Finally got a little ahead in life, and including a few gun purchases the past few months, I made room for the price of a pretty good sized gennie.

Generac 15000 watt portable.

I had hopes of running my entire house, but, I'm total electric and the heating elements are 10k each

Anyway, I'll be able to run almost everything with the 50A plug.  I figure that should give me 11,000-12,000 watts.

My question..

What size wire should I use on this 50A plug?  I plan on about 25ft reach.

Short answer is #6 copper, or #4 aluminum.  I used copper on mine.

Ops

I bought my generator from the same place!  

Thanks

#6 SOOW cable and a CS6364 plug.  this mates with a Reliance PB50 50A generator inlet.

http://www.amazon.com/Reliance-LL550C-Generator-Connector-Generators/dp/B000HS0HQW/ref=pd_sim_lg_1/176-8852566-0349158
http://www.amazon.com/Reliance-Controls-PB50-Generator-Generators/dp/B000HRWGBW

ETA here is a pre-made cable:
http://www.amazon.com/GenTran-Generator-Extension-Connections-RJB06410-1450P/dp/B001ULBRTG/ref=pd_sim_lg_2/176-8852566-0349158

ar-jedi

use the biggest wire you can afford.

Why?
What does bigger than required do for you, assuming the length is within voltage drop allowances?

Ar-Jedi

It gives you more exercise lugging the extra weight around I've got a 50' length of 2/4 SO and that is a real pain to move, I only use it when I need to run my welder further from the panel than normal and at full output, and even then it's overkill since you can undersize wiring for welders based on duty cycle.

If you plan to run electric HEAT from a gasoline generator... You will Need a LARGE volume of gasoline.

Tremendous, not just large.

It is well worth investing in a new heat pump which is far more efficient than resistive electric heat by 3-4X, i.e. 1/3 to 1/4 of the power required to get the same amount of heating. I replaced 20KW electric heat in my place with a new heat pump a few years ago and it dropped my electric bill substantially. I did a DIY install with a friend helping with the final charging (I have my EPA license now too) and it cost me about $3k total.

Got wire and other stuff at Lowe's.

I do have a heat pump, house built in 2000.  The heating elements are used when it gets cold and the heat pump does nothing.

I do have a very small wood stove, but it doesnt do much for the upstairs...

You should be able to run the heat pump from that generator when temps are ~40+ and it doesn't need to use the backup heat. You can easily disable the backup heat and/or partially disable it since it's usually in a couple banks. Running the air handler fan when using the wood stove should also help distribute that heat to upstairs.

Grrr, double tap.

Using a larger gauge wire reduces the I sq R resistive losses [heating of the wire] and is more efficient.

This isn't nearly as important for a generator with plenty of fuel as it is with, say, solar panels. [I know you know this A-J]

For example, a #6 wire from a charge controller that may carry currents of 40 amps or more warms quite noticably as the sun ramps up the power and cools as clouds shadow the panels.

[I don't care in this particular application --most of the time, because when one charge controller is putting out that much current, usually the other banks are charging at a heavy rate and I have a surplus of available power. The few % of the panels' output/charge isn't really missed, although I wish I could find a way to utilize it and then I'd do something different]

When the clouds are out, the charge current is much less and the wire size is sufficiently large vs the current passing, that there is little resistive loss.

OP, if you plan to run that 15kw genny a lot, I seriously hope you have a fuel farm in your B-Y.

AC and DC current runs thru conductors differently.

OP. Number 6 or maybe 4 will serve your needs. Your genie will rarely run at max load for extended periods.

I'd like to figure out how to disable one of the heating banks.  I turned one of their breakers off experimenting one time, and the unit wouldn't start at all



I hope I never have to use it!  The likelihood of that is slim to none, however.  I intend to get a small gennie at a later time for running the bare essentials.

I bought this honking unit to keep the AC running when it's 90+ degrees out, and keep some heat in the house when it is below zero.

In 2008? we lost power for 13 days, it was 37 degrees in my living room.  My wood stove downstairs was glowing cherry red.  All I had to circulate the heat from the stove was a box fan.  Didn't work so well

Wife was not too happy either

Hopefully, I can figure out how to get my circulation to run with one or both of the heating elements disabled.  I think the borrowed 3500w gennie i was using at the time just didn't have the balls to do what I was trying.

My goal is to keep my freezer froze, and my water hot (when I need it), and keep the house somewhere above 60 and below 80 degrees.  Even if I only run the gennie twice a day for a couple hours, that should do what I need done, I just needed the horsepower.


If all else fails and it doesn't do what I need it do....  I just have to wait for the next big power outage and sell it for a profit

Say what?  Somehow I think I missed that during classes for my Physics and Electrical Engineering degrees.  

Most DC applications are low voltage, at least compared to common household AC power.  As a result, transferring a significant amount of power in a DC circuit requires much higher current than if higher voltage AC is used (or higher voltage DC for that matter).  The resistive power losses are therefore much higher as they scale with the square of the current.  For example, when transferring power in a 12V DC circuit, the current will be 10X the current needed to transfer the same power in a 120 VAC circuit.  As a consequence the resistive losses will be 100X higher.

DC flows thru the whole cross section of a conductor while AC flows on the outside of a conductor. Guess you did miss that.

He didn't miss it, he remembered that the skin effect only applies at much higher frequencies than 60HZ.

You'll have to look at the diagram for your unit to find the exact details, and that diagram should be pasted inside the access panel cover. On the air handler I replaced at my place (and now use for shop heat), there were two 50A power feeds to the unit, one powered one 10KW heater and the other powered both the second 10KW heater and the blower. If you shut off the feed for the heater only (or just don't connect it), the unit will run just fine with only one heat bank which is how I have it in my shop now. If your unit has a single power feed, you will need to look at the diagram to see how the heat banks are connected where you will probably find a couple contactors (relays) used to control the banks. You will be able to interrupt the control circuit to one of the heater banks to disable it. This could be as simple as wiring a switch neat the thermostat to control it, or if one heat bank is sufficient for the times it is needed you could just disable it permanently. The heaters will be used at two times, first during the periodic de-ice cycle when the outdoor heat pump calls for EM heat while it reverses and de-ices for a few minutes, and of course when it's below 35F or so and the heat pump can't keep up and the thermostat calls for EM heat to meet it's setpoint. If you find the diagram and post a good picture of it we can help more.

Higher frequency definitely exaggerates the skin effect, but it is there at 60 Hz also. Definatly a different transmission than DC.

From: http://en.wikipedia.org/wiki/Skin_effect

"At 60 Hz in copper, the skin depth is about 8.5 mm" - Thus unless your conductor is larger than 17mm dia there is no skin effect. A quick check indicates that 4/0 (0000) gauge solid wire good for 200A+ (depending on insulation) is 11.684mm diameter, so nobody doing anything residential will get even close to a diameter where there actually is a skin effect.

For copper wire and 60 Hz, the skin depth is approximately .33 inches.  Size 0000 gauge wire (4/0) has a diameter of .46 inches.  So I think we can safely say that for any wire size relevant to a home power system, AC current flows through the entire conductor, just like DC.

I did some looking...  I have two feeds.  There are also two 60A breakers on the face of the unit.

I turned the bottom breaker off while the furnace was running, it shut down.

A little while later I turned off the top breaker, and it continued to run.

It is only 30F outside right now, so I don't know if it's cold enough to affect anything right now.

Anyway, I snapped some pics.  The diagrams leave a lot to be desired, but I tried the best I could.

That looks like exactly the same unit I replaced and now use in my shop. Leave that second breaker off and you've reduced it from 20KW heat + blower down to 10KW heat + blower which is how I have it in my shop. You could take it down to 5KW heat by disconnecting the wiring for half of the remaining heat bank. In fact, you could disconnect that half of the 10KW bank that is on the power feed with the blower, and then when both breakers were on you'd have 15KW heat which should be plenty, and if you mark and turn off the secondary when running on generator you take it down to 5KW heat which should be plenty under power outage conditions.

Correct me if I'm wrong...

It looks like I can just pull one of the heavy red wires connected to the upper CB to disable 5k of it?

Assuming I don't pull the wire for the blower, of course.

You need to get the correct one since one of that pair is also providing power for the blower and control. And of course insulate the disconnected wire properly if it's still connected at the other side. At any rate, 15KW should be plenty under normal operation, the new unit I put in is closer to 15KW on it's backup heat and no issues in several years of operation.