#8 for 80 amps?

[yeldogt]

My Cummings Generator was delivered a few weeks ago .... being curious I uncrated and removed some of the panels to better understand how it's hooked up and operates .. how the battery is installed etc.

No shortage of wires in the thing -- what did surprise ... the feed wires to the SD QO breaker where you connect to the house only look to be about a #8.

This is a 20k generator .. what's that around 85 amps? It's obviously enough .. but surprising .. think we need a # 2 or # 3 feed back to the house.

 

[ishiboo]

Yes, inside a rated device the rules do not exist... and it's perfectly safe because they have a known load, distance, duty cycle, temperature rating of insulation and enclosure, etc. Lots of things will require a big wire to it and then inside you'll see it's much smaller.

 

[Norcal]

If it is part of a listed and labeled item, don't worry about it.

 

[Layvon]

Idk aboht the #8 but its Cummins.

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[yeldogt]

I'm not worried ... at first I did think they forgot the wires! The battery cables are much larger. It's surprising that it's enough ... I guess it's about heat and not capacity?

I'm not sure if it has a 90 or 100amp breaker on it -- never looked close .. evidently that's the determining factor on the lines to the house. I did see they used a QO ... my guess is it's a 100 .. because a 90 is an odd duck and I think I would have noticed.

I'm reading Generac is now shipping the 20 they sell with a 90 ..... so you can use a #3 vs the 2.

 

[wyliesdiesels]

I'm not worried ... at first I did think they forgot the wires! The battery cables are much larger. It's surprising that it's enough ... I guess it's about heat and not capacity?

I'm not sure if it has a 90 or 100amp breaker on it -- never looked close .. evidently that's the determining factor on the lines to the house. I did see they used a QO ... my guess is it's a 100 .. because a 90 is an odd duck and I think I would have noticed.

I'm reading Generac is now shipping the 20 they sell with a 90 ..... so you can use a #3 vs the 2.

Look for the wire gauge on the wire jacket.

The temp rating on the insulation matters also.

And #3 cu is good for 100a so you wouldnt need #2 cu for 100a...

 

[jpinca]

If it is part of a listed and labeled item, don't worry about it.

This. The NEC is dealing with an nearly infinite number of unknowns/variables and has a lot of margin built into the requirements.

A listed product has a limited number unknowns and the margin can be much lower/optimal. Also, various failure modes have been explored to ensure that a hazard is not created.

 

[mackwrench]

Not tying to jack thread but I'm thinking about the same generator, which model/fuel type you get? ...is it the air cooled engine?

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[yeldogt]

Not tying to jack thread but I'm thinking about the same generator, which model/fuel type you get? ...is it the air cooled engine?

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This is the newly redesigned air cooled unit -- Propane. 20kw is the largest air cooled in the line. Nice unit -- I got the one that comes with the service entrance transfer switch. Simple load shedding with separate relays (2 relays in each kit) ... can do 4 loads (2 kits). I ordered the pad/ service kit/ 2x load kit and the second control for remote in the house. little over 5k.

Have not figured out the internet on it. The transfer switch is huge.

It's designed to be a bit more fuel efficient -- and to cut the exercise cycles by only running the starter motor.

 

[larry4406]

This is the newly redesigned air cooled unit -- Propane. 20kw is the largest air cooled in the line. Nice unit -- I got the one that comes with the service entrance transfer switch. Simple load shedding with separate relays (2 relays in each kit) ... can do 4 loads (2 kits). I ordered the pad/ service kit/ 2x load kit and the second control for remote in the house. little over 5k.

Have not figured out the internet on it. The transfer switch is huge.

It's designed to be a bit more fuel efficient -- and to cut the exercise cycles by only running the starter motor.

I'm jealous. Of course this being Garage Journal we fully expect a dedicated thread on the installation and commissioning of the genset with lots of photos.

 

[mackwrench]

Thats the same one I'm looking at. I'm subscribed, install pics along with fuel usage, please,
ha-ha

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[American Locomotive]

On a side note, who makes the engine? The literature says it's a Cummins engine, but it convienently has the same displacement, bore and stroke as Kohler CH980.

 

[yeldogt]

On a side note, who makes the engine? The literature says it's a Cummins engine, but it convienently has the same displacement, bore and stroke as Kohler CH980.

Don't know -- read the same thing. It's a tight package and all covered up -- checking the oil is easy as it has the dipstick available through the case when you open the lid. They have a thumbscrew cover for adding oil. To change the air filter requires the actual removal of one of the internal covers --- I'm not sure what's necessary to change the oil .. guess I will find out.

The house in under construction -- many months till it's in.

 

[arkieguide]

A lot of equipment is wired that way - internal factory wiring is not subjected to the building NEC. I scratch my head some when I run into say #1 factory wire to connection and I have to bring in 500 mcm. But I play by the rules.

 

[The Tool Tyrant]

On a side note, who makes the engine? The literature says it's a Cummins engine, but it convienently has the same displacement, bore and stroke as Kohler CH980.

This is really strange as Cummins bought out Onan, which is now badged Cummins Onan...AND Kohler has their own line of generators.
Sounds like they all may be in bed together.

 

[larry4406]

Yeldogt - any update on your installation?

Can you post a link to your genset and transfer switch?

 

[Gerald O]

Wiring ampacity is derived from the resistance of the conductor. When current flows in a conductor some heat is produced from the energy lost to resistance. So wire ampacity ratings aim to reduce heating of the conductors and to reduce energy loss.

Resistance is a function of the wire length. In a building, wire runs are long compared to inside equipment where the runs are very short. In simple terms the shorter the run the more current the conductor can carry. Look at how small the conductor cross section in a fuse is.

 

[Stuff]

I don't think the NEC is worried about energy loss here. More about heat and the possibility of catching something on fire. Multiple wires in a cable jacket in insulation passing through wooden studs vs. a single loose wire in an appliance that can dissipate the heat.

You get the same BTUs per inch if you run the same current through a short or long piece of the same wire.

A cross section of a cartridge fuse or fusible link isn't really that small.

 

[Norcal]

What matters in terms of ampacity is what insulation is used.

 

[ard]

As has been disucssed here and elsewhere, there are many things that determine the allowable wire size for a specific ampacity rating.

We had a thread on a listed 400 or 320A residential load center with a #x set of conductors used inside for a 200A sub lug. The NEC would not allow that wire size, yet it was listed. Some thought it had been modified. I contacted the manufacturer who had documentation on the SPECIFIC wire (special metallurgy AND very fine stranding) that was rated for that use. A solid bus, or a 19 strand conductor or a 80 strand conductor can all have different ratings.

NEC is fine for a global guide for 'installers'. (Aka electricians). Once you are inside a listed cabinet, it is an engineered process. As otehr have posted, a cabinet will be instrumented with temp sensors and run at Max conditons- it can't fail nor hit certain temp limits, even if individual internal componets are way over what would be allowed in a wall.