Revisiting the PTO-generator question

[WVBill]

Bob:
I think you've got the basic concept down right - two switches, mechanically connected so that when one is "ON", the other is "OFF". Well, that's what the "transfer switches" you can by do. Some do it "automatically and some do it manually but either way, they're not cheap.
Yes, you could get the parts and put something together yourself but you would then assume a whole bunch of potential liability.
The issue people are concerned with is not "lighting up the whole neighborhood" with your generator. It's when the power company lineman comes out to repair the downed wires, he makes sure that all of his safteys are OFF and expects the lines to be dead when he grabs hold. If someone has a home made transfer switch that didn't work just right and the line is NOT "dead" - well, you see the potential.

 

[hazmat]

<font color=blue>I figure my new PTO generator is rated for 17KW with 35KW surge, but I only have about 28 HP at the PTO. So figure I can put out about 13KW. This should probably (I'll find out by experimenting) power our whole house. If not, I just turn off some circuits at the main box</font color=blue>

Trev first off your 13 kW is conservative

28 HP * .7457 kW/HP = 20kW Factor in some ineffeciency in the generator & you'll probably be close to the 17kW number. Note: Due to the laws of physics (Darn Isaac Newton) you won't have the surge capability to 35kW as your tractor won't put out enough power. Likely you'd stall the tractor if you managed to load it that much.

As far as running your whole house on 13-17kW you probably can. You need to do a (for lack of a better term) "power survey".

17kW at 110Volts = 154 amps. or half that at 220V. You probably have a 200 amp service, but chances are good that you aren't using all of it.

Here's how to do a "power survey"

Add up all the electric appliances in your house

Lights are easy, they're rated in watts already
For everything else multiply volts * amps to get watts
For example my table saw at 110 volts draws 18amps, = 1,980 watts. If the power consumption of anything is unknown, you can take a worst case, ie an electric dryer is on a 220V, 30amp circuit = 6,600 watts. Check your appliance owner's manual for power consumptions

This survey doesn't take into account "start up" power requirements for electric motors, but statistics are on your side, unless you've been without power for a while, the cycling of the fridge vs. the heat vs. the well pump should be pretty random. If the power has been out for a while, you probably want to turn those circuits on individually.

If you find that you're over the 17kW, you can identify & shutdown non essential circuits. Big power users are electric ranges, microwaves, dryer, HVAC & the fridge.

 

[Trev]

Hi WVBill,

<font color=blue>Yes, you could get the parts and put something together yourself but you would then assume a whole bunch of potential liability.</font color=blue>

Well, I would have the electrical inspector come out and look at anything we did and approve it before use.. just like when we wired the place initially (or our electrician did.)

<font color=blue>The issue people are concerned with is not "lighting up the whole neighborhood" with your generator. It's when the power company lineman comes out to repair the downed wires...</font color=blue>

I honestly do understand this issue, and my "solution", if indeed it turns out to be one, would circumvent this problem *totally*.

Imagine the line coming from the pole to my house. I break this line, and run it into a box *prior* to my main electrical box.

Into the same box, I run the wire from my generator.

Into the same box, I run a wire that goes out to the main breaker box where the line from the pole *used* to connect.

The box contains a heavy switch. The switch *either* connects the line from the pole, *OR* the generator, to the line running to my main breaker box.

Now I have one single switch that let's me choose between being "on the grid" **OR** being on the generator. BUT NEVER BOTH AT ONCE.

And nothing else has to be done.. just a single switch that chooses power grid versus generator. Everything from that point on can remain the same. No changes to the main breaker box. No need to turn off the main breaker (indeed, if I did, nothing would be connected to the house circuits at all!)

Does this make my idea (albiet perhaps a flawed one) any clearer?

It's as if a (electrocution-resistant) guy with an axe chopped the line from the pole and hooked up the line from the generator. When the power comes back on, the same guy chops the line from the generator and hooks up the line from the pole. Never can the two be connected simultaneously.

What I'm missing is: what is so expensive about this?? It's just one box, two input lines, one output line, and a switch to choose one or the other of the two inputs.

I think it's my lack of knowledge of electrical lingo (and, indeed, electrical knowledge) that is confusing this issue.

Thanks for your patience!! /w3tcompact/icons/smile.gif

Bob

 

[MJB]

I understand what you are saying. What you need to do, however, is price out a transfer switch capable of handling the full rated amperage of your service. Probably either 100 or 200 amps. I sure that switch would cost way more that $20-$50.

 

[hazmat]

<font color=blue>What I'm missing is: what is so expensive about this?? It's just one box, two input lines, one output line, and a switch to choose one or the other of the two inputs.</font color=blue>

I might be missing something here, but I think that they make automatic transfer switches that are expensive. They can even be set up to automatically turn on a generator (not the case with your tractor powered unit) I'm sure a manual one is far less expensive. Give your electrician a call

Check out this link <A target="_blank" HREF=http://www.nooutage.com/manual.htm> No Outage</A>

 

[Trev]

<font color=blue>Trev first off your 13 kW is conservative
28 HP * .7457 kW/HP = 20kW Factor in some ineffeciency in the generator</font color=blue>

Well, actually I lied. /w3tcompact/icons/smile.gif I think my PTO is really rated 27.5 HP, but I always round up. /w3tcompact/icons/smile.gif

Thanks for the analysis.. It will take me a while to figure out what kind of loads I'm looking at here.

The real issue for me right now is that I think there's an easy/cheaper way to do the transfer box.. but I can't explain it in layman's language.. so everybody is telling me about the need to not electrocute linemen. /w3tcompact/icons/laugh.gif I understand that part.. I'm trying to find an affordable way to hook up this generator which keeps everyone safe and everything within code.

I'm leaving for home now.. my wife called.. trouble with the foster kids, social services, lawyers, judges, and so on. Nobody can agree on anything. Makes my generator questions pale by comparison. /w3tcompact/icons/smile.gif

Thanks again, to everybody... back soon...

Bob

 

[Inspector507]

Trev,
I think it would be hard to find a 2 pole double throw switch to use for what you want to. Besides, to be in accordance with the National Electrical Code, the switch would have to have over-current protection. The first switch or disconnecting means needs to have the overcurrent protection.
Thats why people put the "transfer switch" down stream of the main, not ahead of it.
Let me know if I can help any way.

Jerry

 

[djradz]

Bob, your theory is basically sound, except for a couple of things. If your service comes underground, the power company usually will only connect to their meter box, not a transfer switch, so you'd have to put the transfer switch on the load side of the meter - shouldn't be a problem. Secondly, if the service is overhead to your house, I'm not sure the NEC allows this, and the utility might not either. Maybe the utility has some sort of transfer switch connection, but I wouldn't count on it. Nonetheless, you proposal is safe and sound. Have you priced out a 200 amp, double-pole / double-throw switch. They can't be cheap either although the amount of wiring would be less and you'll have a more flexible installation.

 

[beenthere]

<font color=blue>""It will power up one side of the 220 system in your main box""<font color=black>

I think, just to keep the information straight, that the 220 hookup will power up both 'sides' of your main box. That is where the 220 comes from - both sides.

 

[Anonymous Poster]

OK, let me take a stab at simplifying, or complecating the issue further.
There are 3 types of transferr switching devices. These are all for single phase loads, since I presume none of you are operating 3 phase systems.
1) Automatic transferr- 2 relays, one witch drops out when the power goes off, and a second witch energises when the genset is up to speed. When the first relay drops, it activates a controller that starts the genset, and enables the set load control relay to close.
These start at a wholesale cost of around $2500.oo wholesale. Additional functions such as exercize cost more.
They also monitor the commercial power for return, and shut the genset down as well as switch the load back to the commercial power. 99% of the time, they work. When they don't, they can brun off the wall and destroy the genset. I have seen both situations happen.

2) Manual Transferr Switch- This is basicly a 100 amp 3 pole double throw switch, much like a disconnect switch. It is installed between the meter and the breaker pannel. When the power fails, you start your genset, and then throw the switch from power Co (up) to Genset (down), and the breakers have power.
Wholesale for a 100 amp transferr switch is about $500.oo.

3) the Gentran typs switch pannel- basicly a group of 20 amp single and double pole toggle switches mounted in a box with a couple pilot lights and a small (unnecessary) meter.
These appeared in the late 80s when America fell in love with the generator inthe garage syndrome for power failures.
Technicly, these systems are NOT code compliant because they require splicing of wires inside the breaker box. Your inspector may or may NOT accept these devices at inspection.
Prices vary from $169.oo to whatever the sucker will pay.
Essentially, they are nothing more than a group of 3 way switches, with the load wire connected to the point wire and a breaker connected to one of the swing leads and the second swing lead connected to one side of the generator.

The #3 device is UNSAFE because it does NOT isolate the generator from the Commercial Power system. The Neutral wire is still connected.

SIZING GENERATORS-
Unless you need to be the guy with the BIGGEST on the block, buy an Amprobe and determine your actual load. Chances are you never run all your electrical loads even on commercial power, so why would you run them from your generator?

Additionally, if you have a heat pump, freezer, dehumidifier, and or refridgerator, it is best to employ a 5 minute delay between the time the power goes off and generator power returns to these appliances. If you don't, the compressor may start against a head of liquid and self destruct.

If you aren't conversant with generators, DON'T buy one from a catalog or box store, you will wind up short of cash and with a bad system. The goof in the orange apron doesn't know any more about gensets than you do. The low price will be forgotten long before the dissatisfaction of an improper installation!