How do 3+ A/C's work?

[jcthorne]

Coaches with 3 ac units from the factory typically power 2 from one leg and one from the other, the remainder of the convenience outlets on the leg with one ac.

Coaches with 5 ac units typically have 2 50a connections.

[jesilvas]

Originally Posted by jcthorne

Coaches with 3 ac units from the factory typically power 2 from one leg and one from the other, the remainder of the convenience outlets on the leg with one ac.

Coaches with 5 ac units typically have 2 50a connections.

That was clear and concise.
I know that's what everyone said, but I want lots of input and that's what I got
Tricked you all into it.

[gemini5362]

I was told once by a dealer that coaches with three A/C units have a different thermostat and the thermostat controls which A/C units will be on. I am curious whether or not the 50 amp circuit on the pedestal is actually out of phase 120 volt line power. I am going camping tomorrow so I can check and see. I would assume that each pedestal would run two 50 amp 120 volt lines of the same phase to the pedestal. That would eliminate some of the horror stories of blowing up electrical systems if a neutral were missing. The park would wire one pedestal off of one phase on the incoming main and another pedestal off of the second phase on the incoming main. Balance the load by alternating phases per pedestal.

[FlyingDiver]

Originally Posted by gemini5362

I would assume that each pedestal would run two 50 amp 120 volt lines of the same phase to the pedestal. That would eliminate some of the horror stories of blowing up electrical systems if a neutral were missing. The park would wire one pedestal off of one phase on the incoming main and another pedestal off of the second phase on the incoming main. Balance the load by alternating phases per pedestal.

In a word, No. A 50amp RV outlet has (or should have) two 120V lines of opposite phase, so that you have 240V between the hots. If the hots are on the same phase, it's wired incorrectly. Unless the neutral is much heavier wire than the hots, it's also dangerous. Correct wiring for these circuits depends on opposite phases for the hot lines to reduce the current on the neutral.

[FlyingDiver]

Originally Posted by gemini5362

I was told once by a dealer that coaches with three A/C units have a different thermostat and the thermostat controls which A/C units will be on.

The probably depends on the brand of the RV. In ours, each of the three has it's own temperature sensor, so they work more or less independently. The EMS can shut down one or more if we're on limited power.

[JDL]

Originally Posted by FlyingDiver

In a word, No. A 50amp RV outlet has (or should have) two 120V lines of opposite phase, so that you have 240V between the hots. If the hots are on the same phase, it's wired incorrectly. Unless the neutral is much heavier wire than the hots, it's also dangerous. Correct wiring for these circuits depends on opposite phases for the hot lines to reduce the current on the neutral.

This is the most correct answer concerning the pedestals.

The 120 volt AC used in the US is a split at the transformer from 1 phase of electricity. This split is what creates the "180 degree phase separation". To keep it simple, lets accept the power from downstream of the transformer; this is what the general user’s works with.

That being said, in any environment where as the primary load is 120 volts, like the majority of items in an RV, it requires that the neutrals (2) be sized at a minimum the same size as the "hot" lines. This is because the current is being carried from one hot to one neutral. The items in the RV that have double pole breakers are using both hots; therefore the neutral doesn’t carry any significant load, as mentioned earlier. 50 Amp RV cables have 2 hots and 2 neutrals of the same size to deal with this, and so will a correctly wired pedestal. This is why "Cheater boxes" are known to cause problems when there is a common neutral on the 30 and 20 amp circuits. The neutral becomes overloaded.

Compare this to your home, and the majority of large appliances (power consumers) run on the true 1 phase of 240Volts AC delivered to your home. That is why your power feed to your home does not require a neutral that is larger than the "hots" on the service entrance.

[FlyingDiver]

Originally Posted by JDL

That being said, in any environment where as the primary load is 120 volts, like the majority of items in an RV, it requires that the neutrals (2) be sized at a minimum the same size as the "hot" lines. This is because the current is being carried from one hot to one neutral. The items in the RV that have double pole breakers are using both hots; therefore the neutral doesn’t carry any significant load, as mentioned earlier. 50 Amp RV cables have 2 hots and 2 neutrals of the same size to deal with this, and so will a correctly wired pedestal. This is why "Cheater boxes" are known to cause problems when there is a common neutral on the 30 and 20 amp circuits. The neutral becomes overloaded.

Do you have an RV with 50 amp service? Because they do NOT have 2 hots and 2 neutrals. They have 2 hots, 1 neutral, and a ground. The neutral is the same size as the hots, the ground can be slightly smaller. That's the cable going to the pedestal, of course. In the panel, there is one neutral bus bar and one ground bar. They are NOT connected as they would be in the main panel of a residential panel. The RV panel is considered a sub-panel in the NEC.

[JDL]

Originally Posted by FlyingDiver

Do you have an RV with 50 amp service? Because they do NOT have 2 hots and 2 neutrals. They have 2 hots, 1 neutral, and a ground. The neutral is the same size as the hots, the ground can be slightly smaller. That's the cable going to the pedestal, of course. In the panel, there is one neutral bus bar and one ground bar. They are NOT connected as they would be in the main panel of a residential panel. The RV panel is considered a sub-panel in the NEC.

I do have 50 amp service in my RV, had it in the previous three toyhaulers also, I also have transfer switches. I will agree with you that one of those is a ground, however, downsize it and let me know what you get inside your coach at full load.

The RV world doesnt exactly play as a true sub-panel. Take a look at how the generator/transfer switch is wired. Why do we brake the neutral and "ground" in the transfer switch?

[MustangGT]

my '97 Fleetwood southwind 34LS sports 2 a/c ,but only runs them simultaneously if everything else is off. otherwise it "sheds" one A/C giving priority to the other accessories. That ems works overtime in the Alabama/florida heat. 30amp
On a side note: I was startled to see 6 A/C's atop a nice Prevost I was following heading north on I65 on my way home last night. I had to count 3 times since the two TV satelite domes had the A/Cs squeezed nose to tail. Why are so many "necessary" or even "wanted"?

[FlyingDiver]

Originally Posted by JDL

I do have 50 amp service in my RV, had it in the previous three toyhaulers also, I also have transfer switches. I will agree with you that one of those is a ground, however, downsize it and let me know what you get inside your coach at full load.

The same thing you would get with a "full size" ground. There is no current on the ground unless you have a ground leak somewhere. If it's significant, you have other problems than wire size. Here's the link to a 50amp extension cord. The 2 hots and neutral are 6 gauge. The ground is 8 gauge:

Power Grip Heavy-Duty 50A Extension Cord - 30 ft. - Camco RV 55195 - Electrical Cords - Camping World

Originally Posted by JDL

The RV world doesnt exactly play as a true sub-panel. Take a look at how the generator/transfer switch is wired. Why do we brake the neutral and "ground" in the transfer switch?

Brake? You mean break? As in keep them separate? Because that's what the NEC calls for. The transfer switch switches all four lines. The Neutral and Ground are tied together at the generator (or maybe the generator side of the transfer switch) because when you're on generator you're longer connected to shore power and the NEC required separation is no longer applicable.

[FlyingDiver]

Originally Posted by MustangGT

On a side note: I was startled to see 6 A/C's atop a nice Prevost I was following heading north on I65 on my way home last night. I had to count 3 times since the two TV satelite domes had the A/Cs squeezed nose to tail. Why are so many "necessary" or even "wanted"?

If it had 6 AC units it was probably a tour unit set up with multiple zones and it was easier for the ducting to have each zone on an AC rather than try to use dampers or some such. Tour units are set up very different from RVs.