Greetings, hope all of you are well!

I have an electrical question, and after reviewing various books, my notes, and trying to access something in my memory, I can't seem to draw a confident answer.

Here's the diagram, in jpg format.

http://frederic.woodbridgedata.com/_...-generator.jpg

On the left is the main panel. The top circuit in the diagram is a 120V, 20A circuit that goes to the sump pumps next to the racks my servers are mounted in.

The servers and related network gear, are on four 120V UPS units that are hard-wired to a subpanel, which has one 15A breaker for each UPS, two 15A breakers on each leg of a 240V circuit, which is feed by a 240V 30A circuit from the main panel.

So far no fires

I have a portable generator outside that provides 240V through an ordinary L14-20 connector, providing two hots, a neutral, and a ground on this connector, just as one would expect.

When I have a power failure, I have to feed a homemade 240V extension cord through the basement window and on the other end I installed two 120V 20A duplexes, one on each leg, and I unplug one of the UPS units for the server farm from it's mains fed duplex off the subpanel and plug it into one of of the duplexes on the 240V extension cord, and I also unplug the sump pumps from the mains fed duplex and plug it into the other duplex on the 240V extension cord.

This puts one server farm UPS on one leg of the generator, and the pair of sump pumps on the other leg, manual style. Works without issue.

Moving the sump pumps over is easy - unplug from one and plug into the other. The UPS however is in a rack and it gets it's power from the back wall, so to unplug this during a power failure to move it to the generator takes a long time - I have to remove equipment from the rack to reach back there because I'm too fat to fit behind the racks.

So, I bought a pair of 20A "industrial grade" 3-way switches, and planned to connect them as per the above diagram where I can switch between the "hot" of the mains and the "hot" of the generator. I tested the switches thoroughly and they are break-then-make as I had hoped.

I would do this for the UPS and for the sump pumps.

Seemed very easy and I have it wired out, except I'm confused about what to do with the neutrals.

Tying the generator's neutral to the neutral buss bar in the subpanel makes sense... however neutral for the sump pumps would have to back-feed through the subpanel to the main breaker box's neutral buss bar, then back out again through the sump pump's neutral to the electrical box they're plugged into.

I just know this is bad.

A friend suggested tying an extra 20A capable neutral between the sump pump duplex's neutral and the sub panel, and I just know this is even worse.

If the server farm's subpanel also feed the sump pumps this wouldn't be an issue because all the neutrals are tied to the same bar in the subpanel, but because the sump pumps are off the main breaker panel, I have become rather confused about what to do with the neutrals.

Is there any legit way of doing this safely? Ideas welcomed.

What's sad is I should know this... but that's another story.

 

I'm not qualified to analyze your situation, but I have a couple of comments.

They do make switchovers just for generator hookups -- some manual and some automatic. I'm guessing that they switch both sides of the circuit to avoid issues such as yours.

Otherwise, not really knowing what the code says about this, I wonder if you could run a 2nd neutral from your generator to your main box. The only real issue that you have is the integrity of the various connections, and that would give you a little more control over them.

Hopefully one of the electricians around here will chime in.

 

The easiest safest and legal way to do this would be to re feed the sump pumps to the sub panel and add a Gentran Switch to take care of distributing the power from the generator.

I am a lic electrician in Massachusetts. There are a couple of other options but I would need more information, size of main service etc for them.

 

Thank you for the comments thus far.

The main panel is a 100A 240V single phase murray, installed in or about 1970.

The sump pumps are fed off a 20A single pole circuit directly from the main panel.

The server farm is fed off four 15A single pole circuits in the subpanel, and that subpanel is fed by a 30A 240V double pole circuit from the main panel.

I agree, feeding the sump pumps off the subpanel would make this easy, however there are no slots free, and it cannot provide more than 30A which is in use by the server farm.

So the generator, which provides 240V @ 20A, would be feeding the servers AFTER one of the 15A breakers in the subpanels off one 120V leg of the 240V, and the other 120V leg would be for the sump pumps.

This arrangement is poor planning, I know. Just trying to deal with what I have.

 

I have a couple of idea that will work for you. I have to look up a couple of things to make sure of the ratings first. I will do that after dinner tonight.

 

No problem Jim. I'm happy to provide as much detail as necessary, all the way down to actual current draw of the various devices. Can do voice on my dime if that's easier for you. Whatever works

 

I think that the best way is to get a Gentran switch and mount it by the main panel you can then switch your UPS between utility and main power you then will run 2 wires from sump pump source to the gentran switch and tie it in from there. You do not have to worry about the neutral the Gentran takes care of that as well. There is no provision in the code that says that you have to disconnect the neutral when switching over to generator power. I have installed many auto start generators and the auto transfer switches just switch the hot legs.


By the diagram that you have you are only powering one sump pump and 1 ups. Is this what you actually want to power or is it for illustration purposes?

 

That is actually what I want to power.

The generator provides 240V @ 20A, one 120V 20A leg matches the 20A circuit for the sump pumps, so that leaves one 120V 20A leg for something else.

My server farm has a lot of built-in redundancy by design, and I took the time to pick off the critical pieces and put them on the one UPS. In an emergency, I can live with just that one UPS running, to meet service level agreements I have with clients. There is a contractual difference between "slow" and "completely dead" even though clients will complain the same

 

Well, wired it up per the diagram and tested all the outlets with a 1000W worklight.

No sparks, no fire, none of the wires are warm. So, I cut everything over permanently and dressed things accordingly.

Now to test the generator.... lol.

 

Please don't take this wrong but yes it works but it is not legal. I would really consider using a Gentran switch instead of the three way switches. God forbid something happen and your ins co sees something like that they may not cover the damages.

 

Yeah, that's a good point. Thanks for the tip. I'll get one as soon as I can.

 

Looking at various Gentran transfer switches, I see they connect to the main panel, or more precisely to several circuits in the main panel. Switching the sump pumps would be easy - they attach there.

How would I switch a circuit off a subpanel though? I think it's the same confusion I had originally, just in reverse?

 

Very easy, just run 2 wires (1 line and 1 load) from the subpanel where the sump pump is fed from. I wire will connect the breaker and go to the Gentran the other will connect to the wire that feeds the sump pump itself. Like I said dont worry about the neutrals, they are all joined and not broken through out the system.

 

Sorry to bring up an old thread, but I'm revisiting this because I'm replacing the four 1500va UPS units with two 3000va units of a different brand.

The wiring is easy, no sweat, but I do have a question about choosing an automatic transfer switch.

While I can go the generac/GE/Reliant $400+ route, I found a two-pole "RV" style unit that does 50A @ 240V with a 30 second delay to switch over to the generator and that's perfect for my application.

My question is... what is the obvious or not so obvious difference between RV stuff versus home stuff?

It's UL and CE listed/rated/approved, and in a NEMA-1 enclosure, even though it's supposed to be in an RV.

Any ideas?

Thanks!