Generator 220 30A plug limiting factor?

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  #1  
Old 01-17-07, 05:07 PM
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Generator 220 30A plug limiting factor?

I'm looking at the B&S 8000 Watt (13,500 peak) generator. I would be using it's 220 30A plug to tie into my service panel (w/lockout). But using only the single 220 30A plug, doesn't that limit my continuous load to 6600 watts (the rating of the plug) even though the generator can do more? I understand that peak starting watts can well exceed the 30A plug ok, but I assume that the continuous load could not. Is this correct? What confuses me is that the generator says 56amps max @240. Is this the total amps possible if using all the generator's plugs?
 
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Old 01-17-07, 08:40 PM
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Your generator is 56 amps at 240 volts because they are figuring max start current...ie...13,500watts/240volts= 56 amps.

Using the 120/240 plug ( NEMA L14-30) you would have 33.3 amps per leg (rated current) either in 240 volts or you could power two independent 120 volt loads totaling 66.6 amps. 33.3 A x 240 V= 7992 watts available... so they round up to 8000 watts.

This essentially means you will have 4000 watts (running) available per leg at your house panel. But you really have a lot of extra to start motors with this generator. If you had all 8000 watts used up when things are running you would still be able to produce 5500 watts momentarily for starting motors. This would probably let you start at least two at the same time even at max running watts. Normally you tally up the total running watts of the loads not putting more than 4000 watts on any one buss in the panel, then determine what motor requires the most starting amps. So if I had your generator maxed at 8000 running amps and of all the motors I wanted to start the biggest was an additional 1600 watts to start it... I would need a generator that had capablity of 9600 watts. 8000 running plus the ability to produce another 1600 watts momentarily to start that motor. This of course means balanced loads of 4000 running watts per leg.

The manufacturers may list something slightly less than the values above possibly using 30 amps instead of 33.3 but you would just have to change the math some, which would give you 7200 watts a 30 amps 240 volts... 3600 watts per leg.

Roger
 
  #3  
Old 01-17-07, 11:21 PM
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I don't know why I didn't see that the max current was the peak power. Thanks for pointing that out.

My mistake also in using 220 in my calculation rather than 240. I'm not sure where the 33.3 amps comes from. I found the manual on-line. It states clearly that the 220 30A receptical is breaker protected at 30A (makes sense!) and is therefore limited to 7200 watts. And yes, as you point out, to get to that level, all loads would have to be perfectly balanced to reach the maximum (3600 watts for each half).
 
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Old 01-18-07, 08:59 AM
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Since they rate the generator at 8000 watts (running) and you divide that by 240 you get 33.3 amps.

Yes if they are rating the plug you would be correct at 30 amps, I'm speaking of the factory specification of the generator output based on how they list it. Make sure you are looking at the correct generator, make sure it is the one with 13,500 peak watts. They make several that are 8000 watts with 10,000 peak.

Roger
 
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