jfn1000
I have purchased a Generac 5875 with 200 amp SE rated ATS. To save on some of the installation costs, I intend to do some preliminary wiring from generator back to the transfer switch, then having electrician make utility and meter connections to ATS. The main breaker from generator is 100 amp 240v, and the unit is rated at 83 amps at 240v. My local electric supply house suggested a 3-3-3-5 SER aluminum armored cable for the generator to ATS power feed. For the dc and control wires, we are looking at single 6 conductor 14 awg THHN in aluminum armored cable. The run from generator to ATS is about 30-35 feet. Do those cables make sense? Any input would be appreciated.
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Hotwire
The NEC shows that #3 Al has a amp rating of 85 amps @ 90 degree Celsius or 194 degree F. If this was me, and I was wiring from the 100 amp breaker on the genset back to the ATS I would jump up to #2, it's rated at 100 amps. #3 copper THHN has a amp rating of 110 @ 90 degree C. I typically use copper wires in conduit for my installs.
As for the #14's that would work just fine, it's what I use.
Check your local codes or with your electrician to make sure your installing something he'll approve of. I'm sure he'll answer any code questions.
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ceb58
Hotwire;8754 wrote:
The NEC shows that #3 Al has a amp rating of 85 amps @ 90 degree Celsius or 194 degree F. If this was me, and I was wiring from the 100 amp breaker on the genset back to the ATS I would jump up to #2, it's rated at 100 amps. #3 copper THHN has a amp rating of 110 @ 90 degree C. I typically use copper wires in conduit for my installs.
As for the #14's that would work just fine, it's what I use.
Check your local codes or with your electrician to make sure your installing something he'll approve of. I'm sure he'll answer any code questions.


Depending on which code cycle he is on nether one of those sizes will work. First you do not size the wire by the 90deg. column unless you have some super heat resistant equipment. For a standard gen. and ATS the terminations on the equipment will be 75deg. That is the column you use. If he is under the 2005 code then it would be #1alu or #3Cu. But if he is under the 2008 or 2011 SER cable has been derated into the 60deg. column which would change it to 1/0Al or #3Cu THWN in conduit

jfn1000;8750 wrote:
I have purchased a Generac 5875 with 200 amp SE rated ATS. To save on some of the installation costs, I intend to do some preliminary wiring from generator back to the transfer switch, then having electrician make utility and meter connections to ATS. The main breaker from generator is 100 amp 240v, and the unit is rated at 83 amps at 240v. My local electric supply house suggested a 3-3-3-5 SER aluminum armored cable for the generator to ATS power feed. For the dc and control wires, we are looking at single 6 conductor 14 awg THHN in aluminum armored cable. The run from generator to ATS is about 30-35 feet. Do those cables make sense? Any input would be appreciated.


I hope you do not plan on direct burying this cable. The aluminum will last about a year in the ground.
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jfn1000
thank you both for your replies, I made an error in my question. The armored conduit is aluminum - but the 3-3-3-5 wires are copper. Sorry for the confusion and thanks again.
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ceb58
jfn1000;8759 wrote:
thank you both for your replies, I made an error in my question. The armored conduit is aluminum - but the 3-3-3-5 wires are copper. Sorry for the confusion and thanks again.


I still question the alum. part. Is this going to be direct burial and is it listed as such?
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jfn1000
Thanks for the concern. The cable will not be buried. The generator is about 20 inches behind the garage, so I'll be coming out that wall with an LB fitting and the line will be exposed to the elements for that distance. What would you recommend? I was looking at the armored cable so that I won't need to run separate conduit along my basement concrete wall.
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Skip Douglas SkipD
I would suggest that, for the "control" set of wires you run 12 gauge as long as you're going to have extra wires in the package. That way you could run a separate 20-amp 120 VAC feed to a receptacle inside the generator. That could be very useful in the future. I use such a receptacle in my generator for a battery warmer and an aftermarket battery maintainer/charger as well as the occasional electric tool.
Skip Douglas
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jfn1000
Thanks Skip, I may be mistaken, but I think the 5875 generator already has a 120 VAC via control wire T1, which is one of the six "control wires" I mentioned. (the others are N1 & N2 (240V), and dc lines 0, 194 & 23). There is a gfci outlet on the outside of the generator in the breaker box that I presume works as a convenience outlet.
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Skip Douglas SkipD
jfn1000;8764 wrote:
Thanks Skip, I may be mistaken, but I think the 5875 generator already has a 120 VAC via control wire T1, which is one of the six "control wires" I mentioned. (the others are N1 & N2 (240V), and dc lines 0, 194 & 23). There is a gfci outlet on the outside of the generator in the breaker box that I presume works as a convenience outlet.
Is there a separate neutral wire for that? I ran separate neutral and equipment ground wires plus the "hot" for my receptacle (which is inside the generator cabinet) to make it like any other branch circuit.
Skip Douglas
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ceb58
jfn1000;8762 wrote:
Thanks for the concern. The cable will not be buried. The generator is about 20 inches behind the garage, so I'll be coming out that wall with an LB fitting and the line will be exposed to the elements for that distance. What would you recommend? I was looking at the armored cable so that I won't need to run separate conduit along my basement concrete wall.


From your OP running 30-35ft of #3-3 w/g mc cable would be an expensive install. If that is what you plan on using you will still need another for the control wiring.
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jfn1000
CEB58, What do you mean by "expensive install"? Are you referring to the wire cost or labor or both. What would you recommend?

And Skip, I think the neutral for the 120 v gfci is shared.

Keep the suggestions coming - much appreciated.
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ceb58
jfn1000;8768 wrote:
CEB58, What do you mean by "expensive install"? Are you referring to the wire cost or labor or both. What would you recommend?

And Skip, I think the neutral for the 120 v gfci is shared.

Keep the suggestions coming - much appreciated.


To give you an honest answer you must give an answer. In your OP you stated the supply house recommended 3-3-3-5 Al. armored cable with copper conductors. (MC cable) Is this correct? If so, if you don't mind, what was their price per ft?
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jfn1000
Actually,I suggested the armored cable part as I thought having the cabling would save installation time as I would not need conduit. The supply house spec'd the size of the copper wiring based on the 83 amp output at 240v. Price was about $6.70 per lf. I've been rethinking that strategy of the mc cable and thinking liquid tight conduit may be a better answer. What are you thinking Ceb58?
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ceb58
jfn1000;8772 wrote:
Actually,I suggested the armored cable part as I thought having the cabling would save installation time as I would not need conduit. The supply house spec'd the size of the copper wiring based on the 83 amp output at 240v. Price was about $6.70 per lf. I've been rethinking that strategy of the mc cable and thinking liquid tight conduit may be a better answer. What are you thinking Ceb58?



OK, if I were doing the job. I would install 1 1/4" EMT conduit on the wall and pull 3- #3Cu with a #8 green EGC ( in a cable they way oversize the EGC)
By the way you do not size the conductors by the rated amps. It is size to the over-current protection which is 100amp, #3Cu still good.

Using mc or flex is going to look like a snake on the wall no matter how close you strap it.

This hasn't been brought up yet, and I don't care what the NJ guys say:D, but you will need a disconnect for the generator. It must be located at the closest point of entry ether inside or outside.

I would install a indoor rated disconnect ( saves $) and go out of the back through the wall with a nipple to an LB and change over to liquid tight to the gen.
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jfn1000
ceb58, you raise some good points. I see what you are saying that the liquid tight or mc may sag a bit. Would pvc conduit be acceptable vs EMT. I think that may be easier to install than the EMT. And why the disconnect - I have the 100 amp shutoff in the exterior side door of the generator?
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Skip Douglas SkipD
One advantage of metal conduit is that it shields any electrical noise that may be created by the generator and which would be radiated through non-conductive conduit.

The down side of a homeowner using metal conduit is that you'd need a bender or two and some experience bending the conduit properly. I have several benders and some experience doing conduit work, and the result of what I did (a 75-foot run in the basement) looks nice enough to please my better half. PVC conduit is much more flexible than EMT and is harder to make the installation look as good as a well-done EMT installation, though you can buy elbows that you glue in and don't have to bend the conduit itself.

The one thing that you must know is that you may need pull boxes at intervals, depending on the installation. You cannot have more than a total of 360° in bends (four 90° bends, for example) between boxes.
Skip Douglas
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ceb58
jfn1000;8775 wrote:
ceb58, you raise some good points. I see what you are saying that the liquid tight or mc may sag a bit. Would pvc conduit be acceptable vs EMT. I think that may be easier to install than the EMT. And why the disconnect - I have the 100 amp shutoff in the exterior side door of the generator?


When you are looking at the gen. can you SEE the breaker with out opening the door? If not then there must be a disconnect installed per code.

SkipD;8776 wrote:
One advantage of metal conduit is that it shields any electrical noise that may be created by the generator and which would be radiated through non-conductive conduit.

The down side of a homeowner using metal conduit is that you'd need a bender or two and some experience bending the conduit properly. I have several benders and some experience doing conduit work, and the result of what I did (a 75-foot run in the basement) looks nice enough to please my better half. PVC conduit is much more flexible than EMT and is harder to make the installation look as good as a well-done EMT installation, though you can buy elbows that you glue in and don't have to bend the conduit itself.

The one thing that you must know is that you may need pull boxes at intervals, depending on the installation. You cannot have more than a total of 360° in bends (four 90° bends, for example) between boxes.


I agree with the noise factor. When I run any thing bigger than 1" EMT I just buy factory bends. Most jobs are not worth bringing out the hyd. bender and setting it up for two or three bends. The thing about using EMT is you can paint it to match the wall color.
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