Disconnect Shore Power Before Turning on Generator

[ColoradoBnd]

I have always made it a practice to unplug the shore power before I crank my generator. Not sure where I picked up that rule, but I have always used it. So I am asking the question in the context of exercising my generator during the winter months. I live in a very cold environment and hate to exercise any connectors at very low temps (cords, plugs, etc.). So is it necessary to unplug before I startup the generator or not???

[HarryStone]

Not from what I understand. Make sure there are no big loads on the system first. (AC unit, etc.)

[wildtoad]

The transfer switch will handle the swap just fine. It is a good idea perhaps to make sure AC/HP is not running when you make the switch.

[wolfe10]

OK, gets into the issue of "best practices" vs "can I get away with it".


You have to decide into which category you fall.


Can you switch A/C loads while under load-- YUP. Will it pit the contacts in your ATS-- YUP.


You don't necessarily need to disconnect shore power, but turning off loads before switching power sources gives your ATS a longer life.


SO, best practices is to turn off all loads, turn off breaker at your CG outlet, start generator and let it warm up for a couple of minutes (no A/C loads on) and then start adding A/C loads. For exercising the generator, best is to run it for at least 30 minutes under at least 50% load.

[Rob_M]

Originally Posted by wolfe10

OK, gets into the issue of "best practices" vs "can I get away with it".


You have to decide into which category you fall.


Can you switch A/C loads while under load-- YUP. Will it pit the contacts in your ATS-- YUP.


You don't necessarily need to disconnect shore power, but turning off loads before switching power sources gives your ATS a longer life.


SO, best practices is to turn off all loads, turn off breaker at your CG outlet, start generator and let it warm up for a couple of minutes (no A/C loads on) and then start adding A/C loads. For exercising the generator, best is to run it for at least 30 minutes under at least 50% load.

I’m assuming best practice is doing basically the same thing going the other way from generator to shore power? That is what I have been doing, but this is the first time I’ve actually read it on here. It just makes sense in my small mind to not arc your switchgear for longer life.

[Unplanned Tourist]

Your ATS will switch over, but try to have as little power draw as possible when you start the genset. Is saves the contacts inside the ATS like others have said.

Good on you for exercising your genset. So many don't and next Spring it's a gong show.

[radar]

It’s a break before make switch so no requirement to unhook shore. I would make a habit of not having high current appliances running though.

[wolfe10]

Originally Posted by Rob_M

I’m assuming best practice is doing basically the same thing going the other way from generator to shore power?

CORRECT.


And for an additional reason. Letting your generator cool down before shutting it down is better for it.


Think of it in "car terms+: Same as allowing your car to slow down and idle for a few minutes before shutting down rather than running 75 MPH and just shutting down the motor. Can you just shut if off from 75 MPH-- absolutely. Is it good for it.............


This in addition to the arcing of the points in the ATS if shut down under heavy load.

[Eighthc]

Coming out of a 21 Tiffin Bus and a 16 Bus before that. Moving to a DS 4311 to assist my disabled wife. Tiffin provided for this issue by installing a 2 1/2 minute pause on generator draws before allowing power to the HVAC units.

This helps when you are running down the road and you need roof air. I have to leave the units on as my wife cannot get up while we are moving. So the pause protects the generator.

Ron

[twinboat]

They call it a automatic transfer switch because it's automatic.

If your running inside and out to switch over, you may just as well just go back to the big outlet in the cord compartment that you plug your cord into.

How many times does the tiny 20 amp relay open and close, up in the AC unit, without burning the contacts ?

The ATS has 50 amp magnetic contactors designed to switch high HP air compressor motors on and off .
Most fail from poor wiring.

[Suburbazine]

I don't know how far back it goes, but my ATS has a 2 second neutral safety. It's not transferring anything under load, everything big has been dropped already and will have to restart itself after power is connected. My AC units have a 150 second delay on compressor restart, the fan will start immediately but it's a next to nothing load.


Your house AC units have a similar load relay in the outdoor condenser. It makes thousands of engagements UNDER FULL SURGE LOAD (40+ AMPS) before it fails.


I had a 400A ATS that would transfer to standby power once a week under full load (205A). 750+ cycles without service (to the amazement of the manufacturer) later it only needed the contacts polished. I doubt your tiny 30A loads are doing much to your even faster RV ATS.

[Clemson]

Originally Posted by wolfe10

OK, gets into the issue of "best practices" vs "can I get away with it".


You have to decide into which category you fall.


Can you switch A/C loads while under load-- YUP. Will it pit the contacts in your ATS-- YUP.


You don't necessarily need to disconnect shore power, but turning off loads before switching power sources gives your ATS a longer life.


SO, best practices is to turn off all loads, turn off breaker at your CG outlet, start generator and let it warm up for a couple of minutes (no A/C loads on) and then start adding A/C loads. For exercising the generator, best is to run it for at least 30 minutes under at least 50% load.

You have the best practices covered! Great job….

[Rev. Roy]

You didn't share if you are plugged into a 50, 30, or 20 Amp circuit. To some that may make a difference. I have 50 amp in my RV garage but it has a breaker that I can flip off before unplugging or starting the RV generator If I'm there. Having said that, I have it start automatically when I an not home by keeping the "exercise" setting set. That leaves the question: why is there an exercise setting if you should cut the power first? I have never seen a label saying, "disconnect external power before starting generator" anywhere. Is there one I just haven't noticed?

[dons2346]

When switching from one power source to another, I always disconnect the active one before connecting to the other. There is that chance that the transfer switch will not act as it should, so why tempt fate.