July 20, 2016

TT #93 Replacing the Transfer Switch & Automated Electrical System Protection Unit (Part 2)

By: Rob Lowe

Featured Picture

In Technical Tip #92, I detailed how we determined that our RV’s Automatic Transfer Switch had failed and that it was contained within an integrated Transfer Switch and Electrical System Protection (ESP) unit supplied as original equipment by TRC (Technology Research Corporation). I provided a simple work around to get the RV electrical system operating on Shore Power that you can apply should something similar occur on your RV. Shown in the photo to the left is the area under the bed in a bedroom slideout in our RV, where the TRC unit was mounted. Under the slide movement mechanism at the bottom of this photo, there is a large bundle of cables leading through the floor. Some of the wiring in this bundle goes to this system. Fortunately, in our coach there is a good amount of space. Some that I have looked at have had little free space in which to replace or install a new unit. 


In this Technical Tip, I’ll move past the failure and provide a complete solution that we implemented. The original equipment Automatic Transfer Switch and Electrical System Protection unit (shown in photo to the left) has three strikes against it:

1)    It defaults to the generator requiring a relay to activate to transfer shore power to the coach.

2)    The original equipment unit has been discontinued and repair parts are difficult, if not impossible, to find.

3)    The comprehensive display of voltage and electrical conditions is limited to the main unit which in our coach hidden under the bed under a panel. The Remote Panel displays the incoming voltage, changing only if there is an Error Code.


When one thinks about the number of times the RV is supplied power by the ‘shore line’ versus the number of times it is supplied power by the ‘generator’, it is only a matter of time before the transfer switch fails. My coach had sat on a dealer’s lot for almost two years before I bought it, so one can only guess at the number of times it was moved and connected to ‘shore power’ before we took delivery. In addition, the vast majority of the time we use it, it is connected to shore power.


As a discontinued product, replacement is required. I have seen the TRC replacement unit (40350-RVC) in other coaches that experienced the same failure and it is larger in size, has a different footprint (meaning connections need to be moved around and the remote panel (and often the interconnecting wiring) also need to be replaced. The heavy wiring used in 50 Amp applications is very awkward to work with, the space where the ‘box’ fits is tight with little space and the new remote requires a larger cut-out in the control cabinet. Prior to January 2016, the phone cable (that's right a telephone cable) that interconnected the remote to the main box would have had to be replaced, however TRC finally came out with an adapter, since running the similar looking but different network cable from the back to the front of a large RV is a monumental task.

Today’s displays are generally in the remote panel and many scroll through the readouts without user action, such that you need only observe the display for a minute to learn a lot about the power source.

I set some criteria that allowed me to compare alternatives: They were as follows:

The new system had to have the following:

1)    A Separate (replaceable) Transfer Switch with Shore Power as the default power source,

2)    A Comprehensive Electrical System Protection (ESP) including Surge Protection similar to the original unit,

3)    Be Field Repairable or contain Field Exchangeable Components,

4)    Have a Scrolling Display of conditions and errors,

5)    Be UL and/or C-ULC listed and

6)    Have a physical size that would fit in the area where the original unit was located.


The TRC unit is RV-C compatible which means that it can communicate with other on-board electronic units and displays that meet the RVIA’s RV-C communication protocol. Since my coach does not have such an electronic communication system, that feature was not required. The TRC model requires the purchase of a separate Remote Panel which also requires a new network cable to be installed. 

Progressive Industries HW50C

Electronically the Progressive Industries, Model HW50C meets or exceeds the specifications of the TRC version. I have sold this brand of components for many years and had one installed in a prior RV. It now comes with a lifetime warranty to the first buyer and the surge protection circuit board and Contactor is field replaceable with minor effort. It also comes with a comprehensive display which scrolls the information and including error codes (or the E-0 – all good).   


The Automatic Transfer Switch I selected was made by ESCO (Elkhart Supply Corporation), Model LPT50BRD. This unit (see photo below of the connection area) is a high quality, dependable transfer switch. The two components met all of my criteria and were priced considerable less than the TRC model and provided a comprehensive display of operation without buying an additional component. 


It is always best to have someone with specific electrical knowledge, such as a licensed electrician, make the wiring changes, especially if you are unfamiliar with proper wiring techniques, procedures and regulations.  All AC power to the RV must be turned off and the inverter should also be turned off (some would say disconnected). Before removing any wiring carefully label the wiring cables coming into the existing box. (Coach, Utility/Shore Power and Generator).

Installing a new transfer switch requires that all of the wiring removed from the TRC ESP unit. With this unit out of the way, place the new Automatic Transfer Switch and HW50C in suitable positions so that the existing wiring can be installed to the appropriate connections. The Coach wiring is connected to the HW50C output side, ensuring that the Black and Red ‘Hot’ wires are routed through the current sensors so that the unit can display the current draw on each ‘leg’ of the 50 Amp AC power. A new two foot (0.6m) long jumper wire of 6 gauge / 3 wire (plus ground) known as 6/3 copper wire is connected to the new Transfer Switch in the Coach position. The other end of this new wire terminates at the Utility/Shore Power position on the Input side of the HW50C unit. This approach passes all sources of power through the HW50C, which allows it to monitor the Generator as well as the Shore Power. Today’s Generators are well regulated inverter models that do not need this extra monitoring, however by doing this we can easily tell if all electric circuit breakers are operating, since if the display is providing information, then ‘we have power’. The only downside risk is that it is possible that a severe power surge could damage the transfer switch, however it is passive when connected to Utility/Shore Power, so in my opinion this risk is minimal.

ESCO Transfer Switch Connections 

One lesson learned in reworking the wiring on our RV is to ensure that the factory prepared wiring is not nicked or damaged. On the Utility/Shore wiring, one of the ‘Hot’ wires had been nicked when the outer rubber covering was removed in production. This nick would have provided a path to ground when installed in the new transfer switch’s metal box. Each of those wires was covered with heat shrink to eliminate the potential of a short circuit. Check and if necessary cover all of the wires with heat shrink to remove any risk.


Ensure that all connections are tightened as specified and that all ground connections are connected to the junction point for ground wires. Connect the supplied Remote Panel network cable to the HW50C and to the Remote Panel


At this point you should ensure there is no metal objects or tools near the exposed transfer switch and HW50C. Test the system by having an assistant reconnect the Shore power cord to the campground pedestal and turn on the 50-Amp circuit breaker. Within a second or two, the Remote Panel will display '888' then go blank with a pulsing ‘dot’. Once all the checks are completed the HW50C will connect the power source to the RV and the Remote will begin scrolling the Voltage on L-1, the Current draw (in Amps) on that ‘Leg’, then it will read the Voltage and Current Draw on L-2, finishing with the line Frequency (60Hz) and E 0 unless there are error messages. This scrolling continues while power is connected.

Components Installed


Turn off the power and repeat this test with the generator running. In this case, there will be a 15-20 second delay, then the transfer switch relay will activate and the Remote Panel will display the same information as before. Turn off the generator. The final test involves setting the AutoGen Start (AGS) function on the Generator Remote panel, then removing the Shore Power and waiting for the generator to start and begin to provide power to the coach. After all tests are completed, with satisfactory results, power should be disconnected, all covers should be reinstalled and all wiring checked for secure mounting. Locate the Remote Panel in a suitable location and mount it. If the system units are mounted in a bedroom slideout, ensure that the slide mechanism and wiring are clear of each other. Since the TRC interconnecting cable is a telephone wire, and modern power management units use a similar looking network cable, the existing cable needs to have adapters installed on each end. I elected to mount the Remote Panel on the Bedside pedestal facing away from the headboard, as the transfer Switch and Power Monitor main unit is mounted there. This meant that the Remote Display moves in and out with the Bedroom Slide-Out and with the closet mirrors we can see the red display from the mid coach area. If there is a display, there is power present. In many ways this is easier that having to open the 'over-the-entrance-door' cabinet doors to check the system. Those doors are not left open, so when power was lost in the past, we needed a separate ‘alarm’ to let us know.

The final steps are to turn on the inverter, connect to the power pedestal and check that the Remote Panel is reading the incoming voltage. Reinstall the covers over the area and enjoy your updated electrical system. We are!         


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