Certification Candidate | Introduction to Service
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Knowledge Requirements > What you need to know to become an RV Service Technician Candidate. |
| Electrical |
Electrical 12 VDC
Electrical 120VAC
Electrical 12 VDC Battery Disconnect Switch (MH)
Motorhome battery disconnect switches come in different styles, both mechanical and electronic. They are found on motorhomes with ratings up to 500 amps. The mechanical switches are normally rotary type (often red in color) and located in the battery compartment. Control panels for electronic switches are located by the entry door, or in the front overhead cabinets. Battery disconnect switches are normally used when the motorhome is put into storage to prevent battery discharge over time. All of the electronic devices in a motorhome may draw as much as 1 amp, even when turned off. On some units the disconnect switch will cut off all power. When turned back on clocks and other electronic devices need to be reset. Other types maintain some power to the engine control module or electronic devices to prevent loss of memory. Many companies will run small separate wiring for essential items such as propane and carbon monoxide alarms directly to the battery so they are not controlled by the disconnect switch. If you are trying to perform service on a motorhome but everything is dead, check the battery disconnect switch first. Light and Fan Operation
Roof vents and fans are available in a wide variety of styles. A typical fan may have 3-speeds and be designed for low noise operation. Some 12-volt roof ventilation fans are thermostatically controlled to provide consistent temperatures. They operate when the thermostat calls for cooler air. Once the thermostat is satisfied, the fan shuts off automatically. Some models have a built-in rain sensor that activates when it becomes wet, closing the dome. Once the sensor dries, the dome will re-open automatically. Polycarbonate domes and a removable screens are common features. Range Hood Operation
A wide variety of range hoods are found in RVs. Switches to operate the fan and light are manufactured in many configurations and operation is usually self-evident. The range hood above uses rocker switch's to operate the fan and light. Power Converter
With the introduction of the power converter, it became possible for RV manufacturers to eliminate most of the dual-voltage components found in early RVs. Power converters have enabled the RV manufacturers to install almost all devices for 12 VDC only. When the RV is connected to 120 VAC, the converter converts the 120 VAC to 12 VDC. A circuit within the converter called a rectifier accomplishes this. This circuit consists of a transformer that steps down the 120 VAC, a set of diodes that converts the lower AC voltage into pulsating DC voltage and a series of filter capacitors that filter out any unwanted AC voltage that is left in the DC output. The result is the 120 VAC shore power has been converted into 12 VDC. Electrical 120VAC Distribution Panelboard
The 120 VAC is distributed within the RV the same as it is in a home. The AC voltage is fed into a distribution panelboard that distributes the power through circuit breakers to circuits that are connected to outlets or designated appliances. Wiring practices for RVs are the same as residential and the wire used is usually 14-2 or 12-2 non-metallic sheathed cable (type-NM), commonly called Romex. The outlets may be conventional or special outlets designed for NM cable. No splices or connections are allowed when adding or removing outlets, unless they are enclosed in a box. The three wires used in 120 VAC lines are black (hot), white (neutral), and bare or green (ground). These must never be interconnected or mixed. When connecting to a plug or outlet, the white wire goes to the silver terminal, also the wide prong or slot; the black wire to the brass terminal, and the bare or green to the green screw. Describe the purpose of a GFCI device Ground fault circuit interrupter (GFCI) protection is a special type of protection for a circuit that will shut the circuit down immediately in the event of a fault current. This function protects RV users from electrocution. GFCI protection can be provided through the use of either specific GFCI receptacles or GFCI circuit breakers located in the panelboard that protect the entire circuit. Regardless of the means employed, receptacles in the following locations must be provided with GFCI protection 1) in bathroom; 2) within 6 feet of any sink; 3) on the exterior of the vehicle. Identify GFCI receptacles and or breakers
Ground Fault Circuit Interrupter Receptacle |
