Another generator thread (transfer switches, portable vs. standby whole house)

[aunsafe2015]

I read through the other generator thread and have some questions for the collective wisdom of the forum.

1) Can somebody briefly explain a "Service Disconnect" vs a "Load Center" style transfer switch? I see some that are referred to as "Service Disconnect" switches, such as this one: https://www.electricgeneratorsdirect.com/Kohler-RDT-CFNC-200ASE/p2207.html. The other main type I see are apparently called "Load Center" transfer switches, like this one: https://www.electricgeneratorsdirect.com/Generac-RXG16EZA3/p77439.html.

Am I correct that the "service disconnect" style connects to your main breaker and would be easier to wire because you do not have to wire each individual circuit? And it provides power to every circuit in your main breaker box? And that with the "load center" style, you select some number of circuits from your main breaker and the "load center" disconnect switch is almost like a subpanel?

With a "service disconnect" style breaker, what happens if you try to use more power than the generator can provide? Your entire house shuts off?

2) Apparently Generac makes "portable" style gas powered generators up to 17.5 kW: https://www.electricgeneratorsdirect.com/Generac-5735-Portable-Generator/p2685.html?akamaifeo=off. The main alternative I'm considering is a natural gas standby type such as https://www.electricgeneratorsdirect.com/Kohler-14RESA-Standby-Generator/p8198.html.

The portable type would presumably be cheaper b/c all I'd have to do is get a transfer switch wired up. The standby type would require a new gas line and probably a meter upgrade to handle the extra BTU requirements, as well as clearing a space, creating a pad, etc. I suppose the benefit of the standby is that it would automatically switch over, I would never have to refuel it to maintain power. I guess it would probably also be quieter.

In terms of the "quality" of the power generated by each, is "total harmonic distortion" (THD) the relevant measure? I saw one review claiming the Generac portable is <5% THD, which is the same as most of the whole-home standby styles. Does that mean the Generac portable would provide the same quality power as the standby types? And at < 5% THD would be safe for things like TVs, computers, etc?

Thanks in advance for any input.

 

[theoldwizard1]

You need to backup a couple of steps and explain "WHAT IS YOUR GOAL ?"

Do you want a backup generator your WHOLE HOUSE, including well pump, sump pump, A/C, electric water heater, electric clothes dryer and electric stove ? Then don't mess around with a "portable" system. With that 17.5kw "portable" generator, 50 gallons of fuel will only last a few days at best. That Kohler would require a lot more $$$$ pieces to get installed. Have a whole SYSTEM professionally installed.


If your goal is to get through an outage from a storm, you have municipal water, a small sump pump, can live with a microwave and coffee pot, a gas forced air furnace, a couple of fans and maybe a window A/C, then a 2kW-3kW inverter generator is all you need and 20 gallons of gas will last you 5+ days.

If you go with the second option, you will have very low THD and it can be easily wired into an existing breaker panel through a "generator interlock" (no 240V appliances).

 

[wyliesdiesels]

I agree with above.

Need to define the loads you want to run in an outage.

As far as the service disconnect vs. load center style transfer switch:

The service disconnect style transfer switch is actually more complicated since it will go between your meter and current main service panel.

Thats why its rated for use as service equipment.

This complicates things because you need to have the power shut off to wire it in, and you also need to rewire the current main service panel and change it to a subpanel.

This means running a new 4-wire feeder(if existing service entrance wire is 3-wire and not in pipe) and changing the neutral bonding so that the neutral bar is now isolated(can only have one neutral bond on the service and the new service entrance TS should have this bond). You will probably need to buy a ground bar for the subpanel. If this panel is obsolete, this may prove to be a chore to find listed parts. Also, any ground wires on the neutral bar need to be moved over to the new ground bar AND the GEC from the grounding electrodes, as well as bond wires from metal plumbing such as water and gas lines, need to be moved over to the TS...

So a service rated TS can be just as much work if not more than a load center style transfer switch.

But we couldnt tell you which would be easier since we havent seen your electrical system.

 

[wyliesdiesels]

And yes if you use more power than the generator breaker is rated for, the breaker will trip and out go the lights...

 

[High5]

When calculating load be sure to check the startup current draw. In numerous cases, it could be dramatically higher. As an example, we have a grinder pump for the sewage system. At startup, it draws 6,500 watts. During operation, it drops to 500 watts.

 

[yeldogt]

It does get confusing -- there are transfer switches not rated as SE. The SE panels have a disconnect. When installing a "whole house" generator the transfer switch sits after the meter and before any breakers (load center). Must be able to disconnect the power in that box before the auto switch .. otherwise it would always be live. The SE transfer switches have a disconnect (breaker) in them . The non rated ones don't have the disconnect and are for use "downstream" after another disconnect. The existing panel of the house does actually become a sub panel as far as wiring and grounding requirements.

Years ago when there were less options in generators available, the typical way to install a backup generator was to pick those items most important and pull them out of the existing panel and connect them up to the panel supplied with the generator. This panel contained the transfer switch and was also a load center (the breakers are the load center) -- so you wired the items from the main panel to these breakers. The new supplied panel .. became a sub panel to the existing panel using a double breaker in the existing panel (that was the disconnect for the new transfer switch) I have this setup at my beach house -- it's a small 7k unit and it keeps the most important stuff going in the summer (not the AC) .. but, especially the heat in the winter. It's almost 20 years old .. I'm not sure they even had consumer based 22k units back then .. if they did they were few and expensive. Naturally -- after installed they ran a new main cable to the island and we never lose power anymore.

Today with the many choices and the small cost difference -- it's often not much more to simply install a lager unit -- say 22k and do the whole house. This is when you need the SE rated panels. They get installed between the meter and the old panel and the generator gets hooked to the transfer switch. The only problem with this set up is many local officials require a house load be recorded to make sure the generator will not be overloaded should items be running and the switch over occur .. I just did this and mine required what is called "load shedding" -- it's done through relays. The generator can shed high amp items if too many are running at once -- say and electric oven ..or dryer. Mine was all new build -- So no rewiring. I wanted to stay with an air-cooled unit due to fuel usage (propane). With natural gas available -- this is less of a concern.

So, you need to figure out what you want to run and how the total costs add up -- don't just reject a larger unit as being too expensive until you get the actual costs

 

[rjcnaples]

1. A “Service rated” auto transfer switch. Has a “main” breaker built into it. This breaker turns into your property main shut off.

They also have a higher current interruption rating for the breaker usually 22KAIC or larger because they are usually connected after the “meter” but before any panels.
Most of the breaker in residential panels are rated at 10KAIC.

This set up is used for “whole house” power. Meaning that every circuit has the ability to operate. Usually not simultaneously, but with supervision. Unsupervised operation you need a generator sized larger.

Generator load panels mount close to your existing panel.
A power supply feed from the generator is run to it. Then a 120/240 volt feed from the existing panel is connected to the generator load panel for “ normal” power condition.
Then using the pre wired tail supplied with the generator panel individual circuits are transfer over to the new panel.
When you complete that several breakers in your existing panel will now be “spares”.

All generators have a max breaker rating sized into them. And when selecting a unit first determine what it is you need to operate, when what you would like to operate.
Keeping in mind that the larger the unit means. More fuel to operate. With a little supervision as to what breakers to turn off untill needed for the 1/2 hour of water heating, laundry, cooking.
You can get by with 15KW TO 7KW. Will it be a total unsupervised system that runs everything at any time no.
But it will keep you with lights, food and at bedtime cool or warm with manual operation.


Sent from my iPhone using Tapatalk

 

[aunsafe2015]

Thanks for all the responses. Especially helpful to learn more about the transfer switches.

 

[checkthisout]

The portable type would presumably be cheaper b/c all I'd have to do is get a transfer switch wired up. The standby type would require a new gas line and probably a meter upgrade to handle the extra BTU requirements, as well as clearing a space, creating a pad, etc. I suppose the benefit of the standby is that it would automatically switch over, I would never have to refuel it to maintain power. I guess it would probably also be quieter.

You can use an interlock with your portable setup. You get power to every circuit of your choice with minimal cost.

Of course I think those are only available for SquareD panels.

If you are old or physically limited or the generator will be for people who are as such, then the automatic standby type is the way to go.

If you're young and dapper then a simple portable setup with a transfer switch or interlock will save you some serious cashola.

 

[Jim_No_Garage]

You can use an interlock with your portable setup. You get power to every circuit of your choice with minimal cost.

Of course I think those are only available for SquareD panels.

If you are old or physically limited or the generator will be for people who are as such, then the automatic standby type is the way to go.

If you're young and dapper then a simple portable setup with a transfer switch or interlock will save you some serious cashola.

I can confirm what checkthisout just typed about people with limitations and manual setups.

My Dad is in his late 80's and I set him up with a manual interlock setup for his "already owned" 3500 watt generator.

He had a power outage during a snowstorm last winter and things did not go well at all. He had to get a snowblower out to clear the patio for the generator. Then lug the generator out and start it. He then had to connect the generator and flip the interlock.

He can afford a NG powered unit that would have kicked on automatically but doesn't think he needs one.

Cheers

Jim

 

[jkeyser14]

I can confirm what checkthisout just typed about people with limitations and manual setups.

My Dad is in his late 80's and I set him up with a manual interlock setup for his "already owned" 3500 watt generator.

He had a power outage during a snowstorm last winter and things did not go well at all. He had to get a snowblower out to clear the patio for the generator. Then lug the generator out and start it. He then had to connect the generator and flip the interlock.

He can afford a NG powered unit that would have kicked on automatically but doesn't think he needs one.

Cheers

Jim

Even a NG unit wouldn't have helped him if it was buried in snow...

 

[Bretny]

One thing to remember is your going to need to find fuel for those generators. That "portable" one uses 16gal in 10hrs at 50 percent load. Your going to need 38gal to run that for 24hrs. So your basicly going to need a pickup truck bed full of 5gal cans to run it for even a few days.
Have you ever tryed to buy gas in a real wide spread emergency? This is why i push people to get a small gas generator or go nat gas/propane. Or if your really serious about it get a diesel.

Also all the fancy transfer switches, load sheding and automatic start dont help when you have to spend 4hrs in a line at the gas pump just to buy a 5gal jug.

 

[crucible]

One thing to remember is your going to need to find fuel for those generators. That "portable" one uses 16gal in 10hrs at 50 percent load. Your going to need 38gal to run that for 24hrs. So your basicly going to need a pickup truck bed full of 5gal cans to run it for even a few days.
Have you ever tryed to buy gas in a real wide spread emergency? This is why i push people to get a small gas generator or go nat gas/propane. Or if your really serious about it get a diesel.

Also all the fancy transfer switches, load sheding and automatic start dont help when you have to spend 4hrs in a line at the gas pump just to buy a 5gal jug.

After we went through a weeks's worth of power outage following a summer deracho (sp?) event several years ago, I became a believer when my neighbor had a smaller Honda EF2000 and it did everything they really needed quietly and just sipped fuel doing it.

I personally went from a larger generator to a smaller portable inverter Yamaha for this exact reason. In my case I went with a EF2400ishc-sized to run a few loads such as a fridge, utility loads and at the time, my gas furnace with a singular static switch on it, or in summer, a single smaller window a/c unit.)

With that, we could exist for a good long while with 20 stored gallons of fuel, and that would likely be all that we would need. Hopefully

I now find myself figuring out to power a well pump (at a new place no longer on city water) and may just have to get a smaller 240v generator just for intermittant pump use as well.

 

[Falcon67]

>then a 2kW-3kW inverter generator is all you need and 20 gallons of gas will last you 5+ days.

Honda inverter 5500w, 6 hrs w/15K AC full, a few LED lights and misc - maybe 2/5 load. 2.5 gallons. So more like 50 gallons for 5 days.

 

[turbowoodworker]

Not an expert and I can't begin to explain or even add to the above excellent discussions.

BUT, I can tell you that as a consumer, I am so happy to have installed my Generac 22kW with a 500 gal propane tank. During Hurricane Florence, we were only on gen power for about 36 hours. But during that time, the generator probably went on and off 20 times, mostly in the early part of the storm. Having it switch on automatically was great. It got to where the only way we knew we were on gen power was to look at my shop outside lights, as the shop is not on the gen.

Yes it was expensive, but my family was safe and comfortable...priceless!

 

[Bretny]

How much fuel did you burn?

With a 22kw propane a 500gal tank should last about 7 days at 50* load. Im not sure what you pay for propane delivered but im sure its not cheap.

Your also then relying on a propane company to have and deliver fuel when you need it.

 

[wyliesdiesels]

22KW? Holy schnikes thats a lot of power.

Do you have an all electric house?

 

[75gmck25]

I don't want to hijack the thread, but my vote is for a small generator.
A small generator would work if it is wired to only power critical circuits for my gas boiler, refrigerator, etc., and I don't consider A/C a critical circuit. I have natural gas in the house, but running a new gas line to a good location for a generator would get complicated.

I am considering using a small propane generator because the shelf life of propane is much better than gasoline. I already have issues with gasoline in my truck going bad because I forget to use both tanks periodically, so I don't really want to start rotating stored cans of gasoline. I know propane does not have the same power/unit as gasoline, but my understanding is that it does not go bad over time.

Also, would diesel fuel for a generator be better than gasoline if you had to store 20-25 gallons?

Bruce

 

[Bretny]

There are many reasons why diesel is better than gasoline for a generator. Personaly my houses secondary hest source is a oil heater (basicly diesel) so i alreaty stock the fuel. Gas is also one of the first fuels to be in short supply when theres a major outage or supply chain is cut off.

On top of all that theres the stability and easy of storeage of diesel. Yes diesel needs to be treated but once that is done it can be stored alot longer than diesel.

Generaly diesel engines burn less fuel than a gas engine too. If your looking for a diesel generator dont buy a 3,000rpm unit.

 

[wyliesdiesels]

There are many reasons why diesel is better than gasoline for a generator. Personaly my houses secondary hest source is a oil heater (basicly diesel) so i alreaty stock the fuel. Gas is also one of the first fuels to be in short supply when theres a major outage or supply chain is cut off.

On top of all that theres the stability and easy of storeage of diesel. Yes diesel needs to be treated but once that is done it can be stored alot longer than diesel.

Generaly diesel engines burn less fuel than a gas engine too. If youre looking for a diesel generator dont buy a 3,000rpm unit.

Generator rpm would be 900, 1,800, or 3,600 for 60hz operation

 

[Highbeam]

I too converted down to an inverter 3000 watt genset for home backup. I have an interlock panel by siemens so the whole house can be fed 120 power. 240 would be nice but not essential. My genset is gasoline and the current models are gasoline or lpg dual fuel which is great. Gasoline going "bad" is easily resolved by keeping at least 20 gallons on hand, always treated, and rotated through the lawn mower. That way fuel is never over a year old.

I don't want a loud genset. Zombies are real. Not the undead kind but the kind that are jealous of your power and might want to take it.

 

[jade97]

Generator rpm would be 900, 1,800, or 3,600 for 60hz operation

My 38K Propane runs at 1800 RPM. Water Cooled 4cyl turbo Mitsubishi.

 

[Chucktin]

Timely discussion for me. We are in North Central Florida, Marion County, on well water. Am on the beginnings of getting whole-house standby generator. 20 kW had been suggested. The other half, a Propane tank, is the biggest hurdle at this point. I can't seem to get anyone to quote purchase and install of a tank, I think we'll get a 250 gallon. "We'll have sales call you back", then nothing. Good thing it's been a mild storm season. But we already had several temporary outages. PITA at this point.

 

[Bretny]

Around here the propane companys will rent you a tank but you need to meet a monthly minimum in propane useage. A generator wont meet that so unless your converting appliances over buying a tank is really the only option.

 

[brewchief]

Timely discussion for me. We are in North Central Florida, Marion County, on well water. Am on the beginnings of getting whole-house standby generator. 20 kW had been suggested. The other half, a Propane tank, is the biggest hurdle at this point. I can't seem to get anyone to quote purchase and install of a tank, I think we'll get a 250 gallon. "We'll have sales call you back", then nothing. Good thing it's been a mild storm season. But we already had several temporary outages. PITA at this point.

FWIW a 20kw generac has a rated fuel consumption of 2.37 gallons per hour at half load and 3.56 at full load. 2.37 an hour for 24 hours is 56.88 gallons per day. A propane tank can only be filled to 80% so a 250 gallon tank can hold 200 gallons. That would give you right about 3 and a half days run time at half load if you could use all the fuel in the tank.

 

[Chucktin]

Thanks I was trying to come up with the same calculations. Waiting to see _if_ we get a quote. Next set of quotes, if any, maybe I specify 500 gallon.

 

[wyliesdiesels]

OP- have you done load calcs to justify a 22KW generator?

 

[u3b3rg33k]

at our farm we needed new service entrance equipment 'cause it was rusting out. got the electrical company to put in a service entrance rated auto transfer switch, new pedestal, and update inside wiring for under $2k. 200A transfer switch has a 60A inlet on it that we can tie to our 60A PTO generator, or the portable 4kW. maybe we'll put a diesel auto-start out there (no NG service, 1k gal #2 oil tank), but those ain't cheap.

 

[aunsafe2015]

OP- have you done load calcs to justify a 22KW generator?

Op there. This thread has continued without me, but I don't think I ever indicated 22kw generator. I'm probably more in the 12-17 range for what I need.

 

[wyliesdiesels]

Op there. This thread has continued without me, but I don't think I ever indicated 22kw generator. I'm probably more in the 12-17 range for what I need.

yeah whoops i confused you for the other person on here.

Regardless, have you done load calcs?

 

[aunsafe2015]

yeah whoops i confused you for the other person on here.

Regardless, have you done load calcs?

Using online calculators, yes. If I move forward with a generator I'll have my electrician do a real one, though.