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#210362 06/16/13 10:54 PM
Joined: Apr 2005
Posts: 7
New Member
What we have is an existing electrical installation where there is a meter bank with a main 1,000 Amps breaker.

The service is 120/208V, 3 - phase. The meter bank currently serves six meters rated at 100 Amps 3 phase, there is also a 400 Amps service tapped off from the 1,000 Amps supply in the meter bank. this 400 Amps is split up to serve two 200 Amps panel after it leaves a set of C.T.

The owner wants to have a gas generator installed on the roof of the building to serve the units that this meter bank takes care of.
We don't want the power company (CUC) KWHM to be reading power consumption when the generator is running. We don't have any room in the electrical for any large equipment's.

I was told that there are breakers that could be fitted in the electrical panels for these units that would work as a automatic transfer switch which could work in conjunction with a generator panel that is link with the generator.

All the panels and meter bank is G.E.

If we have to replace the existing panels with panels that are fitted with these breakers then the owner would even consider this option.

Many thanks for your help.


Joined: Jun 2004
Posts: 613
I think Square-D makes a kit for their panels.

There is a similar job in my area where the owners signed off that it was ok as set up on the line side of the meter.

Joined: Apr 2002
Posts: 7,333
Likes: 7
There are manual interlock kits available for some manufacturers panels & breakers that allow a backfed cb (generator input) to be installed in a panel and prevent any backfeed into the utility grid..

Note the key word 'manual'!

I do not know of any ATS equipment that may do what you described.

Scott35 is our 'go to EE here & he may have a solution, but IMHO it will not be easy & inexpensive.

Joined: Jun 2004
Posts: 613
Square D makes a QO panel with an automatic transfer built in...but it is expensive.

Here is a link...

Joined: Apr 2002
Posts: 7,333
Likes: 7
Thank you for that link. The brochure is dated 2009; I have not seen this item on any installs.'

Have you seen or installed ?? Any clue on $$$ ??

The OP is looking for 3 phase, I wonder if it's available??

Joined: Jun 2004
Posts: 613
Hot Line, Square-D is a leader in product innovation.

I came across this when searching for another Square-D part. I think they also make a kit that can be adapted to the QO panel. Iím not aware of any 3-phase application...

Joined: Oct 2000
Posts: 2,722
Broom Pusher and

I have never seen any Automatic Transfer type MCCB before, but it would be a good idea!
Have seen Manual Transferring Devices - Three Pole Double Throw Manual Switches.

One of the most difficult obstacles you will be confronted with is how to route and tap the Generator Output Feeders in the existing Switchboard Sections.

The 400 Amp Section would likely be the easiest to deal with - as it would be a "Stand-Alone" item, tapped off of the Line Side Bus Kit.
Place a 400 Amp 4 pole ATS at the 400 Amp Service, route the Load Side Feeders from the 400 Amp Main OCPD to the ATS, then Terminate the Panelboard feeders to the ATS Output.

The SDS Generator's Feeder would be Tapped for each Transfer Switch, with an OCPD included with each Tapped Feeder.

The 100 Amp Meter Sections will be more of a challenge.
If you are able to obtain a direct replacement Transfer Circuit Breaker, with an equal Frame Dimensional size - AND offers Over Current Protection for both inputs (Utility + Generator), then the Generator Feeder could be Tapped with multiple 100 Amp Feeders, Terminated directly to the Tenant Meter Main Transfer devices.

Otherwise, you will need to perform the same installation per each 100 Amp Service Section, as was described for the 400 Amp Service:

  1. One (1) 100 Amp 4 Pole ATS per Tenant Service Section,
  2. Intercept existing Panelboard Feeder at Main Breaker's Load Side - run to Output Side of corresponding ATS,
  3. Install 100 Amp Feeder from Main Breaker Load Side to corresponding ATS "UTILITY" Input,
  4. Install 100 Amp Feeder from Tapped Generator Feeder's OCPD Load Side, to corresponding ATS "GENERATOR" Input.

Each 100 Amp ATS would have a Feeder terminated to the "GENERATOR" Input, which is Tapped off the Generator's Output Feeder. These Tapped Feeders would have an OCPD placed at the Tap point.

This is just a quick assumption, so please explore other options.

Good luck!!!

--Scott (EE)

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Oct 2000
Posts: 3,672
Likes: 2
(posted for TRUEPOWER)
Hello Friends

I am having some problems logging on, however what is the largest propane generator have you ever seen? the calculation work out to be 360Kw needed for this job. NEXT QUESTION do you rate it at full load. the need is 1000A 120/208 3ph and pf at .80 this work out to be 288kw and if this to be 80 of the size then we will need 360kw.

Please for your advice on this


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