Use a 3 way light switch to switch between L1 and L2 for an Air Con.

[jimmarako]

So here is the setup. I have a 30' travel trailer with a 50A feed. Its 50A only because there is an option for a second AC unit. We only have the one main unit, but thats not too important here.

On our last camping trip it was hot out so everyone had their AC's going. I noticed that L1 coming into the trailer was lower voltage than L2. I guess the way the campground is wired between the 30A trailers and 50A trailers L1 was taking a bigger hit. Maybe it was the pedestal, who knows. I was sitting there thinking it would be nice to be able to switch the AC to the L2 line coming in.... Hum......

After thinking about it for a while I said "hey, why not use a 3 way light switch to select between L1 and L2". I figure if I hook L1 to traveler 1 and L2 to traveler 2 then the AC can be feed from the common terminal. Neutral and ground are the same for either leg. I prefer to use "real" type switches and outlets for 120V work in the trailer (vs like panel mount switches) just because it feels better.

To me this seems like it will work fine, nor do I see any safety issues. I'm not sure if it would be up to code..... but since NEC code doesn't really apply to a trailer (yeah I know at the factory it does... sometimes) Thats not an issue. So is this crazy? I see 20A switches at Lowes so I'm at the breaker rating. Obviously the Air Con would have to be off before switching so it doesn't take a big hit.

Thoughts?
Jim M.

[Bama Rambler]

Light Switch Contacts aren't designed for huge inductive loads. Since you'd be switching it under no load conditions, it would last a while, but would eventually burn the internals.

A single pole double throw switch rated for motor loads would be a better solution.

[jimmarako]

Originally Posted by Bama Rambler

Light Switch Contacts aren't designed for huge inductive loads. Since you'd be switching it under no load conditions, it would last a while, but would eventually burn the internals.

A single pole double throw switch rated for motor loads would be a better solution.

Interesting. I couldn't think why a switch would care so I did some research and there seems to be two things to think about.

The first is that when switching on/off a running inductive load there is a surge/arc in the switch which a motor rated switch is designed for. The second is the startup current is larger than the running current as we all know.

It seems that some "light" switches are also HP rated. Many typical ones are not in which case your suppose to only control a motor load of 1/2 the switch rating. This is how everyone uses typical light switches to control ceiling fans, vent fans, furnaces, shop equipment,...... So my AC is ~13A which would be more than 1/2 the 20 amp rating.

I'll have to think a bit more. I couldn't quickly find a "normal" looking SPDT motor rated switch.

Thanks
Jim M.

[Bama Rambler]

Here's one that allows 80% rating on motor loads, so it should work. Especially since you won't be switching it under load.

Leviton 1286W 20 Amp 277 Volt Double Pole Switch

It's double pole double throw, but you can just use one side of it.

[Mike134]

Following, curious what answers might appear.

[CHICKDOE]

you currently have 1 circuit breaker in your distribution panel for the a/c. that breaker is fed from one of the hot legs. to power the a/c from the other leg you would have to install a second breaker in the distribution panel that is fed from the other leg. then you would take the two hots from the two breakers and run them to the switch you propose.

[jimmarako]

Originally Posted by CHICKDOE

you currently have 1 circuit breaker in your distribution panel for the a/c. that breaker is fed from one of the hot legs. to power the a/c from the other leg you would have to install a second breaker in the distribution panel that is fed from the other leg. then you would take the two hots from the two breakers and run them to the switch you propose.

Yep. The panel/trailer is already pre-wired for the second AC so the breaker exists on the other leg. Was just going to pull that wire out for now and replace it.

Jim M.

[jimmarako]

Originally Posted by Bama Rambler

Here's one that allows 80% rating on motor loads, so it should work. Especially since you won't be switching it under load.

Leviton 1286W 20 Amp 277 Volt Double Pole Switch

It's double pole double throw, but you can just use one side of it.

Thanks. Using a switch with a ON-OFF-ON type action would guarantee that I would "break before make" when switching the legs. I'm not sure if 3 way switches do that.

Last night I got caught up in looking for "motor rated" SPDT or 3-way switches and got distracted. Found some nice actuators and contactors but not really what I needed. I think at some point I may have even looked at some DPDT switches and never put 1&1 together. I did find a bunch of DPST which won't work obviously.

I already bought the 20A version of this switch below for another part of this project. Its rated for 1hp motor which after all of this makes me think it may be a bit under duty. I think this 30A version rated for a 2HP motor should fit the bill. Its $10 buck cheaper, comes in brown, and Amazon will have it tomorrow. Winner winner chicken dinner. Only down side is I'm 5 days past my return window on the 20A version.

Thanks again.
Jim M.
https://smile.amazon.com/Legrand-Pas..._t3_B00R8MMBWS

[jjuscg]

Good creative thinking to suggest a light switch for the fan speed control. I wouldn't have thought about a light switch being inadequate for the load - especially when I look at the puny switches built into the thermostat which serve that purpose. I guess I don't fully understand amperage vs dynamic load...

[CedarCreekWoody]

Are you sure that L1 wasn't just reading lower because you had more load on L1 in your camper?

[AFDON]

Originally Posted by jjuscg

Good creative thinking to suggest a light switch for the fan speed control. I wouldn't have thought about a light switch being inadequate for the load - especially when I look at the puny switches built into the thermostat which serve that purpose. I guess I don't fully understand amperage vs dynamic load...

As I understand it, the t'state and wiring do not handle the high amperage loads. What happens is that when the t'state calls for cooling, a low voltage low amperage signal is passed to a relay that closes sending the line voltage and amperage to the motors.

If I have it wrong I'm sure someone will be along shortly to enlighten both of us!

[Mike134]

Originally Posted by AFDON

As I understand it, the t'state and wiring do not handle the high amperage loads. What happens is that when the t'state calls for cooling, a low voltage low amperage signal is passed to a relay that closes sending the line voltage and amperage to the motors.

If I have it wrong I'm sure someone will be along shortly to enlighten both of us!

You are correct how it operates

[DouglasReid]

Our primary AC is also on L1.............Im guessing the vast majority of campers are wired like this.


Why not simply switch the wiring in the Load Center to make the primary AC fed from L2. No muss, no fuss and you are on the leg least used?

[mmartin_tdc]

Originally Posted by DouglasReid

Our primary AC is also on L1.............Im guessing the vast majority of campers are wired like this.


Why not simply switch the wiring in the Load Center to make the primary AC fed from L2. No muss, no fuss and you are on the leg least used?

IF you moved it to L2, wouldn't that cause a problem when only a 30amp post is available and you have to adaptor to the 50amp? I was under the impression that 30 to 50 would only power 1 leg of the 50 circuit.

[DouglasReid]

Originally Posted by mmartin_tdc

IF you moved it to L2, wouldn't that cause a problem when only a 30amp post is available and you have to adaptor to the 50amp? I was under the impression that 30 to 50 would only power 1 leg of the 50 circuit.

No, a 30 to 50 adapter feeds both sides of the 50 from one 30 amp hot leg. The entire camper has power just limited to 30 amps total instead of the 100 amps (50 x 2) that you have in a 50 amp setup

[Mike134]

/\ /\ /\ what he said above

[CedarCreekWoody]

Originally Posted by DouglasReid

Our primary AC is also on L1.............Im guessing the vast majority of campers are wired like this.


Why not simply switch the wiring in the Load Center to make the primary AC fed from L2. No muss, no fuss and you are on the leg least used?

Exactly. That is what I was going to suggest. Balance your loads.

[jimmarako]

Originally Posted by DouglasReid

Our primary AC is also on L1.............Im guessing the vast majority of campers are wired like this.


Why not simply switch the wiring in the Load Center to make the primary AC fed from L2. No muss, no fuss and you are on the leg least used?

Do not try to bring logic and reason to this problem when there is plenty of time and money I can be wasting.

You make a valid point and believe it or not I actually never considered that. And I have considered moving a different load to the L2 side to better balance the two legs. Maybe I'm not too bright.

I'm actually not sure what to do now. Parts are on order. I stopped at HD to get some supplies. Everything (mostly) can be returned.... I have been complaining about spending too much $$$$ lately.. but I kinda want to go crazy and do this...... And what if L2 is the weaker leg for some reason......

hum.....
Jim M.

[Larry-NC]

Originally Posted by DouglasReid

Our primary AC is also on L1.............Im guessing the vast majority of campers are wired like this.


Why not simply switch the wiring in the Load Center to make the primary AC fed from L2. No muss, no fuss and you are on the leg least used?

Good idea, Doug. I was just going to suggest that.

A similar option is to make an external dogbone that does the same thing.

[llr]

I use a light switch to turn my table saw on an off under load and I need to replace it after a few years. I would think no load you would be fine for a very long time, probably much longer then you care about. I forget the rating on the switch but it is the heaviest I could find at the big box stores.

Don't forget the 2nd breaker and you may not want the switch out were it can be accidentally hit.