Making an automatic transfer switch

[Bill Arden]

The generator is 5KW. The sub-panel is wired for 100A from the main panel. It would be easier to leave that alone. But I may reduce the breaker there. The loads on the sub-panel should be fine at 30A. The sub-panel is specifically configured to be only the backup loads.

My original intent was to get a generator in the 15KW range, but that seems unnecessary. There is also a very large jump in price between 60A and 100A breakers/ATS. I will run wire for 60A to the outside to allow for any future upgrade.

It looks like all you need is a manual transfer switch bracket for that sub panel and to add a 50 amp breaker from the main panel

It's ok to power the sub panel using a 50 amp outlet, 60 amp wire and a 50 amp side breaker. The key here is that the outlet has a 50 amp breaker and that all the house wiring is UL certified.

On the other hand, any transfer switch that is installed between the sub panels "main breaker" and the main panel has to be UL certified and rated for 100 amps.

That is why I'm saying it would be cheaper and easier to route the power to a smaller transfer switch threw a smaller breaker and then run the power back in the side of the sub panel.

Note: The small bracket on the sub-panel prevents the main breaker from being turned on while the side breaker is on.

Edit: The other advantage of this side-breaker plan is that you don't have to pull an electrical permit every time you change something since you can use 50 amp outlets to divide the "house wiring" from the transfer switch and generator.

Note: You will have to run a separate hard-wired ground wire between everything, but that does not require changing the house wiring.

Here is an image of a metal bracket Interlock for a sub-panel.
http://www.interlockkit.com/images/MEPanel033a.jpg

[maintenanceguy]

If you install a UL listed generator with it's UL listed ATS according to all the rules and codes and something goes wrong and it kills somebody, you don't go to jail.

If you self-engineer the most brilliant system ever seen by man without following all the rules and codes and without UL listing and it kills someone, you go to jail.

For the same amount of work and less liability, you could invent a freezer that will stay cold for longer in a power outage. I see CO2 tank with a solenoid valve that opens to trickle liquid CO2 into a dry ice generator when the power drops.

[alternety]

Do you perhaps have a link to the UL procedure for testing ATSs? Or the stamped metal plates that prevent you from manually turning the breakers to the wrong position before the other has been changed (kind of like a DPDT relay)?

[jwelectric]

Do you perhaps have a link to the UL procedure for testing ATSs? Or the stamped metal plates that prevent you from manually turning the breakers to the wrong position before the other has been changed (kind of like a DPDT relay)?

This is contained in the UL Standards and one must buy a copy of the Standard in question. Access is not available without cost. See UL Standard 1008 for transfer switches.

[jimbo]

First step in the procedure: take the item to be tested to a UL Certified Testing Facility. second step...pay the fee....Approx. $25,000

[Bill Arden]

For the same amount of work and less liability, you could invent a freezer that will stay cold for longer in a power outage. I see CO2 tank with a solenoid valve that opens to trickle liquid CO2 into a dry ice generator when the power drops.

*grins and says sarcastically* (no offense intended)

1. If you use R-744 Freon (Co2) or vent it without a license you will get a big fine.

2. You need a license to re-fill that Co2 tank.

3. Storing pressurized Co2 Tanks in a residence is also dangerous.

*sighs*
One thought would be a brine and water ice tank. There is a site (I can't remember the link) where this guy shows how his heat pipe based freezer works. It freezes ice during the winter and then stays frozen all summer.

Scaling this down could be as simple as packing some of those "blue ice" packs in the freezer and bottles of something in the fridge.

What I'm saying is that people have to chose between buying off the shelf items that are UL approved OR they can do "research" and build what they want to as long as it's not part of the house wiring.

I've done UL testing and it's more about liability and not about product safety. I once had a UL approved power strip short out and smoke. It was poorly designed and could have done more than smoke, but it was UL listed since the chances of it starting on fire was low.

We sometimes have to ask ourselves where we draw the line between safety and cost. In Europe for example they decided that outlets must be safer than here in the us. There outlets are huge and expensive. Here in the US on the other hand we allow people to drive while talking on cell phones...

[alternety]

Oddly I have had the same experience with a surge strip. Manufactured by a major computer company, UL rated. Power did not go out; the lights dimmed. The strip blew smoke all over the place. It did not start a fire (hurray UL) but I am not sure that it would not have done so with some paper dropped on it.

The reason I asked about UL procedure for the product is because I was curious if they did anything that actually evaluated the safety function of the device or just that it would not catch fire.

I don't disagree about the liability aspect of no UL label.

[jwelectric]

I would think that the job of a Nationally Recognized Testing Laboratory would go a little future than checking to see if something caught on fire.
One of the labs for UL is located in Research Triangle Park in Raleigh, North Carolina just a little over an hour from where I live. I get to talk with some of the persons that work with UL on a regular basis, see the Education Committee and look for my name as well as Mark Ode. Once you see that we sit this committee together then Google search Mark Ode or just click here Mark is one hell of a nice guy and will bend over backwards to help anyone he can.

The one thing that no NRTL can do is idiot proof anything that they test. A power strip will be tested at it rated amperage and voltage. Should someone buy one and load it in excess of its rating it will surly be damaged. Should someone buy a power strip and abuse it by throwing it in the floor and letting anything and every thing fall into it surly it will fail. Any of these would not be the fault of the NTRL but the fault of the end user.

I am sure that the power strips was never tested as they are being used below;

[maintenanceguy]

*grins and says sarcastically* (no offense intended)

1. If you use R-744 Freon (Co2) or vent it without a license you will get a big fine.

2. You need a license to re-fill that Co2 tank.

3. Storing pressurized Co2 Tanks in a residence is also dangerous.

Ok, we're way off topic here but I use one of these on a fairly regular basis. I have an EPA refrigerant cert but have never needed it to get a tank of CO2.

But I'm not serious about using one to keep a freezer cold in a power outage. No more than I would recommend designing your own ATS and connecting it to the power grid.

[Redwood]

OOOPS!
All the savings of making your own just went Bub-Bye!

[Mikey]

If you do ever build your controller, here's another feature to consider...

I have a 16kW generator and 200A whole-house transfer switch setup all UL-approved and installed by licensed electricians. When utility power fails, the controller waits a while before starting the generator, then waits for the generator to warm up before transferring the house to generator power. Fine. However, when utility power returns, WHAM! -- the house is immediately transferred back to utility power. And the airconditioner controller hard-stops, requiring a service procedure to reset it. Nobody knowlegeable from Carrier has ever told me why this happens, but the installer, AC repair guy, and I kind of agree that the transfer presents a phase change to the AC controller that freaks it out, and it hard-stops the unit to avoid further damage. Carrier (who, BTW, market the entire generator/transfer switch package under their own brand) says my only option is to run the system in manual transfer mode.

Which brings me to my point -- if you're building your own controller, you might consider inserting a delay when transferring back to utility power, to give fussy controllers time to recognize a power failure and take appropriate measures. My AC controller, for example, won't restart for a short period after a recognized power failure. I'm pretty sure I can modify my ATS to accomplish this, but it's a low-priority item on my list right now.

[alternety]

Thank you. I was aware of this. I kind of figured a commercial ATS would know about this. You can't do a simple switch back to the grid with some stuff. As you note, you need to open the generator link, wait, and then connect the grid. It can also damage electronics controlling motors.

There is a way around it but it is expensive. You make a whole house UPS. The inverters built to grid connect renewable energy sources sync their phase with the line. They have an internal ATS that can switch each way in milliseconds. But it means having expensive inverters and a battery bank. You could make the battery bank small and use your backup generator as a continuous charger. If you bought a bunch of battery, you could run the generator intermittently at mostly full power just when the batteries need charging. The idle/low load fuel consumption of a generator can add up during a long outage. This would probably save fuel; but I have no supporting data. You have a number of losses in this configuration. Rectifying and controlling the charging current, chemical conversion on both charge and discharge, inverter losses. If you have some sort of wind, water, or solar electricity, this is the way to go. Unfortunately I have no such resources available.

[maintenanceguy]

I manage a dozen sites with back up generators. One of these has an ATS that "watches" the power utility sine wave when power is restored and waits until both the generator and POCO sine waves are in sync before transferring back to the normal (POCO) position. This typically takes anywhere from 5 to 20 minutes.

I'm not really sure of the advantage since it takes nearly 10 seconds to transfer to the generator during a power outage but at least the transfer back is smooth. (?)

[Mikey]

I manage a dozen sites with back up generators. One of these has an ATS that "watches" the power utility sine wave when power is restored and waits until both the generator and POCO sine waves are in sync before transferring back to the normal (POCO) position. This typically takes anywhere from 5 to 20 minutes.

I'm not really sure of the advantage since it takes nearly 10 seconds to transfer to the generator during a power outage but at least the transfer back is smooth. (?)

I'd love to know the make & model of that switch. The advantage is you don't fry sensitive controllers, and continuous power is maintained. I can do without the latter, but the former is pretty important.

[alternety]

Be careful about basing the transfer on phase congruity. You generator, if it is an inverter type like mine, probably does not vary enough to work properly. Most any mechanically controlled generator will probably drift; but no idea how quickly.