RV Mods: Did you wire your inverter safely?

By Don Wilson

When asked questions at my technical seminars, I often find they begin with, “Should I do this…” or “Should I do that?” As you might expect, these are always hard questions to answer regardless of the topic, because each individual operator will have different needs and experiences that are unique to their situation. However, when it comes to questions regarding the installation of inverters/chargers, my responses apply universally, particularly those that fall in the “should not” category. Some of this issue’s content may seem rather obvious, or a bit tongue-in-cheek. I hope I don’t cause shockwaves (yes – all puns intended!), but follow the logic presented and hopefully, you’ll quickly get up to speed.

Q: Should I rate my fuse based on the inverter size?

TECH DOCTOR: NEVER rate your fuse according to the rating of the inverter. I can’t tell you how often I re-emphasize and repeat this point. Your fuse is not there to protect the inverter, or the electrical load in any circuit. It’s there for one primary purpose: to protect the circuit itself. A 3000W inverter with a 350A fuse seems appropriate, unless it’s wired with 4 gauge wire. At a perfectly acceptable load, the wire will burn well before the fuse fails. The fuse is there to protect the wire (or electrical path) from heat which can cause damage or fire.

Q: Should I put a washer between the cable terminal and inverter, or battery connector?

TECH DOCTOR: NEVER put a washer between the conductor and the connector! All the ground wires in our cars/trucks have those star washers to make a ‘better electrical connection.’ However, that is acceptable in this circumstance for penetration of paint and due to the low current needs of a 14 gauge wire. On the other hand, when you’re putting 4/0 welding cable on a 3000W inverter, and you put a steel (high resistance) washer between the copper, tin, or brass cable ends and connectors (lower resistance), you create an electrical bottleneck that will get extremely hot. I’ve seen tons of inverters in repair with melted insulators around the DC connectors which is a sure sign that the flat washer, or lock washer, was placed between the connector and the cable. The lock washer, or star washers, are intended to be in direct contact with the bolt-head or nut to reduce the chance of loosening.

Q: How do I determine the right cable size?

TECH DOCTOR: NEVER blindly follow the recommended cable size, regardless of the installation. If the manual calls for 3/0 wire for lengths over 5’, don’t assume that it includes installations where the battery is 25’ from the inverter. Voltage-drop calculators are all over the internet and if you can ensure a voltage drop under .25VDC, you’re in good shape. Consider the recommendations as a ‘minimum’ and use your math skills to figure out the proper cable to eliminate excessive voltage drops. After that, don’t be afraid to upsize the cable again. Proper performance is the desired result of any installation, and voltage-drop management is the key to performance.

Q: Can I install an inverter/charger in the engine compartment or battery bay?

TECH DOCTOR: NEVER put your inverter/charger in an engine compartment, battery bay or any location containing fuel or flammable, or corrosive, vapors. Inverter/chargers are an ignition source and are incompatible with combustible fumes. If the only close location is in the battery bay, get bigger cables and move the inverter farther away (see cable size paragraph above).

Q: What should I know about neutral and ground connections?

TECH DOCTOR: NEVER, EVER tie neutral and ground together, manually, in any installation, period! Neutral is tied to ground at the source of AC power simply to allow the ground wire to be an alternate path for return current during a failure where the hot wire touches the chassis of a device or vehicle. This is intended to trip the breaker. However, when neutral is tied to ground in the vehicle, there’s a voltage potential between the ground plane of the vehicle, and the ground plane of the electrical grid connection. If there’s resistance on the ground and neutral wires, the current will find some other potential path back to earth ground and that path may be you as you open the door of your vehicle. This isn’t the kind of excitement you want to experience!

Don Wilson has worked in technical capacities in the automotive, RV and marine fields and for the military since 1989 and has extensive experience in designing and troubleshooting onboard electrical systems. A former customer service manager dealing with electronic issues, Wilson currently serves as a technical instructor for the RV industry’s RVIA Trouble Shooters Clinics and is a full-time sales application engineer for Xantrex Technology.

##RVT832

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7 Thoughts to “RV Mods: Did you wire your inverter safely?”

  1. Wayne

    Excellent! More articles like this, please.

  2. Gord

    Hi,
    Thanks for the information. I’m still a bit confused with this whole ‘ground’ thing. Where is the ‘ground’ on an RV? There is no ground rod sunk in the earth like a house, how is the electrical system on an RV ‘grounded’ if it’s not connected to a power pedestal?

    1. DAVE TELENKO

      Hi Gord, thats a very interesting question, I’ll check back later for a response.
      Dave

    2. Mike Sokol

      The word “ground” is used for a lot of things that have nothing to do with “earth” ground. In the case of a vehicle like an RV, we call the entire chassis and all metal attached (bonded) to it a “ground plane”. A ground plane is a local ground reference that all electrical devices are connected to. What that means is you’ve created a local ground that’s at the voltage potential of the negative terminal of the house batteries. Your RV’s Ground Plane just happens to be connected (bonded) to the safety ground wire in your shore power cord. BTW that safety ground wire is technically called the EGC for Equipment Grounding Conductor. Now when you plug your RV into shore power this EGC bonds your Local Ground Plane to the Neutral-Ground bond in the campground’s main electrical service panel, which is in turn connected to earth ground via a ground rod. Yikes, I really should write an article about this, shouldn’t I?

      1. Gord

        Thanks Mike,
        Yes, I would very much like to see more details about this. It seems to me there are a lot of people (besides me) confused about the term ‘ground’.
        Cheers.

        1. Mike Sokol

          I have this same discussion about the different grounds with a lot of electricians, so the confusion isn’t confined to consumers. I’ll need at least a full video and article to properly explain grounding and bonding, so standby for a Tiny-Class.

      2. DAVE TELENKO

        Hi Mike, thanks for the explanation . I do have a concern as when we are on inverter or generator. What if, I have a short in my Ac wiring, not plugged in & for some reason that circuit isn’t fused & I touch the frame & the ground at the same time what happens, I’m thinking I’ll light up like a light bulb or worse?
        Dave

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