What is "dirty electric"?

[John White]

Thanks fellows for educating me. Really appreciate the information.

 

[joshuabardwell]

One more thing: your generator will have a breaker that should protect it in over-current situations, but that assumes that your generator is actually capable of delivering full wattage to all outlets/breakers. In other words, if you have a 5000 watt generator, at 120 volts, that is 41.6 amps. If you have two 20-amp breakers, that adds up to 40 amps, and you should be good to go. But let's say you had a 2500 watt generator. That's 20 amps or so, total, at 120 volts. If that generator had two breakers, perhaps they would be 15 amps each, in which case the generator's capacity could be overdrawn without flipping any of the breakers.

The real question, and I don't have an answer to it, is whether it is common practice to always spec breakers with a low enough capacity that the generator can't easily be over-taxed. And, of course, that assumes that the breakers are working properly in the first place! I know I have heard stories of people overloading their generator, so the breakers alone can't tell the whole tale.

 

[General Lee]

One more thing: your generator will have a breaker that should protect it in over-current situations, but that assumes that your generator is actually capable of delivering full wattage to all outlets/breakers. In other words, if you have a 5000 watt generator, at 120 volts, that is 41.6 amps. If you have two 20-amp breakers, that adds up to 40 amps, and you should be good to go. But let's say you had a 2500 watt generator. That's 20 amps or so, total, at 120 volts. If that generator had two breakers, perhaps they would be 15 amps each, in which case the generator's capacity could be overdrawn without flipping any of the breakers.

The real question, and I don't have an answer to it, is whether it is common practice to always spec breakers with a low enough capacity that the generator can't easily be over-taxed. And, of course, that assumes that the breakers are working properly in the first place! I know I have heard stories of people overloading their generator, so the breakers alone can't tell the whole tale.

I may have just learned something here. Maybe you can help me understand something a bit more. I have a 5500 watt/8250 surge genny. At the moment I can't remember if the 120 receptacles have their own breaker as well as the 240 volt receptacle. The genny just has one toggle switch that says "breaker on/off"

Anyhow, If I remember correctly the 240V plug is rated at 30 amps. So if I'm feeding my panel off the 240V receptacle the most I can produce is 30 amps to run house hold things??
I ask because based on your calculations above my genny is rated for 45.8 amps. I saw no where in the specs my genny is capable of 45 amps.

 

[joshuabardwell]

I may have just learned something here. Maybe you can help me understand something a bit more. I have a 5500 watt/8250 surge genny. At the moment I can't remember if the 120 receptacles have their own breaker as well as the 240 volt receptacle. The genny just has one toggle switch that says "breaker on/off". Anyhow, If I remember correctly the 240V plug is rated at 30 amps. So if I'm feeding my panel off the 240V receptacle the most I can produce is 30 amps to run house hold things?? I ask because based on your calculations above my genny is rated for 45.8 amps. I saw no where in the specs my genny is capable of 45 amps.

The breaker setup will vary depending on the generator, and I don't know if it's possible to generalize too much. My generator has a single 240-volt receptacle, and two pairs of 120-volt receptacles. It has four 20-amp breakers: one for each pair of 120-volt receptacles, and one for each leg of the 240-volt receptacle. Since the generator has about 40 amp capacity total, you can see that it would be possible to draw 80 amps without tripping a breaker, but only if both the 240 and the 120 lines were being used at the same time, and this usage is not common. Usually, if you're using the 240, you're plugged into an RV or a transfer box or something, and you're not pulling any extension cords direct off the generator. Alternatively, if you're using extension cords off the 120 receptacles, you're probably not pulling anything off the 240. So this is a reasonable generator design, with 40 amps total capacity, and 40 amps of breaker capacity in most common use cases.

Your generator, with a single breaker switch, it's hard to say what exactly is going on behind the scenes. But it would be really silly to have a 46 amp generator without at least 46 amps of breaker capacity, so I would say the most likely scenario is that there is a single on/off/reset switch that controls multiple breakers. But, and this may be too obvious to even mention, let's be sure you're referring to your breakers and not to the main on/off ignition switch, which... I don't know, in some strange world, might be labeled "breaker on/off," although that would be kind of unexpected. I have never seen a generator with multiple breakers that had a single master-switch for them, but that doesn't mean it doesn't exist.

Another question that may give you useful information is whether it is even possible to have the two legs of a 240 volt circuit on the same breaker. In other words, if your generator's total capacity is 46 amps, maybe the manufacturer would just put the entire generator on a 50 amp breaker and be done with. All receptacles on the same breaker and GO. But if one of the circuits is 240, I'm not sure that's even an option. An electrician would have to speak up. My understanding is that the way it is usually wired is the two legs of a 240 circuit are each wired to a separate 120 breaker, but I don't know for sure whether it HAS to be that way.

 

[General Lee]

That sounds more like it. I think I remember my genny manual stating 23 amps. I just don't understand the "both legs" terminology. I'm gonna check the manual again and I'll post a pic of the power panel of the genny. As soon as my movie is over Its a troy built briggs & stratton model. There is an on and off switch AND a breaker on and off switch though. No visible breakers

 

[BobRip]

I have seen generators run at 62 Hz at no load. This is pretty normal and I would not adjust the no load frequency to 60 Hz. It will then droop to 58 Hz and low voltage when loaded.

 

[RandyT]

A small genny that runs at 3600 rpm to produce 60hz at full load may run at 3750 no load. that is referred to as governor droop. The engine rpm determines the frequency of the output. A 2 brush genny runs at 3600 rpm to produce 60 hz, a 4 brush genny turns at 1800 to produce 60 hz. Several appliances will operate at 50-60 hz per the label. American power generation is at 120-130 V and 60 hz, European systems are 230-240 V and 50 hz.

 

[Mace Canute]

Here's a little more information about inverter generators.

http://bellsouthpwp.net/j/o/johngd/files/rv/inverter_generator.pdf

 

[joshuabardwell]

That sounds more like it. I think I remember my genny manual stating 23 amps. I just don't understand the "both legs" terminology.

"Both legs" refers to how 240 volts is made. A 120 volt line consists of a 120 volt potential between ground (0 volts) and positive (120 volts). A 240 volt line (such as an electric dryer or stove would run off of) is made by combining two 120-volt lines, one at +120 and one at -120. The potential difference between them is, therefore, 240. Each of the 120 volt lines is a "leg" of the 240 volt line that is made from them.

You might ask, why not just make a 240 volt line, with 240 volts of potential between hot and ground? Well, an electrician could give you a better answer than I can, but the layman's answer is that it's simpler and better if everything is consistent. So you want 240, you just run two 120 volt lines all the way out to the receptacle and away you go.

 

[joshuabardwell]

That 5500 watts at 240 volts would give you 22.9 amps total. That's for both legs which is where you get the 45.8 figure (120V@22.9A x 2). Your single toggle switch is probably a 240 volt breaker that will handle both legs of 120 volts.

What may not be obvious to John is that the amp draw is determined by watts divided by volts. So 1000 watts at 120 volts = 8.3 amps. 1000 watts at 240 volts = 4.16 amps. When you talk about a generator's capacity, it's usually in watts, but when you get down to the nitty gritty, you usually end up talking in amps, and it's important to be clear about whether one is referring to 120 or 240.

K7LN, if he has a 240 breaker, does it internally consist of two separate 120 breakers? It seems like it would have to because that's how 240 is made--from two 120 legs. Is that right?

I suppose it wouldn't be out of the question to have a single-leg 240 circuit, with a single 240-volt breaker, but I don't know of anywhere that's actually done. Is there such a place?