120 volt generator connection.

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don9355

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Location
Fort Wayne, Indiana, USA
I have a customer that has an older Honda 2000 watt 120 volt generator. They want to be able to connect it to a new Square D 200 amp main breaker service panel. I would use a Square D generator interlock kit with a 20 amp 2 pole breaker. The generator has overcurrent protection built in. The problem is the generator only has 120 volt output using a 15 amp duplex receptacle. I considered using a 20 amp 120 volt flanged inlet, however in order to backfeed the panel and have 120 volt to both phases I would have to connect the two phases together either at the flanged inlet, or at the backfed circuit breaker. With the interlock kit installed there will be no chance of causing a bolted fault unless someone removes the panel cover and then turns on the backfed circuit breaker. The other option would be to use a 20 amp 250/125 volt flanged inlet and connecting the two phases in the cord plug or connector. Are there any code violations here that I am not aware of. I realize that it would be easier to just tell the customer to buy a different generator with a 250/125 volt output. They are aware that they will have to turn off all the 2 pole circuit breakers before they use the generator, and that they will be very limited to what they can run at any one time.
 
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GoldDigger

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Placerville, CA, USA
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Only violation that comes immediately to mind is that an interlock system that is attached only to the cover is not acceptable to the NEC.
 
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don9355

Member
Location
Fort Wayne, Indiana, USA
Can you tell me where in the NEC that a panel mounted interlock kit is not acceptable. I have heard that somewhere before, but out local inspector allows it, and my supply house says that they have had that question asked before, and that their Square D representative says it is listed.
 
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don9355

Member
Location
Fort Wayne, Indiana, USA
I really appreciate the input. I think that if I do go ahead with this installation, that I will install a 250/125 4 wire twist lock flanged inlet to back feed the panel with. Then I will make a cord with a 15 amp 125 volt cord cap on one end and a 20 amp 250/125 volt four wire twist lock connector on the other end, and install a jumper in the connector to tie the two phases together. This way there is absolutely no way of having a bolted fault occur. That leaves just one more question? If the customer forgets to turn off all 2 pole circuit breakers, is there any chance of current flow through these appliances and could it cause any damage?
 
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GoldDigger

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Worst case the motor or heating elements of an appliance would not work (no line to line voltage) but the controls (120 to neutral) might work, making for great confusion.
 
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GoldDigger

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GerryB said:
I would try to talk them into a bigger generator. I don't know if there is a Harbor Freight in your area but they have good prices on generators.
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Just do not depend on Harbor Fright/ Chicago Electric for anything that is mission critical or has to last. You get what you pay for (or less than that.)
I have no personal experience with their generators.
 
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GerryB

Senior Member
Location
woodbridge, ct. USA
GoldDigger said:
Just do not depend on Harbor Fright/ Chicago Electric for anything that is mission critical or has to last. You get what you pay for (or less than that.)
I have no personal experience with their generators.
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Mission critical:D That is true. Some of there stuff is throw away tools. Two of my customers did buy generators that started the day I was there though.
 
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10fords

Member
Location
California
don9355 said:
I really appreciate the input. I think that if I do go ahead with this installation, that I will install a 250/125 4 wire twist lock flanged inlet to back feed the panel with. Then I will make a cord with a 15 amp 125 volt cord cap on one end and a 20 amp 250/125 volt four wire twist lock connector on the other end, and install a jumper in the connector to tie the two phases together. This way there is absolutely no way of having a bolted fault occur. That leaves just one more question? If the customer forgets to turn off all 2 pole circuit breakers, is there any chance of current flow through these appliances and could it cause any damage?
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I have just about the same setup at my own house so I can run off my Honda 2000 genny. It works great so long as I manage the breakers properly. I have to shut everything off and turn on the breakers to the fridge, freezer, and whatever else might be running, at separate times. I would never do it for a customer though. Too many things to understand and remember. My experience has been that if they are capable of understanding and remembering that much, they probably wouldn't be calling me!
 
kwired

kwired

Electron manager
Location
NE Nebraska
GoldDigger said:
OK, not in the Code. Just the opinion (enforced) of some AHJs.
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Was sort of understandable when only people making such interlock kits were third parties, but most of the loadcenters today have such kits made for and listed by the manufacturer of the panel.

don9355 said:
I really appreciate the input. I think that if I do go ahead with this installation, that I will install a 250/125 4 wire twist lock flanged inlet to back feed the panel with. Then I will make a cord with a 15 amp 125 volt cord cap on one end and a 20 amp 250/125 volt four wire twist lock connector on the other end, and install a jumper in the connector to tie the two phases together. This way there is absolutely no way of having a bolted fault occur. That leaves just one more question? If the customer forgets to turn off all 2 pole circuit breakers, is there any chance of current flow through these appliances and could it cause any damage?
Click to expand...

Putting in the 125/250 4 wire inlet also allows for easier integration of a larger generator down the road - but consider a 30 amp instead of a 20 amp inlet, if/when they decide to go bigger they probably go to something with 30 amp output receptacle.
 
iwire

iwire

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Staff member
Location
Massachusetts
kwired said:
Was sort of understandable when only people making such interlock kits were third parties, but most of the loadcenters today have such kits made for and listed by the manufacturer of the panel.
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We have a rule in MA that requires the inspector to accept listed equipment when used per its listing. :)
 
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