I am needing to size a generator for our annual town days. What is needed is a 240v 200 a service. So I took p= IXV which gives me about 48kw for sizing of the generator. Is this correct cause I would hate to undersize this thing. Also is a ground rod needed at the generator and what about bonding
generator sizing
- Thread starter fireryan
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ericsherman37
Senior Member
- Location
- Oregon Coast
I'm not sure (maybe one of the more experienced gentlemen could elucidate further) but I think a generator would just need to be sized for the load served. However, there is a certain point that will result in ideal generator operation. This probably varies from generator to generator. Too little load will result in inefficiency, too much will bog down the generator. This info would probably be in the machine's documentation, I would think...
NEC 2008 Article 445 is on Generators. Article 250.34 has the grounding requirements for portable or vehicle-mounted generators.
NEC 2008 Article 445 is on Generators. Article 250.34 has the grounding requirements for portable or vehicle-mounted generators.
im not sure of the exact load but all I know is the band requires 100 amps and there will also be a few roasters roasters going. I know that they have had a 200 amp temp service put in every year but that is no longer a option. I guess over sizing a little wouldnt hurt anything since the generator is donated through our local rental place
not sure what you mean here
Rick Christopherson
Senior Member
Simply add up all of the loads and size the generator to that. Your stage should probably be the highest demand, and you may want to derate the generator slightly to account for the strong fluctuations in power that an excessive light show can have.
About 20 years ago myself and my father powered a concert for "Ratt" and "Poison" in Minot ND. (I think the pun was intended). After seeing so many bands over-inflating their power needs as a sign that "they were big", my father undersized the generator because that is all he had left in inventory at the time. At the end of the show, as the lighting technician was slamming the light board from ALL-ON to ALL-OFF every couple of seconds, the generator was literally bouncing off the ground--lifting each pair of tandem wheels off the ground as it went from full-load to no-load.
We thought the generator went down on high temp because the exhaust manifold was glowing cherry-red, and were cooling the radiator with a garden hose, all while my father was holding down the safety override next to the cherry-red manifold to keep it running. We later discovered that it went down on over-speed, and that is why the safeties wouldn't automatically reset. (Sorry, I just love telling that story, because it is pretty amazing seeing a generator bouncing off the ground.) I was a 15 year old kid, and I had beautiful women propositioning me for back-stage access.
Alight, back to your setup. You might want to check with the rental outfit with the generator to see what they have for portable power distribution. Most rental houses that have generators also have the distro too.
Oh, before I forget, the generator should be bonded, because all of the distro is unbonded (typically).
You would come out of the generator with 2/0 or 4/0 cam locks (4/0 are oversized, but more common.) and feed into a splitter panel. The most common splitter panel is 400 amp IN, 2x 400 amp OUT, unfused, and that is fine. (Most of the distro is either 50 amp 1P, 100 amp 3P, or 200/400 amp 3P.)
Your stage most likely just needs a power drop into their own equipment with either 1/0 or 4/0 sized cams. For the food vendors, you will need a second distribution panel that feeds them single-phase power from a 3-phase supply. Most food vendors will use Quad Strings at 120 volts, 20 amps.
It has been years since I set up a generator for special events like this, so I don't know if things have changed, but we always grounded the generator for these. Even if there is/was a loophole for trailer mounted generators not requiring ground (too tired to look it up tonight) we always grounded them.
About 20 years ago myself and my father powered a concert for "Ratt" and "Poison" in Minot ND. (I think the pun was intended). After seeing so many bands over-inflating their power needs as a sign that "they were big", my father undersized the generator because that is all he had left in inventory at the time. At the end of the show, as the lighting technician was slamming the light board from ALL-ON to ALL-OFF every couple of seconds, the generator was literally bouncing off the ground--lifting each pair of tandem wheels off the ground as it went from full-load to no-load.
We thought the generator went down on high temp because the exhaust manifold was glowing cherry-red, and were cooling the radiator with a garden hose, all while my father was holding down the safety override next to the cherry-red manifold to keep it running. We later discovered that it went down on over-speed, and that is why the safeties wouldn't automatically reset. (Sorry, I just love telling that story, because it is pretty amazing seeing a generator bouncing off the ground.) I was a 15 year old kid, and I had beautiful women propositioning me for back-stage access. Alight, back to your setup. You might want to check with the rental outfit with the generator to see what they have for portable power distribution. Most rental houses that have generators also have the distro too.
Oh, before I forget, the generator should be bonded, because all of the distro is unbonded (typically).
You would come out of the generator with 2/0 or 4/0 cam locks (4/0 are oversized, but more common.) and feed into a splitter panel. The most common splitter panel is 400 amp IN, 2x 400 amp OUT, unfused, and that is fine. (Most of the distro is either 50 amp 1P, 100 amp 3P, or 200/400 amp 3P.)
Your stage most likely just needs a power drop into their own equipment with either 1/0 or 4/0 sized cams. For the food vendors, you will need a second distribution panel that feeds them single-phase power from a 3-phase supply. Most food vendors will use Quad Strings at 120 volts, 20 amps.
It has been years since I set up a generator for special events like this, so I don't know if things have changed, but we always grounded the generator for these. Even if there is/was a loophole for trailer mounted generators not requiring ground (too tired to look it up tonight) we always grounded them.
Last edited:
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
We lighting folk dont do "slamming the light board from ALL-ON to ALL-OFF every couple of seconds"; we just gently press the button we've programmed for "all on full". It feels good having a quarter of a megawatt of power under one finger, and hearing a lot of people scream when you press it...
I've heard gensets grunt a bit when you load them a bit but never seen one jump off the deck!!! Thats just a wow.
Back in the day there were usually seperate gensets for lights and "the rest", but now up to a couple of MVA one genset is fine (though I'd like a fault tolerant twin-pack please), especially with the change of lighting from rigs full of parcans to rigs full of movers. The voltage and frequency regulators now work so much better than they did back then...
Rick Christopherson
Senior Member
It was the rapid no-load/full-load/no-load that had the thing bouncing, and this was also the reason why it went into overspeed.
On a similar note:
It was somewhere around this same time frame that a band was putting on a concert out at some beach. I can't remember the exact numbers, but I think they ordered 75KW prime power and 75KW backup for the show.
Back then, inventory was pretty thin, so the backup unit was undersized, and the band made a big stink about not having enough power if the prime unit went down. I was supposed to deliver the backup generator just before the show, so my dad asked me to check the ammeter on the prime unit to see if they were close to capacity.
When I got back he asked what the ammeter read, and I said, "I couldn't tell, it never left the peg." When he asked if I was sure, I said I was pretty sure, considering they had 4, 15 amp extension cords running up the beach from the stage to the generator.
They had two 75 KW generators for four extension cords!!!- Status