Home Standby Generator

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sparkync

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I am getting ready to install a 13 kw home standby generator. I am planning on putting the customer's a/c unit and water heater on the transfer switch with other selected circuits ( the manufacturer spec's says this is ok). The water heater and the a/c unit are coming from a different panel than the other circuits ( from an outside panel). I am trying to determine the easiest way to tye these into the same transfer switch as the inside circuits will be in. I can't seem to get in my mind exactly how to do this ( right now I'm tired, been working constantly almost day and night for a while:) Any help would be appreciated. Thanks...
 
Two thoughts:

That's quite an ambitious load for a 13Kw unit.

What kind of TS, and where will it be located?
 
LarryFine said:
... That's quite an ambitious load for a 13Kw unit ...
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Indeed it is.

While the OP didn't include the actual equipment ratings, I would be concerned that there might be some difficulties starting-up the A/C if the water heater were already running.
 
One way to include a water heater on a standby system is configure it for 120 Volts when operating on the generator. That way, you will be heating the water, but at a slower rate, saving valuable capacity for starting loads such the A/C, fridge, freezer, water pump, etc.

A simple DPDT relay can accomplish this task.
 
stickboy1375 said:
Generac Generators are bragging they have a 10kw generator that can start a 3-ton AC unit and still have power to spare....
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They can brag all they want. The last generator I bought and installed (6kVA, but I forget the brand ...) couldn't run a 1HP well pump and more than 2 100W bulbs at the same time -- and it insisted it could operate all sorts of household appliances.

In practice the generator was fine as long as it had a single inductive load, or if it had two inductive loads (motors), one motor had already started and the second was the only other load at the moment.

(Edited to clarify that I'm talking about inductive loads -- the 5kVA to 10kVA generators I've worked with over the past year have been fine with purely resistive (lighting, mostly) loads, but choke on inductive loads.)
 
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What determines the starting capacity of a generator is the alternator.
For example, I have a 180 KVA generator with a 250KVA alternator. It was sized to start a 100 hp 460 volt motor with only 20 % VD on starting.
The 13 KW may do the trick if the alternator has a good voltage regulator. Also once the first motor is started, it will provide energy to start the second.
A rule of thumb is the generator KW should be twice the motor hP, but again its really dendant on the alternator and voltage regulator.
That 180 KVA generator will run the 100 hp and a 50 hp at the same time. We start the 100 hp first. More than 20 % VD on starting will drop out a mag contactor.
 
I know that Cutler-Hammer's transfer switches have contactors in the actual transfer switch to only permit one heavy load (ie air conditioners and water heaters) to start at a time. Pretty neat feature that permits you to keep your generator size down a bit.
 
I am locating the TS in the hallway where their existing breaker panel is located. I will have to pull new wires between the two panels, since the factory wires only come with a 2ft. flex and I won't be able to put the TS that close to the existing panel. The specs on the generator say it can start 1 4 ton and 1 3 ton A/C unit, and 8 more 120 volt circuits(2 kitchen, bathroom, family room, 120 volt furnace, garage, bedrooms and a sump pump. I figure I can swap one of the A/C units for the water heater.
As far as gas consumption, the homeowner realizes it will cost. They are more concerned with comfort when the power goes out than with the cost. The lady of the house has some physical problems and went through a power loss last year, and don't want to do it again. My main concern right now is how to get the a/c circuit and the water heater circuit inside to the TS. I seem to have a brain lock up since they are coming from the outside panel instead of the inside panel.
 
sparkync said:
I am locating the TS in the hallway where their existing breaker panel is located. I will have to pull new wires between the two panels, since the factory wires only come with a 2ft. flex and I won't be able to put the TS that close to the existing panel. The specs on the generator say it can start 1 4 ton and 1 3 ton A/C unit, and 8 more 120 volt circuits(2 kitchen, bathroom, family room, 120 volt furnace, garage, bedrooms and a sump pump. I figure I can swap one of the A/C units for the water heater.
As far as gas consumption, the homeowner realizes it will cost. They are more concerned with comfort when the power goes out than with the cost. The lady of the house has some physical problems and went through a power loss last year, and don't want to do it again. My main concern right now is how to get the a/c circuit and the water heater circuit inside to the TS. I seem to have a brain lock up since they are coming from the outside panel instead of the inside panel.
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If not too late i would check to if it could run on propane.She will end up with gas going bad on her before its used.

I would simply make a wp junction box outside near old panel and run wires to the new panel.Just how often and long are the outages ?
 
It's going to be run on NG and not PG. Thanks for the input. I can just take it out of the outside panel, and put j box under house and run to inside panel
if I have enough room then to the TS switch. I'll have to check the feeder size to the inside panel to make sure it will handle the load of the a/c and water heater. Thanks
 
Sparkync
With that Generac ATS, you will need for all of the load to be fed from the same panel. So, what you are proposing will be feasible only if your inside panel can handle the added load. Otherwise, you will need two transfer switches ($$$). Good luck with the install!!
 
Fuel source is NG??

Do you have enough NG to power it?

The typical residence low pressure system doesn't have the capacity to run a good size generator. I had to put in a commercial gas service and regulators at each load (furnace, water heater, range, and generator.) to handle the load.

Be sure you have a properly configured 12VDC solenoid operated gas shut-off valve to kill the fuel if the generator drops out - and it WILL drop out! You will also need to have a 120VAC time-delay relay to prevent dropping out the seal-in for voltage dips when a large load comes on.

Been there, done that.


Remember, without the above the gas will continue to flow until . . . boom!

Been there, ain't done that.

 
Rajun,

Don't mean to divert this thread, but perhaps you could quantify the largest NG powered generator that could reasonably be put on a typical residential gas service? As I recall the 13kW Generac generator requires 225cfm at full load. The seems a bit high, but on the other hand, a minute is a long time for 225 cubic feet of gas to come out the end of the pipe ...
 
tallgirl said:
Rajun,

Don't mean to divert this thread, but perhaps you could quantify the largest NG powered generator that could reasonably be put on a typical residential gas service? As I recall the 13kW Generac generator requires 225cfm at full load. The seems a bit high, but on the other hand, a minute is a long time for 225 cubic feet of gas to come out the end of the pipe ...
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It's been 7 years since I installed it and I don't remember. When I get back to the office (and remember!) I will see if I can find the data.

At the very least, you need to get with a mechanical engineer who is familiar with the issues, that's what I did. 225CFM is a LOT of gas.
 
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