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OK we get a lot of RV and Camper folks here on the forum asking a variety of questions. Many ask about hooking up the bits and pieces of the system, some even have circuit diagrams wanting feedback. No way can I address every question on a thread about RV’s and Campers; however there are a few common oversights.
My biggest concern is safety first. The most common errors are SAFETY related to a properly designed electrical distribution system and implementation. Although the logic in the design is not difficult, but unless you have some training and experience you stand little chance of getting it right. For example coordinating Fuse/Wire sizes, grounding, and what goes where.
I say a picture is worth a thousand words. What you see below is a Cookie Cutter design template of a 500 watt, 12-Volt, 200 to 400 AH Battery, 1000 Watt Inverter, and 12 Volt House Distribution. I put in all the Bells and Whistles (Alternator charge connection, and House Distribution) which are optional to demonstrate how and where to connect them. So allow me to logically go through the design points.
Let’s start with the batteries as they are the highest order power SOURCE, and the world revolves around the batteries. So very first thing you do is select where the batteries are to be installed. Place them where you can also fit the Charge Controller, Inverter, and House Fuse Block close by so no 1-way wire length exceeds 3 to 5 feet. Second thing is to locate them near or on chassis frame because that is where we need to connect the most important wire of all, GROUND. More on that later and is the LAST connection you make.
Note on the drawing you will see a Dual Fuse Block. It is physically bolted onto the battery term post with ¼ x 20 hardware. Remember I said the batteries are the power SOURCE, not the panels or alternator if used. The battery can supply extremely high fault currents. Enough to vaporize the large copper wires you are using. Fuses are for one thing and one thing only. To protect the wire connected to it. Fuse size and wire size are directly related. The larger the fuse, the larger the wire must be. So how large of fuse and wire do you need? In this example we need two circuits. One to the Charge Controller and One to feed Equipment Loads.
Charge Controller is a No-Brainer and first up. It is a 40 amp controller so we need 40 Amp Fuse as shown in the drawing. 40 Amp fuse with open air wiring requires a minimum 10 AWG wire. Kept to 5-feet One-Way or less distance, voltage drop is of no concern, otherwise use 8 AWG. Make the connections between battery and controller as shown, and the controller should come to life. If not figure it out.
OK the 100 Amp Fuse is to Feed Loads. A 100 Amp Fuse requires a minimum 6 AW in open air, but is pushing it both thermally and with excessive voltage drop issues with length. Note I show a 6 AWG to the Battery Isolator (Alternator). I can do this because it is a Current SUPPLY, not an Equipment Load. The Other end of the wire is to the Alternator Battery Isolator, and it should also be fused. Current from the alternator flows to either the Battery to charge it, to the equipment if battery is charged, or both. Normally load current does not flow from the Battery to Alternator unless there is a Fault.
OK the Equipment Loads are fed with a 100 Amp Fuse. Use 4 AWG or larger to each Load as shown. Do not exceed 2 Loads when using a Single Fuse as a Feeder because you cannot get more than two on the Fuse Block Term Post and comply with codes. In the drawing I show two. One for the Inverter, and one for the House Distribution Fuse Box. With a 100 Amp feeder requires the House Fuse Box to be rated for at least 100 Amps. 12 Volt 1000 wat Inverters require a 100 Amp Circuit.
Take note and be aware sharing the 100 Amp Fuse on the Battery Term Post between two loads makes it a FEEDER as opposed to a Branch Circuit. It is possible that the two combined loads could exceed 100 amps and operate the Fuse. This is done intentionally as to limit maximum load current on the battery to 100 amps. That poor little 200 to 400 AH battery cannot really do more than 100 amps without excessive voltage sag and Term Post overheating. So if it happens is not a safety issue, but a design goal. Replace the fuse and reduce loads.
OK now that the Controller, Alternator, and Loads have been connected time to deal with the panels. As shown I have two-250 watt panels connected in series for 500 watts. 250 wat panels are higher voltage grid tied panels aka GT Panels. Reason is simple they are less expensive and require less material which saves more money and maximize efficiency. They are also lower current which makes them easier and safer to deal with. Connected in series the maximum fault current is roughly 10 to 12 amps. What that means and the code allows is we do not need any fuses provided the wire size we select can safely handle the 12 amp fault current. Minimum wire size requirement is 14 AWG or larger.
OK we almost have everything hooked up, but ready to test. Turn the Inverter on and make sure it works OK by plugging a high wattage appliance in and turning it on. Check and see that the battery is charging from the panels. Start the motor and make sure the Alternator is charging your house batteries if you installed it. Test your DC Distribution if installed by testing every circuit. Everything should work normally and as expected.
OK time to make the most important connections. Those funny looking Green Wires at the battery negative post and Inverter Ground Terminal if it has one. These wires MUST BE as large as or larger than the largest wire used in the system. Largest wire I used in this example is 4 AWG. Before you connect these wires, you must have the system fully tested and operational as instructed above. The sole purpose of the Ground Wires is to make all your fuses and breakers work as intended and designed. It returns Fault current back to the Source, the battery negative terminal.
The Green Chassis Ground Wires are to be kept as short as possible without sharp bends. One end connects directly to the Battery Term Post with ¼ x 20 locking hardware. Route the other end to the frame of the vehicle, Prepare the frame/chassis connection surface area by removing all paint, grease, dirt, down to bright shiny metal. Lightly coat connection surfaces with No-Ox Grease to prevent corrosion. Use Dragon Tooth Lock Washers if using Self Tapping screws, or ¼ x 20 locking hardware preferred. NOTE: If your Inverter or Charge Controller requires a Ground Connection duplicate above procedure and use the exact same connection point on frame/chassis used for the battery so you have a Single Point Ground Connection. This will prevent normal Return Load Current from flowing on ground wires and the frame of your vehicle. It will also keep things electrically quiet and avoid interference issues with sensitive electronics.
Hope that helps. Keep it Safe and Sane.
Dual Battery Fuse Block shown below Single Fuse Block. Blue Sea Part # 2151 shown with MRB Fuses installed.
DC Distribution Block. Deep Sea Part # 5026
My biggest concern is safety first. The most common errors are SAFETY related to a properly designed electrical distribution system and implementation. Although the logic in the design is not difficult, but unless you have some training and experience you stand little chance of getting it right. For example coordinating Fuse/Wire sizes, grounding, and what goes where.
I say a picture is worth a thousand words. What you see below is a Cookie Cutter design template of a 500 watt, 12-Volt, 200 to 400 AH Battery, 1000 Watt Inverter, and 12 Volt House Distribution. I put in all the Bells and Whistles (Alternator charge connection, and House Distribution) which are optional to demonstrate how and where to connect them. So allow me to logically go through the design points.
Let’s start with the batteries as they are the highest order power SOURCE, and the world revolves around the batteries. So very first thing you do is select where the batteries are to be installed. Place them where you can also fit the Charge Controller, Inverter, and House Fuse Block close by so no 1-way wire length exceeds 3 to 5 feet. Second thing is to locate them near or on chassis frame because that is where we need to connect the most important wire of all, GROUND. More on that later and is the LAST connection you make.
Note on the drawing you will see a Dual Fuse Block. It is physically bolted onto the battery term post with ¼ x 20 hardware. Remember I said the batteries are the power SOURCE, not the panels or alternator if used. The battery can supply extremely high fault currents. Enough to vaporize the large copper wires you are using. Fuses are for one thing and one thing only. To protect the wire connected to it. Fuse size and wire size are directly related. The larger the fuse, the larger the wire must be. So how large of fuse and wire do you need? In this example we need two circuits. One to the Charge Controller and One to feed Equipment Loads.
Charge Controller is a No-Brainer and first up. It is a 40 amp controller so we need 40 Amp Fuse as shown in the drawing. 40 Amp fuse with open air wiring requires a minimum 10 AWG wire. Kept to 5-feet One-Way or less distance, voltage drop is of no concern, otherwise use 8 AWG. Make the connections between battery and controller as shown, and the controller should come to life. If not figure it out.
OK the 100 Amp Fuse is to Feed Loads. A 100 Amp Fuse requires a minimum 6 AW in open air, but is pushing it both thermally and with excessive voltage drop issues with length. Note I show a 6 AWG to the Battery Isolator (Alternator). I can do this because it is a Current SUPPLY, not an Equipment Load. The Other end of the wire is to the Alternator Battery Isolator, and it should also be fused. Current from the alternator flows to either the Battery to charge it, to the equipment if battery is charged, or both. Normally load current does not flow from the Battery to Alternator unless there is a Fault.
OK the Equipment Loads are fed with a 100 Amp Fuse. Use 4 AWG or larger to each Load as shown. Do not exceed 2 Loads when using a Single Fuse as a Feeder because you cannot get more than two on the Fuse Block Term Post and comply with codes. In the drawing I show two. One for the Inverter, and one for the House Distribution Fuse Box. With a 100 Amp feeder requires the House Fuse Box to be rated for at least 100 Amps. 12 Volt 1000 wat Inverters require a 100 Amp Circuit.
Take note and be aware sharing the 100 Amp Fuse on the Battery Term Post between two loads makes it a FEEDER as opposed to a Branch Circuit. It is possible that the two combined loads could exceed 100 amps and operate the Fuse. This is done intentionally as to limit maximum load current on the battery to 100 amps. That poor little 200 to 400 AH battery cannot really do more than 100 amps without excessive voltage sag and Term Post overheating. So if it happens is not a safety issue, but a design goal. Replace the fuse and reduce loads.
OK now that the Controller, Alternator, and Loads have been connected time to deal with the panels. As shown I have two-250 watt panels connected in series for 500 watts. 250 wat panels are higher voltage grid tied panels aka GT Panels. Reason is simple they are less expensive and require less material which saves more money and maximize efficiency. They are also lower current which makes them easier and safer to deal with. Connected in series the maximum fault current is roughly 10 to 12 amps. What that means and the code allows is we do not need any fuses provided the wire size we select can safely handle the 12 amp fault current. Minimum wire size requirement is 14 AWG or larger.
OK we almost have everything hooked up, but ready to test. Turn the Inverter on and make sure it works OK by plugging a high wattage appliance in and turning it on. Check and see that the battery is charging from the panels. Start the motor and make sure the Alternator is charging your house batteries if you installed it. Test your DC Distribution if installed by testing every circuit. Everything should work normally and as expected.
OK time to make the most important connections. Those funny looking Green Wires at the battery negative post and Inverter Ground Terminal if it has one. These wires MUST BE as large as or larger than the largest wire used in the system. Largest wire I used in this example is 4 AWG. Before you connect these wires, you must have the system fully tested and operational as instructed above. The sole purpose of the Ground Wires is to make all your fuses and breakers work as intended and designed. It returns Fault current back to the Source, the battery negative terminal.
The Green Chassis Ground Wires are to be kept as short as possible without sharp bends. One end connects directly to the Battery Term Post with ¼ x 20 locking hardware. Route the other end to the frame of the vehicle, Prepare the frame/chassis connection surface area by removing all paint, grease, dirt, down to bright shiny metal. Lightly coat connection surfaces with No-Ox Grease to prevent corrosion. Use Dragon Tooth Lock Washers if using Self Tapping screws, or ¼ x 20 locking hardware preferred. NOTE: If your Inverter or Charge Controller requires a Ground Connection duplicate above procedure and use the exact same connection point on frame/chassis used for the battery so you have a Single Point Ground Connection. This will prevent normal Return Load Current from flowing on ground wires and the frame of your vehicle. It will also keep things electrically quiet and avoid interference issues with sensitive electronics.
Hope that helps. Keep it Safe and Sane.
Dual Battery Fuse Block shown below Single Fuse Block. Blue Sea Part # 2151 shown with MRB Fuses installed.
DC Distribution Block. Deep Sea Part # 5026
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