How long can a postwar Lionel 252 crossing gate be activated without overheating or damaging it?

On my 5x9 (maybe larger than what you're talking about but still a fairly small layout) I use an insulated track section to trigger the gate when the train passes. It is connected to AUX power.

I've had this hooked up for many years and no problems with gate operation/burning out.

I too have a small layout and decided that the gate crossing sorts of accessories would be best operated by toggle or momentary switches. The advantage of that too, is not having the reduction of power to the track (if you're using track power without an accessory voltage post) via the operating accessory.

Another advantage is being able to customize the voltage to the accessory by using a separate accessory transformer. The small starter set transformers are really cheap and very useful for this type of thing.

Now my crossing gate is a MARX/K-Line version that has served me well for many years. But I was doing some wiring work on my control panel, and inadvertently hit the switch for the crossing gate. It had been on for maybe 5 minutes before I had noticed what I'd done. At that point, it had melted the inner chamber of the solenoid. Luckily for me, I had another one from my previous larger layout. So I was able to replace it easily.

Lesson learned. Now whether having yours on an insulated track section would do the same...? I think the break from the train passing would be enough to keep it from getting as hot as mine did. But mine was constantly on: And that was the thing that did mine in.

But I still like the idea of using buttons versus insulated track sections. I have several crossing items and don't need them all operating with every passing of the train. Having buttons allows a higher level of operator involvement. And in the case of kids, one can be running the train, while another is activating the crossing gate, banjo signal, crossing flasher, etc.

You also could look into timing relays. I bought some off the bay and they have different functions and user adjustable time settings. That way you'd never have to worry about something being left on accidentally

I have a 35 foot by 8 foot layout, where there are double Lionel Postwar crossing gates (a total of 4) in the vicinity of 2 reverse loops in one place on the layout, triggered by insulated rails. See photo below:

These crossing gates, which powered from the transformer through an Atlas Connector, are very reliable and durable, having worked flawlessly for 25 years. Fixed voltage is set at 18 volts. Arnold

I don't think the question was about how long the gate would last on a layout, but rather how long it could be left on. I think Brianel pretty much answered that. To be completely safe, the momentary switch would be the best solution. A timing relay would be the next option, but involves a little more electrical work. I say go with your #2 on your list. Kids do like to push buttons.

On the grandkid's layout push button just in case.

I always used the lowest auxiliary power needed to activate the gates. In the past I've ran 25 car trains continuously with no over heating at all. that's a pretty long activation time so i doubt you'll have problems. I think they are one of the most reliable accessories made. 

I had a similar concern with overheating in relation to another Postwar Lionel accessory that also uses a solenoid namely a 151  semaphore signal. I had a couple of times where the 151 signal did overheat and I came up with a different solution than what has already been mentioned. I purchased off Ebay a temperature sensing shutoff switch and attached this special switch to the underside of the signal and up next to the base of the solenoid. The temperature sensing switches were available with a whole range of available trigger shutoff points. I picked one that sounded logical to me and that was it. When triggered the signal shutoff as desired and after a good cool down time the signal came back on again automatically. These switches were from China and very inexpensive.

What he said.  A ~$1 thermal cutoff switch would easy-to-install by splicing it into one of the wires going to the solenoid.  Here's a photo showing the broad selection (you choose a cutoff temperature) from an OGR thread about protecting against an overheating smoke unit.

If you choose the timer route and want to tinker a bit, consider a reduced solenoid "holding" current.  I don't know about the 252 solenoid in particular, but many solenoid accessories with a spring-loaded return mechanism will stay activated with a reduced applied voltage/current.

Apply full 14V to lower the gate.  Once down, apply less than 14V to keep it down.  Lowering a solenoid driven gate takes less than a second.  Then, let's say you only need 10V to keep it down.  Since heating power is proportional to voltage-squared, going from 14V to 10V drops power in half.  This may be enough of a drop in heat to allow continuous solenoid operation.  Your mileage may vary.  Again, this would take some tinkering/experimentation but maybe 50 cents in parts (in addition to the timer) using a resistor or some diodes to drop the 14V to a lower holding voltage.

Option #2 would be great if you want the kids to play with it. Every accessory on my layout has a button on the side of the layout to encourage interaction from visitors, as well as making it easier for me to operate them (I'm conventional only).

When I used them on a large layout years ago, I would sometimes stop the train as the gate went down. The solenoid would get hot and it wouldn't work anymore. I don't think running even on a small layout where the solenoid got a bit of rest, would hurt your gate at all. Don

I likely wont be able to follow up soon, but..

My uunitsholdingvoltage isn't much lower than what it takes to drop the gate. The thing relies heavily on balance.

This trick is how pinball flippers used to work. High volt except at the very end of the stroke. It helps keep a coil cool as possible.

A timed drop or cut off would work.

I think my gate is on a 12vac doorbell transformer. I took the time to  test for heat and so feel safe parked there.   1min, 3min, 8min, 15min, 30min, 1hr, 2hr, 4hr, etc

Pressure switches are kinda my go to.(Older are better imo. Better leaves/points) Isolated rail is fine mostly, but sometimes a traction tire Loco or lighted/powered car may object to loosing the one outer rail's connection. A minor concern really.

Isolation in curves; isolating the inside rail seems to have less impact on rolling stock operation to me.

A thermal disconnect is a good idea too. Note your coffee makers warming plate uses at least  two inline thermal devices. One regulates "normal temp"  trips off at X° and resets upon cooling below that.  The other is a  higher temperature device; a "fuse" that doesn't reset once temp. is maxed. This latter prevents disaster should the first unit fail stuck closed (on)

Having toasted my fair share of crossings and semaphores, all I can add is:  Keep the voltage to the bare minimum needed for reliable operation.  Even intermittent operation at, say, 18VAC will cook coils in short order!  

Mitch

Food for thought for you guys suggesting momentary buttons over insulated track. It's just as likely that some young kid is going to "lay" on that button and hold it for a period of time as it is for the train being stopped on the insulated track section. Kids will be kids!

Just sayin'... 

John's quite right.  Particularly if you have a whistling station set up.   Don't ask me how I know...  ;-) 

Mitch 

Wow, thanks for all the great ideas!  I am pleasantly surprised at how many responses my slightly vague question generated.  John and Mitch, I agree about kids laying on the button, which is why I would do a logical AND between the button and the insulated track (which I realize still isn't foolproof if the train is parked on the insulated track AND the kid lays on the button).  Maybe I'll add a thermal switch for good measure.

I hadn't thought of delay relays, and for this little starter layout I don't think I want to make things more complicated then they need to be, but it's a neat idea.  I did find this nifty jack-of-all-trades relay that I might try if I had one laying around: https://www.amazon.com/GAEYAEL...-240V/dp/B07CH84BF6/