Go Back  DoItYourself.com Community Forums > Electrical, AC & DC. Electronic Equipment and Computers > Electrical - AC & DC
Reload this Page >

Connecting an Automatic Transfer Switch at the Service Disconnect

Connecting an Automatic Transfer Switch at the Service Disconnect

Reply

  #1  
Old 10-22-14, 05:17 AM
Member
Thread Starter
Join Date: Oct 2014
Location: USA
Posts: 5
Connecting an Automatic Transfer Switch at the Service Disconnect

Based on the variety of responses to other questions in this forum, I have tried to be thorough and include the main significant details. My assessment is that people trying to help seem to want more info rather than less. Apologies in advance if I have included too much info and thank you in advance for taking time to read this and respond.

My project is to connect a 12kw standby generator to my house via an automatic transfer switch so that the generator is auto started on loss of utility power and the power source transferred from the utility feed to the generator feed, then the reverse when utility power is restored. I plan to feed the main panel / entire house and rely on load shedding modules controled by the transfer switch to ensure the generator is not overloaded.

My main questions relate to the physical placement and the electrical connection of the transfer switch.

Here is some background information which will hopefully help when attempting to answer my questions.

Description of the existing service:

The utility meter / handoff is on the pole 300' from my house. Following that, there is a 125A disconnect owned by me just below the meter and on the pole. From the pole disconnect to my house is 300' of buried conduit with what appears to me to be 2 strands of 4/0 and 1 strand of 2/0 Aluminum wire. This goes to the back of my house and terminates in another 125A breaker/ disconnect box. This house disconnect is wired to the main panel from the back of the service disconnect box. The main panel is about 60' away. The wire from the main panel to the service disconnect appears to be 3 strands of what looks like 4, 3 or 2/0 and one strand of bare for ground. Pictures of the existing service disconnect are available online from a link below.

Proposed auto transfer switch implementation.

The wire feed from the back of the house disconnect to the main panel has only 4" of wire coming out the back of the house into the existing service disconnect so there is not enough room to connect it to the transfer switch as needed. I do not want to re-do the run from the main panel to the service disconnect to add wire length as the run it is about 80', would be somewhat expensive and probably would be a challenge to pull the wire through.

To extend the main panel wires so as to reach the transfer switch, I plan to

1 - disconnect the main panel and service wires from the service disconnect box and relocate the box about 18" to the right.
2 - install a 12"x12" outdoor enclosure as a junction box where the service disconnect box used to be. Install 1-4 pole and 1-3 pole insulated terminal blocks into this enclosure
3 - in the new enclosure, connect the main panel wires to the 4 pole terminal block and connect that to the transfer switch
4 - in the new enclosure connect the incoming service wires to the 3 pole terminal block and connect that to the relocated service disconnect box

I plan to use 4/0 Aluminum wire for the connections from the junction box to the transfer switch and from the junction box to the transfer switch with the following exceptions. The transfer switch ground terminal block to the service disconnect neutral/ground terminal block and the transfer switch ground terminal block to the main panel ground terminal block. For those I will use 2/0 Aluminum because the transfer switch ground terminal block appears to be too small for 4/0.

Once that is done I can connect the service disconnect to the transfer switch and the generator to the transfer switch as required.

I haven't sized the wires for the generator to transfer switch run yet but since the generator is 12kw and only of wire away, I think 2/0 is adequate.

I have read the thread at : http://www.doityourself.com/forum/el...nce-cable.html and http://www.doityourself.com/forum/el...ce-panels.html.

I have posted diagrams of the existing and propose connections/equipment and pictures of the service disconnect and transfer switch here:

http://internetworkz.net/Generator/A...d-proposed.pdf.

I am not an electrician but have read as much info as I can find on the code related to installing standby generators. The main points that seem to stand out are

1 - generators which do not have the neutral feed switched in the transfer switch are not considered separately derived systems and therefore should not have neutral and ground bonded in the generator or the transfer switch. My equipment does not have the neutral switched and therefore is not considered a separately derived system. I also understand that the only appropriate location for bonding the neutral and ground w/ in the system is in the service disconnect box on the back of the house. My wiring plan will be done so as to ensure this is the case.

2 - In order to power the 'whole' house, the generator must meet the load requirements of the house, or must make use of appropriate load shedding technology to ensure the generator is not overloaded. I will install load shedding modules on several circuits to ensure this is the case. This is depicted in the proposed diagram.

The more routine / obvious things like use the right size wires, physical placement of the generator in relation to the building, requirement to use a transfer switch, etc.

My first general question if the proposed installation of the junction box to extend the main panel wires to the transfer switch is an acceptable solution? Aside from re-doing the wiring from the main panel to the service disconnect, is there a better solution for this problem?

Assuming the junction box is a decent/acceptable solution, then my second question is if the wiring diagram I have proposed (page 4 of the pdf file) is correct?

Thank you in advance for your assistance.
 
Sponsored Links
  #2  
Old 10-22-14, 10:51 AM
Member
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
What, in Watts of Kilo-Watts, is the "power-rating" of the transfer-switch ?
 
  #3  
Old 10-22-14, 12:11 PM
Member
Thread Starter
Join Date: Oct 2014
Location: USA
Posts: 5
Transfer switch rating

PATTBAA -

The rating on the ts box is 200Amps and 240Volts. I cannot find any documentation in the transfer switch manual or on the transfer switch indicating a watt rating. Assuming a power factor of 1 the max Watts with 200A current and 240 volts is 48kw.
 
  #4  
Old 10-22-14, 12:43 PM
Member
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
Could you please direct us to the "On-Line" installation instructions of this transfer-switch ?

Using the components such as the fuse-block as a "size-gauge" , the 200 amp transfer relay (?) appears unusually compact for one with this specific amp-rating.
 
  #5  
Old 10-22-14, 12:53 PM
Member
Thread Starter
Join Date: Oct 2014
Location: USA
Posts: 5
Genarc RTSR200A3

Genarc support page for RTSR200A3:

Generac Power Solutions | Service and Support | Online Product Support | Generac Power Systems

Product manuals are all available from there or the direct link to the manual is here:

http://soa.generac.com/manuals/RTSR200A3/0K0170

Thanks again for taking the time to look at this.
 
  #6  
Old 10-22-14, 10:35 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 46,127
The Generac transfer switches are fairly compact as compared to the Kohler ones.

200A is the rating. It will transfer a 200A service to a 200A generator. Your generator at 12kw is fine. Have you done a load calculation ? Here in NJ the inspectors are requiring it during the permitting process. They may question such a small generator on a 200A service. They will definitely look for load shedding.

Is it your plan is to integrate a different brand generator to the Generac switch and have that switch perform the auto start functions ?
 
  #7  
Old 10-23-14, 09:15 AM
Member
Thread Starter
Join Date: Oct 2014
Location: USA
Posts: 5
PJmax -

Actual service to my house is 125A ( I specified 120 in my original post but that was a typo on my part as the breakers on each end of the service connection are 125A). Generac TS come in 100A, 150A and 200A. As I understand it you can't put a 100A TS on a 125A service. The price diff between 150A and 200A is small and so I figured why not use 200A so at least I don't have to upgrade the TS if I ever upgrade the service > 125A.

I got a fantastic deal on the 12kw propane generator and it would have cost me $1k or more to go w/ something much larger (even 14kw). Rough load calcs using online tools put my overall lighting and appliance load at about 30amps. My well pump is on a 15amp circuit breaker. All other major loads (dryer, hottub, range/oven, ac) will be on load shedding control. If this is still too close for the Inspector to approve, I will put the well pump on load shedding control as there is one more load shedding circuit on the TS.

The generator is a Generac Honeywell branded unit. Since I bought the TS and gen separately I spent quite a bit of time on the phone w/ Genarc to make absolute certain they would work together. I actually called Genarch and Honeywell multiple times, talked to different reps at each and got the same answers/recommendations so I'm pretty confident they will work together.
 
  #8  
Old 10-23-14, 09:54 AM
Member
Join Date: Sep 2013
Posts: 85
A couple of issues to be aware of. Load calculations follow specific rules, i.e., CB amperage is irrelevant. You need an electrician or the town inspector to guide you. You are correct that load shedding can allow a smaller generator to pass inspection, but load shedding is primarily there to protect you during the initial changeover. You should not rely on load shedding once on generator power. You should rely on some method of monitoring your power use to manage the loads - deciding which appliances you turn on at any given time. I use the CurrentCost EnviR combined with free online KW graphing from Meniscus Energy to manage my 200amp service with a 9kw whole home setup. There are other comparable monitors available - Google "power monitors". The graphing services have an additional benefit of letting you monitor KW hour usage and cost.

 
  #9  
Old 10-23-14, 10:45 AM
Member
Thread Starter
Join Date: Oct 2014
Location: USA
Posts: 5
patmurphey -

Thanks for the tip on the power monitoring tools. I couldn't agree more about managing power by ongoing monitoring of load and adjusting use to ensure the generator is not overloaded. I do intend to monitor it very carefully so appreciate the tip on the tools.

IMO the main reason load shedding control is there is to pass inspection .
 
  #10  
Old 10-23-14, 11:23 AM
Member
Join Date: Sep 2013
Posts: 85
"IMO the main reason load shedding control is there is to pass inspection."

...and the inspection rules make it so that when there is a power outage with everything on, the generator can safely start. Good luck, it sounds like you're trying to do everything right.

Lots of good information here about electrical and gas plumbing issues, that might save you from some hassles:

http://zillerstore.com/forums/index.php
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes