2Q's - Minimum Enclosure Size & Minimum Disconnect Height

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Anode

Member
Location
Washington, USA
Here is a web link to a picture of my equipment as of right now. The upload attachment feature kept down sampling my picture...

Equipment_Riser.jpg

http://s3.postimg.org/mgcjrg6wz/Equipment_Riser.png


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First question: The two 3" EMT conduits coming down into the electrical room have 32 #10 PV Wire Conductors & #6 Ground, total of 33 conductors. Is there a minimum size requirement for the pull box they go into? I've read through 314.28 and it seems as if since my conductors are no bigger than #4, then there is no requirement other than 20% fill for the wireway.. Is that right?

Second question: 404.8 Gives me 6' 7" to my disconnect switches on the stacked inverters (there's never enough room in electrical rooms... especially for the solar guys), my question is if there is a minimum requirement for the two that are closer to the concrete floor? The switches on those two inverters would be roughly 20 -24".


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A few side questions if you want to tackle them..
Any suggestions on the conduit runs or enclosures from the rendering please fire away. The knock-outs for the inverters made it a real head-scratcher with how to fit all the conduits nicely in that space... It seems as if the type T fittings (1.25") are going to work perfectly with a close nipple to hit the dc knock-outs. Then some pipe easy pipe bends on the 3/4 EMT ac run to the combiner panel.

I think I will add another ac knife blade disconnect under the auxiliary production meter, this will be in addition to the one that is required by the utility on the exterior. Sound like a good idea?

No plan yet for communications, but the dotted rectangle indicates where the enclosure for that may live. On from there I don't know the path yet... May do egauge or something in that enclosure and ct's for the combiner, or bite the bullet and implement the Solrenview into each of the 4 28kW Solectria Inverters..

Image uploading... I kept my image under the kb size, and within the pixel size, and couldn't get the board NOT to down sample it... No sure what I was doing wrong there, do you?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
To answer the 1st two:
With #6 & #10 your j (pull) boxes would be sized for cubic inches per 314.16.
There is no minimum height for a switch in this situation.

I assume you have taken derating into account. Rare to find (32) #10s in a raceway.
 

Anode

Member
Location
Washington, USA
To answer the 1st two:
With #6 & #10 your j (pull) boxes would be sized for cubic inches per 314.16.
There is no minimum height for a switch in this situation.

I assume you have taken derating into account. Rare to find (32) #10s in a raceway.


Thanks so for 314.16 if I have a 8x8x24, I have 1536 in?, and with 32 conductors either per the 314.16(B) table, or even a little more area (PV Conductors), I am way way under.. Correct? Seems that way.


Yes, derating was taken into account, and it's close, but it works along with the vDrop, so it's a go for now.. 30A * 40% > 8.81A * 1.25 ... Perhaps some combiners on the roof may happen, will be looking at that soon enough.
 

Anode

Member
Location
Washington, USA
I rescind my 32#10's. It is 32 #8's... Conduit on a roof exposed to UV + Temperature derating... Still looking good in 3" conduit, but the price just went up!
 
It's expensive but when you have no other choice if you don't have enough room you can hang your inverters high you just need to add a separate DC disconnect. It has to be under 6'7 and with the BOS. As far as the pipping what do you think about just putting a 90 on your 3" and go into a 6"*6"*4' trough?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I think I will add another ac knife blade disconnect under the auxiliary production meter, this will be in addition to the one that is required by the utility on the exterior. Sound like a good idea?

In my opinion it's unnecessary. A cheaper solution, probably, would be simply making that combiner panel a main-breaker panel. But I don't see why this is different from the many, many main-lug-only subpanels in this country which require access to a different location and LOTO if you need to work on them de-energized.
 

Anode

Member
Location
Washington, USA
Thank you all, again.

It's expensive but when you have no other choice if you don't have enough room you can hang your inverters high you just need to add a separate DC disconnect. It has to be under 6'7 and with the BOS. As far as the pipping what do you think about just putting a 90 on your 3" and go into a 6"*6"*4' trough?

Well, it seems as if I'll be code compliant with the stacked inverters, so I will avoid the extra equipment, but it's good to know this, and I read that in some other threads. Thank you. On the second suggestion, I thought about it, but the inverters require 12" of clearance when stacked... I guess a trough would be not much different than some conduit runs in there, and certainly would be cleaner and easier......

If you can't think of any reason why either my conduits between the 12" area I provided, or the trough, would go against manufacturers requirements, then I would opt for your suggestion. I guess it's a question both for you folks here, and for the final say being the interpretation of the manufacturer, in writing of course..

Do you really want to run that much PV wire in conduit instead of transitioning to THWN-2 at a j-box on the roof?

No, actually I don't. It is expensive and unnecessary. After looking at the inverter specifications for landing DC wire in connection box, I realized that they only allow 10 or less, and 8 AWG is "not reccomended". Since my close to roof, ambient temp, and current carrying derates all put me to 8AWG on the roof, I added two transition points just through the roof on the second level where we will transition from 10 PV Wire, to 8 THWN-2.

In my opinion it's unnecessary. A cheaper solution, probably, would be simply making that combiner panel a main-breaker panel. But I don't see why this is different from the many, many main-lug-only sub panels in this country which require access to a different location and LOTO if you need to work on them de-energized.

Agreed. The utility let's us use a load center MCB as a utility disconnect on the residential side when the system is less than 7kW. In this case, a much larger commercial system, that certainly isn't allowed as an exterior disconnect, and I was thinking that perhaps the old Frankenstein switch would be more obvious in the event a shutdown was needed in the main electrical room. But none-the-less, I'm not going to add significant work into the project when some labeling could easily indicate that shutdown point in the load center.

Question, both that MCB, and the Utility Disconnect would then be labeled "MAIN PHOTOVOLTAIC DISCONNECT", yes? One doesn't take precedence over the other?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Question, both that MCB, and the Utility Disconnect would then be labeled "MAIN PHOTOVOLTAIC DISCONNECT", yes? One doesn't take precedence over the other?

From a firefighter's point of view, the one that is more accessible from the service probably takes precedence. I don't think you're required to label more than one but if your just using stickers (and not the $30 placards that some AHJ's require around here) then it's easy enough to label both.
 

Carultch

Senior Member
Location
Massachusetts
Here is a web link to a picture of my equipment as of right now. The upload attachment feature kept down sampling my picture...

View attachment 12582

http://s3.postimg.org/mgcjrg6wz/Equipment_Riser.png


--


First question: The two 3" EMT conduits coming down into the electrical room have 32 #10 PV Wire Conductors & #6 Ground, total of 33 conductors. Is there a minimum size requirement for the pull box they go into? I've read through 314.28 and it seems as if since my conductors are no bigger than #4, then there is no requirement other than 20% fill for the wireway.. Is that right?

Second question: 404.8 Gives me 6' 7" to my disconnect switches on the stacked inverters (there's never enough room in electrical rooms... especially for the solar guys), my question is if there is a minimum requirement for the two that are closer to the concrete floor? The switches on those two inverters would be roughly 20 -24".


--


A few side questions if you want to tackle them..
Any suggestions on the conduit runs or enclosures from the rendering please fire away. The knock-outs for the inverters made it a real head-scratcher with how to fit all the conduits nicely in that space... It seems as if the type T fittings (1.25") are going to work perfectly with a close nipple to hit the dc knock-outs. Then some pipe easy pipe bends on the 3/4 EMT ac run to the combiner panel.

I think I will add another ac knife blade disconnect under the auxiliary production meter, this will be in addition to the one that is required by the utility on the exterior. Sound like a good idea?

No plan yet for communications, but the dotted rectangle indicates where the enclosure for that may live. On from there I don't know the path yet... May do egauge or something in that enclosure and ct's for the combiner, or bite the bullet and implement the Solrenview into each of the 4 28kW Solectria Inverters..

Image uploading... I kept my image under the kb size, and within the pixel size, and couldn't get the board NOT to down sample it... No sure what I was doing wrong there, do you?


I'd recommend running your wireways across the base of each inverter pair. It is easier to enter the inverters with a simple nipple, than to use complicated conduit bodies. Also helps avoid crossing raceways, which can be challenging to construct.

If you are trying to separate AC and DC conductors, you still can do so with a partition inside the wireways. I've seen vinyl siding, and split loom tubing. I've also thought of using plastic wire duct for one of the two kinds of conductors. In my opinion, I believe that this rule is total overkill.

The 20% fill is usually still a good rule to follow when sizing wireways, whether it is mandatory or not. Remember, you want to be able to comfortably close the cover, without jamming your wires in there. You don't want a situation where you pound the cover with a mallet, wedge it closed with a screwdriver, and think "MAN, I sure hope I'm not around when they turn this thing on".

Also, make sure you keep track of all inverter manufacturers' clearance requirements. It is required on the sides, top, and bottom, to assist in airflow management for cooling. You don't want other inverters and wireways to encroach upon this space.

24" sounds reasonable to the bottom of an inverter. Try to make the displays of the upper inverters no higher than the eye-level of a 6 ft tall person. I often import a photo of a person to my drawings and scale it to 6 ft height, to anticipate working height issues.


I think I will add another ac knife blade disconnect under the auxiliary production meter, this will be in addition to the one that is required by the utility on the exterior. Sound like a good idea?

Not needed. There already would be methods available to completely disconnect the AC combiner, in the unlikely event that you need to service its main supply conductors. I'd recommend a main breaker in your AC combining panelboard, as a master-shutoff means. One less piece of equipment to fit on the wall, mount, and wire.
 

Anode

Member
Location
Washington, USA
Also, make sure you keep track of all inverter manufacturers' clearance requirements. It is required on the sides, top, and bottom, to assist in airflow management for cooling. You don't want other inverters and wireways to encroach upon this space.

24" sounds reasonable to the bottom of an inverter. Try to make the displays of the upper inverters no higher than the eye-level of a 6 ft tall person. I often import a photo of a person to my drawings and scale it to 6 ft height, to anticipate working height issues.

I am within all the parameters of inverter mounting with clearance. With the exception of the conduits coming into the inverter (I am wondering what Solectria's take is on those conduits being an obstruction to ventilation, as opposed to perhaps a wireway..). I would love to put in a wireway, but the height of the inverters, and my 6'7" limit on disconnect, means it just won't fit. I'm hoping the conduits in between the inverters are going to fall into a gray area...
 

Zee

Senior Member
Location
CA
Definitely transition to thhn from pv wire, once you leave PV array.
3" EMT is insane. the fill factor on pv wire is triple that of thhn. same gauge. At least.
 

Zee

Senior Member
Location
CA
hmmmm.
If inverter vents top and bottom, and if you have no/minimal side clearance on inverters.......and you transition to THHN on your DC Spaghetti wires above this room, thus significantly downsizing your (2) emt's from 3" ....
can you squeeze in 4 inverters in a row?
That would make everything exponentially simpler. One gutter underneath it all. Even running to load center on right.
On the left you can feed into top of gutter to save space laterally.

(--hang the gutter in air with the vertical rigid nipples that go up into inverters. )
 
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Zee

Senior Member
Location
CA
I imagine that vertical, dc, double 3" conduit could be furtehr reduced if you combined on roof.
So....2x32 conductors= 64 wires/4 inverters = 16 per inverter = 8 strings each?
WHy aren't you combining on roof? You are getting hit hard with the 50% derate factor for over 10 hot wires per conduit.
 

Smart $

Esteemed Member
Location
Ohio
...

Image uploading... I kept my image under the kb size, and within the pixel size, and couldn't get the board NOT to down sample it... No sure what I was doing wrong there, do you?
Your image is not within the pixel limits of 620x280. Yours is 1239x651.
 

Smart $

Esteemed Member
Location
Ohio
You can also upload to Imageshack.com, and include the copyable direct link to here.
A direct link [to any accessible internet address] enclosed in image tags will display [inline] in the post...
Code:
[IMG]<link>[/IMG]
The Insert Image button, URL tab in the dialog without Retrieve... option ticked, does the same.
 
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