Here Is Probably A Stupid Question

747

I was watching this old house today. They were showing the electrical system on the house. It consists of Two 200 amp breaker boxes for a total power of 400 amp to the house. They were showing the installation of a natural gas backup genator 25000 watts cost 11,000 dollars. I was thinking that thing is so huge it could probably provide power to my hole house. My question is this 25,000 watts equals how many amps? The manufacturer rep said they have smaller models around 3,000 dollars for the typical homeowner.
So does anyone know how many amps is 25000 watts.

mikesewell

Volts x Amps = Watts

jproffer

Just FYI also, 2-200amp panels equals 800 amps total, 200 per phase, per panel. Most people forget this or just don't know. :Thumbs:

mdshunk

Mr. Proffer is obviously not an electrician. Two 200 amp rated panels can be connected to a 60 amp service. The rating of the panel is the maximum rating, and has nothing to do with the service size. You may feed any panel up to (but not over) its rating. This is very often done. This house with two 200 amp panels may have only had a 200 amp service. The second panel may have been added to provide more "slots", since the NEC artificially limits the max panel spaces to 42. Two 200 amps panels are often hung behind 200amp, 320amp, and 400amp service equipment.

Besides the above, 2-200 amp panel IS NOT 800 amps. What an outrage this statement is to a real electrician. IF these panels were supplied by a full size service, the panels would only provide 400 amps at 240. This is how services are described, by their current capability at 240 volts. True, if you had only 120 volt loads, then you would load it at 800 amps at 120, but this is NOT A NORMAL WAY TO DESCRIBE A SERVICE.

The 25 kilowatt generator that the was originally asked about is about 100 amps. The second 200 amp panel in this thread could have been the "emergency panel" for the emergency circuits, connected through a transfer switch to the genset.

Speedy Petey

Exactly Mark. Good, descriptive post.



What most people forget or don't know is that AMPS are meaningless without regard to voltage. One without the other is useless.

True, one can, and typically does say "I have a 200 amp service". But the true meaning is "I have a 200 amp @ 240volt service".






Yes, a 25kw genset is good for 104 amps @ 240. More than enough to run most essential loads in most homes.
We have done gensets this size in this same situation. Split 400/320 amp service with one panel transferred to the generator. This is a pretty common installation.

PipeGuy

May it be said then that the 25KW generator is also good for 217 amps at 115V?

mdshunk

True, if you only had 120 volt loads connected, then you'd have an availability of 208 amps at 120 or 217 amps at 115. This depends a little on what the precise phase to neutral voltage is set at on the genset. Most of the good ones are semi-adjustable. When you're into a genset that big, you normally have at least some 240 volt loads connected. Things like well pumps, water heaters, some central air are often hooked to larger gensets. In smaller generators or portable generators, you often only have 120 volt stuff hooked up like the fridge and freezer and the furnace blower motor. With a mixture of 120 and 240 volt loads on the genset, you'd realistically have to convert all the loads that will run at once to WATTS to see what size genset you'd need. This is the primary reason that generators are rated in watts. Also, there's some marketing confusion adding to the frey nowadays. Some generators are advertised in "peak watts", which has nothing to do with the watts that they will provide for hours on end. Peak watts just means that you can draw over the gen's nominal wattage for short periods to accomodate the surge of motors and compressors starting. Motors can draw many times their nominal current for a second or two while they start and get to full speed.

747

Wow you guys are AWESOME. Thanks for the excellent perspective.

mdshunk

Yes, that is true. My college minor was in 'Awesome' with study emphasis on 'Groovy' and 'Swell'. Speedy is awesome too. I wish we lived a little closer together to do a big job together. We seem to have similar work methods, since I've run across him on a few different sites.

Spidermonkey

I have a problem with the statement below...if a 200A panel was connected to a 60 amp service I dont think that would be good. A 60A service is designed for 60 amps....meaning the wiring from the high KV transformer on the pole to the meter houseing would be designed to handle 60A...could be as little as #6 Gage wire. If on a coold winter day with the cloths dryer going, Stove cooking dinner and other lights on...and your new 20KW electric furnace kicks in....those little wires are going to get pretty darn hot and possibly melt the sheathing....

"Two 200 amp rated panels can be connected to a 60 amp service. The rating of the panel is the maximum rating, and has nothing to do with the service size. You may feed any panel up to (but not over) its rating. This is very often done."

mdshunk

If you have a problem with that statement, you need a little education as to the difference between panel ratings and overcurrent protective device ratings. They're two different animals, and you've sorely confused the two.

Spidermonkey

Sorry..My Bad...in my head I was picturing this as I have seen this done twice....not pretty.
Yes...as long as the main breaker was still at 60A your good to go.
Thanks for clearing my diluted vision.

TempestV

the other thing about generators is that they can be run to charge batteries when you aren't using the full wattage. Then, these batteries can be drawn on to power the house in addition to the generator when you are using peak power. I was reading about an installation of a backup power generator that was set up to fully power your average single family house so that it would be like you were still getting power off the lines, and the generator that they used was 7000 watts. It would charge batteries when the house wasn't using as much power.

mdshunk

Those "off grid" type systems can get into some major bucks. The batteries alone can be many 1,000's of dollars. We're not talking about a couple of marine batteries. We're talking about racks and racks of batteries, with an equally high dollar rectifier-charger-inverter.

TempestV

The house that they were installing it on was in a residential neighborhood, and it was designed to be a backup generator. They had the whole system installed in one of those cheap sheds that they sell kits for at building supply stores. Supposeably the whole kit was suppose to be cheaper than a big generator that could power the whole house at once.

JamesNLA

Many powered products one can buy have that "X" amount of watts rating. Say a car stereo for example. It will say 100 wats X 4. Customer thinks oh, ok I can have 25 watts per speaker (4 speakers) well that is peak wattage and is usually not very efficent (Q) if you read a little closer, it may mention the term RMS. Root Means Squared, in a basic description that means the consistiant supply of wattage. So that same car stereo is probably running at about 13 watts RMS per channel. This carries true for ANY type amplifier as well as transducers (aka speakers). When people go and buy the latest and greatest JL Audio 500 watt 12" sub woofer. They think it takes 500 watts of power to run it. While that is a good idea, it's not really benificial. Peak vs. RMS. I do agree with MD that the marketing collateral more often than not will mention "peak" somewhere in there. And remember lab results and real world results are 2 different things. If the manufacturer can get that 500 watt (or whatever amount) power level even for 1 second, they can now print and advertise it is a "500" watt......whatever. Real world and marketing are different. And typically the higher the quality of product the more efficent and more accurate the numbers will be.

747 -- Think of it like a RAT you have on board your 57's. They produce just enough to keep your essentials running. Which BTW I'd love to hear any stories of you popping one of those out!!!
hmmmmm, do any planes have more than one?