What is the PROPER conduit for DC solar wiring??? (HELP!)

cupcake · February 2015

Hi pals,

Gonna put my battery bank outside on an exterior concreteblock wall soon, ..gotta an expensive aluminum box for this task...

anyway, I plan to bust a 2" hole in the wall to take the wires from the batteries to the inverter directly on the other side of the wall...

SO: I'll have 2 battery leads AND 2 charge-controller leads (4 leads total) coming through a hole in the wall..., battery-to-inverter leads are 2/0 and charge-controller leads are 6 guage...

MY QUESTION:

What's the proper conduit to run the DC leads from outside to inside?

IS 2" grey PVC proper?

EMT?

METAL CONDUIT?

Nothing?

What?

Thank's pals.. love you all...

-cake

peace

mike95490 · February 2015

Re: What is the PROPER conduit for DC solar wiring??? (HELP!)

If you penetrate a fire rated wall in a building ( a wall that is required to have drywall on it for some fire resistance) you need to use metal, not PVC.

vtmaps · February 2015

Re: What is the PROPER conduit for DC solar wiring??? (HELP!)

cupcake wrote: »

Gonna put my battery bank outside on an exterior concreteblock wall soon
<snip>
I'll have 2 battery leads AND 2 charge-controller leads (4 leads total) coming through a hole in the wall.

Don't forget that you will need to run your battery temp sensors through the wall also.

If you put your battery box up on blocks (top of batteries at about 40 inches above ground), it may be easier to service them (less bending over). Also, that makes the battery cables shorter because the battery box is closer to the inverter.

As you know (from some of your other threads), five batteries in parallel is not likely to be a long lived battery bank. Think about your next batteries and buy a battery box that can hold them... for example, your next batteries may be taller than your current set.

The conduit should enter the battery box below the tops of the batteries so that hydrogen gas does not rise up into the conduit.

Another way to wire up your system is to set up a DC electrical panel next to your inverter and have a positive and negative battery bus bar in the panel. Then you need only 1 pair of 4/0 cables connecting the battery box to the panel. The electrical panel can hold circuit breakers for the inverter and the controller, and you can run your cables (#2/0 and #6) to the inverter and controller from that panel. This has a number of advantages... for example it is easier to connect other things (battery monitor, DC loads, battery charger, etc) to the bus bars than it is to connect them to your battery posts (which already have inverter and controller connections).

--vtMaps

cupcake · February 2015

Re: What is the PROPER conduit for DC solar wiring??? (HELP!)

Mike,

I should have mentioned it's a CONCRETE BLOCK WALL that I will be penetrating, the box will be mounted to the wall, about 3-4 above the slab...

So with a block wall, will grey PVC suffice, or shoudl I use metal, and if so is EMT proper to use?

Thanks

cupcake · February 2015

Re: What is the PROPER conduit for DC solar wiring??? (HELP!)

vtmaps,

Yes 5 wires total, I forgot to mention the temp sensor wire... so yes 5 leads total in the conduit going through block wall - do you reccomend grey PVC or metal (emt) or something else?

Also the box can only fit 3 group 27 batteries in there so I'm gonna drop down to 3 in parrallel with the intention of getting more proper batteries later on -- right now I'm going 3 years on ChinaZone Marine batteries hooked up 5 in parrallel....

But I'm gonna switch to something more proper soon, thus why I got the fancy outdoor box.. for now my priority is to get the batteries out of the inside of the cabin...

so going through block wall... grey pvc, emt, somethign else???

thanks again pals

--cups

cupcake · February 2015

Re: What is the PROPER conduit for DC solar wiring??? (HELP!)

Attachment not found.

This is the BOX by the way... alumunum..

cupcake · February 2015

OK - so I got hole busted out of the block wall to get a 1.5" conduit through... this should be enough for a two 2/0 wires, two 6 guages, and a skinny temp wire...

So does anyone yet know the proper conduit TYPE for block wall?

Otherwise I'll just go for grey PVC conduit...

thanks pals...

BB. · February 2015

As I understand, PVC / Plastic conduit is not to code when going through a "fire wall". You need standard metal conduit (EMT?) as a minimum.

Rigid Metal Conduit (RMC) is a thick-walled threaded tubing, usually made of coated steel, stainless steel or aluminum.
Galvanized rigid conduit (GRC) is galvanized steel tubing, with a tubing wall that is thick enough to allow it to be threaded. Its common applications are in commercial and industrial construction.^[1]
Intermediate Metal Conduit (IMC) is a steel tubing heavier than EMT but lighter than RMC. It may be threaded.
Electrical metallic tubing (EMT), sometimes called thin-wall, is commonly used instead of galvanized rigid conduit (GRC), as it is less costly and lighter than GRC. EMT itself is not threaded, but can be used with threaded fittings that clamp to it. Lengths of conduit are connected to each other and to equipment with clamp-type fittings. Like GRC, EMT is more common in commercial and industrial buildings than in residential applications. EMT is generally made of coated steel, though it may be aluminum.

I would suggest, if you can, put a second hole in the wall for another conduit. Put the temperature wires and shunt wires (if any) through this. The DC wiring and AC wiring can put a lot of noise onto the lower voltage/signal wires--Possibly causing interference/erratic readings.

-Bill

cupcake · February 2015

BB. wrote: »

As I understand, PVC / Plastic conduit is not to code when going through a "fire wall". You need standard metal conduit (EMT?) as a minimum.
Rigid Metal Conduit (RMC) is a thick-walled threaded tubing, usually made of coated steel, stainless steel or aluminum.

Galvanized rigid conduit (GRC) is galvanized steel tubing, with a tubing wall that is thick enough to allow it to be threaded. Its common applications are in commercial and industrial construction.^[1]

Intermediate Metal Conduit (IMC) is a steel tubing heavier than EMT but lighter than RMC. It may be threaded.

Electrical metallic tubing (EMT), sometimes called thin-wall, is commonly used instead of galvanized rigid conduit (GRC), as it is less costly and lighter than GRC. EMT itself is not threaded, but can be used with threaded fittings that clamp to it. Lengths of conduit are connected to each other and to equipment with clamp-type fittings. Like GRC, EMT is more common in commercial and industrial buildings than in residential applications. EMT is generally made of coated steel, though it may be aluminum.

I would suggest, if you can, put a second hole in the wall for another conduit. Put the temperature wires and shunt wires (if any) through this. The DC wiring and AC wiring can put a lot of noise onto the lower voltage/signal wires--Possibly causing interference/erratic readings.

-Bill

So what consitututes a 'fire-wall'?? this is an exterior concrete block wall...

BB. · February 2015

Any wall that has/needs Sheet Rock, and any exterior walls. (at least at a basic level).

So an exterior wall, walls to garage, ceilings, would typically be a "fire wall". I am not a code guy--So I cannot give you the "legal" answer. My 60 year old (cheap at the time) track home, had plywood walls between bedrooms (closets+plywood walls).

-Bill

cupcake · February 2015

Well.. I think im gonna go with 1.5" grey PVC, the wall is 8" concrete block, so the whole wall is plenty 'fireproof' on its own...

BB. · February 2015

Just make sure to bring a ground wire into the box from your main system ground.

-Bill

cupcake · February 2015

BB. wrote: »

Just make sure to bring a ground wire into the box from your main system ground.

-Bill

Why so? The box should never come into contact with AC current... everything in the box is DC. The DC wires will go from the box to the inverter which IS grounded to the main AC grounding rods

cupcake · February 2015

..Or is the purpose of grounding the box for lighting-related currents?

BB. · February 2015

Both Lightning grounding, and if there is a "Hot DC" short to the metal box.

The idea is that if the box "becomes hot" somehow, that current is returned to the common ground rod. And, normally, the battery bank negative bus goes to the ground rod too.

The ground wiring is large enough to "trip a fuse/breaker" (if battery or other power source), or manage to short the solar array, etc.

Electrically, you don't want a metal electric box to become "energized" where somebody can get shocked (somewhere, over 12 volts, or 40-60 volts is considered "hazardous" energy).

And if the box does become "hot", you don't want some secondary circuit path to conduct the current (i.e., thermo couple shield ground, etc.) through some secondary ground connection.

-Bill

cupcake · February 2015

BB. wrote: »

Both Lightning grounding, and if there is a "Hot DC" short to the metal box.

The idea is that if the box "becomes hot" somehow, that current is returned to the common ground rod. And, normally, the battery bank negative bus goes to the ground rod too.

The ground wiring is large enough to "trip a fuse/breaker" (if battery or other power source), or manage to short the solar array, etc.

Electrically, you don't want a metal electric box to become "energized" where somebody can get shocked (somewhere, over 12 volts, or 40-60 volts is considered "hazardous" energy).

And if the box does become "hot", you don't want some secondary circuit path to conduct the current (i.e., thermo couple shield ground, etc.) through some secondary ground connection.

-Bill

Questions:

Does DC current 'want to go to ground' like AC current?

If a hot DC lead in the box comes loose and hits the metal enclosure, nothing would happen since the box is attached to concrete block on the wall...

If a there is short in the box, it simply blows the 600a fuse on my battery (+) terminals.. right?

So other than wanton lighting currents (which is logical) why ground the box?? Its no more lilkley to come into contact with AC current than the BBQ grille outside next to it...

What am I missing here??

BB. · February 2015

Charging a 48 volt battery can get you to 60+ volts--And the solar array could be over 100 VDC... Those are considered hazardous voltages (~40-60 volts maxium is considered hazardous, i.e., possible fatal voltages, under various conditions--Wet/Dry/service person, etc.). If somebody with wet feet fell against the box with DC+ short (with to ground) and could electrocute somebody.

DC is "worse" to deal with... People do not "release" their grip with DC as easily as AC. DC cannot be "Ground Fault Protected" near as easily as AC (with AC GFI/Breakers/Outlets).

It takes only 10's to 100's of milliamps to stop a person's heart (hand to leg connections... Leg to leg shock does not go through heart, etc.).

If you have a 600 Amp fuse--Then you probably need something much heavier than 6 AWG cable (fusing current around 600 Amps)... Check NEC, but it would probably be closer to 2 AWG or something to "properly" ground a box with a 600 Amp feed (guessing, need to do more research).

-Bill

cupcake · February 2015

BB. wrote: »

Charging a 48 volt battery can get you to 60+ volts--And the solar array could be over 100 VDC... Those are considered hazardous voltages (~40-60 volts maxium is considered hazardous, i.e., possible fatal voltages, under various conditions--Wet/Dry/service person, etc.). If somebody with wet feet fell against the box with DC+ short (with to ground) and could electrocute somebody.

DC is "worse" to deal with... People do not "release" their grip with DC as easily as AC. DC cannot be "Ground Fault Protected" near as easily as AC (with AC GFI/Breakers/Outlets).

It takes only 10's to 100's of milliamps to stop a person's heart (hand to leg connections... Leg to leg shock does not go through heart, etc.).

If you have a 600 Amp fuse--Then you probably need something much heavier than 6 AWG cable (fusing current around 600 Amps)... Check NEC, but it would probably be closer to 2 AWG or something to "properly" ground a box with a 600 Amp feed (guessing, need to do more research).

-Bill

The battery to inverter wiring is 2/0 stranded with a 600a blue-sea terminal fuse at the battery (+)

it's a 12v system, thus the rediculous wire size...

I just don't understand the DC grounding thing... 120v AC current jumps all over the place at such high voltages... but 12v DC can't even handle a 'loose connection' such as when your batery cables are loose on your car, the starter will just 'click'...

BB. · February 2015

If 12 volts--More or less, that is considered "touch safe"... However, the high available current is not. Voltage is on the edge of sustaining an arc (around 12-15 volts or so--Don't remember the specifics).

-Bill

Ethan Brush · February 2015

cupcake wrote: »

Questions:

Does DC current 'want to go to ground' like AC current?

If a hot DC lead in the box comes loose and hits the metal enclosure, nothing would happen since the box is attached to concrete block on the wall...

If a there is short in the box, it simply blows the 600a fuse on my battery (+) terminals.. right?

So other than wanton lighting currents (which is logical) why ground the box?? Its no more lilkley to come into contact with AC current than the BBQ grille outside next to it...

What am I missing here??

Neither AC NOR DC wants to go to ground. Current ALWAYS returns to its source. It could care less about dirt. The purpose of equipment grounding is to provide a low impedance path back to the source that thus trips a fuse or breaker. Note you need a grounded system for this to work that means one of the battery terminals is bonded to the equipment grounding system - otherwise no path back to the source. You can leave it an ungrounded system and the advantage is you get a "free" first fault - nothing happens it's just a grounded system now. Personally, I don't like having a metal battery box acting as a big negative battery terminal in close proximity to all the other battery posts. At that voltage I'd take the very slight shock risk over the lessened arc blast risk. As an electrician working on 120 to 600 volts, I feel my greatest chance of injury is from arc blast in the eye not shock

cupcake · February 2015

Ethan Brush wrote: »

Neither AC NOR DC wants to go to ground. Current ALWAYS returns to its source. It could care less about dirt. The purpose of equipment grounding is to provide a low impedance path back to the source that thus trips a fuse or breaker. Note you need a grounded system for this to work that means one of the battery terminals is bonded to the equipment grounding system - otherwise no path back to the source. You can leave it an ungrounded system and the advantage is you get a "free" first fault - nothing happens it's just a grounded system now. Personally, I don't like having a metal battery box acting as a big negative battery terminal in close proximity to all the other battery posts. At that voltage I'd take the very slight shock risk over the lessened arc blast risk. As an electrician working on 120 to 600 volts, I feel my greatest chance of injury is from arc blast in the eye not shock

A DC arc blast in the eyes would stink wouldnt it...

it would be like staring into a welder right?

BB. · February 2015

Arc Flash is serious and can be deadly form of electrical fault.

It is difficult to understand the dangers--It can be a highly technical discussion about voltage/surge current/etc... I am certainly not qualified to discuss the details--But it is not the same as looking at an arc welder which only has 10's to 100's of amps available.

It is when you have a high amount of current (more of a current issue vs a pure voltage issue) when the copper (or other metal) is flash converted into a plasma (highly energized/extremely hot cloud of "copper gas") and it expands ("explodes") to engulf whatever is nearby.

https://www.youtube.com/watch?v=4bBvmPRqfmo

I am not sure that your installation is subject to such an Arc Flash--But it is something to be aware of when working on high current capable circuits.

Note, from the comments, the person did survive.

-Bill

cupcake · February 2015

Ethan Brush wrote: »

Neither AC NOR DC wants to go to ground. Current ALWAYS returns to its source. It could care less about dirt.

Then why is AC power (ie power-lines) grounded? They are grounded becasue lightining (ie electrical current) would rather go to DIRT (ground) than through a copper conductor....

Current wants to return to its source, but that source IS the ground ultimatley...

Like rain, it want to fall down and return to the ground/ocean

If current cannot find it's way 'home' it goes to dirt...

BB. · February 2015

It is a bit more complicated than that... Basically, lighting is a time varying current--Sort of more like AC with a maximum frequency of something like ~7.5 kHz (not much energy above that point).

Which means, that you need to look at the inductance of the conductor as well as its resistance. Large/wide flat "braided" conductors have lower impedance than a compact/round solid inductor.

So--For standard electrical wiring, lightning will follow it for a few ten's of feet before it wants to find an "alternate path" to travel. Also, the inductance of "sharp corners" (bends in the wiring) also increases impedance--Hence why lightning grounding cable should have gentle radius (something like 18" minimum--As I recall) rather than a sharp bend)..

You can also Google for images of Fulgurites--Fused sand/minerals from lightnings. You can see that the path of lighting in the ground can have a main shaft and leaders. With lots of different physical shapes.

-Bill

Ethan Brush · February 2015

cupcake wrote: »

Then why is AC power (ie power-lines) grounded? They are grounded becasue lightining (ie electrical current) would rather go to DIRT (ground) than through a copper conductor....

Current wants to return to its source, but that source IS the ground ultimatley...

Like rain, it want to fall down and return to the ground/ocean

If current cannot find it's way 'home' it goes to dirt...

Current doesn't prefer one path over another, it follows All paths back to it source. That "path of least resistance" saying is nonsense.

Yes a cloud to ground lightning strike is returning to its source - a potential difference has developed between a portion of the atmosphere and the ground. Note however that most lightning is intracloud or cloud to cloud.

When you question why power lines are grounded, I'm not sure if you are talking system grounding or equipment grounding. For system grounding well there are a mix of grounded and ungrounded utility systems in the US. The difference is in what happens when and how faults are handled, insulation requirements, and number of transformer bushings required. I think grounded systems allow utilities to cut some corners and costs a bit. Both have advantages and disadvantages.

For equipment earthing, in grounded systems utilities can use the earth as a fault path back the source to trip utility OCPD - that horrible high resistance of dirt starts to not be such a big deal when you get up to tens or hundreds of thousands of volts. Us low volts guys just can't use dirt as a conductor. There are aspects of grounding on utility systems that help with lightning protection but I don't really think that is often the main purpose or motivation.

What is the PROPER conduit for DC solar wiring??? (HELP!)

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