Generator Transfer Switch Question

[CompactTractorFan]

With all the talk about generators recently, I was think back to this question I had back when were were looking into purchasing a generator:


Let's say you have a nice big 15kw generator, like this one: Generac 5734 Portable Generator - GP15000E - 15,000 Watt Electric Start Portable Generator). You want to hook up a 50 amp manual transfer switch like this one: Reliance Controls Q510C - 50-Amp (120/240V 10-Circuit) Transfer Switch w/ Interchangeable Breakers (the 50 amp/12,500 watt unit is the biggest they make in this style)

The switch is rated for 50 amps/12,500 watts. The generator is rated for 63 Amps @ 240 Volts/15,000 running watts. It has one 50 amp (240v x 50 amps = 12,000 watts) outlet among other smaller ones. Assume you have the proper 50 amp cord going from the generator to the transfer switch inlet. Would it be safe and legal to use the higher powered generator with the smaller transfer switch???

The wattage coming from the largest generator outlet should be less than the 12,500 watt max input for the transfer switch, right?

 

[schmism]

youll never pull more current through the breaker that protects the transfer pannel, than what the breaker is rated for.

Think of it this way... the "grid" that powers your house is a generator (which the power plant is) capable of putting out 300 MW or 300,000KW. but the wireing and breaker that feds your house is only capable of 200 amps. certantly much less than the 300MW that the generator can put out.

in short as long as the cord and recepticals are matched to the transfer pannel, you could power it with a full size power plant and it wouldnt matter to the plug/receptical/transferpannel

 

[JHTFarmer]

Shouldn't the transfer switch be rated above the amperage required for the generator or that of the line supply to the home, whichever is greater?

i.e., if your are powering your home with a little 15kw generator but have say 200 amp service to the home don't building codes require installation of a transfer switch rated above 200 amps?

 

[Larry Caldwell]

Just install a whole house transfer switch and load balance using your breaker panel. The smaller transfer switches require a lot of rewiring, and if you someday add a load not covered by the transfer switch you are out of luck. Generlink has a meter base transfer switch that doesn't require any rewiring at all, it just mounts under your watt meter. You can use any size generator you want, so if you replace your generator someday with a larger one, you will be all set.

 

[techman]

I have found if you don't need an automatic transfer switch, then the best solution is: Generator InterLock Kit

You just need to add a breaker and this kit and you can power your entire panel. Safe and easy.

here is my panel:



paul

 

[Stimw]

I have found if you don't need an automatic transfer switch, then the best solution is: Generator InterLock Kit

You just need to add a breaker and this kit and you can power your entire panel. Safe and easy.

here is my panel:

View attachment 272649

paul

That's a pretty slick way to handle the transfer but they sure are proud of it at $149.00 !!!

 

[techman]

That's a pretty slick way to handle the transfer but they sure are proud of it at $149.00 !!!

Well the picture is my own version, based on those available for purchase. Of course it is best to show the commercial product that is UL approved. For many people it is not worth the time to do a DIY. The price is a bit high, but much lower than the other transfer switches discussed.

Paul

 

[Highbeam]

I dislike those small generator subpanels. They only allow a few circuits to be transfered. Much better is the interlock kit. I replaced my whole house panel with a generator panel that has a version of the interlock built into the cover. Great idea.

It is nice to have all circuits powered up during an outage. I can walk into the bathroom and flip the switch on and there is light. Just like normal. Bad part is that you don't know when the line power is back on.

 

[techman]

Bad part is that you don't know when the line power is back on.

I solved that problem with a small pilot light on the panel (looking at my panel's picture). It is a neon light (1/25 watt) mounted on an insulator with a spring contact to touch the main lug on the main breaker. Small fuse for protection in wired-in. The light will always show utility power no matter the position of the main breaker. Only thing is I need to occasionally go to the basement to check the indicator light.

paul

 

[bobm6996]

This is exactly what I did last year and it works great.

 

[General Lee]

I have found if you don't need an automatic transfer switch, then the best solution is: Generator InterLock Kit

You just need to add a breaker and this kit and you can power your entire panel. Safe and easy.

here is my panel:

View attachment 272649

paul

I think this is what the electrician I had come out today was referring to. I told him I am purchasing a 12-15Kw generator capable of 50 amps. I was expecting to have a separate sub panel for generator use, but he said a transfer switch installed over the main breaker would serve the same purpose and I control my existing panel. Does this sound correct?

 

[clemsonfor]

SOO, if i was going to do this without the interlock kit, just saying. I would connect my generator via my 30 amp plug in the house and then back feed the panel. But the main breaker will be off isolating my panel from the grid allowing me to run my whole house up to the capacity of my generator? I know if i were to do this it would be illegal as there is not disconnect that will not allow the grid to be energised, but say i were to do what i said this is how it works right?

 

[wyeguy]

That's how it works, clemsonfor, and how utility workers like me get killed when someone makes a simple mistake.....

I am the modern man...my smart phone smells of diesel & grease.

 

[AJE]

There are interlock switches that are much cheaper than the one in the link posted. I found one for my Square D Panel for $55.

Of course I had never heard of them when I purchased my transfer switch a couple of years ago....

 

[General Lee]

Are there any benefits of using a transfer power switch/box over the interlock kit? Only thing I really see is with a transfer power box you'll have specific/dedicated circuits you can only run instead of possibly turning on to many circuits from the original panel and overloading the genny.

 

[bdeboer]

I have one of these at my house:

GenerLink.com - About GenerLink - The easy way to connect a home generator

Purchased/Installed through the local electric co-op for roughly the internet price. The only thing I had to do was put my generator plug on the end of the pigtail they supplied.

 

[CompactTractorFan]

Interesting...I had not read about interlock kits. So you could install a 50 amp breaker, interlock kit, and inlet plug and run the genny through that via a 50 amp cord attached to the 50 amp genny outlet. If too much current came through it would trip the dedicated 50 amp "generator breaker" on the panel. Right?

 

[aczlan]

That's a pretty slick way to handle the transfer but they sure are proud of it at $149.00 !!!

I agree. Looking at going with a meter base with a 200 amp breaker/passthrough (this one) a interlock kit for another $40 and a generator breaker for another $9 (ie: this or smaller)
Then I can also run some other power I need to run at the same time.

Interesting...I had not read about interlock kits. So you could install a 50 amp breaker, interlock kit, and inlet plug and run the genny through that via a 50 amp cord attached to the 50 amp genny outlet. If too much current came through it would trip the dedicated 50 amp "generator breaker" on the panel. Right?

Yes. The 50 amp breaker could also be replaced with a smaller one to match your generator size if needed.

Aaron Z

 

[clemsonfor]

yes tractor fan. Your right. If you pull to much power your Genny has a breaker or a reset that will trip, you cant pull more power through the properly sized breaker as the jenny cant put more to it. if you overload any one breaker that will trip.

 

[Pirate]

I put in an interlock kit. I think my "input" breaker is only 30amp though, I can't remember. I also cut a hole in the upper panel cover and installed two wattmeters. When on the generator, I can watch my load balancing. It is a nifty system with one quick plug on the outside. Of course, since I installed it, I haven't had a single power outage.