Generator question (household wiring to be more accurate)

[Xfaxman]

This is what our rural electric co-op recommends: GenerLink.com - About GenerLink - The easy way to connect a home generator

 

[Threepoint]

[snip]
So, back to my question...

If I have two wires (I only have one but I don't recall if it's 6 or maybe 8 gauge. It's a heavy bugger)

If I have a 6-2 w/g going from the second panel to a 50 amp in the main panel, how large of a generator might work on that line?

If I have an 8-2 w/g going from the second panel to a 50 amp breaker in the main panel, how large of a generator might work on that?
[snip]

Richard, I'm not an electrician, and perhaps I'm misunderstanding you, but when you state it that way I think you're asking the wrong question. The size of the generator is not limited by the size of the cable and breakers feeding the various loads. You could have a 100 Kw generator feeding that 6 or 8 gauge cable and it would work just fine without risk of damaging the generator or creating a hazard. What matters is the total amperage draw of the loads that the feeder cable (and its breaker) serves. So, assuming the loads from your two panels are served by properly-sized breakers and cables, you can go as big on the generator as you want.

As I understand your set-up, the 50 amp breaker is in the main panel and protects the 6 (or 8) gauge cable running to the subpanel. How could you use that same cable to "back feed" the main panel from your proposed generator and still have current to the subpanel fed through that breaker? :confused3: Now, if you're planning on running a separate, new cable from the generator (via a transfer switch) back to the main panel, this would make sense to me, as the 50 amp breaker would continue to protect the subpanel. And the existing 100 amp breaker in the main panel would continue to protect the main panel (and of course the subpanel as well) when it is disconnected from the incoming utility service by throwing the transfer switch to generator mode.

So with this understanding, I think the question you're really asking (at least what I would ask) is: Given that the 100 and 50 amp breakers in the main panel are protecting the main and subpanel of your proposed setup, what is the maximum size generator that makes economic sense, i.e., beyond which you'd just be wasting money to buy it and fuel to run it? This assumes, of course, that the various breakers are correctly sized to the respective feeder cables they serve. Seems to me you simply need to total up all the watts you're likely to be using at any given time without tripping your breakers. Then size your generator such that your expected total prolonged demand would not exceed about 80 percent of the generator's capacity. That additional 20 percent is the cushion I often see recommended by pros to avoid overworking the generator.

 

[doxford jim]

I have 12kw Kubota diesel generator that feeds our 100 amp service with no problems. It runs all of our equipment including the geothermal heating unit.

 

[aczlan]

So to recap, you have a 6/3 with ground wire running to the subpanel?
If its not feasible to run a new wire from the main panel to where the generator is located, I would look into a Kirk Key type trapped key interlock system such as: Lot of 2 Kirk CK43670 Key Interlock with Key | eBay

Then one goes on the main breaker and the other goes on the generator breaker in the subpanel. The way it works is that in order to get the key out, it needs to be locked (with the rod on the lock extended).
In your system, you install one on the main breaker (so that the rod can only extend if the main breaker is off), and the other on the generator breaker (so that the rod can only extend if the generator breaker is off).
Then to switch, you shut off the main breaker, lock the main breaker interlock, remove the key, walk over to the generator breaker, unlock it and turn on the generator breaker.
The 2nd set of keys is to be stored in a safe place marked for what they are for and marked that only one set is to be used at a time.

Aaron Z

 

[mbrule]

We're getting a bit into the weeds.

My brother in law happens to be an electrician. I am always running to him for this & that so I'm trying to get some education without bothering him.

(which is also why I mentioned that I know I need a transfer switch)

So, back to my question...

If I have two wires (I only have one but I don't recall if it's 6 or maybe 8 gauge. It's a heavy bugger)

If I have a 6-2 w/g going from the second panel to a 50 amp in the main panel, how large of a generator might work on that line?

If I have an 8-2 w/g going from the second panel to a 50 amp breaker in the main panel, how large of a generator might work on that?


Our main breaker is in the basement. It would be nice to have something that would power the "whole" house. Meaning I'd like it to be big enough to run the water heater and pump at same time (more if possible) so that we don't have to do the endless run downstairs and play musical switches to get the various items working.

It's not like we're having a party when the power goes out and maximizing our hot water use....while at same time burning all the lights while at the same time turning the A/C system on.....

It would however, be nice if the generator had enough oomph to allow some overlap of above items without triggering breakers somewhere.

wifes, and for that matter, electrician brother in law have a niece who's in a wheelchair. When she visited last time it happened right at the beginning of an ice storm and we were without power for a week. We rigged (correction, "HE" rigged) his generator to the second panel and backfed the main panel (main breaker was off) It was during this week of daily use that I felt the 10Kw unit was underpowered. It "worked" in that we could do some things but there was an issue if some of them overlapped so I'd like to look at a larger unit so I don't feel everything is so stressed.

I know it would cost more.

I'm just presuming that if the idea works (at all), then the limiting factor is this wire going from the second panel to the main panel.

I think the answer to your question is simply 50 Amps * 120 VAC = 6000 Watts....

 

[Dutch445]

So to recap, you have a 6/3 with ground wire running to the subpanel?
If its not feasible to run a new wire from the main panel to where the generator is located, I would look into a Kirk Key type trapped key interlock system such as: Lot of 2 Kirk CK43670 Key Interlock with Key | eBay
View attachment 456392
Then one goes on the main breaker and the other goes on the generator breaker in the subpanel. The way it works is that in order to get the key out, it needs to be locked (with the rod on the lock extended).
In your system, you install one on the main breaker (so that the rod can only extend if the main breaker is off), and the other on the generator breaker (so that the rod can only extend if the generator breaker is off).
Then to switch, you shut off the main breaker, lock the main breaker interlock, remove the key, walk over to the generator breaker, unlock it and turn on the generator breaker.
The 2nd set of keys is to be stored in a safe place marked for what they are for and marked that only one set is to be used at a time.

Aaron Z

Very interesting Aaron, i didn't see any pictures of them in service panels but it sounds like a logical solution. would this system be acceptable to the safety police?

i have the exact same situation as OP, exterior garage with small sub panel about 50' away from the home's 200amp panel, and i just got
my old 5500 watt generator up and running and was looking for an easy way to power the critical circuits in the house from that garage panel.
I would imagine I could pull another set of wires but with this solution i don't see why i would have to. of course with a larger
whole house generator I would have the automatic transfer switch, but to get thru with the current gene this trapped key might be just
the ticket.

"I think the answer to your question is simply 50 Amps * 120 VAC = 6000 Watts...."

this is good to know, my 5500 watt gene should be ok thru my subpanel.

thanks

 

[aczlan]

Very interesting Aaron, i didn't see any pictures of them in service panels but it sounds like a logical solution. would this system be acceptable to the safety police?

The electricians I have spoken with would be ok with it (once it was explained in detail). Will have a conversation with the electrical inspector when he comes out to inspect the pole barn.
Edit: See:Kirk Key and http://pdf.kirkkey.com/websiteimages/downloads/KirkKeyBrochure.pdf

Aaron Z

 

[Deere Dude]

Following this thread because I planned on back feeding the house from a 100 amp shop sub-panel. Maybe something good will come out of this.

 

[aczlan]

Following this thread because I planned on back feeding the house from a 100 amp shop sub-panel. Maybe something good will come out of this.

That is my plan as well. We have a 100 amp subpanel in our barn and the inlaws have the same in theirs.
I would much rather have the noise out there rather than right next to the house.

Aaron Z

 

[BHD]

but if you back feed the house and some one screw up and energizes the power line and kill a line man, it will not be so good, it is illegal to set up a hook up like that,

do it right or do not do it at all,
use a transfer switch that is approved,