# Portable generators and grounding **URL:** \ **Category:** Factual Questions\ **Created:** [May 1, 2004, 12:26am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912 "2004-05-01T00:26:55Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [May 1, 2004, 12:26am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/1 "2004-05-01T00:26:55Z")
I’ve got a portable generator that puts out 20 amps of 240 (or do you prefer to think of it as 2 20-amp 120 circuits?) on an L14-30 four-contact twist-lock connector, as well as a pair of standard 20-amp 120 volt receptacles. Rather than run multiple long extension cords off the 120-volt receptacles, I was planning on getting some heavy cable and putting an L14-30 plug on one end (it came with the generator) and hard wire the other end to a panel with outlets on it. Due to being an exhaust-belching noisy thing, the generator will be banished to the far end of the site, and the power distribution will be more or less in the center of the site. The alert may remember my earlier [thread](http://boards.straightdope.com/sdmb/showthread.php?t=251579&highlight=generator) on keeping this rascal quiet. Internally to the generator, the ground and neutral terminals of all the receptacles are tied together. Can I use something like 10-3 cable - connected to the 2 hots and the neutral at the generator, and tie the neutrals and grounds of the outlets at the other end together? There isn’t a true ground to begin with here - the generator is on rubber tires, so the power it produces has no ground reference. ---
**Author:** ![MrFantsyPants](https://avatars.discourse-cdn.com/v4/letter/m/7ba0ec/32.png) [@MrFantsyPants](https://boards.straightdope.com/u/MrFantsyPants)\ **Post date:** [May 1, 2004, 1:01am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/2 "2004-05-01T01:01:19Z")
Another alternative might be to run your hot and neutral wires to the panel, but to connect the ground on the panel to a 5 foot length of rebar driven into the ground. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [May 1, 2004, 4:34am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/3 "2004-05-01T04:34:09Z")
> [@MrFantsyPants](#): > > Another alternative might be to run your hot and neutral wires to the panel, but to connect the ground on the panel to a 5 foot length of rebar driven into the ground. Rebar tends to be painted I think. Wheather it’s conductive paint or not I don’t know. You’ll probably want to sand or sandblast it off if you use that. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [May 1, 2004, 4:50am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/4 "2004-05-01T04:50:49Z")
No rebar that I have ever seen is painted. It sounds like you are looking for what we used to call a tem-power box. I could not find one just like what we used to use, but check [this out.](http://www.jbn-duraline.com/duraline_power_distribution_panels.htm) I know that somebody makes these available off the shelf, I just can’t seem to find them on the web tonight. ---
**Author:** ![trey\_goesh](https://avatars.discourse-cdn.com/v4/letter/t/e9c0ed/32.png) [@trey\_goesh](https://boards.straightdope.com/u/trey_goesh)\ **Post date:** [May 1, 2004, 4:53am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/5 "2004-05-01T04:53:55Z")
\>\>Rebar tends to be painted I think no. and i think the op is okay with floating ground - the question was how to run wire for the 120 v outlets - whether you’re running 2 phase or 3 phase, and i suspect the answer depends on that. but maybe not - it’s possible that the two grounds may be moving relative to each other, and wiring them together would be bad. however, my brain shut off for the weekend, and i’m quite content to be completely wrong in my above assesment. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 1, 2004, 5:04am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/6 "2004-05-01T05:04:04Z")
> [@Rick](#): > > No rebar that I have ever seen is painted. It isn’t, but it’s got a pretty good oxide layer on it that makes it unsuitable as a grounding rod. In any case, a floating ground isn’t such a bad thing, in this case. The reason it’s bad in a typical residential setup is that the ground can float up to the primary voltage of the pole transformer, which is typically 7200 V. That isn’t the case here. If ground is bonded to neutral, you’ll be about as safe as you can be. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 1, 2004, 11:12am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/7 "2004-05-01T11:12:37Z")
> [@Q.E.D.](#): > > A floating ground isn’t such a bad thing, in this case. Agree. In fact, it would probably be safer _not_ to ground the generator… ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 1, 2004, 2:08pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/8 "2004-05-01T14:08:45Z")
> [@Crafter\_Man](#): > > Agree. In fact, it would probably be safer _not_ to ground the generator… Ok, I’ll bite. Why is that? ---
**Author:** ![MrFantsyPants](https://avatars.discourse-cdn.com/v4/letter/m/7ba0ec/32.png) [@MrFantsyPants](https://boards.straightdope.com/u/MrFantsyPants)\ **Post date:** [May 1, 2004, 2:30pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/9 "2004-05-01T14:30:27Z")
> [@Q.E.D.](#): > > Ok, I’ll bite. Why is that? Yeah, I could see it would be a bad idea to hook the ground/neutral from the generator to the grounding post, but to leave that seperate, and hook only the ground of the junction box/outlets to the grounding post seems like a fine way to go. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 1, 2004, 2:35pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/10 "2004-05-01T14:35:25Z")
> [@MrFantsyPants](#): > > Yeah, I could see it would be a bad idea to hook the ground/neutral from the generator to the grounding post… I don’t see that, either. This is, in fact, exactly what is done in a typical residential setup. Go look in your breaker box, if you feel comfortable removing the front panel. You’ll see all the white neutral wires and the copper ground wires all connected together on a fat bus, with a heavy-gauge bare wire running from that to the system’s Earth ground. ---
**Author:** ![MrFantsyPants](https://avatars.discourse-cdn.com/v4/letter/m/7ba0ec/32.png) [@MrFantsyPants](https://boards.straightdope.com/u/MrFantsyPants)\ **Post date:** [May 1, 2004, 2:40pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/11 "2004-05-01T14:40:06Z")
> [@Q.E.D.](#): > > I don’t see that, either. This is, in fact, exactly what is done in a typical residential setup. Go look in your breaker box, if you feel comfortable removing the front panel. You’ll see all the white neutral wires and the copper ground wires all connected together on a fat bus, with a heavy-gauge bare wire running from that to the system’s Earth ground. Not in any of the ones I’ve worked on, but perhaps it is done differently in Canada ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [May 1, 2004, 3:15pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/12 "2004-05-01T15:15:38Z")
> [@MrFantsyPants](#): > > Not in any of the ones I’ve worked on, but perhaps it is done differently in Canada Then it must be done differently in Canada. The US practice is as Q.E.D. described it. In many places now, two ground rods some distance apart (I think it’s at least 8 ft. but am not sure) are required. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 1, 2004, 4:17pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/13 "2004-05-01T16:17:47Z")
> [@Q.E.D.](#): > > Ok, I’ll bite. Why is that? I’m trying to figure out what advantage there would be to hooking a generator’s common (center tap) to _ **earth** _ ground. Seems it would only increase the likelihood of getting zapped, since a person is often grounded. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 1, 2004, 4:29pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/14 "2004-05-01T16:29:35Z")
> [@Crafter\_Man](#): > > I’m trying to figure out what advantage there would be to hooking a generator’s common (center tap) to _ **earth** _ ground. Seems it would only increase the likelihood of getting zapped, since a person is often grounded. I don’t know as there _is_ any advantage, unless you want to guarantee a stable zero-volt reference WRT Earth. But, without a connection between ground and neutral at the generator at the very least, you’ve got the potential for a hot-to-chassis fault which will _not_ trip a breaker. And if hot and neutral are bonded together with no Earth ground, you’ve got the potential for an open hot neutral situation, no? ---
**Author:** ![MikeG](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mikeg/32/4329_2.png) [@MikeG](https://boards.straightdope.com/u/MikeG)\ **Post date:** [May 1, 2004, 4:32pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/15 "2004-05-01T16:32:50Z")
This is why I hire electricians. I’ve been zapped once and I’m not about to repeat that thankyouverymuch. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 1, 2004, 4:39pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/16 "2004-05-01T16:39:57Z")
> [@MikeG](#): > > This is why I hire electricians. I’ve been zapped once and I’m not about to repeat that thankyouverymuch. It’s not all that bad. I’ve been zapped three or four times by 120 VAC, and more times than I care to count by the 10-30 kV inside TVs. The most painful was the HV from a car ignition system. _That_ I don’t care to repeat. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 1, 2004, 6:18pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/17 "2004-05-01T18:18:32Z")
> [@Q.E.D.](#): > > I don’t know as there _is_ any advantage, unless you want to guarantee a stable zero-volt reference WRT Earth. But, without a connection between ground and neutral at the generator at the very least, you’ve got the potential for a hot-to-chassis fault which will _not_ trip a breaker. And if hot and neutral are bonded together with no Earth ground, you’ve got the potential for an open hot neutral situation, no? I agree the “ground” and neutral conductors should be tied together at the generator. I just don’t see any advantage of (in addition) tying this junction to earth ground. (Perhaps you could elaborate on a “open hot neutral situation” and we could go from there.) ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 1, 2004, 6:30pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/18 "2004-05-01T18:30:12Z")
> [@Crafter\_Man](#): > > Perhaps you could elaborate on a “open hot neutral situation” and we could go from there. I had in mind a situation from the other thread, where a bunch of current-carrying neutral returns from upstream, and one of them came loose. But thinking further, this wouldn’t be any more or less dangerous here than if the hot wire came loose, so I suppose it’s moot. And I jsut noticed I misspoke. I meant to say “if _ground_ and neutral are bonded together…”, not “_hot_ and neutral”. The former is good, the latter makes smoke. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [May 1, 2004, 6:49pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/19 "2004-05-01T18:49:47Z")
In my fire company, we have a special service truck which has an on board 50kW generator. To ground or not to ground became an early question, as some felt we should drive a temporary ground rod when the truck was providing light and power at an incident. We ended up deciding not to do so for this reason: If the generator is grounded solidly, and there is a faulty connection of the neutral in a cordset or appliance, the user of that cordest/tool combination could constitute a better or parallel path for neutral current, exposing the user to risk of electrocution. If the generator ‘floats’ with respect to earth ground, given the scenario above, the cordset/tool combination likely won’t work, triggering investigation (hopefully)before someone is exposed to potential harm. FWIW, I refitted all receptacles and cord reels on the truck with GFCI protection several years ago, as part of a belt and suspenders approach. Another observation-not all panelboards in the US have a common neutral/ground bus. **Sub panels** are supplied with four conductors (2 hot, 1 neutral, 1 ground), and the neutral bus is not mechanically/electrically bonded to the panelboard, while the ground bus is bonded. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 1, 2004, 7:16pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/20 "2004-05-01T19:16:53Z")
> [@Q.E.D.](#): > > I had in mind a situation from the other thread, where a bunch of current-carrying neutral returns from upstream, and one of them came loose. But thinking further, this wouldn’t be any more or less dangerous here than if the hot wire came loose, so I suppose it’s moot. On a home wiring system, if the neutral is broken, and you touch the neutral segment that’s connected to the load, then you’re liable to get zapped. But this is because the system is ground-referenced, and you’re assumed to be grounded. If the system is _not_ ground-referenced (such as a portable generator that’s floating), then touching a broken neutral would probably not be all that dangerous. In fact, touching the _hot_ wire of a floating generator shouldn’t be all that dangerous. That’s why it’s generally safer to _not_ tie a portable generator’s common (“ground”) conductor to earth ground. [Next page](https://boards.straightdope.com/t/portable-generators-and-grounding/242912.md?page=2)