[mikekap0120]

Hi all,

I am getting ready to install a whole house generator (Sandy victim) and I am in the process of submitting my plans to the inspector and wanted to get some advice before submitting. Attached is a diagram of what I am planning.

Questions I have are:

1. Is the #1 AWG wire I have specified between the generator and the transfer switch support the 100 AMPs? Could I use smaller? Can I use Aluminum or does it need to be Copper?

2. Do the conduit sizes I have listed here suffice for the power and control wires or am I oversized? I am planning to use PVC for the conduit

3. Is there any way to tell the size of the existing SEU cable currently in use?The jacket of the cable does not appear to be marked, so the 2/0 I have listed is an assumption based on the size of the wire and the fact that it currently supports 150 amp service.

Also any other input on the design or pointing out anything else I am doing wrong would be appreciated.

 

[Auger01]

Just a few coments off the top of my head. I may have missed a few things. A 12kw unit will only do 50 amps and 6 gauge is big enough for that if the distance isn't too far.

Looks like you have 150 amp service and are planning to run that though a 100 amps switch? That might be a problem.

Have you done a load calc as required to determine what you need to shed to keep from overloading the generator?

Have you considered hooking the transfer switch up as a sub panel? It might be easier that way.

 

[diystephen]

[A 12kw unit will only do 50 amps]

That would be if the loads were all 240VAC. 12KW @ 120VAC is 100A.

 

[frenchelectrican]

There are two thing it did come up to my mind real quick.,


A) you have 150 amp service and the transfer switch you have is 100 amp that will not fly at all.

B) You should have SER instead of SEU cable after the main outside breaker box which that is 4 conductor.

That two thing it will pop up very fast so you may want to find a alternative way to slove the issue there.

Merci,
Marc

 

[granitefan]

Hi all,



Questions I have are:

1. Is the #1 AWG wire I have specified between the generator and the transfer switch support the 100 AMPs? Could I use smaller? Can I use Aluminum or does it need to be Copper?

You can use either. Copper is more expensive. If you use alum, you need bigger sizes. #1 cu would be 2/0 alum. Always use THHN rated wire and the 75 degree ratings when you figure this stuff. #1 is big. #2 would be better for your run length and that's if the breaker on the generator is 100 amps.

Here's a link for basic wire amperage vs size.
http://www.cerrowire.com/ampacity-charts

If your service is 150 amps, then the whole house switch needs to be 150 or larger. If it's the EZ switch, then it's limited circuits and the size is your choice depending on how many circuits you want to carry over.

You should make sure the breaker on the generator is 100 amps. That sounds too big for a 12KW. 20KW's have a 100 amp. My 17 KW has a 65 and smaller gens typically ave 50 amp breakers. Don't confuse the gen breaker with the transfer switch size. They're two different things. Size your wire (from gen to xfer switch) to the breaker on the generator, not the transfer switch amps.

2. Do the conduit sizes I have listed here suffice for the power and control wires or am I oversized? I am planning to use PVC for the conduit

Type "conduit fill calculator" on the internet and you'll find some easy answers for sizing conduit. For example your power conduit from gen to xfer switch can be 1 1/4 for 4 #6's. You can use 1/2 inch for your control wires.

Here's an easy one to use http://www.electrician2.com/calculators/rf_calculator.html

3. Is there any way to tell the size of the existing SEU cable currently in use?The jacket of the cable does not appear to be marked, so the 2/0 I have listed is an assumption based on the size of the wire and the fact that it currently supports 150 amp service.

If it's alum (and I think most SEU and SER is) it's probably 3/0 or 4/0 to handle 150 amps.

 

[Auger01]

That would be if the loads were all 240VAC. 12KW @ 120VAC is 100A.

You are correct, but it is still only 50 amps per leg and 6 guage would still be perfectly adequate for that amount of current.

 

[mikekap0120]

Hi all,

Thanks for the reply. I mis-represented the size of the breaker in the generator. There are two 50 AMP breakers. 100 amp total service.

On the size of the transfer switch vs the actual service, I had the same concern that the 100 amp switch was not sufficient for the 150 amp service (sounds like common sense as I type it)

However I had a licensed electrician look at the job and asked the local inspector, and they both said that the 100 amp transfer switch was sufficient as long as the generator only put out 100 amp total service.

Is there anything in the code that addresses this specifically?

Thanks for the help!

 

[Auger01]

Here it is:


"702.5 Capacity and Rating .5 Capacity and Rating.
(A) Available Short-Circuit Current. Optional standby system equipment shall be suitable for the maximum available short-circuit current at its terminals.
(B) System Capacity. The calculations of load on the standby source shall be made in accordance with Article 220 or by another approved method.
(1) Manual Transfer Equipment. Where manual transfer equipment is used, an optional standby system shall have adequate capacity and rating for the supply of all equipment intended to be operated at one time. The user of the optional standby system shall be permitted to select the load connected to the system.
(2) Automatic Transfer Equipment. Where automatic transfer equipment is used, an optional standby system shall comply with (2)(a) or (2)(b).
(a) Full Load. The standby source shall be capable of supplying the full load that is transferred by the automatic transfer equipment.
(b) Load Management. Where a system is employed that will automatically manage the connected load, the standby source shall have a capacity sufficient to supply the maximum load that will be connected by the load management system. "



Even though there is only one hande on the 150 amp main it is switching both legs. So if you are calling the 12kw generator a "100 amp" unit then keep apples to apples and call the service disconnect 300 amps.

 

[mikekap0120]

Thanks Auger01,

I read this as addressing whether the generator is sufficient to handle the load transfered to it, not whether the transfer switch has to match the service coming into the house. Am I misinterpreting it.

The Transfer switch and generator are matched (shipped in the same box)
The generator has plenty of capacity to support the load in the house. I only have one AC unit, and all of the other major appliances work of off gas. Also, the transfer switch has load shed capabilities for the AC unit, which I am planning to hook up as well.

 

[HVACTECH96]

Control wires should be minimum 16 awg

 

[HVACTECH96]

Also put gen up at least 6" off ground , makes changing oil alot easier when your not trying to make oil flow uphill into drain pan.

 

[Missouri Bound]

Hi all,

Thanks for the reply. I mis-represented the size of the breaker in the generator. There are two 50 AMP breakers. 100 amp total service.

Thanks for the help!

Mike, do you mean a 50amp dbl. pole breaker? That is considered a 50 amp, 240v service. You don't add them together. Use that in your communication with the inspector and use that for your wiring sizing.:wink:

 

[Missouri Bound]

That would be if the loads were all 240VAC. 12KW @ 120VAC is 100A.

...but that's not how a service is figured. And it's a 12K generator, at 240v. It has a dbl. pole 50 amp breaker.:whistling2:

 

[diystephen]

...but that's not how a service is figured. And it's a 12K generator, at 240v. It has a dbl. pole 50 amp breaker.:whistling2:

Sure, but reread my post (and the line I responded to.) My response was not in regards to the correct gauge of wire or breaker (as you and the other poster are correct in that regard.) I stated a 12K genny @ 120VAC adds up to 100A. It's the same as 100A service in a residential home; each leg can draw 100A which would equal a 200A total @ 120VAC.

 

[Missouri Bound]

Sure, but reread my post (and the line I responded to.) My response was not in regards to the correct gauge of wire or breaker (as you and the other poster are correct in that regard.) I stated a 12K genny @ 120VAC adds up to 100A. It's the same as 100A service in a residential home; each leg can draw 100A which would equal a 200A total @ 120VAC.

Yeah....it's the same, but your description and explanation is totally inaccurate.:laughing:

 

[diystephen]

Yeah....it's the same, but your description and explanation is totally inaccurate.:laughing:

How so?

 

[Missouri Bound]

We're done. You aren't grasping this and it's not up to me to teach you.

 

[HVACTECH96]

Watts / volts = amps 12000w/240v=50a output

 

[diystephen]

We're done. You aren't grasping this and it's not up to me to teach you.

Sorry if I aggrevated you. I thought this was a DIY site to share knowledge. All I'm saying is what the above poster said, but for 120VAC loads.

12000W/120VAC=100A

 

[Missouri Bound]

Sorry if I aggrevated you. I thought this was a DIY site to share knowledge. All I'm saying is what the above poster said, but for 120VAC loads.

12000W/120VAC=100A

I'll try again. The generator does NOT provide 12kw @ 120v. It provides a total of 12kw @ 240 volts. Let me give you an example. Lets say you own two cars which each can go 120 MPH. That does not mean you can go 240 MPH. Back to the generator. You have 50 amps available at the generator for a 120v load. The wiring for the generator will be calculated at that amperage. I see that you are arguing semantics. Good for you, but this is an electrical forum and there are certain facts which apply in any answers or discussion here. The best thing we can do here is make the answers simple and proper within the guidlines of the NEC. :yes: