Wire gauge for generator hookup

[PWash]

I'm installing a 30amp L14-30 reliance inlet box into the wall of my garage, and connecting it to my service panel and will be using an interlock device (QO panel & interlock kit). My wire length between inlet box and service panel is 50 ft. I will connect the generator to the inlet using a 20ft 10gauge flexible connector.

Can I use 10ga 3-wire for the internal romex wire or do I have to step up to 8gauge? My generator is only rated for 4400 watt (surge), generating up to 18amp on each 120V leg, so 10gauge should be fine for my usage, but I want to meet the code-compliant requirement, but that seems to be as clear as mud.

Does the NEC require to size the house wiring with 50 ft in mind only, or also consider the 20ft flexible cord for 70ft total? Is the continuous amperage used in a L14-30 connector allowed to be 30 amps, or is it supposed to be limited to 80% of the listed amperage?

The southwire voltage drop calculator tells me I could have up to 57.18 ft and still limit the voltage drop to 3% or less for 120V 1 phase with 30amps. At 24 amps, the maximum length increases to 71.5 ft.

 

[KB007]

I think you could use 10ga in that situation, unless there is some local code requirement. I used 75' of #10 stranded to make up my generator cable (also with L14-30) and it works just fine. I spoke to the folks at the local electrical supply and they said #10 was fine for a fair bit longer than that as well. As always, double check with someone local if you can to make sure you don't have any weird local code additions.

As for the continuous - you're not supposed to exceed the 80% under normal operations, the headroom is there for start-ups and surges etc. What are you planning on running with this genny? At 4400 watts (I presume that's running watts) you want to be a little careful if you're using an interlock as you could end up having someone turn on something like the stove or dryer inadvertently and cause some issues while the genny is running. Hopefully the breakers on the genny would pop, but it's something to be aware of.

 

[PWash]

thanks for sharing your experience. I'll try the 10awg, and will give the city inspector a chance to sign off on my work.
My highest load for generator is going to be my fridge and only planning to additionally run blower fan on my wood insert and some led/cfl lights so should be no problem staying under 80% of 30amps..

 

[moey]

I would use 8ga so if you decide in 5 years to get a bigger generator your not kicking yourself. Remember you also have 25ft or so of cord going from the generator to the hookup on the wall.

 

[PWash]

I was actually considering going to a smaller generator (800 watt chinese special) after reading several other generator threads. In an emergency, I only need the larger wattage every 4-6 hours to keep food from spoiling in the freezer. rest of the time, i only really need a few watts to run lights and a fan, and a .5gallon/6hr burn rate sounds good in event of an extended power outage. I converted all appliances over to gas so my electric use is pretty minimal.

 

[Highbeam]

I actually have an interlock panel as well and have been through this.

1) The breaker protects the wire. If your generator inlet breaker is a 30 amp breaker then 10 gauge is the corresponding correct size. It is of course a minimum but 10/3 is fine. Note I said 10/3. You need a four wire cable.

2) Voltage drop in a residential application is a non-issue. Forget about it.

3) Plan on flipping off breakers to the automatic load circuits like electric water heaters, hot tubs, or anything else undesirable that might want to turn on when you're on genset power.

4) The power inlet plug L14-30 you chose is obviously rated for 30 amps. That matches the generator inlet breaker, matches your 10 gauge wire, and matches the commercially available extension cord that you run between the inlet and your genset. The portable genset interlock world is built around a 30 amp feed.

5) Finally, when you backfeed a panel with 240 you are only able to feed half of the genset wattage to each side of your panel. Kinda sucks. So you will be loading the genset unevenly and the cheaper 240 generators only regulate the voltage such that the sum of the legs is 240. This means when you load one side a lot, the voltage will drop on that leg and rise on the other. Keep an eye on it. Be sure your panel is balanced as best you can.

6) Your 4400 watt genset can only provide 2200 to each side of the panel so it is reasonably easy to overload the genset. Your 30 amp breaker on the genset feed will allow 30 amps of 120 power down each leg which is 3600 watts. So don't worry about the 10 gauge being too small or the 30 amp being too small. It's plenty.

7) You can easily run burners on an electric range with a 4400 genset. I've made a lot of top ramen this way!

8) I finally got rid of my 3500 watt 240 volt genset and now run the house with a 3100 watt inverter genset that only makes 120 volts. I feed the whole panel with 120 volts so no 240 volt appliances will work. The benefit is a much quieter genset and vastly superior power quality. Voltage regulation, sine wave, Hz, all rock solid with a nice inverter genset. Plus, I now have 3100 watts available to any circuit on any side of the panel which is the same as a 6200 watt 240 genset could provide.

 

[Highbeam]

I was actually considering going to a smaller generator (800 watt chinese special) after reading several other generator threads. In an emergency, I only need the larger wattage every 4-6 hours to keep food from spoiling in the freezer. rest of the time, i only really need a few watts to run lights and a fan, and a .5gallon/6hr burn rate sounds good in event of an extended power outage. I converted all appliances over to gas so my electric use is pretty minimal.

That 800 watt genset will only be a 120 volt and might not be able to start the refrigerator. Once the refrigerator is running it only needs like 100 watts but the startup surge (and an auto defrost cycle too) are much higher. Plus those two stroke 99$ HF generators are known for very poor power quality.

All appliances on gas? Do you even have any 240 volt breakers?

 

[Highbeam]

My highest load for generator is going to be my fridge and only planning to additionally run blower fan on my wood insert and some led/cfl lights so should be no problem staying under 80% of 30amps..

The 80% thing does not apply here. The 80% rule is for circuit sizing (breakers and wire) with hardwired loads. Your breakers are fine with that small genset. The generator has a "continuous" rating from the manufacturer and a surge rating from the manufacturer that are what you will pay attention to. Also, watch voltage to make sure that you don't cook your appliances.

 

[cableman]

I actually have an interlock panel as well and have been through this.

1) The breaker protects the wire. If your generator inlet breaker is a 30 amp breaker then 10 gauge is the corresponding correct size. It is of course a minimum but 10/3 is fine. Note I said 10/3. You need a four wire cable.

2) Voltage drop in a residential application is a non-issue. Forget about it.

3) Plan on flipping off breakers to the automatic load circuits like electric water heaters, hot tubs, or anything else undesirable that might want to turn on when you're on genset power.

4) The power inlet plug L14-30 you chose is obviously rated for 30 amps. That matches the generator inlet breaker, matches your 10 gauge wire, and matches the commercially available extension cord that you run between the inlet and your genset. The portable genset interlock world is built around a 30 amp feed.

5) Finally, when you backfeed a panel with 240 you are only able to feed half of the genset wattage to each side of your panel. Kinda sucks. So you will be loading the genset unevenly and the cheaper 240 generators only regulate the voltage such that the sum of the legs is 240. This means when you load one side a lot, the voltage will drop on that leg and rise on the other. Keep an eye on it. Be sure your panel is balanced as best you can.

6) Your 4400 watt genset can only provide 2200 to each side of the panel so it is reasonably easy to overload the genset. Your 30 amp breaker on the genset feed will allow 30 amps of 120 power down each leg which is 3600 watts. So don't worry about the 10 gauge being too small or the 30 amp being too small. It's plenty.

7) You can easily run burners on an electric range with a 4400 genset. I've made a lot of top ramen this way!

8) I finally got rid of my 3500 watt 240 volt genset and now run the house with a 3100 watt inverter genset that only makes 120 volts. I feed the whole panel with 120 volts so no 240 volt appliances will work. The benefit is a much quieter genset and vastly superior power quality. Voltage regulation, sine wave, Hz, all rock solid with a nice inverter genset. Plus, I now have 3100 watts available to any circuit on any side of the panel which is the same as a 6200 watt 240 genset could provide.

Good info, im looking into this now. I have 2400 yamaha inverter gen which actually out did my 3000 kipor inverter gen. Did you make a pigtail or buy one to go l5 to l14 30amp?

 

[Highbeam]

Good info, im looking into this now. I have 2400 yamaha inverter gen which actually out did my 3000 kipor inverter gen. Did you make a pigtail or buy one to go l5 to l14 30amp?

It's probably not an official method, it might be unsafe, it might make you go bald, I don't recommend you do it unless you know what you're doing.

I had a 20 foot long 30 amp generator cord with the 4 prong twistlocks on each end. I removed the male twistlock and replaced it with a 30 amp RV plug to match my 120volt inverter generator. I landed both hot lines (red and black) on the single hot prong of the RV plug. Works extremely well. I shut off all of the 240 breakers in my panel when I do this just in case some internal computer within a 240 volt appliance tries to do something naughty.

The one thing to worry about is that you have the potential for 60 amps of 120 volt power to run between the panel and the genset. Each wire is 10 gauge and each wire is protected at 30 amps. So the wire can handle this, the breaker protects the hot wire. The trouble is the neutral. On a 120 volt circuit, the neutral carries current. In this case, the neutral will be carrying up to 60 amps before a circuit breaker pops. That's too much for the 10 gauge neutral so that would be bad. The way to eliminate this risk is to only use a genset that makes less than 30 amps of 120v power which is a 3600 watt genset which is a huge amount of power.

 

[PWash]

Thanks for the detailed info HB!

All appliances on gas? Do you even have any 240 volt breakers?

I've got two 240V breakers. I left the 240V 40amp for the oven since the wire was already there, and just added a separate 120V outlet & circuit breaker for the gas oven. Also, while I had the wall open I went ahead and installed a 240V 50amp outlet in the garage. I installed 6-3 (4 wire) so I believe I could use it with NEMA L6-50, 10-50, or 14-50 outlets for welding or some other high current device.

I remember that before you shunt the two red and black wires together to operate your whole house on a single 120V phase generator, you also will want to confirm that your house doesn't have any "multi-wire branch circuits." Since I'm not 100% sure there aren't any of those hiding in the walls somewhere, I just went with a 240v generator. Because i do not have any 240 breakers left, and no breaker ties, i'm sure there are no 'legal' multi-wire branches, but I think an enterprising homeowner could have still effectively wired one in thru mistake or idiocy.

I'll also mention that I had to unbond my ground/neutral wires in my generator. Just had to pop the endcap off the motor housing, and remove the blue wire:


Work is complete, and city inspector signed off. Currently, I'm still sanding the horrible mud job I did on my drywall.

 

[cableman]

It's probably not an official method, it might be unsafe, it might make you go bald, I don't recommend you do it unless you know what you're doing.

I had a 20 foot long 30 amp generator cord with the 4 prong twistlocks on each end. I removed the male twistlock and replaced it with a 30 amp RV plug to match my 120volt inverter generator. I landed both hot lines (red and black) on the single hot prong of the RV plug. Works extremely well. I shut off all of the 240 breakers in my panel when I do this just in case some internal computer within a 240 volt appliance tries to do something naughty.

The one thing to worry about is that you have the potential for 60 amps of 120 volt power to run between the panel and the genset. Each wire is 10 gauge and each wire is protected at 30 amps. So the wire can handle this, the breaker protects the hot wire. The trouble is the neutral. On a 120 volt circuit, the neutral carries current. In this case, the neutral will be carrying up to 60 amps before a circuit breaker pops. That's too much for the 10 gauge neutral so that would be bad. The way to eliminate this risk is to only use a genset that makes less than 30 amps of 120v power which is a 3600 watt genset which is a huge amount of power.

Wiring and hooking up for me is no problem, i understand fully.
What your saying with the neutral is the same when someone uses a 3 wire with ground for 2 120v circuts, the neutral has the potential to carry more then it should. I think in this case the correct way is to make sure each breaker is on separate poles.
I guess my 2400 gen meets the under 3600w requirements!
I use an rv plug on gen side and l5 on other, i figure ill make a pigtail l5 to l14 and attach the hot to both hots on the l14.
Im only gonna power up my den and fridge and maybe a room somewhere. Gotta be better than extension cords all over.

 

[Highbeam]

MultiWireBranchCircuits are very uncommon here other than in commercial builds. It would be possible to verify the lack of MWBCs with relative certainty by looking in the panel. If I can see the sheathing of every romex cable entering the panel and verify that it is only a three conductor cable.

 

[cableman]

I'll also mention that I had to unbond my ground/neutral wires in my generator. Just had to pop the endcap off the motor housing, and remove the blue wire:
View attachment 177737

Whats the reason for unbondong the neutral at the genny? Is this something i have to do also on my yamaha inverter gen?

 

[PWash]

an electrical system is only supposed to have one location where neutral and ground are bonded (connected) together. when you connect to a house, the service panel already has the bond so the generator shouldnt.

if there is more than one gnd/neutral bond, its a potential safety issue and not per code.

you can verify if your yamaha came bonded with a multimeter. some generators come bonded and others dont..

i made a neutral bonding plug so i can easily rebond the generator when using it by itself and not connecting to the house

 

[Highbeam]

Whats the reason for unbondong the neutral at the genny? Is this something i have to do also on my yamaha inverter gen?

The whole floating/bonded neutral thing is a non-issue with portable generators. Forget about it. Don't mess with your genset. Use it as delivered. There is a vast amount of confusion and no consensus on what the floating neutral means when using a portable generator.

I do NOT recommend modifying your portable genset's internal wiring in any way. A recipe for disaster, fried genset, liability, personal injury etc.

If you insist, it doesn't hurt anything to drive a ground rod and clamp it to the generators ground lug or frame.

 

[cableman]

The whole floating/bonded neutral thing is a non-issue with portable generators. Forget about it. Don't mess with your genset. Use it as delivered. There is a vast amount of confusion and no consensus on what the floating neutral means when using a portable generator.

I do NOT recommend modifying your portable genset's internal wiring in any way. A recipe for disaster, fried genset, liability, personal injury etc.

If you insist, it doesn't hurt anything to drive a ground rod and clamp it to the generators ground lug or frame.

Ok cool. Moved some stuff around in my panel last night to get the 30amp breaker up top, just gotta tie the 10awg in then mount the interlock kit.

 

[PWash]

There is a vast amount of confusion and no consensus on what the floating neutral means when using a portable generator.

I discussed the floating neutral with my city inspector and he knew exactly what it means and how it should be used. Also, my reliance inlet box included decals stating to use floating neutral or bonded neutral generators only. The NEC does have a clear requirement.
As long as theres at least one ground somewhere, noone is likely to ever get hurt. I think you could even say "fogetta bout it" about operating ungrounded as injury is still unlikely.

 

[BrotherBart]

If you insist, it doesn't hurt anything to drive a ground rod and clamp it to the generators ground lug or frame.

That is what I thought. But when I attached ground rods to my two portables the "good ground" light went off on both of my distribution panels. Disconnected the ground rods and the panels started indicating a good ground again.

 

[Highbeam]

That is what I thought. But when I attached ground rods to my two portables the "good ground" light went off on both of my distribution panels. Disconnected the ground rods and the panels started indicating a good ground again.

I've never seen a panel with "good ground lights". I would already assume that the good ground light needs to have a better wiring job since all of your panels and subpanels should have a ground.

 

[BrotherBart]

We are talking about portable generators and the aforementioned panels are rack mount 20A power distribution strips with "good ground" indicators.

 

[cableman]

Everyone loves pics! Got er done, just need to mod my pigtail so i power both banks.
I could always hammer in a separate ground rod just outside for the genny, but i dought i ever will.
Highbeam, what gen you use?

 

[Highbeam]

I use this one and really like it. Very clean power, very quiet. Fuel tank is a bit small for my uses but it's really that I was spoiled by my previous genset's huge fuel tank.

http://www.costco.com/Champion-2800...ertified,-Low-Decibels.product.100139466.html

Mine is a year or two old now and my model has a 3100 watt peak rating but otherwise looks the same. That's 120 volt output only so to use it with a whole house interlock you would need to do some "custom" electrical work and of course no 240 circuits would work.

WOw, looks like for an extra 50$ you can get a model with electric start, dual fuel propane or gas, AND a parallel cable to attach two of these together to make 5600 watts! I would buy that one today. It's probably heavier but wow, they made big improvements.

http://www.costco.com/Champion-DUAL...ertified,-Low-Decibels.product.100284958.html

Previously for almost 10 years I used the very popular champion 3500/4000 watt non-inverter genset. It has a huge fuel tank, was much quieter than a typical open frame genset and made 240 for a more typical interlock use. It was very easy on fuel and started very easily. I couldn't find it online anymore, it appears that this genset is now 120 volt only.

Both of these had low oil shutdown. The champion brand is well respected. You call their number and an American person in America answers.