Generator Install

[rob4ara]

Customer wants a whole-house backup generator. Right now 4/O AL SEU runs from service to Main Panel with 200 Amp service. We are installing a Generac 20K with Nexus Smart Switch ATS. Length of run from generator to panel/transfer switch is less than 20'. Generac calls for the SEU to run straight into the transfer switch, and thereafter, the distribution panel. The install calls-out for a new run of the SEU to reach the transfer switch (2' longer). Generac instructions calls for 250 MCM wire. Under the most restrictive interpretation of the NEC:
1. Does the NEC require a service disconnect between the utility service and the transfer switch?
2. Does the NEC require a service disconnect between the generator and the transfer switch?
3. Am I misreading NEC 310.16, or can I run 4/O AL SEU from the utility service to the transfer switch, and then run 2.5'' pipe with 4/O THHN from the transfer switch to the generator and from the transfer switch to distribution panel?
4. Why would Generac be calling for 250 MCM?

Thanks.

 

[billyzee]

Gen Install

Gen Install

1. Article 230.66 Marking says that the service equipment must be specially marked. If the Xfer swithc meets the marking requirments for a service then you can use it. I suspect that it does not.
2. If #1 is not met then Yes you need a service disconnect.
3. SEU = USE (right?), as I see it?.4/0 Al is only good for 180A (Table 310.16, 90 deg column for USE). Suppose your continuous load current is determined to be 160A. Then by Article 230.23 and 230.42 you need 200A worth of conductors (1.25 x 160). In this situation your 4/0 Aluminum would not be OK, but the 250kcmil Al would be OK.

 

[augie47]

Customer wants a whole-house backup generator. Right now 4/O AL SEU runs from service to Main Panel with 200 Amp service. We are installing a Generac 20K with Nexus Smart Switch ATS. Length of run from generator to panel/transfer switch is less than 20'. Generac calls for the SEU to run straight into the transfer switch, and thereafter, the distribution panel. The install calls-out for a new run of the SEU to reach the transfer switch (2' longer). Generac instructions calls for 250 MCM wire. Under the most restrictive interpretation of the NEC:
1. Does the NEC require a service disconnect between the utility service and the transfer switch?.

There are a couple of things to consider. As BillyZee states, the service must terminate in listed service equipment. I also doubt your TS is service rated.
Also keep in mind the requirements of 230.70 as far a location

2. Does the NEC require a service disconnect between the generator and the transfer switch?.

Since the generator is located outside the structure, 225.32 will require the genrator feeder have a disconnect at the structure...See 445.18 in regard to this requirememt also.

3. Am I misreading NEC 310.16, or can I run 4/O AL SEU from the utility service to the transfer switch, and then run 2.5'' pipe with 4/O THHN from the transfer switch to the generator and from the transfer switch to distribution panel? .

The use of 4/0 AL SE can depend on how your AHJ enforces 338.10(B)(4), the calculated load, and it's being classified as a feeder or service.
That can vary from jurisdiction to jurisdiction

4. Why would Generac be calling for 250 MCM?

Thanks.

No idea.

Also note the requirements of 702.5(B)(2)... Your 20 KW Generator on a 200 amp service may not satisfy that requirement.

 

[rob4ara]

Generator Design Plan Questions under 2008 NEC

Generator Design Plan Questions under 2008 NEC

I need some help with this install.

My Plan:
Make runs from meter to service disconnect, to transfer switch and then to distribution panel. Also make run from 20 kw generator (which has a built-in 100 amp circuit breaker disconnect) to transfer switch. I am operating under the 2008 NEC rules.

Questions:
SEU from meter to service disconnect (interior mount):
-as long as I mount it within 10 feet, is that ok or does it have to be the closest box to the meter?

- 75 degree column for AL SEU only has ampicity of 180 amps. Does that apply to residential or all applications?
-Is that ok for a 200 amp service or do I need 250 kcmil ?

At Service Disconnect?1st entrance point:
Separate neutral from ground?

From Service Disconnect to transfer Switch:
-Can I run SER or do I need to run THHN in conduit?

-Since it is an interior feed, does it get derated under the 60 degree column?
(See NEC 338.10)

-If so, can I run 4/0 copper of 4/0 copper THHN in conduit (note the 60 degree copper column has 195 ampicity. Do I have to push it to 250 kcmil to get ampicity to 215?

From transfer Switch to distribution panel:
-Can I run SER or do I need to run THHN in conduit?

-Since it is an interior feed, does it get derated under the 60 degree column?
(See NEC 338.10)

-If so, can I run 4/0 copper of 4/0 copper THHN in conduit (note the 60 degree copper column has 195 ampicity. Do I have to push it to 250 kcmil to get ampicity to 215?

From Generator to Transfer switch (25 foot run):
-Instructions calls wire size for ampicity for 75 degree column. Since the generator has a 100 amp breaker/disconnect my plan was to run copper THWN in rigid pipe.

-Since it is in a runway, as opposed to free air, can I rely upon the 75 degree column and use AWG 2 copper, or do I need to push it to AWG 1?