View Full Version : Standby/Shop Generator

09-20-2004, 10:15 AM
There has been a lot of threads on generators recently so I thought I would post the setup that I have. Maybe it will help others with theirs.

My generator is a 12.5 KW Onan 4 cylinder air cooled unit with a complete instrument package and is manually operated. It can be setup for single or 3 phase power up to 600 volts. The unit at present is setup to run on natural gas or propane. It is setup for single phase 120-240 volts at present. I use it for a standby generator to power my house when we lose power but it also has a dedicated panel that can be used with the generator alone while we still have power from the electric company. When I wired the unit I sized everything for a 30 KW unit in case I want a larger generator later.

Power Company meter, electric breaker panel and transfer switch.
Wiring inside 200 amp transfer switch.
Generator unit.
Hot air exhaust duct to outside.
Engine exhaust to outside.
Fuel supply piping, natural gas and propane.
Electrical panel from generator.
Hot air exhaust and exhaust outside of building.

Hope this helps someone with their installation. The installation was inspected by the power company and the local city code office and approved.


09-20-2004, 10:47 AM
How much did this all cost you? What was the cost of the generator separate from everything else?



09-20-2004, 11:15 AM
That looks very good Joe, with one very serious exception. The propane tank should be outside. I can't imagine how the installation would pass inspection with a tank that size inside the structure. That is a violation of the National Fuel Gas Code.

"Recent EPA rulings require stricter standards for installations of fuel tanks. An approved LPG fuel tank must be used to store liquid propane. All appropriate shut-off valves and pressure gauges must be included. An LPG tank should never be installed inside a structure; it should be installed outside, some distance away from any structures and away from open flames, sparks, or electrical connections."


[This message has been edited by Evan (edited 09-20-2004).]

Paul Alciatore
09-20-2004, 12:26 PM

Neat setup. I've installed and maintained emergency generators for many installations and the only thing you left out is the automatic startup and changeover. Just another $5K or so.

One thing, I have found is that any generator will only reliably start and work if it has been run in the last week or two. If you let them set without use, they will always fail when needed. Credit to Murphy or sone such person. I would test run it at least monthly, UNDER LOAD. Better yet weekly or bi-weekly. 15 - 30 minutes.

As for the propane, I would definitely move it outside; even if the local inspectors let you get away with it. A small leak and the next morning BOOM, no more building. I've seen it happen. Those tanks frequently leak. I've got a bigger one that has been repaired several times. Not if it will leak but just WHEN. Move it out, please.

Paul A.

09-20-2004, 12:33 PM
Jerry,the total installation cost about $5000. The generator was used with very low hours and cost $2500.

Evan, the tank is approved for propane and is a portable tank. The tank is normally used for BBQ. It is shown in place to show the two fuel supplies. Normally it is only connected to the natural gas. It has all of the required regulators. One at the generator and one at the piping from the tank. Larger tanks do have to be located outside and away from the structure.


09-20-2004, 12:39 PM

I belive the legal limit for fuel gas containers that may be stored inside is 1.1 lbs. That's why propane torch bottles are 1 lb.

09-20-2004, 12:41 PM

I start the unit once a month and run it for about 15 minutes. It a hurricane is near I will run it again just to make sure it operates properly. The auto start was left off on purpose. We have a lot of power blips and I didn't want the unit to start up automatically. Some of the other people in the area have auto starts and that has caused them move failures than anything else on their units. It has never failed to operate. The heater connected to the panel is for a load when it is run.


09-20-2004, 12:41 PM
I appreciate your taking the time to post this. I am contemplating just such an installation. Should have been an easy one on my end, but it seems my electrical friend has now gotten married and moved over 300 miles.I talked to him a couple of months ago and he didn't even have a girlfriend... Have to contemplate a different angle on it now.
David from jax

Have gun, will travel.

09-20-2004, 12:44 PM
Double post, sorry.

Evan, if the 1.1 lbs is the legal limit then just about everybody in this area is in violation. With propane fueled BBQ grill that are stored inside the garage when not in use.


[This message has been edited by WJHartson (edited 09-20-2004).]

[This message has been edited by WJHartson (edited 09-20-2004).]

Mike W
09-20-2004, 02:46 PM
Nice installation. I have a 5 kw Onan out back. My transfer switch is a bunch of extension cords. http://bbs.homeshopmachinist.net//biggrin.gif

On the propane, what about the heaters that attach to the propank tank?

Mark Jones
09-20-2004, 03:21 PM
I know nothing about generators ,
but know how to look after engines.
... 15 mins running is not enough
your going to get condensation problems in the oil.
in the end your oil will turn into a mayonaise like soup/paste...i would recomend you run it for over an hour each time .
btw nice set you got there.
all the best..mark

09-20-2004, 04:35 PM
That may well be the case Joe. I sure wouldn't store propane inside, or gasoline either. I have a storage shed 30 feet from the house for storing exactly those types of things. The floor of the shed is 2X4s with a 1" gap between pieces so any fumes or gases released can immediately vent from the shed. There is also a vent at the top of the shed under the eaves. That is where I store gasoline, propane, chainsaws, paint, solvent etc. I keep nothing larger than a spray paint can in the garage or house. The only exception to that is the acetylene tank of my gas welding gear which stays in the garage.

I also have five fire extinguishers of different types scattered around the house and garage. Dry chem in the garage, pressurized water at the top of the basment stairs, foam in the kitchen and a halon in the basement shop as well as a CO2. In winter I also have a 50' hose connected to the water system in the basement and coiled ready to use about 10 feet from the wood heater.

[This message has been edited by Evan (edited 09-20-2004).]

09-20-2004, 05:04 PM
Around these parts, the BBQ size tanks are required to be stored outdoors. The boss bought a propane grill for the shop. One day the Fire Marshall was driving past and saw the setup in the garage. Next thing you know, we've got a cage chained to the fence at the far end of the parking lot. That's were the tank is now kept when not in use.

09-20-2004, 08:18 PM
<font face="Verdana, Arial" size="2">Originally posted by Evan:
acetylene tank of my gas welding gear which stays in the garage.

[This message has been edited by Evan (edited 09-20-2004).]</font>

http://bbs.homeshopmachinist.net//eek.gifAcetylene!Holy s---!Pot calling the kettle black ain't it?

09-20-2004, 08:20 PM
Nice setup Joe,I have an Onan 4cylinder too,but its diesil and currently has four stuck pistons,one more thing to work on.I think I'm going to unload it and buy a pto generator for one of the tractors,one less motor to keep running.

09-20-2004, 11:52 PM
Acetylene!Holy s---!Pot calling the kettle black ain't it?

No. The single most dangerous aspect of storing propane inside is the fact that it is considerably heavier than air. Even small quantities from a slow leak will pool in low areas and remain for long periods of time. Acetylene is very slightly lighter than air and will mix freely to form a mixture too lean to burn in a large space. A small slow leak from an acetylene tank is not likely to pose a hazard. My garage is 4800 cubic feet. With the small tank I have which holds 40 cubic feet even if the entire full tank were quickly emptied into the closed garage it would not form an explosive mixture. The ratio would be 120 to 1, far too lean to support combustion.

[This message has been edited by Evan (edited 09-21-2004).]

09-21-2004, 09:49 PM
Its not the mixture,its the odd sprak that ignites the leak,which heats the bottle,which causes it to explode,trust me I am well versed on this occurance.Ever see flame run from the ceiling down to a acetylene bottle?I have,quite scary.

09-21-2004, 11:51 PM

For some reason propane is not allowed to be stored inside a shop but acetylene is.

09-22-2004, 09:58 PM
Ya,I know,kinda like copper,galvanized or black iron for gas service,no two codes agree,ever.

09-22-2004, 11:05 PM
The most dangerous item you can store in your garage is the car. Yep, I keep all the bad stuf out in an insulated and vented shed. The car(s) sit outside. (No room in the garage.) http://bbs.homeshopmachinist.net//biggrin.gif