Multiple Generators

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shortcircuit2

Senior Member
Location
South of Bawstin
Has anyone here ever hooked up multiple generators to a dwelling for redundancy?

I?m trying to figure out how it can be wired. There is a job in our area that wants to connect three 20KW generators thru separate transfer switches to separate load panelboards? and be able to connect any of the generators to any panelboard if any generator fails during an outage.

One idea is to connect each panelboard feeder thru a pin & sleeve connection so one can be disconnected and connected to the other.
 

John120/240

Senior Member
Location
Olathe, Kansas
Heck if I know. Three generators connected to three panels & then interconnected if one generator fails:

#1 These people have way too much money to throw around (anyway the electrician makes money)

#2 Get an engineer involved to figure out grounding, Automatic transfer switches etc

#3 How often does an outage occur ?
 

shortcircuit2

Senior Member
Location
South of Bawstin
Heck if I know. Three generators connected to three panels & then interconnected if one generator fails:

#1 These people have way too much money to throw around (anyway the electrician makes money)

#2 Get an engineer involved to figure out grounding, Automatic transfer switches etc

#3 How often does an outage occur ?

#1 I agree with you about the money.

#2 What does an engineer know about grounding?

#3 The home is at the end of long dirt road, many trees that knock power out frequently.

#4 Below is a diagram of an idea...see any code violations?
 

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ceb58

Senior Member
Location
Raeford, NC
#1 I agree with you about the money.

#2 What does an engineer know about grounding?

#3 The home is at the end of long dirt road, many trees that knock power out frequently.

#4 Below is a diagram of an idea...see any code violations?
I would suggest putting a manual transfer switch between the ATS and the panel. Bring the feed from the ATS to the utility side of the MDS, install the pin connector and run it from the gen lugs. Then suggest they buy a portable unit, with the N-G separated, as a back up. In your drawing it is the flex cord between the connector and panel that I would question.
 

masterinbama

Senior Member
get paralleling gear and parallel 2 larger gen sets to feed a 400 amp distribution panel . From there feed the 3 subs and do selective load shedding should either of the 2 generators fail during an outage (a slim possibility).
 
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George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
#1 I agree with you about the money.

Ditto.

#4 Below is a diagram of an idea...see any code violations?

Depends on the cord you use. Table 400.5(A)(1) only goes up to 80 amps, if you were planning on 100A OCPD. 400.7 would permit a cord in this application IMO.

What about a generator feeding a panel with priority loads? You could sell this idea by stating that the Rube Goldberg contraption you'd have to design would be very confusing for the end user.
Nice idea if you really need 240A of standby, BTW.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Retraction: if 120/240, you have 95A, not 80A.

Another thought: if all three panels are priority loads, you actually need a fourth generator. Every generator is accounted for, so if one fails...

Make them select priority equipment, buy one panel and two generators, call it a day. :D
 

masterinbama

Senior Member
#4 Below is a diagram of an idea...see any code violations?



Permanent use of rubber cord.

400.8 Uses Not Permitted. Unless specifically permitted in 400.7, flexible cords and cables shall not be used for the following:
As a substitute for the fixed wiring of a structure
Where run through holes in walls, structural ceilings, suspended ceilings, dropped ceilings, or floors
Where run through doorways, windows, or similar openings
Where attached to building surfaces Exception to (4): Flexible cord and cable shall be permitted to be attached to building surfaces in accordance with the provisions of 368.56(B)
Where concealed by walls, floors, or ceilings or located above suspended or dropped ceilings
Where installed in raceways, except as otherwise permitted in this Code
Where subject to physical damage
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
get paralleling gear and parallel 2 larger gen sets to feed a 400 amp distribution panel . From there feed the 3 subs and do selective load shedding should either of the 2 generators fail during an outage (a slim possibility).

Probably the best way to do this, Genercrap is famous for parralelling small units like this, all three can be parralelled, and just load shed non critical loads.
 

templdl

Senior Member
Location
Wisconsin
My concern would be synchronization, that is to assure that all paralleled generations at in sync. Generators that are not in sync would be a big issue in my opinion.
 

brian john

Senior Member
Location
Leesburg, VA
1. Do a load study and determine the size of generator you actually need.
2. Install 2 generators of equal capicity where one can handle the full load through a generator ATS (each source is a generator) and this feeds a utility/generator ATS.
3. Install an alternator circuit in the ATS to utilize each unit equally.

If the generator service is that crappy in your area that they need 3 generators for reduncy, START A RELIABLE GENERATOR SERVICE COMPANY.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
My biggest concern, not mentioned yet, is that the diagram shows three independent transfer switches, but the pin connectors are on the panel side of the transfer switch. This would allow the generator connection from an activated transfer switch to be patched to a sub-panel whose transfer switch is still in the utility postion.

This would not cause a conflict, as the original source to the second panel would have to be disconnected, but it could cause a hazardous condition in which somebody working on the system could not rely on the transfer switch position to indicate the power source to that panel. I would put the patch connections on the generator side of the transfer switches.
 

shortcircuit2

Senior Member
Location
South of Bawstin
The intended approach was to set up the generators separately, not paralleled. I don?t think paralleling switchgear is available for a small scale project such as this.

I guess this separate approach will only work as a permanent installation without the pin & sleeve setup.

Another concern is that all the generator system neutrals are interconnected. Is this a problem? Would transfer of the neutral be needed also?
 

RB1

Senior Member
I think Brian John has the right idea. Typical N+1 redundancy with each generator capable of carrying the full load. Or you colud use ten two-pole double-throw contactors and three transfer switches. The controls would be fun and exciting
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
The intended approach was to set up the generators separately, not paralleled. I don’t think paralleling switchgear is available for a small scale project such as this.

I guess this separate approach will only work as a permanent installation without the pin & sleeve setup.

Another concern is that all the generator system neutrals are interconnected. Is this a problem? Would transfer of the neutral be needed also?

Finally the second page opens now, Generac does these on a small scale, did four 40 kw on a distribution center a couple of years ago, customer bought everything, so as long as they were willing to pay for installing four instead of one............Maybe it was a good idea, because one shut down because it was leaking coolant. Not a good sign for brand new generators.
 
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brad9m

Member
Location
Alpharetta, GA
I'm sure it's overkill at $1750, but the SEL-751 could do the job. It would handle the reclosing, 50/51 protection, and sense the loss of voltage for starting the generators.
 
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