home back-up generator help

[ccatfish]

i am about at my wits end on this problem, so any help would be appreciated. when my home was built last year, i had the electrician wire it to accomodate a back-up generator. i'm now in the market to buy that generator and i have some questions that are proving to be difficult to answer, at least by the people selling the generators. here is the question: the receptacle on my house is a NEMA# 14-50, which i believe indicates a 50 amp connection. 90% of the generators i have seen do not have such a plug, but they all have 240v and 20 or 30 amp outlets. my question is if i buy one of these generators, how do i reconcile the differences in receptacle types? Is it as easy as a custom made cord with mail connectors that correspond to the receptacle on each end? do i need a generator with a 50-amp outlet? lowes, home depot, tractor supply, northern and even a speciality power supply company in the area have been of no use, but they clearly do like to guess and i'm not in the mood to experiment with my life.

also, if anyone living in the north texas area knows a good retailer where i can buy a medium-duty generator, i am all ears. the mass retailers only carry the 5500 watt variety and i'm looking for something a tad bigger: 7500-10000.

 

[TWINKLE_TOES]

ccatfish,

This will help with your plug problems. I'm a little hesitant to climb out on any limb for sizing without knowing a little more about you house loads. For example, do you have a heat pump? Heat pumps loaf along on a day to day basis @ a few horsepower. When its cold and they reverse cycle they turn on 10 to 20Kw of electric coils.

http://www.quail.com/locator/nema.htm

Hope this helps/w3tcompact/icons/smile.gif

 

[MChalkley]

I'm a little afraid to comment too much about your specific question, considering the trouble you can get into if you make a mistake, but you can make (or have an electrician make) a cord that has the correct type of plug on each end.

I'll tell you what I did, in the hopes that it might shed some light on your situation. My situation was a little more difficult than normal because I've got two panel boxes (side by side, fortunately). I put an extra 40-amp breaker in each box and wired a 50-amp outlet box into each breaker below the panel box. These allow me to easily connect the generator to both panel boxes. Then, I made up a cord with a 50-amp plug on one end and two 50-amp plugs on the other. To run with the generator, which is just a 7500-watt Generac, I turn off the mains breakers (thereby disconnecting the house from the utility company service), plug the custom cord into the generator and the two panel box outlets I installed, start the generator and let it warm up, turn off the two heat pump breakers, the two heat pump electric backup strip breakers, and the water heater breaker, then turn on the 2 "generator breakers" in the panel boxes.

My generator isn't powerful enough to power the heat pumps, or the water heater and water pump at the same time, because the water pump is a huge submersible almost 600 feet down, so I leave the heat pump breakers off and alternate the water heater and pump as necessary.

A few caveats about this setup: It's important to do all that stuff in the right order. You MUST plug the panel end of the cord end before you start the generator, or you've got 220 volts on the exposed prongs of the plugs. And NEVER plug a generator into your house wiring in any fashion whatsoever without turning off the mains breaker. Doing so backfeeds the voltage onto the utility lines and the step-down transformers which supply the electricity to your house will step the voltage from the generator up in reverse, putting enough voltage on the line to potentially kill utility workers trying to restore power.

Obviously, it's best to put in a transfer switch that handles all that automatically. When I find enough money on the street to put in a big 20kw diesel generator, I'll do that. /w3tcompact/icons/smile.gif

I hope this helps.

MarkC

 

[ddl]

I have one question about using generators, can you use them to power house hold devices with motors? Generators used to have a varible frequency, which caused big problems with motors. A motors voltage can vary but varing the frequency will burn out motors pretty fast. Has the improvments in generators overcome this problem?
Dan L

 

[TomG]

Installation of backup generator connections to electric utility service equipment requires permits and inspections. I guess your electrician's work involved a permit and inspections, and you know that further work may require additional permits and inspections. However, maybe not. If I interpret you question correctly, your generator feed line terminates in a 50A 220V receptacle, rather than a line with a 50A plug. If that's true, I can't believe that it would be an acceptable connection anywhere. That would mean that somebody could be wondering around with a line from a live generator that ended in exposed male plug ends. I must not understand this. Anyway, an adapter cord with double male plug ends is a definite no no.

I'm guessing that you have a backup panel that is run from a breaker in the main service panel. That's the most common setup, because a transfer switch ahead of the service panel must be rated for the full service load. A 200A transfer switch is a very expensive thing to provide a connection for a 30-50A generator. I note that in my area, the main breakers for backup generator panels must be 3-point, rather than the more common 2-point breakers. 3-point breakers break the neutral as well as both hot service lines. I'm guessing that you have a backup panel with 50A mains, a 50A feed line (#6 wire I believe) and a 50A plug. Such a setup would be conventional. Everything has the same rating.

In my case, I have a 60A backup panel off a 200A main panel. Most of the house is wired on the 60A panel, so I can pick and choose a lot of different circuits. However, my generator isn't quite 30A. I ran 30A wire (#10) to the generator main in the backup panel the wire terminates in a junction box in the generator shed. A length of #10 flex line, which ends in a 14R-30P is spliced to the generator feed in the junction box. Incidentally, your Nema number usually has some letters with it. R/L is left or right twist (I think) and P/R is plug or receptacle. The inspector passed my installation, because the generator mains provide overload protection. Technically, he could have required me to replace the 60A-generator main in the backup panel with a 30A main to match the feed wire rating. I might make the replacement anyway.

The easiest thing to do would be to replace the existing plug with a junction box and splice on a length of flex line ending in a plug that matches the generator's 220V out receptacle. However, as I noted, your inspector almost certainly would have to specifically approve such a connection. If the permit is still active, then inspectors often can be contacted. They'll often tell you what they will approve. I'd take a lot of care with this subject, you could burn down your house and find that any un-inspected work compromised the fire insurance.

 

[TomG]

I've got a Honda 6500. Pretty good generators, but I wouldn't run my computer or other electronics off it. It does just fine with electric motors though.

 

[Thomas]

ccatfish,
I'm glad to read that your at a stand still and willing to ask for help.
First of locate a darn good electrican and show him what you have plan.
Second don't really trust your main breaker even more so if located in the basement and the older style,have a disconnect box install the type you can put a lock.
Use twist locking plugs.
Have your electrician do a voltage test.
Contact your local power company and inform them you have a back up system,for the last thing a line man wants is a feed back nor you want a phase back if the power been restore.
Purchase a system that will tell you when the power been restore,don't depend on viewing street lights the neighbors etc..

After hot sticking for 15 years w/4160 volts and seeing some back up power install the cheap way /w3tcompact/icons/frown.gifjust take your time an spend the extra $$$ on saftey.

Thomas..NH /w3tcompact/icons/wink.gif

 

[gordon]

That is a tough question to answer. Any generator is going to have some voltage swing in relation to the rpm of the engine. When voltage changes so does the frequency guess that goes without saying. It also depends on if it's a gas or deisel engine running the genset as to how quick it's taken care of at times.
The older carb models with a governor for voltage and frequency settings. Your voltage specs run from 128+or-4 volts no load with a frequency of 63. Minimun volts 108 and frequency of 59 at full load. Pretty good spread.

The newer models that use a microprocessor have a much closer tolerence. Depending on make and model. Some of the newest models are bumping up frequency very high then bringing it back down to give a much cleaner sinewave then that of the basic microprocessor regulated gensets. By doing this they are also able to give much closer voltage and frequency specs.

On some of the newest gensets voltage stays the same reguardless of engine rpm! They use a roter/stator that produces a high frequency, high voltage 3 phase ac. Then the converter changes the 3 phase ac into DC voltage. Then it goes through the invertor changes the DC voltage into a even 60hz single phase ac voltage.---Times are a changin

Bottom line on all the above mumbo jumbo is that it depends on how deep you want to go in your pocket. They still manufacture all of the above styles of genset from the basic governer/carb style to the automatic voltage regulation models.
Gordon

 

[ccatfish]

Thank you for all the replies. My house actually has two 200-amp panels, and yes, the transfer switch is "behind" them, not in front. Because there are two, I think this was the reason the electrician who wired the home used a rather large, commercial-looking transfer switch. It sits in its own electrical box thats probably 12" x 20" in size.

From the transfer box, there is the 14-50R. I'm do not know how to tell if the "R" is a twistlock, but it sure doesn't look like one.

TomG's comment on a cord with two mail ends got my attention. Think I'll call an electrician. On yeah, since I live outside of all city limits, there were no inspectors for my house (except for the power company for their stuff). I had to hire an independent inspector to do this for me.

Thanks again.

 

[Wingnut]

I know I should just stay in the back and keep the muzzle on ... but I'll just tell you what I did ... after the second major power outage caused by storms here in Michigan. We're in deep doo-doo when we have no power 'cause a well means no power, no water ... no drinkie, no clean bathrooms, etc.
So, I have a setup pretty similar to what Mark described ... a 7500W Generac (that will peak at 50A) and a second panel that allows me to switch from mains to the generator.
I had a problem similar to what you described with different plug styles ... and my solution was pretty simple ... I bought a new male plug that matched the female end on the genrator and rewired. The plug is not the critical thing here ... having it wired properly is ...
Now ... like Mark said ... if we could just win the lottery and put in a 40KW genset wired for immediate failover ...

too bad that common sense ain't