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Old 06-02-2023, 01:48 PM   #1
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When to safely turn on generator

Stupid question but can I run my generator while on shore power?

For instance, Im in my driveway getting ready to leave in the massive heat and running the air conditioners etc.

Can I start the generator THEN unplug from the house and hit the road so there is no interruption? Or do I need to disconnect from main power before running the generator.

I know this is likely a stupid question.
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Old 06-02-2023, 02:02 PM   #2
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I know if I run my baby Genny, start big Genny, big Genny takes over immediately
Vice versa, it reboots everything

I did have my Genny going today as I drove from storage to home, plugged in, and didn't skip a beat, but never done the reverse

But I'm sure it's fine
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Old 06-02-2023, 07:19 PM   #3
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Verify that your coach has an automatic transfer switch. If so then you can safely start your onboard generator while connected to shore power and everything should switch over. When you disconnect from shore power your generator will continue to run and operate everything without interruption.
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Old 06-02-2023, 07:23 PM   #4
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Firing up the generator will cause the system to switch over to generator and ignore the shore power feed. There is no problem in doing this, but....

Do not do this switch over when heavy current draw items are running. Temporarily turn off the air conditioners until the generator is in control. When the switch over takes place and there is a heavy current draw, the transfer switch will get a nice electrical arc take place on its contacts. Switching a few amps is not a problem but if you are switching 15 amps from an air conditioner, you could damage the contacts.

Many of us use small generators connected to the shore power line. These typically aren't capable of running heavy items so when the need arises, we kick on the big generator. This is perfectly acceptable (I have verified this with a transfer switch manufacturer). When we switch over we may only be pulling 5 amps or so due to fridge and converter. The big genny will then be used for ACs, microwave, etc. When done, these items are switched off and the big genny is shut down causing the transfer switch to revert to the little generator on the shore line. If it is still running, as mine usually is, it will power things just fine.

If you shut down the ACs there will typically be a delay before they can come back on. This is normal and built into the system. Don't worry about it, they will come back on.

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Old 06-02-2023, 07:38 PM   #5
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I know many RV'rs report no issues with simply starting the generator while on shore power and running appliances while doing the transfer of power. My recommendation is to turn off every major appliance you can (heater, A/C, microwave, water heater, etc) prior to switching between one source to another. Failure to do so may not cause an issue (or it may take many occurrences) however, the transfer switch isn't designed to be switched under a heavy load like that and if there is a heavy load on during the change from shore power to generator, the transfer switch can become damaged (contacts can arc and damage them) which would require a new transfer switch to repair the issue (and usually at a time that is not optimal for such a failure). Also, many A/C's can be damaged by a short interruption of power and why most of them now have a protection timer where if the power is lost for a second or more, the A/C compressor will stay turned off for a period of a few minutes (~5 maybe) which is a good thing, but shouldn't be relied upon for complete protection. ~CA
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Old 06-02-2023, 07:42 PM   #6
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I didn't see Jim's response until after I replied. However, Jim's response is inline to my advice and I highly suggest following his bolded comment portion in particular along with the other detail Jim mentioned. ~CA
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Old 06-03-2023, 05:03 PM   #7
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I'm with JimD and Craigav. Search this forum for auto transfer switch failures and you'll see that the failure almost always occurs when switching power sources under high load. The safest way to do this switch is to shut down all the heavy loads (A/C, water heater, etc), unplug from shore power then start the genny and re-energize all the heavy loads.
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