But maybe the primary *is* broken on your dead end street. Or there are several breaks in the line and the only thing still connected to your house is the transformer. You don't know what the state of the distribution lines are, so you can't rely on them to stall the generator if you forget to open the mains. So you need another failsafe.
-Bob
Or don't connect it at all... You can do pretty well with a generator and a couple of long extension cords.
Bob
Then you haven't lived long enough, or inspected enough installations..... Having a Transfer Switch that doesn't switch the Neutral is applicable in the NEC, and legal in some situations. However, and this is a BIG However, if the System Ground should become faulty or the Netural resistance to ground start to rise due to corrosion or other problems, then out of Ballance Backfeeding on a 120/240Vac Single Phase system can happen. Nothing mechanical stays the same forever, and forever is a very long time. Shit Happens, and folks that don't understand that are doomed to live the results, for when the wrong "Shit Happens" in their world....... Some folks choose to only switch the Hot Legs, but the better way to do it is to switch both Hot and Neutral, and only keep the Ground continious.....
Me
Well, that is what they attempt to do. They do however fail on occasion.
Your generator hookup is a permanent installation, even if the generator itself is not part of the installation. Pretty common to see at telecom sites as well, permanently installed transfer switchgear and a big ol' IEC style plug on the outside of the building (or ped) to connect a towable generator to when needed. Allows a smaller fleet of towable generators to service multiple sites and also allows central storage and servicing of those generators.
Also quite common to see a small Honda generator chained to the base of a pole and powering a cable TV power supply. No transfer switch here, just switch of the main disconnect and wire in the extension cord.
An isolating transfer switch would be one type. Also have less common make before break paralleling transfer switches.
Everything is relative, but in an ice storm where there is a real risk of damage from frozen pipes in a short time period that would meet my definition of emergency. If there are children or elderly who are not as able to handle the cold as a typical healthy adult that would be an emergency. In hot weather were some people would be at risk without A/C.
You have a permanent installation of generator connection facilities. The generator itself need not be a part of that installation.
And that means can include the knowledge of how to make a safe temporary connection for the one or two times a year they may need it. If it's a fairly frequent occurrence then it justifies at least a basic transfer switch installation, once or twice a year does not if the user is competent.
Pete C.
That other failsafe is the training of the line crews and the "Assume all downed power lines are live" campaigns.
Pete C.
The entire public power utility distribution grid is not built to a "two failures for a life threatening fault" standard.
Pete C.
So it's OK to backfeed? Thanks.
I rarely resort to this type of language, but what moron believes a second failsafe procedure is a waste of time, especially when the first one is relying on the human factor?
True. I can only comment on the lack of reason and knowledge in your post. You may be a genius in other respects.
The last time I looked at "real" transfer switches from the major brands through about 600A, virtually all were solid neutral units. You could of course use a three pole (a.k.a. three phase) unit to switch the neutral in a 120/240V application, but you'd likely have to special order it to get the single phase monitor and control electronics. All of the little "Gen-Trans" and similar consumer level units I've seen are solid neutral as well.
I'm pretty sure that it's unlikely you'll see a transfer switch that switches the neutral as well outside of a fairly large industrial / commercial application.
Pete C.
No, but you won't kill a utility lineman as many have asserted.
Pete C.
My transfer switch switches both hots and neutral.
Trolling anonymous coward.
The second failsafe procedure is the utility workers training which tells them to treat everything as live, always use their protective gear, ground lines they are working on as applicable, etc.
If you want "two failures for a life threatening fault", then redesign the entire electrical distribution infrastructure so that every transformer is isolating and every line segment is floating, no grounds anywhere. That way any single fault will not in itself cause a life threatening fault. One fault would only reference the voltage on that segment to ground or whatever and not cause a dangerous situation without a second fault to provide another contact point at a different relative voltage.
Pete C.
My transfer switch is bigger than your transfer switch.
Your point sounds valid, and I certainly believe "ship happens" (given enough time shit will always happen), but can you cite a specific make and model transfer switch for a residential application that switches the neutral? John
The picture is a bit small, but it sure looks like a pair of 2 pole contactors. I can't tell if they have auxiliary contacts installed for electrical interlock. It looks rather like the auto transfer switches I've seen on RVs. If they are indeed 2 pole contactors then you're either running 120V only or have a solid neutral.
I built a small transfer switch myself with a pair of contactors with auxiliary contacts installed to allow for electrical interlock of the contactors coils. When a contactor is energized the NC aux contacts open the circuit to the coil of the other contactor preventing it from being energized. Three possible states, one contactor on, the other contactor on or both contactors off.
Pete C.
Come to think of it, if it is the RV type it could indeed switch the neutral by using the contactors together and utilizing the NC and NO sets of contacts with no provision for an "off" state. NC to connect to one source until the other source is available, cycles the time delay relay and then energizes both contactors. Of course this type of setup has the potential for a nasty failure mode if one contactor fails.
Pete C.
yes,
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