30 Amp or 50 Amp for Generator


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Old 06-02-15, 05:30 PM
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Question 30 Amp or 50 Amp for Generator

Hi, we have a gasoline generator, has 9375 starting watts, and 7500 running watts. An electrician is installing a transfer switch and doing anything related to get the generator properly set up. The generator has to power hook ups, as follows:

120/240 Volt AC, 30 Amp Twist-Lock Receptacle
(NEMA L14-30R) – May be used to supply
electrical power for the operation of 120
and/or 240 Volt AC, 30 Amp, single phase 60 Hz
electrical loads.

OR IT ALSO HAS THIS:

120/240 Volt AC, 50 Amp Twist-Lock Receptacle
(NEMA 14-50R) – May be used to supply electrical
power for the operation of 120
and/or 240 Volt AC, 50 Amp, single phase 60 Hz
electrical loads.

The electrician is supplying everything except he asked that we get the power cord. Do you guys think I should go with the 30 Amp or 50 Amp. We will be using the generator in a power outage and will be running a refrigerator, the blower on the gas furnace, some lights, TV, cable DVR, and computer.

Would getting a 50 Amp be better, have any benefits? Our electrical panel is 100 amp.

Any help would be greatly appreciated as I need to get the cord ASAP. Thanks!
 
  #2  
Old 06-02-15, 05:52 PM
Tolyn Ironhand's Avatar
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Yes, use the 50 amp output.
 
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Old 06-02-15, 06:05 PM
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7,500 watts at 240 volts is 31.25 amperes or just slightly over the rating of the L14-30 receptacle. The peak output of 9,375 watts is 39 amperes or a 30% overload on the 30 ampere receptacle. While it is common to use the 30 ampere receptacle on a 7.5 kW generator it IS an overload and will cause the plug/receptacle to overheat if the overload continues for any significant time.

If it were mine I would use the 50 ampere receptacle and no less than a #8 copper conductor interconnect cable. The connection at the house should also be rated at 50 amperes.

All that stated, 7.5 kw is a fairly large generator for emergency usage. I can run everything on your list in my home with a 2.8kW continuous, 3.0kW peak, 120 volt only generator. Using that criteria you could probably get away with using the 30 ampere receptacle with a #10 copper conductor interconnect and matching inlet at the house with no problems at all.
 
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Old 06-03-15, 06:24 AM
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...also those ratings are what the generator produces when it's brand new in the manufacturer's test lab. In practice knock at least 20% off that for real world conditions.

From a practical point of view I don't think it matters which you choose. From the code point of view go with the 50A since the generator technically exceeds 30A wiring. Also make sure your electrician knows which inlet to put on the transfer panel to match the cord you got.
 
 

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