Portable Generator Main C.B. Hookup Question

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Old 08-06-12, 10:19 AM
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Portable Generator Main C.B. Hookup Question

I have bought a portable generator, Duromax XP8500, and am planning on hooking up to my house. I have a 200 amp Square D main circuit breaker panel which I am planning on purchasing one of their interlock kits. My generator has a 30 amp NEMA L14-30P twist lock connector which I will use. On the generator is switch that allows you to choose 120 or 120/240. I will run a 4 prong 30 amp cable and connect this to a 30 amp inlet box mounted outside my house. From there I will run wire to a 2 pole 30 amp circuit breaker, HOM230CP, in spots 2 and 4. Here is where my question comes, I have no 240 volt appliances in my house, only 120 volt. So I guess the switch on my generator will stay in 120 volt only?? Now when going from the inlet box to my interlock breakers do I need 10/4 or 10/3 wire? If 10/4 do I run the Red and Black hot 120 volt wires to the 2 connections on the breaker to send 120 volts to both sides of the main panel?? Or if 10/3 do I run the Black hot 120 volt wire to one of the inputs and jump over to the other?? I assume the reason for placing the breaker in spots 2 and 4 is to power both sides of my main panel. Again have no 240 need in my house, just want to provide 120 volts to both sides of my main panel. Thanks and if needed will try to clear up any confusion from my post
 
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Old 08-06-12, 10:51 AM
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Oh and just to add I have been doing a ton of reading about having 2 neutral/ground ties at the generator and main panel. I don't want to modify either my generator or main panel so I will be doing as the majority apparantly are and leaving well enough alone. Spent the last 3-4 hours reading posts about this so not going into this blind.
 
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Old 08-06-12, 11:34 AM
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You would use a 10-4 cable and feed two hots into the panel. It does not matter if there are no 240 appliances in your house. If you don't feed 240, one half of the panel will not have power.
 
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Old 08-06-12, 11:53 AM
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If you choose to run it in 120 volt mode then each hot wire (red & black) will supply 30 amps
Of power to the panel and the white wire will complete the circuit and return the 60 amps back to the generator. 60 amps is a bit much for a 10 gauge wire, although if you don't unbound the ground at the generator the ground wire will carry some of that.
 
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Old 08-06-12, 12:05 PM
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If the generator is run in 120 mode, only one hot leg will carry power into the panel.

The grounding conductor should only be carrying current in the event of a fault.
 
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Old 08-06-12, 12:17 PM
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PC, IF the service panel has the equipment ground bonded to the neutral (and we know it does) AND the generator has equipment ground bonded to neutral then the equipment grounding conductor between the service panel and the generator WILL be a parallel path for return (neutral) currents.

Further, if you don't know exactly how the 120 vs. 240/120 selector is wired it IS possible that both "hot" wires will be energized when in the 120 volt only position. In most cases these selector switches will parallel two 120 volt generator windings in the 120 volt only position and connect those two windings in series for the 240/120 volt position.
 
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Old 08-06-12, 12:21 PM
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If he does t unbond the generator there WILL be current on the ground. It depends how it's wired, but most likely the 120 volt mode will provide power to both hots on the 14-30 outlet.
 
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Old 08-06-12, 12:45 PM
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Hey thanks for the replies!! Just went outside to test my generator to find out about which lines have 120 volts and when. This is what I found:

1. Switch in 120 volt mode and main C.B. on, only 120 volts on one leg
2. Switch in 120/240 volt mode and main C.B. on, 120 volts on both legs
3. With main C.B. off no voltage on either leg no matter where the 120 switch is located.

So its sounds as if I will need the switch to 120/240 volts to power both sides of my main C.B. panel. And I would then need 10/4 wire for ground, neutral, and two hots.

As far as the ground issue I don't to modify my generator as I will be using it also for running extension cords and also will forgo the warranty. And I really don't want to modify my main C.B. panel for obvious reasons. I am aware of the issues this causes but don't know any other way around this.
 
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Old 08-06-12, 01:24 PM
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I wouldn't really worry about it, either. I kind of doubt you'll ever have a problem.
 
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Old 08-06-12, 03:10 PM
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To avoid the problem of a parallel neutral on the equipment grounding conductor simply do not connect the green equipment ground from the generator inlet at the service panel. You DO need to screw a wire nut over the unstripped end of this wire to keep it from shorting out on anything in the panel.
 
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Old 08-06-12, 07:21 PM
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Thanks for the advise all!! So I found out I need to have the generator switch in the 120/240 position. I need to use a 10/4 wire from the inlet box to my main C.B. panel. I need to hook the 2 hot wires to both my interlock breaker inputs to power both sides with 120 volts. And if I want I can cap the ground wire coming from the inlet box to my main C.B. panel to avoid parallel bonding issues. Now all I have to do is complete it!!
 
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Old 08-06-12, 08:31 PM
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Understand that my instruction is for a generator that has the neutral and equipment ground bond at the generator. Not all generators are connected in this way. If your particular generator does NOT have a neutral-equipment ground bond then you DO need to connect the equipment grounding conductor from the generator to the service panel ground.

Read the instruction manual carefully to see if the neutral-equipment ground bond does exist in the generator. There may be a label on the generator itself identifying if a bond does or does not exist. If all else fails do a continuity check between the equipment ground terminal in one of the 120 volt receptacles and the frame of the generator. If this shows continuity the bond exists.
 
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Old 08-06-12, 08:55 PM
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Furd,
Guess my error for not saying that info in my original post. I have done the continuity check from the ground terminal to plug neutrals and generator frame and there is a dead short. So yes my generator is neutral ground bonded.
 
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Old 08-06-12, 09:13 PM
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Then not connecting the equipment grounding conductor in the service panel is the best that you can do.
 
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Old 08-06-12, 10:19 PM
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Personally, I would have zero problems with the leaving it bonded and connecting the ground wire. I will say however that weather or not you leave the ground wire hooked up or not, there is still a slight hazard with the both the panel and generator bonded.

If you can hook up an interlock kit, then you probably have the skills to remove the bonding jumper in the generator and do it right. If you are worried about the warranty or whatever, save the jumper wire and reinstall in before getting service. Doing it right isnt really much more difficult, but like I said, it will work either way.
 
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Old 08-06-12, 11:19 PM
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From post #8.

As far as the ground issue I don't to modify my generator as I will be using it also for running extension cords and also will forgo the warranty. And I really don't want to modify my main C.B. panel for obvious reasons. I am aware of the issues this causes but don't know any other way around this.
There is a definite hazard in using the generator away from the house with extension cords without having the neutral-equipment ground bonded at the generator. There is a problem in having a neutral-equipment bond at BOTH the service panel AND the generator when using the generator to power the service panel. The hazard in NOT having the generator equipment ground connected to the service panel is minimal.
 
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Old 08-07-12, 06:31 AM
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Furd,
Just to be clear on the subject you are NOT talking about the extension cord running from my generator to the inlet box on my house. You are talking about the 10/4 wire running from the inlet box to my main C.B. panel correct?? And leaving the bare ground wire disconnected from where it would enter and connect to the main C.B. panel correct?? Just connect the 2 hot wires and neutral.
This would obviously break the connection of a ground/neutral loop, but in your opinion does it create any other issues?? Guess what I'm asking is this serves exactly the same purpose as modifying my generator it seems only on the other end of the circuit right?? So it should make my installation safe according to electrical standards. Just trying to put this into perspective...thanks..
 
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Old 08-07-12, 11:28 AM
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Just to be clear on the subject you are NOT talking about the extension cord running from my generator to the inlet box on my house.
I call that an interconnect cable. An extension cord would be used to connect the generator to a piece of equipment utilizing the generator power. And no, I am NOT referring to this interconnect cable.


You are talking about the 10/4 wire running from the inlet box to my main C.B. panel correct?
Correct.

And leaving the bare ground wire disconnected from where it would enter and connect to the main C.B. panel correct? Just connect the 2 hot wires and neutral.
Also correct. If this is a bare wire I suggest "sleeving" it with plastic tubing. I do not recommend cutting it off in case at some time in the future the electrical codes change or you get a generator with an unbonded neutral-equipment ground.


This would obviously break the connection of a ground/neutral loop, but in your opinion does it create any other issues?? Guess what I'm asking is this serves exactly the same purpose as modifying my generator it seems only on the other end of the circuit right?
Yes.


So it should make my installation safe according to electrical standards.
In my opinion, yes. Understand that the NEC (National Electrical Code) takes a different position and most, if not all, installations of portable generators will not meet the current code. While there IS a very small chance (in my opinion) of a fault between one of the "hot" leads between the generator and the service panel to "ground" (earth) having an impedance so high as to not let sufficient current flow to trip the circuit breaker on the generator I personally feel as long as the interconnect cable and wiring between the inlet connection and the service panel is protected from physical damage the risk is only slightly more than zero. Others may (and do) disagree with my stance.
 
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Old 08-07-12, 04:52 PM
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thank you for your detailed explanation furd....you have been very helpful
 
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Old 08-07-12, 07:04 PM
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Here is a good explanation from Honda explaining how the selector switches typically work.

http://mayberrys.com/honda/generator/html/120-240.htm
 
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Old 08-07-12, 09:13 PM
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Sounds exactly how the switch on my Duromax generator works according to my voltage tests yesterday I posted in post #8 above.
 
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