House Calls: March 2017

March 1, 2017

GFCI Question

Dear RV Doctor:

I have been one of your many fans for the past 25-plus years. I would like some information about GFCI operation. How do they actually work in a motorhome? I know how to test them — just push the test button, right? What does the test do? I’ve never understood how they do what they do.

Robert Willard

Mukilteo, Washington

Ground fault circuit interrupters (GFCIs) have been required in all RVs for a number of years and probably can lay claim to saving quite a few lives. In the RV realm, there are two types: a duplex receptacle type with the ground fault test function; and a circuit breaker type.

The receptacle type usually is mounted in the kitchen or bathroom, typically near a water fixture. Also, any receptacle mounted on the exterior of the coach is required to be GFCI-protected. It’s not that there should be individual GFCI receptacles in those three locations; the coach may have only one that protects all other receptacles downstream of it. Perfectly legit. If a coach has a GFCI circuit breaker, then obviously every receptacle on that one circuit will be protected.

It is a common misconception that the GFCI is an over-current protector. Such is not the case. While breakers and some fuses obviously do protect against over-current, they cannot sense or protect against potentially lethal low-level ground faults. In addition, GFCIs will not sense a direct short to ground. The exception, of course, is the breaker-type GFCI, which does both. The benefit of the GFCI is that it will sense the low-level current leakage that might occur in an alternating current device — lethal current that a circuit breaker would overlook. The GFCI used in motorhomes will sense and monitor current leakage up to 5 milliamps (mA), which is 0.005 of one amp, and then it quickly will open (interrupt) the circuit.

Here is how it works:

Alternating current from the grid, generator, or inverter flows through one wire (the hot wire) to an electrical load and back to the power source through the neutral wire. In most cases, this current to and from the load is equal and is said to be “balanced.” The GFCI constantly monitors this balance between the hot and neutral wire. If the GFCI detects an imbalance between the two currents, and that current differential reaches 4mA to 6mA, the GFCI will trip, interrupting the current before a shock hazard can develop. Depending on the type of GFCI and how it is wired into the circuit, the circuit will open and current flow will stop to all protected receptacles downstream, as well as at the GFCI location.

The means by which the GFCI senses and opens the circuit determines the speed at which it opens the circuit. One method involves the use of a mechanical relay, such as commonly found in a circuit breaker. Another more common method of sensing is the use of an electromagnetic electronic shunt-trip solenoid.

As you’ve noted, the GFCI contains a test function that verifies the internal electronic components. Coach owners are encouraged to push that test button at least once a month. I further encourage my technician students to test the GFCI using an independent device that applies an increasing level of current leakage to determine the exact level of current imbalance that causes the GFCI to trip.

Short Vent Stack?

Dear RV Doctor:

I purchased a used RV. At some point, someone sawed off the top of the sewer vent pipe. Only about three, maybe four inches stick up through the roof. Is that enough to install a 360 Siphon vent cap? If not, what do I do? How do I add pipe to the black plastic?

Tina Gallagher

Via Email

If you have three or four inches of pipe showing above the roof, chances are a sewer cap was never installed in the first place. It’s not a code requirement to have a cap, although most manufacturers do install one to keep leaves and other debris from falling into the holding tanks.

The first generation of the 360 Siphon required only 1/2 inch of exposed ABS pipe above the roof surface for proper installation. In fact, in most cases, owners have to cut the vent stack down to 1/2 inch. The new 360 Siphon Gen 2 is available, one that simply attaches to the pipe itself and requires no trimming of the vent pipe or removal of the stock base assembly. But if you have to add height to any vent stack, for whatever reason, simply purchase an ABS slip coupling (usually 1 1/2 inch) and a short section of piping from one of the big box stores and cement it in place. I think you’ll end up trimming your vent stack down to 1/2 inch unless you obtain a 360 Siphon Gen 2.

Generator/Alternator Altercation?

Dear RV Doctor:

I have a 1999 Allegro Bus. Can I use the generator while driving down the road without causing damage to the engine alternator? I did this last October while traveling to Mississippi, and on the return trip the alternator had to be replaced. The dash air is not enough, and I’d like to run the generator and roof air-conditioning. Thanks!

Ken Lear

Columbia Station, Ohio

It is quite okay to run the generator and the roof air conditioners while driving down the road. Barring something totally off the wall that I cannot even comprehend, the faulty alternator would have been unrelated to use of the generator/air conditioner, since the generator produces 120 volts AC. And with the generator running, the inverter/charger would have been energized and charging the house battery bank, thereby possibly reducing the stress on the engine alternator. The component regulated to the higher voltage (inverter or alternator) at that snapshot in time would be the dominant charging device. So, when a smart charger or smart inverter/charger is first powered on, it is in bulk mode at a higher voltage than after it has been on a while and reaches float mode. But I cannot fathom how that could cause an alternator to fail. Somewhere in the circuit there should be a dual battery separator that would prohibit any crossover or feedback from one charging source to the other.

LED Difference

Dear RV Doctor:

First, I want to thank you for your informative seminars! My question is regarding LED lighting. Many companies make LED bulbs for RVs. Are all LED bulbs created equal? Is there a brand that you find superior to others?

Dede Ruth

Via email

That’s a great question. I have not evaluated any of the various lighting products that feature LED technology. I’m sure they vary in sophistication and quality. When considering aftermarket products, I recommend those made in the USA. If any of our readers have suggestions, I’ll gladly include them in a future column. In the meantime, members of Family Motor Coaching magazine’s Technical Advisory Committee offered the following information

“A factor to consider when selecting LEDs for interior RV lighting is the light color, or color temperature, which is measured using the Kelvin scale. The three primary types of color temperature are soft white (2,700k-3,000k), bright white/cool white (3,500k-4,100k), and daylight (5,000k-6,500k). Also, offshore devices cost a lot less than those made in North America, and for small, low-risk items such as LED bulbs, the cost difference is worth it.”

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House Calls: March 2017

Tech & Travel Tips: March 2017

Recall Corner: March 2017

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