By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.
I purchased these generators with a parallel connection. The claim in the ad says it will produce 50-amp service. But according to my RV it is only giving me 30 amps. How can they get 50 amps if each generator puts out 30 amps? And if it can put out 50 amps why can’t I get 50 amps? – Don
Here’s the picture you sent me of the dual generator kit being offered on etrailer that you purchased. Let’s discuss briefly what 50-amp shore power is, and why this pair of generators can’t supply the same amount of power as a properly wired 50-amp pedestal outlet.
If you take a close look at the ad you’ll see that it says it produces 6,000 watts total, not 6,000 watts per generator. And the price of $1,349.95 sounds almost too good to be true for a pair of 6,000-watt generators that could supply 12,000 watts total. But if you look down in the copy a bit you see the rating for each generator is actually for 2,900/3,200 watts. It adds up to around 6,000 watts total for a pair of these generators.
- Starting (surge) power output: 3,200 watts
- Running (rated) power output: 2,900 watts
Now, the only way you could actually supply a full 12,000 watts of power into your RV would be if each generator could make 50 amps of 120 volts, and there was a way to synchronize them 180 degrees out of phase for 120/240-volt output. And they definitely DID NOT state that in their ad copy.
The most confusing thing about 50-amp RV shore power is that it’s actually 100 amps of 120-volt power. That’s right… there are two separate legs of 120 volts, each of which can supply up to 50 amps of current. But in order to get that amount of power into your RV it HAS to be supplied as 120/240-volts split phase. That’s beyond the scope of this JAM Session, but here are the simple facts.
A 50-amp pedestal with 2 legs of 50 amps each can supply a total of 100 amps of current at 120 volts, which equals 12,000 watts of power (because 50 amps + 50 amps x 120 volts = 12,000 watts). However, a single 50-amp leg of 120 volts (which is what this pair of generators can supply) can supply only 6,000 watts of power (because 120 volts x 50 amperes = 6,000 watts).
Yes, if someone could sell a 12,000-watt 120/240-volt inverter (quiet) generator for a mere $1,349.95 they would be selling a LOT of them. But it’s simply not the case here, and the ad clearly states that a pair of these generators 6,000 watts total.
However, the good news is that the little parallel box etrailer supplied you with does indeed have a standard 50-amp RV outlet (a NEMA 14-50 receptacle) that’s been wired internally to supply both legs of your shore power cord with 120 volts, but only at 50 amps of current in total (6,000 watts) – just not the 100 amps at 120 volts (12,000 watts) you were hoping for.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 40+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.