You plug the unit in and then need to wait a few mins until the unit cycles through a series of tests to determine if the power source is safe. Then you can plug it in as long as the power source is good to go.
The PI unit is set by default to delay the closing of the contacts by 136 seconds. It only takes a couple of seconds to determine if the voltage, cycles, hot/neutral/ground are all proper, but the time delay is there in case the power drops and comes back on. The A/C unit will try to come on before the pressures have dropped if power is restored too quickly. If you have a newer A/C unit that has its own built in time delay, an internal jumper change on the circuit board will reduce the time delay to about 5 seconds.
My PI EMS has a bypass switch which allows me to function even after my surge protector is cooked..
The EMS units will function even with a blown surge protector, however you have no surge protection. The bypass is to force the contactors closed to give you power even if the unit says you should not, such as high or low cycles, high or low voltage or crossed neutral/hot or crossed hot/ground (the units are unable to differentiate between ground and neutral so if they are crossed, you won't know it. The only reason to use the bypass is if you have measured all of the above mentioned parameters and found them OK and have determined the EMS is WRONG.
It's either
Progressive or
Southwire's EMS. The advantage of both of these unit's is that they disconnect your RV from the pedestal when things go south.
The
Hughes Watchdog is functionally the same as either of the other two EMS units you linked to above, and is also available as portable or hardwired. The Hughes unit uses Bluetooth to an app to allow you to monitor the volts, wattage draw, etc. If you are in a campground long term that meters power, it keeps track of Kwh consumption and allows you to see how close the campgrounds meter is to it. Of course we all know about apps, some work, some don't, depending on the device you are running it on and the generation of operating system. The app can be a crapshoot so you have to take that into consideration, but it does allow me to monitor the device out on the pedestal.
The Progressive Industries units will protect against accidental 240v across the plug, without damage. I have found thru personal experience that the Hughes unit, when powered with 240 via an accidental miswiring of a TT-30 receptacle, will BLOW UP the MOVs in the surge protector. The Hughes technician could not explain why it did this, but they did send me a new unit. No, I did not miswire the outlet, someone who supposedly knew what they were doing did that for a neighbor, and I got caught in the trap with the Watchdog. That won't happen again.
Also, the Hughes units have a illuminated face, and I do mean illuminated. It is BRIGHT, and screams "steal me". I am not particularly concerned about theft, I think it is extremely rare, but having the face illuminated is not cool. Hughes SELLS a stick on face that DIMS this, but I simply opened up the unit and unplugged the wire connector for the LEDs in the face, from the circuit board. Hughes claims that the illuminated face is to inform you that the unit is working. I hear it clunk when the contactor closes, and I can look at either the app, or at a Kill-a-watt meter I keep plugged in, inside the trailer to verify the function. I don't need the face lit up.
If you desire the hardwired PI unit, get the one with the remote display, so you can install the display somewhere inside the RV. The hardwired units with the display in the top of them are not too handy to look at. I installed my remote just below the control panel inside my MH. It uses a standard phone cord, and the one provided is quite long.
Charles