Combining Two Neutrals in a Single Generator

Keep in mind while you are doing it that you do have two phases here...not single phase as your post infers, i.e., "which has two 120V output connectors" and "There are no 240V outputs". The specs on the link you provided say otherwise.

Otherwise...

No problem...they are the same neutral behind that panel on your new separately derived output.

A violation would be to use two distinct neutrals for the same source of power...i.e., running two neutrals to your disconnect from the generator. There should only be one neutral to your disconnect.

But...

You have a three conductor four wire (240V) and a duplex outlet out the gennies panel. Your switch has the mating cable for the three conductor (240V) cable. How else were you going to connect this? All of the work/questions are done for you.

The output from the switch allows you power four 120V 15A circuits and one 20A 240V circuit. Removing the gang on the 20A would provide two additional 120V circuits...but again keep in mind that those two breakers are on two different "phases".

(Not really, just split phase...but don't get us started on the forum again about that!)

Notice how the neutral from the gennie (W) is bonded to the service...not switched? That is important.

Pete, while I agree about everything you said about the transfer switch and the grounding, I read the generator users manual hoping to find a wiring diagram but discovered none is given, and it clearly shows just two 120 V outlets.

Typically these small generators have two separate stator windings each capable of supplying half the rated load. But there's a wild card, we do not know the way the windings are distributed around the stator.

Logically they should be set up so that with the proper internal jumpers the manufacturer can get 240/120 with a common neutral from the same frame, but and it's a big BUT, if they're not wound that way then they could be in phase with each other (or anything in between) and the single neutral will have to be sized to carry double the output from each phase. That's 40 Amps at full load on both outlets and the transfer switch cord neutral will be overloaded by 33%.

For short duration, no problem, for prolonged continuous operation OP should consider getting #8 or #6 cord and rewiring the plugs, especially if there's a long distance in mind. He'll get less voltage drop and cooler operation.

Didn't look at the manual, but the pic on the HD site shows both 120V and a 240V rececptacles.

The HD page referened also says:

Number of circuits/outlets 3

Voltage rating 120/240

Thanks Cuban Pete! LOL

When you say "The specs on the link you provided say otherwise" are you referring to the generator? I don't see where it says the generator has 240V output. In fact, you can see there are only two 120V outlets in the picture. There is no 240V outlet on the generator.

So the assumption being that "behind that panel" on the generator they are the same neutral, if that's the case, then it should be alright to connect them together at the L14-30 plug to the switch inlet. Again, the L14-30 connector is not on the generator, it is on the transfer switch. I am going to place a test meter on the generator across the two 120V outlet neutrals (with the generator powered off, of course) and see if I get continuity.

What got me skeptical is that I read another user of this same model generator wanted to do the same thing, and he measured the two hots on the generator (while running) and got 0V instead of 240V. That means they are probably two separate coils in the generator, each generating half of the rated power output. Therefore, I didn't know if there were any consequences to connect the two neutrals together.

Thanks, that means that both coils are probably wound together and placed in the same slot, with the leads brought out separately. That makes their output in phase, and if you measure the current in the combined neutral you'll find it to be the sum of each individual neutral.

I don't know what you guys are looking at...I clearly see a round 4W3C recep to the right of the duplex.

My browser is linking to the wrong page?

EDIT:

Yep, I now see the generator you guys are referring to

How the hell did I get to the wrong page?

Another concern... the neutral at the generator should be disconnected from the case. The case of the generator is bonded by the equipment bond going back to the panel via the transfer switch. The way the drawing shows it now, you have a second neutral ground connection point. Which is a no no in both the CEC and the NEC.

Weird...I am having a similar discussion on the www.electriciantalk.com forum.

I'll just post a great link from that discussion here.

Two systems...two different ways of bonding/grounding.

Cuban Pete, I'm glad you found the GEN4000LP generator webpage and were able to solve the confusion. I just received this generator yesterday and I am in the early stages of planning its connection to the house.

After taking it out of the box, I used my test meter to measure continuity across the neutrals in the two 120V outlets. I was glad to find out that my test meter beeped indicating a short. This means that in the wiring inside those two neutral connections are bonded together. Next, I got a bit more curious and decided to place the continuity test across the two hots and see what happened. To my surprise, the test meter also beeped indicating continuity! I then proceeded to discover how the outlets were wired, so I removed the back cover behind the outlets. I found that out of the generator, it has 5 wires: red, white, blue, black and yellow. I then found that the single red wire coming out of the generator is connected to the hot side of BOTH outlets, and also, the single white wire coming out of the generator is connected to the neutral side on both outlets. Same goes for the yellow GND wire. The blue and black are just the + and - for the 12V output.

Now, that explains perfectly what it says in the product description that this is a SINGLE phase generator, so there is no way to make a 240V connection (even if I wanted) since both 120V outlets are simply connected in parallel.

Now, I started wondering the next question, why in the world would they write in the manual that the maximum load of one outlet should not exceed 1800W if both outlets are connected together in parallel to the same generator output anyway? My conclusion: it must be nothing more than wiring gauge. Distributing the load across two outlet wires (even if they are connected together in the end) should lower the risk of overheating the wires.

So, in conclusion, when I make my Y connector to the L14-30 plug on the transfer switch, I'll just use heavier gauge wires to be safe. What number wire should I use to carry a max of 40A?

Thanks to everyone for their feedback. I have a background in electronics, but I am not close to being an expert like you guys. This has been a very educational experience for me.

The minimum wire for 40 amps would generally be #10, however you should use wiring tables for the cable/insulation you are using. For some cables it will have to be larger. The internet has the tables available if you can trick google into giving you the correct information. The other consideration is voltage drop, be sure to take that into consideration if you are using a long run. The reason the instruction book limits you to 1800 watt at each plug is that the plug disconnect is not capable of supplying more. They could have supplied a larger amperage plug like that on a motohome, but then normal cords would not work. What concerns me is that the way the unit is set up, you will not have any protection for the cord you plug in until it is run through a fuse or circuit breaker. Your idea of tying two plugs together will work, but you must do it carefully to avoid creating a safety risk. The unit you describe sounds very much like many of the cheap contractors generators that are sold.

"Now, I started wondering the next question, why in the world would they write in the manual that the maximum load of one outlet should not exceed 1800W if both outlets are connected together in parallel to the same generator output anyway? "

The mfr's. is correct in limiting the maximum allowable wattage for fire and safety reasons. The rated capacity of the duplex outlet, (regular U-Gnd type) used in the generator termination is much lower than the total power the generator can generate and provide! Additionally, the reason for the lines being split into 2, was probably due to the size or wire gauge used was also too small to carry total amount of current or power capacity of the generating unit!

Thank you all. I took a picture of the back of the panel and this is what it looks like. Before it arrives at each outlet, the hot splits in Y. One leg of the Y goes to a reset switch and then to the first outlet, and the other leg of the Y goes to the other reset switch and then to the second outlet. I believe they are GFCI reset switches. Will I have a problem with them resetting due to the connection I am making?

The reset switch for the "hot side" of each outlet is probably a resetable temperature dependent (thermostat). The contacts of which is supposedly close, (shorted together) during normal operation.

Its contacts will open up to interrupt the current flow when it sensed an abnormal condition. Conditions like overloading or when a preset limit of current has been exceeded, which triggers overheating along its path. As you use the setup, additional heat will also be developed between the plugs and gen. outlets due to what is known as contact resistance existing between those terminations. This resistance increases over time due to wear and tear and therefore needs to be replace as necessary or as needed!

As VSAR pointed out, those are simple thermal trip circuit interrupters, not GFCIs! You have absolutely no protection against accidental line to ground contact. If you draw too much current on a particular outlet, the overload will trip, the other leg will continue to operate until it draws too much current.

The big "gotcha" is still the combined neutral current. As was pointed out earlier, there is no protection for the neutral wiring, and any wiring/connections where you pass the combined neutral amps continuously is going to get hot as you approach the full load rating of the generator.

Heck, just try it. Be prepared for a possible short and the generators may trip their breakers. Whats the worst that could happen?

BA

LOL! hahaha!