type	Standard
Array Type	Fixed (open rack)
Array Tilt	20°
Array Azimuth	180°
System Losses	14%
Inverter Efficiency	96%
DC to AC Size Ratio	1.1
Average Cost of Electricity Purchased from Utility	0.06 $/kWh
Initial Cost	3.30 $/Wdc
Cost of Electricity Generated by System	0.21 $/kWh

These values can be compared to get an idea of the cost-effectiveness of this system. However, system costs, system financing options (including 3rd party ownership) and complex utility rates can significantly change the relative value of the PV system.

[Sunking]

The main thing that I had intended to do with DC was lighting, having been told that using LED lights direct to DC (rather than AC converted to DC) is the direction that things are headed. The argument seemed good, given that large factories are busy converting to such a setup for the cost-savings.

I don't know where you are hearing any of this, but I assure you it is completely false. Factories, Warehouses, Sporting Arenas, shopping centers, offices are switching to T5HO High Bay which is a 277 and 120 volt Florescent lighting which is more efficient than LED's. Low voltage lighting is to inefficient. Low voltage is only practical in very small places with very short wiring distances involved like an RV.

[SunEagle]

I don't know where you are hearing any of this, but I assure you it is completely false. Factories, Warehouses, Sporting Arenas, shopping centers, offices are switching to T5HO High Bay which is a 277 and 120 volt Florescent lighting which is more efficient than LED's. Low voltage lighting is to inefficient. Low voltage is only practical in very small places with very short wiring distances involved like an RV.

The only places I have seen Industrial customers using DC is with some of the smaller HVAC units. It seems running small variable DC motors instead of using VFD controlled AC motors can be a little more efficient depending on the humidity and temperature set points.

I have not seen anyone going to DC lighting, although recently there has been more activity to going with LED AC lighting in parking lots, roadways and large cold warehouses.

Still the best bang for your buck in dry environments is the T5HO Fluorescent lighting.

[inetdog]

Still the best bang for your buck in dry environments is the T5HO Fluorescent lighting.

Make that dry warm environments and I will agree. (Although T8 is also up there close to T5. The smaller tube diameter does allow more efficient reflectors in a smaller space.)

[SunEagle]

Make that dry warm environments and I will agree. (Although T8 is also up there close to T5. The smaller tube diameter does allow more efficient reflectors in a smaller space.)

+1 on the warm environment.

What is amazing is the number of cities that have started to re-lamp their streetlights from HID to LED. Big expense up front but they see a payback by cutting their wattage in half without (according to the articles) reducing the light output.

Looks like LED's continue to improve in both lumens per watt output and while the original lifespans were a little exaggerated they should last 3 times as long as the HID lamps.