I thought this information would be good to pass along to someone who is mounting solar panels on there roof, and needs to penetrate the roof to bring in the electrical wires from the solar panels. <br /><br />As an electrician alot of times we are required to bring in our conduits (pipes) , flexible type pipe, or jacketed wire into an enclosure ( electrical box). Sometimes these enclosures are out side.<br /><br />Most of the time we try to avoid penetrating the top of the enclosure. But occasionally we have no other option. <br /><br />When penetrating an enclosure in a wet environment like a van roof we use a couple fitting in conjunction.<br /><br />The first fitting is called a myers hub. Follow the link for pics.<br /><br />http://www.elliottelectric.com/Products/SearchResults.aspx?s=myers+hub<br /><br />This fitting has a water proof seal or gasket which keeps out any water. They come in sizes from 1/2''-6''. To install the hub you must drill the correct hole for the size hub you are using. Example for a 1/2'' hub you would want to drill a 7/8'' hole ( use a hole saw/ knock out set). Basically measure the outside diameter of the threaded nipple part of the hub. The hubs are 2 part. The main body and the ring. After you have drilled your hole insert the threaded nipple end of the main body through the roof. Then from the inside of your Van screw the ring on. Tighten with channel lock pliers. I would recommend a aluminum myers hubs so it doesn't rust. <br /><br />Next you want to use a fitting we call a CGB. This fitting will be the go between the myers hub and your wire. The CGB male end will thread into the myers hub female end. Depending the size wire you are bringing through the roof will determine the size CGB that you will need. The size CGB you use will determine the size myers hub you need. This will make for a weatherproof penetration. <br /><br />http://www.elliottelectric.com/Products/SearchResults.aspx?comm=2330&page=2<br /><br />Both of these fitting can be found at any electrical supply house found in most all city's. If you are confused about any of this just take a small piece of wire with you to the supply house, tell them you need the correct CGB/myer hub combo for this wire. They will be more than willing to help you out. I would avoid home depot/lowes just go to a regular electrical supply house. <br /><br />If you already have installed a solar system it is never to late to adapt to using a CGB/hub. Just disconnect your wiring from you charge controler. Pull you wiring back out through the roof, add the CGB/hub combo and hook back up your wiring at the charge controller. <br /><br />And don't worry if you drilled too large a hole through the roof. All you need to do is buy a larger myers hub to match your hole, and use what we call an "RE" or reducing bushing between the myers hub and the CGB (remember the CGB is based on the wire size). <br /><br />For example say we have a hole that fits a 1" myers hub. But the CGB we want to use has 3/4" threads. What we would need is a 3/4" to 1" RE (reducing bushing).<br /><br />http://www.elliottelectric.com/Products/SearchResults.aspx?s=reducing+bushing<br /><br />If the hole you previously drilled for your wiring doesn't match a hub size you will need to use the next larger size hub and increase your hole size. Do this with a knock out set (preferred method) or a good half/round file.<br /><br />For example lets say you have an existing 1'' hole you previously drilled. You would want to use a 3/4'' hub (needs a 1 1/8'' hole) as a 1/2'' (7/8'') would be to small. <br /><br />What ever method you use , make sure you don't make your hole too large as this will defeat the whole purpose. I can not stress this enough!!! The hub will leak if the hole size is to large. Take your time if you are using a file. File a little then try it, if it doesn't fit file some more. Just enough for it to fit then stop. <br /><br />Make sure that when you make your penetration through the roof that you do so in as flat a spot as possible.<br /><br />BTW... You may ask the question if you have more than one solar panel what should I do? Well I would say that you could do 2 things.<br /><br />#1- Make a separate penetration in the roof for every panel with a myers hub/cgb combo for every wire.<br /><br />OR (what I would do) <br /><br />#2- Combine all your panel's wiring in parallel on top of the roof in a weather proof small junction box and bring just one larger pair down through the roof. Use the same hub/CGB's to bring you wires in and out of the junction box. Mount your junction onto your support brackets for your panels. Use wirenuts inside the junction to combine/splice your wires then tape with electrical tape.<br /><br />To determine the size wire that you will need to purchase you will need to add all the amperage from all you panels together. For example lets say you have 4- 120 watt panels. Each panel is rated at 12 volts so using ohms law P=IxV or 120watts divided by 12volts gives us 10 amp. So we have 4 separate pairs of wires that are rated for 10 amp. When we combine all the wires together in our junction box and we are wondering what size wire to bring out to the charge controller all we need to do is add the 4 wires together. So 4 wires at 10 amp times 4 equals 40 amps. We will need a wire capable of handling 40 amps. The supply house can also assist you in this part.<br /><br />Hears another example Say I have 3 panels rated 210watts at 28v. To figure the size wire I would need to the junction box I would use ohms law P=IxV or 240 watts devided by 28volts = 7.5 amps. 3 sets of wires at 7.5amps= 7.5 x 3 = 22.5amps.<br /><br />P= I x V ( this is where that algebra come in handy)<br /><br />P= Power in Watts<br />I= Current in Amps<br />V= Voltage in volts<br /><br />Think of current like a stream or creek. If we start combining more and more streams/creeks together they become a river. This is the reason you have to increase your wire size going to the charge controller. If we were to combine all the separate solar panels wiring together in the junction box and brought out the same size wire (not increasing it), In a real situation with real water we would have a flood. With electrically the current flow will still try to pass through the smaller wire. What will happen is when you force current through an undersized wire that wire gets HOT. Think of a light bulb. That is exactly how it works. Current is passed through a small element in the lamp and gets so hot that it shines. We don't want that with our solar panel wiring so we need to increase the wire size to prevent this . <br /><br />Now to determine to correct wire size to the amperage we need to use a table<br /><br />http://www.usawire-cable.com/pdfs/NEC AMPACITIES.pdf<br /><br />So in example #1 we would need #14 (10 amps)from each solar panel to the junction box and after we spliced in parallel ( + to + or - to -/ black to black or red to red) We would need to take a # 8 (40 amps)pair down through the myers hub/cgb to our charge controller.<br /><br /> In example#2 we need #14 (7.5 amps) from the solar panels to the J-box and out you would need a #10 pair(22.5 amps).<br /><br />You can use the ohms law formula for any wattage/voltage configuration you could encounter. And remember if never hurts to go larger when it comes to wire size.<br /><br />http://www.leonaudio.com.au/pwheel.pdf<br /><br />For the type of wire I would recommend SO type (welding/locomotive) cable listed for outdoor use. This wire is extremely flexible and has excellent conductive property's. This wire will mate with your CGB very well.<br /><br />http://www.awcwire.com/ProductSpec.aspx?id=Type-SOW-SO<br /> <br />Also I would use a PVC or stainless junction box for longevity. The size will be based on the amount of wires you bring into the the box. <br /><br />These boxes have brackets built in (for mounting)so it stays weather tight.<br /><br />Just ask the person at the parts house and they will let you know the correct size box to use. You may need to use spring nuts and uni-strut to mount the J-box to the solar panels brackets. <br /><br />http://www.automationdirect.com/adc/Overview/Catalog/Enclosures/Metal/NEMA_4X<br /><br />This is the most professional way to do this job that I know of. No silicone required <img src="images/boards/smilies/smile.gif" alt="" align="absmiddle" border="0" /><br /><br />Edit: One other point I neglected is fusing. If you are going to use a junction box on the roof. I would want to fuse each pair of wires from each solar panel. You could use the in line type like you see in the auto parts store along with wire nuts.<br /><br />The more professional way would be to use a back plate that mounts inside the junction box. This system uses no wirenuts, instead you use a terminal block with fusible links.<br /><br />http://www.directindustry.com/prod/conta-clip/fuse-terminal-blocks-14041-474697.html<br /><br />Before you terminate your "home run" wire to the charge controller you will want to fuse it. Size of fuse will depend on several factors best to ask the supply house for help on the correct size for you particular setup. <br /><br />Finely if your charge controller doesn't have it built in, it may be a good idea to add a serge suppressor. This will help protect your charger controller/battery/inverter from a lighting strike/surge.<br /><br />http://www.wholesalesolar.com/products.folder/disconnect-folder/delta-lightning-arrestors.html<br /><br />
Penetrating van roofs
- Thread starter Rollin
- Start date
Help Support Van Living Forum:
Good advise from a pro, Rollin. I ran mine through a rubber grommet,, then a dab of gutter and flashing sealant just to be sure. I'm a contractor, so have seen the hubs you described often, but I'm glad you included links for those not as familiar. Good deal.
VanTrekker
Well-known member
Great advice!<br /><br />I may end up re-doing mine... I used a hole saw, took the burrs off the hole, and pushed a plastic snap bushing down into place. Then I caulked it really good. So far so good but I do worry that if that snap bushing breaks and the wires rub against the hole...<br /><br />This summer would be a good time to re-vamp the setup. Again, thanks for posting!<br /><br />VT
wrcsixeight
Well-known member
- Joined
- Sep 14, 2012
- Messages
- 537
- Reaction score
- 0
Those links are not working for me.<br /><br />My first roof penetration was just a drilled hole sealed with 3M 5200.<br /><br />Later when I added another panel and upped the wire sizes I used cord grips.<br /><br />
<br /><br />Works for me. No leaks.
G
Guest
Guest
In rv's we use a lap sealant called dicor, just clean the surface with brake clean apply sealant let it set 24 hours and you have a water proof seal.
And yes I use a rust paint on any bare metal.
And yes I use a rust paint on any bare metal.
FALCON
Well-known member
- Joined
- Mar 28, 2015
- Messages
- 500
- Reaction score
- 0
Just a heads up, and a bump to a very good old post: myers hubs and cord grippers are sold in big box hardware stores. I just bought some at a Lowes.
If you're using 10AWG cables, they'll be too small for the smallest size of hub/cord gripper (1/2"). 6AWG fits for sure in that. 8 probably would also but I'm not sure.
If you're using 10AWG cables, they'll be too small for the smallest size of hub/cord gripper (1/2"). 6AWG fits for sure in that. 8 probably would also but I'm not sure.
Similar threads
