Generator, a/c, and time delay

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mark32

Senior Member
Location
Currently in NJ
I will soon be installing a 16kw standby generator along with a ats for a friend. He wants to run his central a/c on it, nameplate says min circuit ampacity is 15.5a, I'm assuming this is it's running amps. I didn't get a look at the airhandler yet. I was thinking about installing a time delay in the condensing unit after the transformer that powers the t-stat to avoid the unit from immediately kicking on with everything else on the ats. Haven't installed a time delay for this type of application, anything I need to know? Hooking the timer up in the manner I described will also delay the air handler right?
 

Joethemechanic

Senior Member
Location
Philly Pa burbs
Sounds like a good idea to me. I'd look at the air handler before I worried too much about it. It sounds like I have a similar sized ac system. I also have a generator here so I've at least amp clamped all my circuits back at the panel. My air handler is on it's own 240V circuit. It runs below 2 amps.
 

kwired

Electron manager
Location
NE Nebraska
Some units already have a time delay built in them. If you have an electronic thermostat they usually have a time delay built into them when initially powered. This is to prevent short-cycling and the resulting hard starting while refrigerant is still under high pressure. You may not need to do anything if the unit already has one or the other.

Minimum circuit ampacity marked on units is the result of 125% of rated load of largest motor (usually compressor) plus 100% of all other load (usually just condenser fan). It is for determining minimum ampacity of supply conductors.

So in your case it may be something like: compressor = 11.2 amps x 1.25 = 14 + 1.5 amp condenser fan = 15.5.
 

kwired

Electron manager
Location
NE Nebraska
I will soon be installing a 16kw standby generator along with a ats for a friend. He wants to run his central a/c on it, nameplate says min circuit ampacity is 15.5a, I'm assuming this is it's running amps. I didn't get a look at the airhandler yet. I was thinking about installing a time delay in the condensing unit after the transformer that powers the t-stat to avoid the unit from immediately kicking on with everything else on the ats. Haven't installed a time delay for this type of application, anything I need to know? Hooking the timer up in the manner I described will also delay the air handler right?
mark32 if you need to install a time delay go to HVAC supply house and they will likely have an encapsulated time delay relay that goes in the 24 volt control circuit - probably for only about 10-15 dollars at the most. Some are adjustable some are fixed time - usually 5 minutes. Remember - it will make the thing take 5 minutes to start every time it is turned on. You could probably put it in the transformer common terminal and then it will delay any operation of the entire system but only whenever power is lost and restored again.
 

mark32

Senior Member
Location
Currently in NJ
Great info guys, thanks! kwired, I guess my first step will be to determine if the existing t-stat has this built in delay, if not I'll grab one of those time delays mgraw linked to.
 

kwired

Electron manager
Location
NE Nebraska
Great info guys, thanks! kwired, I guess my first step will be to determine if the existing t-stat has this built in delay, if not I'll grab one of those time delays mgraw linked to.
I did not check mgraw's link earlier - that is exactly what I was talking about. I even stock the same one in the link - they are handy and cheap for more than just HVAC. They work as is for 24 volt. You can also use them for 120-240 volt you just have to cut that little blue wire at the bottom. HVAC supply house usually has them cheaper than Grainger does.
 
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