50 amp wiring question

[dryfly]

I'm getting a new trailer and it will be my first with 50 amp service. I've always noticed the standard NEMA 14-50R 4 pole receptacle on the AC pedestals but never paid any attention to the female shore power receptacles on the trailers. I'm guessing they are a NEMA SS2-50P 4 pole??

Apparently there is no concern in balancing the loads on the 2 legs in the breaker panel when using a trailer wired with a 50 amp service on a 30 amp supply (using a 30 to 50 adapter)? Looks as though the 2 120 volt legs of the 50 amp supply are combined into one leg in the adapter.

[dryfly]

The quote below is from the link provided from Pianotuna in an earlier post. Over all the years with my 30 amp service trailers I have done quite well and have never been overly concerned about an open neutral, although I do keep one of the AC outlet 3 light testers wired at all times for safety reasons, and use a Kill-A-Watt meter permanently installed in an outlet.

With that in mind, I'm seriously considering running my new trailer (with 50 amp service) on a 30 amp adapter anytime I'm not using the 2 A/C units. I don't do a lot of summer camping so my previous trailers did fine most of the time on one A/C.

Guess I'll just have to play around with it but I can see the definite possibilities of issues of 50 vs. 30 amp supplies.


from the link:
"You could make an adapter that connects to only one side of a 50-amp outlet, but feeds both sides of your power cord. That would give you 50 amps instead of the 100 amps you actually get with full 50-amp power (because normal RV 50-amp power is two 50-amp lines). This should be about as safe as 30 amp and you get 20 additional amps.
It's safer because you are only receiving power from one of the two phases, and if the neutral in the pedestal opens, all that will happen is that you will lose voltage, which rarely would cause a problem."

[wa8yxm]

The A/C's both run in very hot weather almost all the time. Thus they are the one item I most want "Balanced"

Water heater is only 375 Watts (I downgraded)( Fridge about the same so they balance.

Microwave runs on the inverter leg the other end of the teeter totter is "Everythign else" and I mean EVERYTHING else save for a pair of special outlets I added. well two pair. and they balance since they are paired.

[BB_TX]

pianotuna wrote:
BB_Tx
wa8yxm did qualify his answer. Balance depends on what devices are running at the same time.
.......

I agree. But it is often stated that it is bad to have both A/Cs on the same hot leg. And that is too simple of an answer. It is not inherently bad as long as other loads are properly distributed.

[pianotuna]

BB_Tx

wa8yxm did qualify his answer. Balance depends on what devices are running at the same time.

For example, my 1400 watt water heater, once it is warmed up, only operates for 15 minutes every 4 hours. On the other hand, my roof air can draw up to 1900 watts (measured), and rarely cycles off on a hot day.

However, when I do have 50 amp shore power, I move the water heater over to L2 from L1. I'll also operate my NuWave hob from L2, and my kettle with other kitchen devices.

On the other hand, if campground voltage is low, I'll use the autoformer to boost L1 and run the kitchen devices from L1 using load support from my hybrid inverter/charger.

It may be quite rare for me to have a "balanced" load on a 50 amp shore power supply, but that really can't be helped given the intermittent nature of the loads.

[BB_TX]

wa8yxm wrote:
I took the time to balance as best I could.. I mean CW when they moved a breaker to install my inverter put both air conditioners on one leg.. Not a good plan.

.....

Two A/Cs, about 30 amps, on one hot leg is not in itself a bad plan as long as most other high current loads are on the other hot leg. You could just as easily say that putting one A/C, the microwave, the water heater, and the converter on one hot leg is a bad plan. It is all about total balance.

[wa8yxm]

With a 50 amp RV plugged into a 50 amp outlet and a GOOD quality EMS like a Progressive INdustries HW-50C and open neutral = NO POWER and an error code on the display.

With a 30 amp RV an open neutral = NO POWER period

With a 50 amp plugged into a 30 amp outlet an open neutral = NO POWER

Yes. I'm suggesting the HW-50/30C for it protects you against many Oh ****!!!s

[pianotuna]

dryfly,

My "break out" box is a 50 amp plug that goes to a little tiny breaker box. L1 is a 30 amp outlet with a 30 amp breaker, and L2 is twin 20 amp outlets with 20 amp breakers.

I've equipped my Class C with two auxiliary shore power cords. In winter I can use them to power extra electric heaters and in summer I can move the electric water heater over. That's done with male and female plugs, so I can move to OEM wiring configuration in a few seconds. Similarly I can wire around the hybrid inverter/charger.

[dryfly]

pianotuna wrote:


Actually when I do plug into 50 amp (I'm a 30 amp rv, so open neutral may be less of an issue) I do check voltage and polarity under load using my breakout box.

What is this "breakout box" you speak of? sounds interesting. How are you creating a load with it?

[pianotuna]

wa8yxm

Great answer!

[pianotuna]

There were some good answers, but the Elephant in the room is an Open Neutral. If that happens when plugged into 50 amp, one leg may zoom up to 240 volts. Say "goodbye" to any item that was turned on with over voltage on that leg. A low level surge device will not shut down power, to protect the RV. A top of the line unit will shut off the power fast enough to protect the devices.

Actually when I do plug into 50 amp (I'm a 30 amp rv, so open neutral may be less of an issue) I do check voltage and polarity under load using my breakout box.

After I've tested, then I feel safe to plug in. I do monitor voltage with a Kill-a-Watt unit.

The other issue is that voltage, at an RV Park, bounces around like a basketball when it is a hot summer day and every one and their dog is using their air conditioner, and all the other devices we have grown accustom to using.

I do use an autoformer to correct low voltage. I have added superior surge protection to it--but it doesn't cut off the power. My Sola Basic does "buck" voltage as well.

There is some additional protection for me due to the Magnum hybrid inverter charger which refuses to connect under low voltage. It is a feature not mentioned in the manual but I know it exists from observations "in the field".

Here is a good explanation of open neutral.

http://www.myrv.us/electric/Pg/open_neutral.htm

dryfly wrote:

pianotuna wrote:


On a fifty amp--I do recommend a top of the line energy management system that may detect an open neutral.

Why "top of the line"? Why not just use the same AC outlet ground tester we use on 30 amp circuits? We are still just testing for open ground or neutral.

https://www.amazon.com/Electrical-Receptacle-Outlet-Ground-Tester/dp/B0012DHVQ0

[wa8yxm]

I took the time to balance as best I could.. I mean CW when they moved a breaker to install my inverter put both air conditioners on one leg.. Not a good plan.

On 30 amps it won't matter because you can not overload a leg. But here is why balancing is important.

_________L1
|
|======Neutral
|
__________l2

Now let's assume you are one volt loss at normal load EACH way from the transformer with the loads perfectly balanced (All but impossible but we can get close)
Balanced you now have 124 volts either side of neutral

IF you Now let's move the loads so it's 2/3 1/3

Now we have more loss on one leg PLUS we have the return loss on the neutral
Slightly less loss on the 2nd leg

But every anp that flows through the neutral has double the voltage loss

[dryfly]

time2roll wrote:

dryfly wrote:
Let me rephrase my OP. I fully understand AC split phase wiring of the 50 amp supply. I guess I don't understand how combing L1 and L2 in the dogbone adapter supplies 120 volts. Seems like it would produce 240 volts.

I'm asking this because instead of buying a 50 to 30 amp dogbone adapter, I want to take an old 30 amp extension cord and modify the trailer end with a 50 amp female plug, in essence build a 25' adapter.

No 240v through the 30 amp adapter. Pulls power from just one side. One hot to neutral is 120v every day.

You can make a 30/50 adapter any length you want.

Well the light bulb finally went off in my head. You ARE measuring from neutral to hot for 120v. I was visualizing measuring between L1 and L2/ My bad...................

[time2roll]

dryfly wrote:
Let me rephrase my OP. I fully understand AC split phase wiring of the 50 amp supply. I guess I don't understand how combing L1 and L2 in the dogbone adapter supplies 120 volts. Seems like it would produce 240 volts.

I'm asking this because instead of buying a 50 to 30 amp dogbone adapter, I want to take an old 30 amp extension cord and modify the trailer end with a 50 amp female plug, in essence build a 25' adapter.

No 240v through the 30 amp adapter. Pulls power from just one side. One hot to neutral is 120v every day.

You can make a 30/50 adapter any length you want.

[DutchmenSport]

CA Traveler wrote:
Dutch,

Doesn't your portable unit display a error code? My PI HW50C has 11 codes.

E-6 Low voltage. It shut down the camper. This was the first time it actually did this. We've had this camper and the EMS since September 2018 and it's plugged in 24x7 non-stop, unless on the road ... which has been a lot lately.