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| Puzzled about Online UPS + GFCI Behavior |
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| Bratster:
--- Quote from: Messtechniker on September 30, 2018, 06:34:59 pm --- --- Quote from: Bratster on September 30, 2018, 06:08:55 pm --- But why do you think adding a UPS would cause your GFCI to trip? --- End quote --- Because I am expecting the UPS while mains powered to cause a current imbalance on the neutral line. Dependent on the construction of the UPS. I haven't found anyone who would reliably recommend a specific type of UPS which will definitely not trip the GFCI. The other problem may be that the UPS disconnects the neutral line from the central gas heater thus floating it so that it won' t work. Connection of the central gas heaters neutral line to mains neutral is mandatory for operation of the heater. --- End quote --- if your heater just has a regular plug on it that goes to the wall outlet I would see no problem plugging that into a UPS and then having the UPS going to the wall outlet. That would not cause a GFCI to trip. the only way I could see it doing that is if the heater has some really weird wiring and there's multiple power paths, but I don't see how that would ever be allowed to happen and have it still be a code compliance safe product. Now the issue of the neutral being broken or not that would depend on the type of UPS. If you get a good quality UPS, it will either not break the neutral, in which case everything is fine or it will break the neutral but then it will make a neutral to ground Bond and again everything will be fine. Sent from my Fi Moto x4 using Tapatalk |
| 6PTsocket:
--- Quote from: DrDeke on September 30, 2018, 05:41:05 pm --- --- Quote from: 6PTsocket on September 30, 2018, 02:34:02 pm ---Can somebody please tell me what is the reason for double conversion? Why can't the battery charger, battery and inverter be simply bypassed all the time there is AC available and kick in when power fails? Why would you need inverter AC power at any time there is AC available from the mains? --- End quote --- In the marketing text, you usually see double conversion UPSes suggested for use with "critical loads which can tolerate absolutely no interruption to their power supply." It is true that the output of a double conversion UPS should remain completely unchanged during interruption or restoration of input power, whereas other types of UPSes can have brief interruptions / phase discontinuities / etc on their output during such events (as shown on the oscilloscope capture in this thread). That said, I have never personally run across a load which seemed to suffer from the switching time on a standby or line-interactive UPS. I suppose it's possible that some equipment would be damaged by or run incorrectly during those events. Or maybe it's more that some loads are some combination of very expensive and in need of very high availability, and their owners don't want to take any chances. For me personally, I ended up with my double conversion UPSes for a different reason. Some years ago, I lived in a house which suffered fairly frequent power outages (thus wanting a UPS in the first place), and also suffered from chronically low voltages during the summer because the utility transformer serving that and several nearby houses was undersized/overloaded. Throughout the day as air conditioners turned on and the load on the transformer increased, the voltage as measured at a receptacle in the house would decrease and when it got below the UPS's low-transfer voltage (somewhere around 96 V for the UPSes I was using at the time), the UPS would transfer to battery power, thereby removing several amps of load from the supply circuit. The lighter load would cause the voltage to recover slightly, enough to make the UPS transfer to line power. The resulting increase in load would cause the voltage to dip again, sending the UPS back to battery power. This cycle tended to play out until either the UPS batteries were drained or the UPS itself had failed from the constant, frequent switching. After letting the smoke out of several APC Smart-UPSes in this manner, my roommate and I ended up getting a couple of these double conversion UPSes on eBay and never looked back. The one I've still got, the GXT1500, can run on line power all the way down to 73 V (if loaded to 70% or less - 93 V at full load), while maintaining a steady 120 V output. (The input current to the rectifier would, of course, increase as the input voltage decreases, to maintain the input power.) --- End quote --- Thanks for rhe explanation. I have no UPS so I know nothing about them. When the power fails I just fire up my 7000 watt standby generator that can carry everything but the central air. It is not seemles. It is more like 10 minutes.LOL. Sent from my SM-G900V using Tapatalk |
| Jeroen3:
--- Quote from: Messtechniker on September 30, 2018, 06:34:59 pm --- --- Quote from: Bratster on September 30, 2018, 06:08:55 pm --- But why do you think adding a UPS would cause your GFCI to trip? --- End quote --- Because I am expecting the UPS while mains powered to cause a current imbalance on the neutral line. Dependent on the construction of the UPS. I haven't found anyone who would reliably recommend a specific type of UPS which will definitely not trip the GFCI. The other problem may be that the UPS disconnects the neutral line from the central gas heater thus floating it so that it won' t work. Connection of the central gas heaters neutral line to mains neutral is mandatory for operation of the heater. --- End quote --- If you have a high leakage load, it might trip the GFCI when it's on battery due to the high frequency components in the sine approximation. However, unless the UPS has galvanic isolation, it will trip the GFCI/RCD. Even on battery. |
| Bratster:
--- Quote from: Jeroen3 on October 01, 2018, 09:48:53 am --- --- Quote from: Messtechniker on September 30, 2018, 06:34:59 pm --- --- Quote from: Bratster on September 30, 2018, 06:08:55 pm --- But why do you think adding a UPS would cause your GFCI to trip? --- End quote --- Because I am expecting the UPS while mains powered to cause a current imbalance on the neutral line. Dependent on the construction of the UPS. I haven't found anyone who would reliably recommend a specific type of UPS which will definitely not trip the GFCI. The other problem may be that the UPS disconnects the neutral line from the central gas heater thus floating it so that it won' t work. Connection of the central gas heaters neutral line to mains neutral is mandatory for operation of the heater. --- End quote --- If you have a high leakage load, it might trip the GFCI when it's on battery due to the high frequency components in the sine approximation. However, unless the UPS has galvanic isolation, it will trip the GFCI/RCD. Even on battery. --- End quote --- Hadn't thought about that, I was thinking if there is any sort of leakage it (the heater) would trip the GFCI by itself, but hadn't considered that not getting a perfect sine wave from the UPS would cause it. Although presumably if the UPS is creating sine wave that means it's on battery power and the mains should be off so the GFCI shouldn't trip. But I could see it tripping when the power is just going out or just coming on. Perhaps the solution is a sine wave UPS to keep the heater happy but the output of the UPS is not connected to the heater itself, it would connect to a small transfer switch. so the heater would be on the output of the transfer switch, with mains straight from the outlet on one input and put the UPS on the other and when the main supply drops out the UPS kicks in and the transfer switch drops off, selecting UPS as the input source. Perhaps this conversation should get moved to its own thread so we can better help the heater OP instead of polluting this thread? Not sure what proper etiquette would be. Sent from my Fi Moto x4 using Tapatalk |
| Jeroen3:
The mains not being present doesn't inhibit the operation of most GFCI/RCD switches. |
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