Originally Posted by CedarCreekWoody
Myredracer a 50 amp RV will use more power than the 30 amp breaker will allow it to use, no matter how big it is.
The NEC provides for a load of 3600 watts per individual 30 amp site and up until 2017, 9600 watts for a 50 amp site. The required allowance for 50 amp sites is now a full 12,000 watts. What the NEC has never provided for is what the required draw from a 50 amp RV should be when using a 50 to 30 amp adapter for demand calculation purposes. Would it be 1/2 of 9600 watts (or 12,000 watts) or some other figure?? It's anyone's guess.
When performing a demand calc. under the NEC using table 551.73, there is no differentiation between 30 amp and 50 amps in terms of reduction of total demand for multiple sites. A few lines from the table are:
1 site = 100%
5 sites = 65%
13-15 sites = 48%
36 sites or more = 41%
So while you can't draw more than 3600 watts from a 30 amp pedestal indefinitely, the typical 30 amp RV isn't going to be drawing anywhere near a full 3600 watts according to code. On a 200 amp feeder for example, 14 x 30 amp pedestals are permitted which is 1728 watts on average. Then along come 50 amp RVs with multiple AC units and various appliances and loads that are higher than 30 amp RVs draw. Again, should it be 1/2 of 9600 watts? It's certainly going to be more than 1728 watts on average.
You could have more than 36 sites in total with 50 amp RVs using 50-30 amp adapters and yet be allowed to derate a feeder (or main service) by 41%. And for older CGs, there can be 95% of sites being 30 amps (and remainder 50 amps).
With 14 30 amp RVs on a feeder run, they could all be trying to draw substantially more than 1728 watts per each though.
The NEC doesn't mandate max. allowable voltage drop which can result in long feeder runs and in older CGS, longer individual branch circuits to sites and thus high voltage drop. Also compounding things is that the NEC doesn't consider RV loads as being "continuous" loads and feeders don't have to be derated 80%. As most know, esp. in the heat of summer, folks can be running their AC units for hours & hours non-stop.
Interestingly, table 551.73 includes a "fine print/qualifying" informational note indicating these demand factors may not be adequate in areas of extreme cold or hot temperatures. The code folks oughta be made to stay in CGs in the heat of summer around the US to see how well the code actually matches reality. The NEC has been woefully behind for too long.
Anyway, we bought an autoformer after being in a few too many CGs with low voltage. It used to be that I would never use one because of what can happen if too many sites in a CG were using them and causing further voltage drop in other sites. But I've seen very few of them anywhere. The last CG we were in was low enough for our EMS to shut us down so just pulled out the autoformer and carried on as usual.