Generator Transfer Switch

[SoonerAviator]

Tulsa had a derecho come through last week with 100mph winds which took out power to about 250K people for several days (some up to a week) and I came to the realization that I'd like to get a transfer switch put it for the house. We were only without power for 2.5 days, so it wasn't some traumatic ordeal in the least, but others aren't so fortunate. We had a "portable" generator given to us by the FIL, which was portable in the loosest terms as it weighs about 300lbs (15K watts, 22.5 surge) and makes one heck of a racket with a 992cc/30HP engine.

Long story short, we were going to back-feed the house via the 30A welder circuit (main breaker off, no lineman to be harmed in the making of this film) in the garage but I looked at the wires and wasn't comfortable with it, especially given that it was some contraption my FIL had wired (4 prong 50A generator plug converted to 3-wire (no neutral)) which would have been wired into the 4-wire welder circuit on my house. I ended up just running a few 110V extension cords to the refrigerator in the house and the deep freezer in the garage to keep food from spoiling.

I would rather just have a transfer switch/generator receptacle wired in next to the circuit breaker on the outside of the house so that we can just do a 4-prong 220/50A straight across. Any thoughts on the best type of transfer switch for this exercise? I have no problem manually selecting which breakers to run, and the generator won't be in place year-round so I doubt that an automatic transfer switch makes any sense unless there are features I don't know about.

 

[Archer Jack]

I lived in Tulsa back in the 80's and don't ever recall hearing the term "derecho." What is that? I know the Spanish meaning. Is that a term for tornado? Thanks.

 

[Bell206]

Any thoughts on the best type of transfer switch for this exercise?

You can also use a mechanical interlock kit to back feed from a generator that meets electrical code. You buy it for your specific main panel by make and model along with an appropriate rated breaker. You wire the outside "generator" plug to the back feed breaker and the interlock bracket will only allow either the main service breaker to be engaged or your back feed breaker engaged. I think it was $60 for the interlock kit for a Siemans panel and I had an extra 40A 220 breaker. I made up a 75ft cable and went from the generator 30A outlet to the house outlet. I color coded all the breakers on which one could be on when on generator. Below are a couple pics.

 

[Sac Arrow]

I'm a little confused. When you say four wire, do you mean three phase?

 

[Stewartb]

I had a bypass switch on my last house and have a blocking type isolating switch on my new house. Both have 250v male plugs to accept a female extension cord end.

 

[SoonerAviator]

I'm a little confused. When you say four wire, do you mean three phase?

220V - (2) 110 wires, 1 bonded neutral, 1 ground. Most new construction uses 4-wire 220V outlets these days. Older construction uses 3 wire (2) 110 wires, 1 ground).

 

[SoonerAviator]

I lived in Tulsa back in the 80's and don't ever recall hearing the term "derecho." What is that? I know the Spanish meaning. Is that a term for tornado? Thanks.

Eh, it's more common in the desert southwest with dust storms. Basically a large wall of straight-line winds generally associated with a big gust front. Tornados are generally fairly localized with regard to extreme winds and damage path. The derecho took out powerlines, trees, etc. across a 30+ mile swath across the metroplex.

 

[Stewartb]

My old house had a switch like this with a male plug installed in the bottom. No current went to the plug when the bypass was off. I attached the gennie cord and threw the switch. I liked it better than the blocking switch I have now but not enough to change what sparky installed. I have a 6kw Honda inverter (quiet) gennie for Alaska and a Generac 6kw standard (loud) gennie for Texas. Both have plenty of power to run forced air, lights, etc.

https://www.amazon.com/SIEMENS-Gene...64-9789-3e0859bab12f&pd_rd_i=B07PS6F5PV&psc=1

 

[Racerx]

I lived in Tulsa back in the 80's and don't ever recall hearing the term "derecho." What is that? I know the Spanish meaning. Is that a term for tornado? Thanks.

I swear weather people keep making up new terms just for the clickbait. Derecho I have actually heard before. Now... bomb cyclone, atmospheric river, and polar vortex... I dont recall reading about them in the Aviation weather handbook...Derecho on the other hand is actually in there. page 22-6

 

[Morgan3820]

I lived in Tulsa back in the 80's and don't ever recall hearing the term "derecho." What is that? I know the Spanish meaning. Is that a term for tornado? Thanks.

Derecho is a long lived straight line winds storm of great intensity. Up to 100 mph. I witnessed one such event on the upper Chesapeake. Sank a bunch of boats. Killed five people. Lasted about 45 minutes. Peak winds 105 mph at Martin State airport.

 

[ElPaso Pilot]

You can also use a mechanical interlock kit to back feed from a generator that meets electrical code. You buy it for your specific main panel by make and model along with an appropriate rated breaker. You wire the outside "generator" plug to the back feed breaker and the interlock bracket will only allow either the main service breaker to be engaged or your back feed breaker engaged. I think it was $60 for the interlock kit for a Siemans panel and I had an extra 40A 220 breaker. I made up a 75ft cable and went from the generator 30A outlet to the house outlet. I color coded all the breakers on which one could be on when on generator. Below are a couple pics.
View attachment 118418

View attachment 118419

Yes, but not compliant to code in all areas. May want to check if that's important to you.

Some of these are attached to the cover, and are defeated when the cover is removed.

 

[SoonerAviator]

My old house had a switch like this with a male plug installed in the bottom. No current went to the plug when the bypass was off. I attached the gennie cord and threw the switch. I liked it better than the blocking switch I have now but not enough to change what sparky installed. I have a 6kw Honda inverter (quiet) gennie for Alaska and a Generac 6kw standard (loud) gennie for Texas. Both have plenty of power to run forced air, lights, etc.

https://www.amazon.com/SIEMENS-Gene...64-9789-3e0859bab12f&pd_rd_i=B07PS6F5PV&psc=1

Yeah, this was a Generac unit, but man is it loud. Not that important I guess, but definitely going to be noticeable. It's enough to run one of the 5Ton HVAC units plus most of the other 110V stuff in the house. Probably won't run both HVAC units though. Who knows, maybe I'll pony up for the 24K watt Generac permanent standby generator, but those are about $6K installed which is pretty steep for covering the few days my power has ever been out in over a decade.

 

[Bell206]

Yes, but not compliant to code in all areas. May want to check if that's important to you

The interlock meets code here which was the reason I went with it. This one installs under the front panel. And a lot cheaper than a transfer switch. But its not as nice as the generac 24kw I have now with auto transfer.

 

[Randomskylane]

I swear weather people keep making up new terms just for the clickbait. Derecho I have actually heard before. Now... bomb cyclone, atmospheric river, and polar vortex... I dont recall reading about them in the Aviation weather handbook...Derecho on the other hand is actually in there. page 22-6

We didn’t know what it was about 10-12 years ago in the dc area… but it knocked out many thousands of people for a week or more

 

[texasclouds]

 

[Dave Theisen]

I swear whether people keep making up new terms just for the clickbait. Derecho I have actually heard before. Now... bomb cyclone, atmospheric river, and polar vortex... I dont recall reading about them in the Aviation weather handbook...Derecho on the other hand is actually in there. page 22-6

That’s because any weather bad enough to have a cool name, you don’t want to be flying in.

 

[EdFred]

Just spring for the standby whole house unit powered by NG or propane. Power is off for 10-20 seconds before it kicks on.

 

[Racerx]

220V - (2) 110 wires, 1 bonded neutral, 1 ground. Most new construction uses 4-wire 220V outlets these days. Older construction uses 3 wire (2) 110 wires, 1 ground).

In my neck of the woods they mandate metal conduit be used throughout and that's the ground.

 

[Dana]

You can also use a mechanical interlock kit to back feed from a generator that meets electrical code. You buy it for your specific main panel by make and model along with an appropriate rated breaker. You wire the outside "generator" plug to the back feed breaker and the interlock bracket will only allow either the main service breaker to be engaged or your back feed breaker engaged.

I have the same setup, except the interlock is a sliding plate on the front of the panel. Made the plate myself.

 

[Zeldman]

Eh, it's more common in the desert southwest with dust storms.

Where folks in Arizona calls 'em haboobs...

Dust storms (also called “haboobs”) are unexpected, unpredictable and can sweep across Arizona's desert landscape at any time. Dust storms can be miles long and thousands of feet high.

EDIT: I found there is a difference between Haboob and Derecho...

Haboob, is a large dust storm. They often form suddenly and can have winds over 40 mph kicking up a tremendous amount of dust and dirt. Derecho, a large line of straight-line winds that often create damage. The definition describes a line of over 200 miles in length with winds of at least 58 mph

 

[SoonerAviator]

Where folks in Arizona calls 'em haboobs...

Dust storms (also called “haboobs”) are unexpected, unpredictable and can sweep across Arizona's desert landscape at any time. Dust storms can be miles long and thousands of feet high.

EDIT: I found there is a difference between Haboob and Derecho...

Haboob, is a large dust storm. They often form suddenly and can have winds over 40 mph kicking up a tremendous amount of dust and dirt. Derecho, a large line of straight-line winds that often create damage. The definition describes a line of over 200 miles in length with winds of at least 58 mph

Not real sure why there needed to be a distinction between it but the weather-folk have to justify their existence somehow lol.

 

[SoonerAviator]

In my neck of the woods they mandate metal conduit be used throughout and that's the ground.

Not a whole lot of metal conduit being used in residential builds anymore, so there's nothing for it to be bonded to if you dont link the ground in each box. Hence why they moved to bonded neutral breaker panels. My home is a bit unique in that it has all metal outlet boxes and conduit, but the breaker panels (and the garage subpanel where I have the welder circuit) are newer because I had them replaced when I did the garage addition on the house. So I have the bonded panels AND metal conduit. Either way I just need a code-compliant way to connect a sizeable portable generator.

 

[Bell206]

In my neck of the woods they mandate metal conduit be used throughout and that's the ground.

All mine is 4 wire by code. I was told if there is a break in the conduit you can become the ground which unfortunately led to some local deaths.

 

[Stewartb]

We have a Generac store in my TX town. They only sell big standby units. I can’t imagine who needs 10kw and bigger generators, and 20kw is the smallest they had that I saw. We have a heat pump and one variable speed AC. I can run everything I own on a 6k generator as long as emergency heat isn’t on, and we added a gas fireplace for that. Maybe they drive Teslas.

 

[ElPaso Pilot]

We have a Generac store in my TX town. They only sell big standby units. I can’t imagine who needs 10kw and bigger generators, and 20kw is the smallest they had that I saw. We have a heat pump and one variable speed AC. I can run everything I own on a 6k generator as long as emergency heat isn’t on, and we added a gas fireplace for that. Maybe they drive Teslas.

In both my last two houses, my 6K generator will puke trying to start the older whole house a/c unit.

Your fancy variable speed probably helps that out.

Depending what chart I pull up I see 3500 watts / ton of cooling.

https://energytoday.biz/blog/what-s...e generator can,to power any other appliances.

 

[Bell206]

I can’t imagine who needs 10kw and bigger generators,

Depends on your location, fuel, and loads. The 24kw is only rated to 21kw on NG or 88 amps. With both of my AC units running and a normal load I pull 65%-70% load on LP which is rated at 24kw or 100A continuous. However, with start up surge I would pop the 100amp gen breaker until I installed soft start kits on the AC units. In heat mode with only one electric heater running it would hit 82 amps. Generac upped the residential line to 24kw based on their experiences around the GOM over several hurricane seasons where the 20-22Kw units basically burnt themselves up over a short period running at 90-100% loads.

 

[Albany Tom]

Suggest something like this for the transfer switch:

https://www.amazon.com/dp/B000BQN4T2

It's simple to setup. Basically, you extend the output of a couple of circuits from your panel to the transfer switch. Then there's one line that goes from the transfer switch to an outside reverse outlet. The transfer switch is configured so it can only connect a circuit from either the main house feed OR the generator, but not both.

It looks a little weird, but it works and it's safe, and less expensive than a switch that will handle the whole house, and probably less expensive than a separate transfer switch and a secondary panel. Friend of mine has one, they work great with a portable generator.

And I made a non-sarcastic post!

 

[donjohnston]

In my neck of the woods they mandate metal conduit be used throughout and that's the ground.

Found the guy from the Chicago area!

 

[Bob Noel]

We have a Generac store in my TX town. They only sell big standby units. I can’t imagine who needs 10kw and bigger generators, and 20kw is the smallest they had that I saw. We have a heat pump and one variable speed AC. I can run everything I own on a 6k generator as long as emergency heat isn’t on, and we added a gas fireplace for that. Maybe they drive Teslas.

Freezer, Frig, lights, HVAC circulating pumps, AC units. 2nd frig. It's easy to exceed the capacity of a 6kw unit.

I had a 6kw standby generac. When the small motor in it died, I changed to a whole-house 20kw unit.

 

[EdFred]

Freezer, Frig, lights, HVAC circulating pumps, AC units. 2nd frig. It's easy to exceed the capacity of a 6kw unit.

I had a 6kw standby generac. When the small motor in it died, I changed to a whole-house 20kw unit.

Electric range, hot tub, (don't need it freezing out when power is out for 10 days in the winter.)...

 

[Gary Ward]

We have a Generac store in my TX town. They only sell big standby units. I can’t imagine who needs 10kw and bigger generators, and 20kw is the smallest they had that I saw. We have a heat pump and one variable speed AC. I can run everything I own on a 6k generator as long as emergency heat isn’t on, and we added a gas fireplace for that. Maybe they drive Teslas.

10KW is small for a whole house genset, 22-24KW is what I see the most when supplying gas to them.
I am not a Generac fan as I have had 3 different ones and they are cheap generators if you ask me.'
I'd buy a Kohler before a Generac.
I am still using a 8KW diesel genset in our RV to back up my home where everything is LP gas powered so not many amps needed. RV sit's there with 2-100 gallon diesel tanks full which will give me over 2 weeks run time and no moving or refilling geneset.

 

[EdFred]

So when the power is out, what are you guys planning on running that you need 24KW of backup power? If I turn EVERYTHING on in my house and workshop, I won't come close to hitting that number.

 

[Gary Ward]

So when the power is out, what are you guys planning on running that you need 24KW of backup power? If I turn EVERYTHING on in my house and workshop, I won't come close to hitting that number.

Mainly need that much power for AC and hot tubs in the winter time to keep them from freezing. And your electric stove if you want full function of your appliances. Then maybe a little extra to help your neighbor out that does not have genset back up.

 

[asicer]

So when the power is out, what are you guys planning on running that you need 24KW of backup power? If I turn EVERYTHING on in my house and workshop, I won't come close to hitting that number.

I'm not even sure I have that much service from the utility company.

 

[Gary Ward]

I'm not even sure I have that much service from the utility company.

I don't I only have 200 amp service but I live in a small home.

 

[PaulS]

I put in a 24kw Generac last fall and have used it now about 4 times, longest 3 days. It came with a 100 amp automatic switch and it works great. Power went out 2 nights ago during a thunderstorm, wait about 30 seconds and viola, we have lights. I have a 4 ton ac unit, which ran fine on the generator. I wanted a generator that I didn't need to worryy about shedding loads to keep it working. I have a 400 gallon propane tank to power it, I figure it will run at least 30 days if it starts out full. The generator with switch was about $6k from Leows. Then I had to have it installed, which wasn't too bad, plus I had a propane tank and piping installed.

 

[Bell206]

what are you guys planning on running that you need 24KW of backup power?

If I turn everything on in my all electric house I will exceed the 100A limit on my 24kw generator. So with 2 AC units running I will manage the load to keep it at 60% or so and since generators do not have unlimited surge ability like a main service does, keeping the load at 60-70% allows for surge loads. With my previous portable 8000kw set up I couldn't run the ACs and was limited with other loads.

I'd buy a Kohler before a Generac.

At the standby level I found Generac to have an edge over other brands but not much as most are built to the same spec. When you get below standby I wouldnt buy a Generac either and only use Honda portables unless I consider the generator a throw away item and go B&S or Northern Tool.

 

[rwellner98]

I'm entirely off-grid in Mexico and our peak loads (including AC and pool pumps, no electric stove) barely touch 10kw. If I'm buying a backup generator, for a utility fed house, I'm buying the smallest I think I can get by with, rather than spending a bunch more to not have to modify my lifestyle even a tiny bit for a few days every other year. For me, I'd be powering fridges, lights, microwave, TV. I'd be skipping AC, electric stove, hot tub. Hopefully my Mexico house will have utility power soon and we'll be out of the business of maintaining batteries sufficient for AC. At that point we'll rewire the system to have the house be able to access the batteries, but not the AC. This will allow the house to operate indefinitely on degraded batteries except without AC.

 

[SoonerAviator]

As mentioned, 24kw would probably be my minimum if I went whole-house. It's not about needing that much for continuous power output, but we have two HVAC units (a 5-Ton and 3.5-Ton) which are fairly old/inefficient and will draw a bunch of power when starting up. The 5-Ton alone probably needs over 10K watts to start-up and occasionally pops the 30A breaker it's on as it is. With the ability to plug in a portable generator I can at least select which circuits to run (probably the 5-ton HVAC since it cools everything except the Master bedroom and kitchen). Less of an issue in the winter when we don't need high-draw loads from the heater which is natural gas fired. When it's really hot and humid, the family gets a bit cranky when it's time to sleep lol.

 

[EdFred]

Mainly need that much power for AC and hot tubs in the winter time to keep them from freezing. And your electric stove if you want full function of your appliances. Then maybe a little extra to help your neighbor out that does not have genset back up.

We went through, and figure with the AC or the hot tub running (don't need to have both since, if it's blazing hot that we need the A/C the tub won't be in use), plus the electric stove, plus the electric dryer, the fridges, etc, we would still be fine with everything else in the house running and that was at 13k. and if I needed to run some items in the shop, I'd still be fine.