Another Generator Question

[Vernon29RW]

Hey Everybody,

I have a 10kw B&S Stand By Gen w/ ATS and I'm in the process of getting it legalized by the town (yeah I need a permit for it!!). I've been going over in my head of how I'm going to hook this thing up. Thanks to the fountains of information available on here I've really educated myself on what is needed for installation of one of these. However I'd still like your opinions. So I have a single story ranch with POCO service drop on one side (call it the west side) and the only place I can really place my gen is on the east side, mostly because of windows on the west side. It's about a 150' run across the house. My question is this: B&S says to use 6 AWG CU from Gen to ATS. So I'm thinking 4 runs of THHN and then I also need, I think, like a 7 wire control cable for the ATS. Its going to be buried in conduit (2"?) from Gen, under yard to the side of the house. Then up the side of the house to the attic. Across Attic to other side of house and then down the other side to the meter. Anyone see any issues I might run into? Can I run a control cable in the same conduit as my conductors? I see a lot of guys like the 2-2-2-4 MHF but I think that may be overkill and I'd like to avoid aluminum if I can. I'm going to power it with a 100g propane tank only because I don't have access to natural gas. I'm looking forward to hearing what you guys have to say. Thanks a lot,
Steve

 

[theoldwizard1]

Someone better than me needs to do the voltage drop calculation on #6 copper, 150' is a long distance !

You also need THWN or other cable rated for 'wet" installation, even insode of a conduit, except when actually inside your house.

 

[rlitman]

Someone better than me needs to do the voltage drop calculation on #6 copper, 150' is a long distance !

You also need THWN or other cable rated for 'wet" installation, even insode of a conduit, except when actually inside your house.

Definitely got to check the voltage drop. That is a heck of a long run. However, what we need to know to figure this out right is the continuous rating of the generator. Is it really 10kW, or is it only 80% of that (or less). Once we know that, we'll know the circuit ampacity, and THEN we can figure out the voltage drop.

THWN is correct, however I have never encountered THHN that is not also THWN rated (I have seen OLD THWN that was not THHN).

Control cable can be run in the same conduit, IF its insulated is rated for the appropriate voltage (i.e. 300V or better would be fine). The Generac control systems I've worked with used 240V signals in the same conduit as 12V (and 24V).

 

[Hohn]

150ft is a pretty good long run.

The ATS should have a much lower current wire for the control line than the actual current supply. Think of it as being like a relay, with high current and low current sides.

I'd recommend against running them in the same conduit, as induced current might cause problems for you.

Wire sizing has to do with ampacity and run length. How many amps are you trying to carry and how far? If you're only going to carry 10 amps that 150ft, then a 6 AWG will drop from 120 to 118.2. (Source here).

If you want to carry the entire 10kW, for 150ft, you'll need a larger cable to handle that 83 Amp max.

The ATS should be close to your main panel, as it will switch from utility to gen set.

If you run the 83 amps for 150ft, you'll need at least a #2 AWG, with a #1 or 0 being better recommendations.

 

[sberry]

6 will work at that but the 2 alum is better and cheaper. Where is one come up with 83A at? For 120, about 1/2 that at 240. The real reason to use number 6 is it could be done with a cable.

 

[Mustang51js]

#6 is plenty big enough. The gen wont put out 10k anyway,and 10k at 240 volts is only 40 amps per leg. Ideally you want it as close to the service as possible. Do you have 5 feet from a window on the west side that it could go. Otherwise if you do pipe it you can get away with 1 1/4 or 1 1/2 pvc. Use thhn this way it can all be put in same pipe. U

 

[theoldwizard1]

6 will work at that but the 2 alum is better and cheaper. Where is one come up with 83A at? For 120, about 1/2 that at 240. The real reason to use number 6 is it could be done with a cable.

Like UF-B !?? At least Southwire UF-B 6-3 uses stranded wire !

 

[ct01r]

We have a 7500w generator we put in the barn, to be rolled outside under roof for actual use. It's 300 feet from the house, and we haven't had any problem with it. Unfortunately, I can't tell you the copper wire size. We installed PVC conduit underground years ago before we paved our driveway, and the electrician ran everything underground from the connection box in the barn to the house basement. He put in the transfer switch/box so it's code, and verified that there's no voltage loss along the run. I didn't want to bother with the noise, the fumes, etc. so I put it as far away as practical, and it's been working fine. Curt

 

[alfredeneuman]

Like UF-B !?? At least Southwire UF-B 6-3 uses stranded wire !

All wire #8 and larger is stranded, except for bare and armored ground wire.

 

[Vernon29RW]

Definitely got to check the voltage drop. That is a heck of a long run. However, what we need to know to figure this out right is the continuous rating of the generator. Is it really 10kW, or is it only 80% of that (or less). Once we know that, we'll know the circuit ampacity, and THEN we can figure out the voltage drop.

Pretty sure it's 10kW......I know if it runs on NG its only rated at 9kW but I don't know why it would be rated the same as its advertised??? I've used voltage drop calculators like the one listed below and 150ft of 6AWG @ 240V should supply around 45A with about 2% drop in voltage. From what I've read anything less than 3% is acceptable.

150ft is a pretty good long run.....................Wire sizing has to do with ampacity and run length. How many amps are you trying to carry and how far? If you're only going to carry 10 amps that 150ft, then a 6 AWG will drop from 120 to 118.2.

If you want to carry the entire 10kW, for 150ft, you'll need a larger cable to handle that 83 Amp max.

The ATS should be close to your main panel, as it will switch from utility to gen set.

If you run the 83 amps for 150ft, you'll need at least a #2 AWG, with a #1 or 0 being better recommendations.

I think you're numbers are based on 120V, the generator is going to be outputting at 240V so those numbers are off man. Correct me if I'm wrong but if wattage and voltage are fixed numbers (like 240V and 10kW) then it can only output around 45 Amps. Can't change that with wire size, that's just how it is. No?

#6 is plenty big enough. The gen wont put out 10k anyway,and 10k at 240 volts is only 40 amps per leg. Ideally you want it as close to the service as possible. Do you have 5 feet from a window on the west side that it could go. Otherwise if you do pipe it you can get away with 1 1/4 or 1 1/2 pvc. Use thhn this way it can all be put in same pipe. U

No I don't have it, unfortunately I have windows that run along the whole length of that side of the house. So I have to keep the gen 5ft away from any of those windows and 10ft from the propane tank. Add in the short property line on the west side as well and it makes it almost impossible to place it there. The other side (the east side) is where my garage is with no windows or door on that side. That makes it ideal to place it there. Plus it's out of the way of my backyard and far enough away from any of the normal living space so noise shouldn't be a problem either.

As far as the conduit goes, I was looking at home depot at the 2" and yeah its really big and overkill but if I ever do decide to upgrade to a larger unit I'll already have the right size conduit to pull the larger needed wires through it. Plus having the larger pipe will make it that much easier pulling the wires through this time.

 

[Vernon29RW]

What is everyone's opinion on thhn/thwn vs XHHW-2. Being that it is going to be buried underground in conduit and I have at least 3 90 degree bends and high heat temperatures in the attic I was thinking that going with the heavier duty XHHW would make more sense. At wireandcableyourway.com THHN is $.040/ft and XHHW is $.49/ft so price really isn't an issue.

Opinions please...

Thanks,
Steve

 

[rlitman]

Pretty sure it's 10kW......I know if it runs on NG its only rated at 9kW but I don't know why it would be rated the same as its advertised???

Because generator kW ratings are like compressor horsepower ratings. Mostly marketing BS. I've seen 6kW rated generators that are only rated for 3.8kW continuous. I'll bet yours is probably around 8. Anyway, with your voltage drop calc based on 10, you seem to be on the right track.

 

[theoldwizard1]

What is everyone's opinion on thhn/thwn vs XHHW-2.

Nothing wrong with it, but I would not pay a premium for it.

 

[pattenp]

What is everyone's opinion on thhn/thwn vs XHHW-2.
Thanks,
Steve

*** for Tat, XHHW not worth the extra 9 cents per foot for your use. All you are getting is some extra abrasion resistance.

 

[Vernon29RW]

thanks guys, thhn is probably easier to get locally too. I know my local HD/Lowe's both carry it for around $.89/ft which is quite a bit more than that website I linked to earlier but I guess we all have to pay a slight price for convenience. Thank you to all you guys who chimed in. I really appreciate all of your input.

*EDIT* I figured shipping would kill buying something heavy like this online but I just priced out (4) 150 ft spools of CU THHN 6 AWG and its still almost $250 cheaper than HD/Lowes!?!? $288 w/ shipping! WOW and you get to pick your color! So much for that!!!

 

[theoldwizard1]

*EDIT* I figured shipping would kill buying something heavy like this online but I just priced out (4) 150 ft spools of CU THHN 6 AWG and its still almost $250 cheaper than HD/Lowes!?!? $288 w/ shipping! WOW and you get to pick your color! So much for that!!!

Where did you find a place that would sell you 150' ?

 

[md21722]

Compare pricing with your local electrical supply house.

 

[reader2580]

Because generator kW ratings are like compressor horsepower ratings. Mostly marketing BS. I've seen 6kW rated generators that are only rated for 3.8kW continuous. I'll bet yours is probably around 8. Anyway, with your voltage drop calc based on 10, you seem to be on the right track.

Whole house generators are usually rated pretty honestly. They will produce less power on natural gas than on LP. My Kohler 10KW produces 9KW on natural gas. It is rated to produce 40 amp on NG. I used 6 AWG because it has a 50 amp breaker.

 

[rlitman]

Whole house generators are usually rated pretty honestly. They will produce less power on natural gas than on LP. My Kohler 10KW produces 9KW on natural gas.

No, they're not. That 10kW or 9kW is PEAK.
Look closely at the ratings and you'll see that the continuous output is always much lower. The number inflation is disgusting.

 

[pattenp]

Where did you find a place that would sell you 150' ?

Wireandcableyourway.com sells it by the foot.

 

[CJ7VFR]

Wireandcableyourway.com sells it by the foot.

Holy ****! That place sells almost every conceivable type of wire or cable you can imagine! And the prices are pretty good too.

Thanks for that link!!

Jim

 

[ishiboo]

No, they're not. That 10kW or 9kW is PEAK.
Look closely at the ratings and you'll see that the continuous output is always much lower. The number inflation is disgusting.

Surge Watts 10000 Watts
Rated Watts 10000 Watts

Seems to be 0% inflation on that.

 

[Diesel Dan]

Compare pricing with your local electrical supply house.

Sometimes you get a surprise.
I found 3/0 copper cheaper at HD than 2/0 copper at the supply house.