Portable generator connection questions

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  #1  
Old 08-11-10, 07:06 AM
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Portable generator connection questions

I have a 4600 Watt portable generator in a shed just outside of my garage for use for emergency power generation.

I'm concerned about how the electrician has configured the connection with the house circuit. He installed a double throw safety switch about 25 ft away on an interior garage wall. A heavy gage cord with a 3 prong male end dangles from the switch box for connection to the power cord connected to the generator. When generated power is needed, a power cord is plugged into the 3 prong 125V outlet on the generator with the other end connected to the cord from the safety switch. I have run this configuration several times for testing and during brief power outages. It seems to work as long as the power draw from my house is kept relatively low ( two refrigerator/freezer combos, 8 or 10 75 watt light bulbs, computer, clocks and other low wattage items). Occasionally the generator seems to falter a bit and I notice the lights dim briefly.

Is this the optimal way to transfer power from the generator to my house circuit? I notice there is a circular 3 prong locking outlet on my generator. This is labeled as a "120 V 30 A Twist-Lock" which "powers 120 Volt AC, 60 Hz, single phase loads requiring up to 2300 Watts of power." The standard 3-prong outlet is labeled "o operate 120 Volt AC, single phase, 60 Hz loads requiring up to 20 A or 2300 Watts of power."

All this suggests to me that I can only supply up to 2300 Watts of power from my generator to my house through one of these connections and I am not getting the full potential 4600 Watts. Is my assumption correct? Is there a way to remedy this so that all 4600 Watts of my generator are available?
Thanks.
John
 
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  #2  
Old 08-11-10, 08:34 AM
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If it's anything like power supplies for computers, the watts is just marketing, what you really need to look at is the amps on the 12v rails. Common sense here would tell you that you are getting, at most, 30 amps from that 30 amp plug. 30amps x 120v =3600 watts. Most likely though based on the labeling, is that only the connection type is a 30a type, and you are actually only getting 2300watts / 120v = 19amps through that "30 amp" plug. Does the generator have an amp meter on it? I can't remember if mine does, but I know it has a volt meter on it. What you could do is get a clamp on ammeter from sears like this http://www.sears.com/shc/s/p_10153_1...u=03482372000P and clamp it around the hot wire and it'll tell you how many amps is running through that wire. Then you just multiply by whatever volts the volt meter is telling you. Should be 120.
Are you sure the 30a plug on the generator is only 120v? I just went and looked and mine says 30a 125v/250v and has 4 prongs. mines a 5500w and doesn't give any other wattage specifically for the 30a plug or the regular plugs. no amp meter on it.

It sounds like the electrician installed the correct wiring for your generator, 125v, and you may have just bought a cheap generator without a 250v outlet.
 

Last edited by sarawent; 08-11-10 at 09:10 AM. Reason: messed up some math
  #3  
Old 08-11-10, 08:41 AM
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The 30A twist lock plug will give you 3600 watts (120v x 30A = 3600 watts) but will require #10 wire to safely deliver those watts to your main panel. If the switch is connected to the main panel with #12 wire the electrician was correct to limit you to the 20A plug.

The generator "faltering" is caused from the higher starting load that a motor draws when starting up. Starting loads from your refrigerators are briefly about double their running loads.

Whether the double throw switch is safe is another question altogether. A proper transfer switch wired to the main panel is the safe method of attaching a generator. If he told you to shut off the main breaker of your house breaker panel when using the generator you have a potentially dangerous setup.
 
  #4  
Old 08-11-10, 08:57 AM
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Originally Posted by roach711 View Post
If the switch is connected to the main panel with #12 wire the electrician was correct to limit you to the 20A plug.
the 20a plugs he was talking about are on his generator, as in, the 4 regular/standard plugs with the GFCI... not the twist lock 30amp plug... on the generator. I read it as the electrician installed a 30a 125v 3-prong plug that plugs into his 30a, 125v 3-prong outlet. The problem seems to be that he should have bought a generator with a 30a 125/250v 4-prong outlet. Then the electrician could have installed a 30a 250v 4-prong plug?
 
  #5  
Old 08-11-10, 09:31 AM
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Originally Posted by sarawent View Post
Are you sure the 30a plug on the generator is only 120v? I just went and looked and mine says 30a 125v/250v and has 4 prongs. mines a 5500w and doesn't give any other wattage specifically for the 30a plug or the regular plugs. no amp meter on it.
Sarawent - Your generator is a two phase generator which will supply 30 amp/120v phases on two of the four prongs of your plug. This will allow you to combine the two phases to power 240v stuff like well pumps. Jbaugh's generator is a single phase unit and is limited to a single 30A 120v phase. In both cases you'll only see 120v +- on your hot lead/s.

You are right about the watt rating of the generators. They are usually labeled with their maximum momentary wattage while their actual running load rating is quite a bit lower.
 
  #6  
Old 08-11-10, 09:56 AM
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The way I'm reading the OP's post (and I may be totally off base here), electrician made up an ext. cord with a standard household 15/20A plug on one end and an undetermined (possibly 30A) 3-prong plug on the other. This would suggest that the electrician meant to limit power to the switch to 20 amps. It could also suggest that he only had a 20A plug with him that day. We just don't know.

The main question is how the switch is wired into the main house panel. If that wiring can safely handle 30 amps then changing the generator end of the extension cord to a L5-30 locking plug would be fine. If the switch is wired to the panel with #12 or lower wire the 30 amps from the generator is going to cause problems.

We need more information before making recommendations here.

Jbaugh - Most non-houshold plugs/receptacles are marked something like L5-30 (three prong, locking) or L14-30 (4 prong, locking). We also need to know the wire size of the extension cord and the wiring between the switch and the house panel. Are you required to shut off the main breaker at the house panel before connecting the genny?

Inquiring minds want to know!
 
  #7  
Old 08-11-10, 10:33 AM
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Generator connections can be a seroius safety problem if not done right.

If you can take some clear pictures of your panel and all the components and post them on a free site like Photo Bucket we can take a look.
Provide a link or use the button above to include them in your post.
 
  #8  
Old 08-11-10, 11:20 AM
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Thanks each of you for your comments. I'm really not very knowledgeable about electrical terms and concepts and I'm not sure I follow all of the discussion. I will do as GregH suggested and post some photos of the various wires and connections. They should be up soon.
Thanks.
jbaugh
 
  #9  
Old 08-11-10, 12:11 PM
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Photos of generator(s) set up

As promised I have posted some photos of the key components of my generator set up. As you can see it is a little more complicated than I mentioned in my original post. I actually have two generators- a gasoline powered and a propane power unit. By going to this site:

MobileMe Gallery

you can view the photos. Clicking on the individual photos will enlarge them so you can read the text on them better.

I can take other photos for better detail if needed.
Thanks for any help.
1) How should I connect one of the generators to my switch box and get the maximum wattage for my house?
2) Would it be best to connect from the 120/240 4-pronged connector on the generator. If so, what kind of electrical cord would I need? Would I have to modify the cord coming out of the switch box to use the 12/240 4 pronged outlet?
Thanks.
John

MobileMe Gallery
 
  #10  
Old 08-11-10, 01:09 PM
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well you've got the white and the black coming in from the cord, but where do those red wires come from? the cord should plug in where those red wires are.

that is the wrong kind of plug. you should have a 4 prong twist lock plug, and the 2 hot wires should go right to where those red wires are. I can't see what's on the other side of that wall to know what those red wires are connected to, but it sure isn't that plug underneath.

you should have a plug like this
Connecticut Electric 30 Amp Twistlock Male Cord End, EGS30TLM at the very least, so you can plug into that 240v outlet that you DO indeed have. Or better yet, have a power inlet like this
30A, Raintight Outdoor Power Inlet Box, For Generator Power Cord Conne

piped in underneath or to the side of that switch, and then a completely removable cord like this
Reliance Controls 10 Ft. Generator Power Cord, 30A - PC3010 at The Home Depot
to go between generator and plug. That cord job doesn't look very professional.





That 4 hole 120/240v circular plug on the right is the one you wanna use. Both your generators have 240 and not making use of it definitely hurts you.
 
  #11  
Old 08-11-10, 01:16 PM
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Both of your generators are two phase units which will power your house quite nicely when hooked up properly. Both have what appears to be an L14-30 lockable power outlet as well as the four 20 amp household style plugs. So far, so good.

The extension cord plug attaching to the genny is a 20 amp plug so that will limit the juice going to the house to about 1/4 of your generator's output. A proper hookup would have a 4-prong lockable plug that would provide full generator power to your house.

***I am not an electrician*** but looking at the size of the conductors, the switch box *appears* to be switching you from utility power to generator power so you can only be attached to one or the other. Not as good as a transfer switch but I would think it would be safe enough. I would definitely have someone in the know confirm this. A quick test would be to flip the switch to the "generator" position without the generator connected. If the house goes dark that would confirm my assumption.

*IF* that is the case you could re-do the extension cord and get full generator power, assuming that you have a proper 10/4 (10 gauge, 4 conductor) extension cord.

Lots of assumptions here. If you don't feel comfortable with electricity, and it sounds like you don't, get another electrician to have a look.
 
  #12  
Old 08-11-10, 01:30 PM
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Originally Posted by roach711 View Post
***I am not an electrician*** but looking at the size of the conductors, the switch box *appears* to be switching you from utility power to generator power so you can only be attached to one or the other. Not as good as a transfer switch but I would think it would be safe enough.
Just what sort of a switch do you think it is? A normal switch like for an air conditioner just has power in, and switched power out, like a light switch. This switch has 2 power ins, and 1 switched power out, making it a transfer switch.

ohhhh, I know what the guy did now, he has a wire nut on that black and 2 reds coming off it, putting the same 120v on both lugs. That is a hack job for sure. there should be 2 separate hot wires, a black and a red, going where those 2 reds are. If you had a professional electrical company install that I would be very mad.
 
  #13  
Old 08-11-10, 01:32 PM
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Looking at the switch hookup again I think it may be dangerous. If the top lugs are utility power and the bottom lugs go to the house panel then there would be the possibility of having both utility power *and* generator power going to the breaker panel at the same time. This would be a very bad situation. Agreeing with Sarawent. This is a hack.
 
  #14  
Old 08-11-10, 01:52 PM
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Originally Posted by roach711 View Post
Looking at the switch hookup again I think it may be dangerous. If the top lugs are utility power and the bottom lugs go to the house panel then there would be the possibility of having both utility power *and* generator power going to the breaker panel at the same time. This would be a very bad situation. Agreeing with Sarawent. This is a hack.
no there is no chance of utility and generator power meeting. when you pull that lever down it makes those arms pull out of the top lugs (power company) and go down to the bottom lugs (generator). The center lugs are house power, so the house power can only be connected to the top or the bottom, but the top and the bottom can never connect. The only thing that looks hack is that cord connection. Was it installed at the same time as the switch or much later?
If you have the generator outside, you should pipe through the wall (or maybe use the pipe that already goes through?) and put one of those power inlet boxes
on the other side. Not good to have a generator running in your garage anyway.
oh and also, it's not good to run your computer on generator power UNLESS you have a universal power supply http://www.newegg.com/Product/Produc...-070-_-Product , because the generator power is very dirty and can harm sensitive electronics. The universal power supply essentially turns the 120v to 12v (how it works as a battery backup when power goes out) and then back into 120v, cleaning the power in the process. Laptops are less affected because the power pack that plugs into the wall already converts the 120v to 12v, and they just run off their batter power.
 
  #15  
Old 08-11-10, 02:18 PM
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Gentlemen,
I very much appreciate all the time you each have spent reviewing my situation. I must say that I feel very uncomfortable with the current set-up.

A few comments:

The 3 position switch on the right side of the switch box seems to function thusly-- when in the up position I get utility power. In the middle position it is off to all power. In the down position the generator power kicks in.

The cord on the switch box was installed at the same time and by the same electrician team as the original switch box installation.

I will get (a different) electrician to come out and look at my set up and make modifications as needed.

Based on my understanding of your inputs this is what I envision doing:

1) Using a Reliance Controls 10 Ft. Generator Power Cord, 30A - PC3010 (except that it needs to be at least 20 ft long to reach to the generators in the outside shed) to connect the generator to the switch box.

2) Have an electrician rewire the switch box so that the external connector is either a Power Inlet Box with the 4 male twist on connection or a heavy gauge wire with the TwistLock male cord end.

Am I correct in assuming that the above two steps should optimize my generator to house current and resolve the current inadequacies?

Can the Generator Power cord be buried under the ground between the shed and the switch in the garage or must I just deploy it above ground each time I need to use it?

Once more, thank you all for your very valuable information and for directing me in the right direction.
John
 
  #16  
Old 08-11-10, 02:41 PM
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Sarawent - OK. I see what you're saying about the center lugs. Couldn't make them out on my work PC. So the switch box is fine, only the extension cord is a problem.

Jabaugh - Your plan sounds fine to me. The underground thing would work also, just more expensive. Reliance Controls stuff seems to be good quality. Glad we could be of help.
 
  #17  
Old 08-11-10, 03:25 PM
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You should get rid of that cable completely, and have a power inlet box connected to the switch through pipe. Where is the shed in relation to the garage? I am assuming it is directly on the opposite side of this wall, and ~20ft away from the house? In that case you should have the electrician drill though the wall and put a junction box on the other side, or if your panel is on the other side? he may be able to just come down out of the panel and pipe down underground and come up either inside or on the outside of your shed. That power inlet box is weatherproof, and inside a well ventilated shed away from the house is probably the ideal spot to have the generator. You want to get put the power inlet box within 10' of where you will have the generator, not have a longer cable to reach all the way into the house.
 
  #18  
Old 08-11-10, 07:30 PM
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I noticed on one generator pic it said neutral bonded to frame or chassis. This is as opposed to a floating neutral. In the case of bonded, the transfer switch in the house needs to switch the neutral wire as well as the 2 hot wires . If not I believe there still a chance that your generator could feed back into the grid and create a hazard.
 
  #19  
Old 08-11-10, 07:44 PM
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On my generator hookup I used the same remote inlet that Sarawent suggested, I put it just inside the garage door so I can run the genny outside the garage with the garage door closed. It also keeps the extension cord length down.

I recently had a new, high efficency furnace installed and the installers told me to use an inverter generator to avoid risking damage to the furnace controller board from the square wave power non-inverter generators output. Even furnaces are computerized now! Most stuff works fine on "dirty" power. Pumps, refrigerators, older furnaces, lights all work fine. TV's seem to be unaffected but other electronics such as computers can freak out or be damaged. Electronic clocks can run slower. I knew some musicians that refused to plug their amps into an un-inverted generator. Inverter generators put out power that's even cleaner than utility power, The only problem with them is price. Check them out, you'll be stunned.
 
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