Electricity 101
The voltage in my coach fluctuates. This is with or with out my power master. Sometimes it is the front half of the coach including the GFI, sometimes it is the back half. The voltage at the pedastal reads 115-116 volts. The power cord reads the same. It is a 30 amp pedastal and I have a 50 amp coach. It happens when nothing is on or when there are things on. It can happen any time of day or night. Any suggestions?
When connecting a 50A rig to a 30A pedestal, you only have 1 hot phase, instead of 2, from the pedestal feeding into the 2 hot phase conductors in the rig. All the AC voltage used in the rig, even when connected to a 50A pedestal, utilizes only 120V load.
By the time electric power reaches the end-users,
(US), some utility companies are only supplying, say...110V, due to many possibile factors: end of the line distance from the sub-station, transformer size inadequate due to load increase since initial installation years ago, property owner and electrical installers sizing service too small, etc...
Most electrical devices these days are rated for 115VAC. This rating takes into account the fact that voltage from a utility will flucuate - some utility companies more so than others. Legally, (according to the NEC), on a service installation, the voltage shouldn't drop more than 5% total between the MAIN service and the farthest outlet for any load, with 3% max on any individual branch circuit and 3% max on the feeders from the service to another panel in between. (Utility companies are regulated differently, I don't know what their range of 'acceptable' voltage is!)
Let's assume there is another breaker box somewhere between the MAIN service and the pedestal. If the MAIN is 120V, the pedestal should be NO LOWER than 114V. MAIN at 115V, pedestal NO LOWER than 109.25V.
So...
IF the voltage at the pedestal is as low as 109.25V, your 115V rated equipment should still operate normally. Sometimes, the voltage is only 109V or 110V at the MAIN "120V" service, anyway. We also know that many times the voltage is actually 120 or more.
All that being said, without any load on at
your RV, does not necessarily mean there is no load on the system, causing a fluctuation in voltage at your pedestal. Nor does it mean the utility company voltage isn't just wigging out (technical term)!
If you are getting the same voltage reading at the pedestal that you are getting inside on your receptacles...chances are real good that it is nothing in your RV causing this. Especially when you have nothing turned on. You could see if they will let you check the voltage at the MAIN and also check around at other pedestals and see what their "120V" voltages are. It may be the utility or different loads in the RV park...either way, at 115-116V, you're good to go!