Posted: 11/7/2010 3:07:30 AM EDT
I'm looking at installing a generator lockout and backfeed breakers in a 100 A home electrical panel rather than going with a transfer switch and sub-panel arrangement. I've got some questions about how much power can be delivered to the panel by a portable generator. I'm pretty sure this is a good place to get answers. 
I've noticed that nearly all portable generators have only one 30A/240v twist-lock output. Does that mean 30A per leg on the 240 out for a total of 60A at 120V? What I'm getting at is that all the generator inlet hookups for home electrical panels I've found locally are 30A. Does that limit the power that can be supplied to a home electrical panel is limited to 3600 W? Or is it 7200W? Given a hypothetical generator that is rated at 10000 W continuous (and assuming it has plenty of capacity for startup loads), how does one get all the rated power to the panel without exceeding the ratings of the typical inlet components? |
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Quoted:
I'm looking at installing a generator lockout and backfeed breakers in a 100 A home electrical panel rather than going with a transfer switch and sub-panel arrangement. I've got some questions about how much power can be delivered to the panel by a portable generator. I'm pretty sure this is a good place to get answers.
I've noticed that nearly all portable generators have only one 30A/240v twist-lock output. Does that mean 30A per leg on the 240 out for a total of 60A at 120V? What I'm getting at is that all the generator inlet hookups for home electrical panels I've found locally are 30A. Does that limit the power that can be supplied to a home electrical panel is limited to 3600 W? Or is it 7200W? Given a hypothetical generator that is rated at 10000 W continuous (and assuming it has plenty of capacity for startup loads), how does one get all the rated power to the panel without exceeding the ratings of the typical inlet components? It is 30a per leg. You cannot combine them. 30a is 30a. If you use one leg with a neutral for 120v it is still 30a. If you use both legs for 220v its still 30a per phase. Pick your generator and then size the wiring to the plug on the genset. If the plug is 120/240 30a then size everything 4wire 30a and you will be fine. |
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Quoted:
I'm looking at installing a generator lockout and backfeed breakers in a 100 A home electrical panel rather than going with a transfer switch and sub-panel arrangement. I've got some questions about how much power can be delivered to the panel by a portable generator. I'm pretty sure this is a good place to get answers.
I've noticed that nearly all portable generators have only one 30A/240v twist-lock output. Does that mean 30A per leg on the 240 out for a total of 60A at 120V? What I'm getting at is that all the generator inlet hookups for home electrical panels I've found locally are 30A. Does that limit the power that can be supplied to a home electrical panel is limited to 3600 W? Or is it 7200W? Given a hypothetical generator that is rated at 10000 W continuous (and assuming it has plenty of capacity for startup loads), how does one get all the rated power to the panel without exceeding the ratings of the typical inlet components? It is 30a per leg. You cannot combine them. 30a is 30a. If you use one leg with a neutral for 120v it is still 30a. If you use both legs for 220v its still 30a per phase. Pick your generator and then size the wiring to the plug on the genset. If the plug is 120/240 30a then size everything 4wire 30a and you will be fine. This. |
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Quoted:
I'm looking at installing a generator lockout and backfeed breakers in a 100 A home electrical panel rather than going with a transfer switch and sub-panel arrangement. I've got some questions about how much power can be delivered to the panel by a portable generator. I'm pretty sure this is a good place to get answers.
I've noticed that nearly all portable generators have only one 30A/240v twist-lock output. Does that mean 30A per leg on the 240 out for a total of 60A at 120V? What I'm getting at is that all the generator inlet hookups for home electrical panels I've found locally are 30A. Does that limit the power that can be supplied to a home electrical panel is limited to 3600 W? Or is it 7200W? Given a hypothetical generator that is rated at 10000 W continuous (and assuming it has plenty of capacity for startup loads), how does one get all the rated power to the panel without exceeding the ratings of the typical inlet components? First, if by “generator lockout”, you mean mechanical interlock, understand a properly installed mechanical interlock kit provides manual transfer capability and is generally NEC (National Electrical Code) compliant. Second, you must look at the generator rating for power/current information. You cannot infer available power from the available receptacles. Just because you have a L14-30 receptacle does not mean the generator can actually provide 30A (per leg) at 230V. If a generator can supply 30A at 240V, a proper connection to premises wiring would make available 30A on 2 separate 120V legs. I am avoiding a direct answer to your 60A question. Single phase, winding center tap, bla, bla, bla. Third, a NEMA L14-30 twist lock receptacle is rated for 30A 125V/250V. 30A at 240V is 7.2kW. NEMA L14-50 is rated 50A 125V/250V. 50A at 240V is 12kW. The L14-50 configuration is available in power inlet boxes; larger, consumer portable generators; and power cord sets. An example of a power inlet box with NEMA L14-50 configuration is the Reliance Controls PR50 . Something like this needs to be ordered online or through an electric supply house. I am not positive, but I think generators with NEMA L14 receptacles generally have the correct receptacle to supply maximum, continuous available current. |
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First, if by “generator lockout”, you mean mechanical interlock, understand a properly installed mechanical interlock kit provides manual transfer capability and is generally NEC (National Electrical Code) compliant.
I was looking at a mechanical interlock kit made by Square D, similar to the InterLock Kit brand suggested by OverScoped Second, you must look at the generator rating for power/current information. You cannot infer available power from the available receptacles. Just because you have a L14-30 receptacle does not mean the generator can actually provide 30A (per leg) at 230V. If a generator can supply 30A at 240V, a proper connection to premises wiring would make available 30A on 2 separate 120V legs. I am avoiding a direct answer to your 60A question. Single phase, winding center tap, bla, bla, bla.
I have a decent working knowledge of home electrical systems, but I'm not an electrician. I think I wasn't articulating the question well as a result, but you answered the question as I intended to ask it. Third, a NEMA L14-30 twist lock receptacle is rated for 30A 125V/250V. 30A at 240V is 7.2kW. NEMA L14-50 is rated 50A 125V/250V. 50A at 240V is 12kW. The L14-50 configuration is available in power inlet boxes; larger, consumer portable generators; and power cord sets. An example of a power inlet box with NEMA L14-50 configuration is the Reliance Controls PR50 . Something like this needs to be ordered online or through an electric supply house.
I am not positive, but I think generators with NEMA L14 receptacles generally have the correct receptacle to supply maximum, continuous available current. If I'm reading this correctly, the max I can feed to an existing electrical panel with a generator cord is 7.2kW with the L14-30 configuration or 12kW with the L14-50 configuration. At that point,any additional generator capacity would be overkill for backfeeding a single 100A panel without going the transfer switch route. (I'm operating under the assumption that the selected generator can actually deliver the max loads through the outlets as described here.) Is this correct? I'm trying to work out a system to maintain maximum flexibility for my home's electrical demands, while maintaining generator portability so one generator can serve house, work, or farm as needed. A permanent genset at home with another portable generator for work and the farm isn't an option at this point. I'd be grateful for additional suggestions or resources on ways to achieve my goal. Thanks to all for the input so far. |
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I was looking at a mechanical interlock kit made by Square D, similar to the InterLock Kit brand suggested by OverScoped………… If I'm reading this correctly, the max I can feed to an existing electrical panel with a generator cord is 7.2kW with the L14-30 configuration or 12kW with the L14-50 configuration. At that point,any additional generator capacity would be overkill for backfeeding a single 100A panel without going the transfer switch route. (I'm operating under the assumption that the selected generator can actually deliver the max loads through the outlets as described here.) Is this correct?............. I'm trying to work out a system to maintain maximum flexibility for my home's electrical demands, while maintaining generator portability so one generator can serve house, work, or farm as needed. A permanent genset at home with another portable generator for work and the farm isn't an option at this point. I'd be grateful for additional suggestions or resources on ways to achieve my goal. If you have a Square D panel and SqD makes an interlock kit for it, use that. Order it from an electric supply house that specifically deals with Schneider Electric (Square D) for the best price: ~$60. L14-xx is a NEMA specification for plugs & receptacles. If you are using un-modified equipment (generator, cord set, and power inlet box), I think the proper connectors will be used for the equipment rating. So, if your generator has an L14-50 receptacle, you need essentially the same configuration power cord set and power inlet box. Let me reiterate; installing the mentioned mechanical interlock on your panel face creates a manual transfer switch. I cannot comment on how much power you want or need to supply loads. That is a decision you must make after you determine which appliances, equipment, etc you want to power. Determine what you want to power. Add up the loads, taking into account surge (motor startup) currents. Select a generator that is rated to supply that load. A portable generator; power cord set; power inlet box; appropriately sized NM cable; appropriately sized double pole circuit breaker (mounted in upper right, two slots); and panel-mounted, mechanical interlock (manual transfer switch) will allow you the greatest flexibility in choosing loads to power, with a code compliant installation. So, you are on the right track. eta I do not kow if your state has any EL code issues relative to this matter not covered by NEC. |