traverse517
Just installed a new 22kw unit, 70432, with a whole house transfer switch.  The other day we had a power outage for about 5 hours. Everything worked fine but when the utility came back on line, the transfer happened without even a blink in the lights. Even the digital clocks did not reset.

I would of expected a little blip in the power as the relay switches from generator back to utility.
But there was no interruption at all.

Any guesses?
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78buckshot
System is operating as designed, utility power was available and the transfer mechanism is energized with 240 volts and a spring to ensure quick transfer. The transfer from utility to generator is just as fast but the delay in powering the house is system response time and generator warm-up.
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cookelec
A lot of it depends on the magnitude of the return voltage and the angle of the sine wave upon the return of the switch. Some of the larger switches have a "time delay in neutral" setting that can be set so there is a definite delay. Running motors suffer the worst.
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Ron Goldstein Rongold
My 70431 & rxsw200a3 is exactly the same. If you don't hear the "click" or hear the generator shut off, you won't realize you're back on utility power---It switches that fast !!!
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Cobranut
cookelec wrote:
A lot of it depends on the magnitude of the return voltage and the angle of the sine wave upon the return of the switch. Some of the larger switches have a "time delay in neutral" setting that can be set so there is a definite delay. Running motors suffer the worst.


My system design required a smart transfer switch.  I chose a Thomsom switch in part due to it's ability to sync phases and transfer when everything is in phase.  Motors, nor anything else in the house even notice the switch.
It does the same thing during exercise runs.
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Birken Vogt
What was smart about the Thomson switch besides inphase transfer?  Just trying to keep abreast of available products, I have used them in the past and they have been good but never used any fancy options.  But inphase monitor I believe is standard with them.
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Cobranut
Birken Vogt wrote:
What was smart about the Thomson switch besides inphase transfer?  Just trying to keep abreast of available products, I have used them in the past and they have been good but never used any fancy options.  But inphase monitor I believe is standard with them.


I designed a system that allows easy shutdown and restart during long outages from a control panel in our laundry room.  It drops the load and runs warmup and cooldown cycles automatically. 
For that I use the genset in 2-wire start mode and the x-fer switch does the monitoring. 
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Birken Vogt
I did that once with a Thomson switch as well and it was a fiasco of unintended behavior, the switch controller was not happy but eventually I got past it.  I would be interested in your design if you don't mind sharing.
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Cobranut
Birken Vogt wrote:
I did that once with a Thomson switch as well and it was a fiasco of unintended behavior, the switch controller was not happy but eventually I got past it.  I would be interested in your design if you don't mind sharing.


Birken,

Here's a link to my install thread.  Unfortunately, all the pictures were lost in the site transition.
You were actually involved and provided a lot of useful input during the process.  Thanks.
https://www.zillerstore.com/post/questions-about-manual-operation-9947428?&trail=25
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Birken Vogt
You used a big contactor if I read the thread correctly?

I do things like that all the time, answer questions and then don't remember I ever talked to somebody.
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Cobranut
Lol. Me too. 
Yes, I ended up using a 150a contactor controlled by the Evolution controllers output that normally triggers the x-fer  switch.
We've used it during a handful of outages and the system works flawlessly. 
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JayH
traverse517 wrote:
Just installed a new 22kw unit, 70432, with a whole house transfer switch.  The other day we had a power outage for about 5 hours. Everything worked fine but when the utility came back on line, the transfer happened without even a blink in the lights. Even the digital clocks did not reset.

I would of expected a little blip in the power as the relay switches from generator back to utility.
But there was no interruption at all.

Any guesses?


This is normal. The transfer switch has very powerful coils and a massive over-center spring. Transfer back to utility is typically a few milliseconds. Lighting loads both incandescent (thermal mass of the filament) and CFL/LED (capacitors in the electronics and phosphor persistence) won't flicker much if at all. Transfer is NOT phase-synchronous, however. Motor loads aren't going to particularly like it and you may hear/feel a thump as they deal with the sudden phase shift. The amount of phase shift is random so the amount of this effect can be minimal to fairly large and isn't predictable.
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kdirk
I have to say I've been impressed with the transfer back to utility and the speed with which it occurs even on my 2008 era transfer panel (integral load center).

Being concerned about phase sync on motor loads when I first put this set up in, I built some relay boxes with time delay for the furnace blower, a/c condenser (motor and compressor) and refrigerator - all of which are on dedicated circuits in the transfer panel - that drop the load for 60 seconds on transfer off of generator and back to utility, and then reenergize those circuits automatically after the time delay has elapsed. This provides a hard break to protect those inductive loads against a bad jump in phase sync. 

I rationalized this also protects somewhat against spikes or sags that may occur right after utility comes back online. That might be wishful thinking on my part,  but sounded good at the time. 
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Cobranut
kdirk wrote:
I have to say I've been impressed with the transfer back to utility and the speed with which it occurs even on my 2008 era transfer panel (integral load center).

Being concerned about phase sync on motor loads when I first put this set up in, I built some relay boxes with time delay for the furnace blower, a/c condenser (motor and compressor) and refrigerator - all of which are on dedicated circuits in the transfer panel - that drop the load for 60 seconds on transfer off of generator and back to utility, and then reenergize those circuits automatically after the time delay has elapsed. This provides a hard break to protect those inductive loads against a bad jump in phase sync. 

I rationalized this also protects somewhat against spikes or sags that may occur right after utility comes back online. That might be wishful thinking on my part,  but sounded good at the time. 


This is another good way to protect motor loads.
Your system should already include a delay on utility restoration, I have mine set to 5 minutes if I remember correctly, to avoid premature transfer before the utility is stable, but giving motors an extra minute is extra insurance.
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kdirk
Yes, the Generac transfer panel and controller electronics in the genset delay the transfer from generator back to utility for 5 minutes to assure stable utility power before the transfer occurs. However, once that time delay has elapsed, transfer back to utility is instantaneous. And that is where the phase sync (or lack thereof) will get you and possibly damage motors and compressors.

Now i just wish there was a way to get my UPS's throughout the house to stop squawking while on generator. Unfortunately the sine wave from the genset is just dirty enough that they will never sync, and keep beeping/cycling on and off inverter unless I shut them off. Kind of a hassle, but a small price to pay for having full backup. 
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grsthegreat
kdirk wrote:
Yes, the Generac transfer panel and controller electronics in the genset delay the transfer from generator back to utility for 5 minutes to assure stable utility power before the transfer occurs. However, once that time delay has elapsed, transfer back to utility is instantaneous. And that is where the phase sync (or lack thereof) will get you and possibly damage motors and compressors.

Now i just wish there was a way to get my UPS's throughout the house to stop squawking while on generator. Unfortunately the sine wave from the genset is just dirty enough that they will never sync, and keep beeping/cycling on and off inverter unless I shut them off. Kind of a hassle, but a small price to pay for having full backup. 
Thats odd. i have 3 UPS that operate just fine under generator load. never beep or take over while under generator load
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kdirk
I suspect the UPS issues are either due to phase sync problems or that the generator's AC frequency is off 60Hz just enough to cause them to not play nicely. I"ve adjusted the genset frequency as close as i can get it to true 60Hz, but i also suspect the sine wave has enough distortion to cause alarms in at least some UPS units.

I have mostly better APC models, but also a giant 3kW Warner Electric from about 2002 that is an industrial duty unit meant for broadcast and similar applications. That one is more forgiving than the others but still has some trouble staying off inverter when the generator is carrying the load. It is on a 30A branch circuit and connects with a large twistlock. I use it in the basement "toy room" to protect my music and effects equipment. I usually shut it down when on generator as it isn't a critical load. 
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Cobranut

I haven't had any trouble with my UPS's when on generator power, but my 30Kw 1800rpm unit may have a cleaner waveform than the air-cooled units.

I've removed the buzzers from my UPS's, as I don't need them to tell me when the power is out. LOL

I have one equipped with a 50ah AGM battery that powers my CPAP machine, cell and smart-watch chargers, and a bedside lamp so I don't have to run the genset at night when asleep.
It also prevents a power interruption from waking me up at night.

I plan to add another 50ah battery to the one on my network and security equipment to extend the backup time on those as well.

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kdirk
I have to imagine the larger liquid cooled units meant for commerical duty have a "cleaner" output waveform and more tightly regulated frequency. Especially since this class of genset is used for backup in facilities like commercial and institutioanl buildings with elevators and a large amount of computer and HVAC gear that needs clean power. I see a lot of this class of genset providing backup for cell tower sites as well. 

The air cooled residential units, as good as they are, are clearly built to a price point and are generally for non-critical load situations, but rather more for comfort and convenience of the homeowner. In fact,  I wonder if Generac has disclaimers against using these units in life support type situations where someone is using critical medical equipment while homebound.

I'd not want to count on it for that, as there are enough things that can go wrong to make it risky to rely upon. Of course, it is still better than having no power at all in such a situation. Point being that the air cooled series is not an industrial grade machine in any respect versus the bigger (30-100kW liquid coooled) series that are used for fairly critical backup needs. I'd figure the quality of the output reflects that difference. 
The problems it causes my UPS's is a minor annoyance, so i don't give it much thought anymore. I do have most of them set to silent (audible alarms off) but have a couple without that option, and even when the beeper is suppressed I can hear those units relays click and inverter hum as they cycle in and out of backup. 
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Cobranut

In fact, my unit is a specific model built for Sprint Cellular.  It has twice the fuel capacity than the standard unit, as well as interface capability with the cell site, though I don't use that function.
It was apparently stored indoors until sold as surplus.  I paid just over half of retail for it, including shipping.
When I got it it still looked brand new.  It was about 2 years old and still had never been started.
The manual does have a disclaimer against using it for life-support equipment, however.

I've been very happy with it so far.

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JayH
kdirk wrote:
Y

Now i just wish there was a way to get my UPS's throughout the house to stop squawking while on generator. Unfortunately the sine wave from the genset is just dirty enough that they will never sync, and keep beeping/cycling on and off inverter unless I shut them off. Kind of a hassle, but a small price to pay for having full backup. 


The better UPSes are configurable as to how sensitive they are to distorted input. I have three APC Smart-UPS units and they're quite happy with the power from my 9KW Guardian.
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