# 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:** 13\ **Page:** 2
**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, 7:27pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/21 "2004-05-01T19:27:16Z")
> [@Crafter\_Man](#): > > In fact, touching the _hot_ wire of a floating generator shouldn’t be all that dangerous. Then _you_ try it. I rather like my hair straight, thankyouverymuch. 😃 ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [May 2, 2004, 11:18pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/22 "2004-05-02T23:18:50Z")
So it sounds like I can use the three wire cable with a combined neutral/ground and tie the neutral and ground terminals together on the outlets? As for the outlets themselves, would GFI outlets be worth the cost? Would they even work properly if their “line” neutral and ground were tied together at the outlet itself? ---
**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 2, 2004, 11:49pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/23 "2004-05-02T23:49:53Z")
> [@gotpasswords](#): > > So it sounds like I can use the three wire cable with a combined neutral/ground and tie the neutral and ground terminals together on the outlets? The neutral and ground conductors should be tied together at the generator. > [@gotpasswords](#): > > As for the outlets themselves, would GFI outlets be worth the cost? Would they even work properly if their “line” neutral and ground were tied together at the outlet itself? GFI’s offer the most benefit & protection for grounded systems. For a floating system, the fact that it is floating offers a lot of protection. One could even argue that GFI’s are not necessary on a floating system. But I would go ahead and install GFI’s for two reasons: 1. Things have a way of getting grounded. Even if they’re not supposed to be. 2. For an appliance with a three-conductor power cord (hot, neutral, ground), a GFI can detect excessive leakage current in the ground conductor. So on a floating system, a GFI outlet would offer some protection if the appliance plugged into the outlet has a three-conductor power cord (hot, neutral, gnd). But it wouldn’t offer much protection if the appliance plugged into the outlet has a two-conductor power cord (hot, neutral). At any rate, GFI outlets are cheap. I’d go ahead and install them. ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [May 2, 2004, 11:53pm UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/24 "2004-05-02T23:53:04Z")
I’d use both 110V and 220V GFCIs for the respective circuits (btw, considering that 110 is often used in a 220V appliance, how do 220V GFCIs work?) NEC (US code) allows GFCIs to be used as a way to get around not having a ground on a 110 circuit. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [May 3, 2004, 1:08am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/25 "2004-05-03T01:08:58Z")
> [@Crafter\_Man](#): > > The neutral and ground conductors should be tied together at the generator. They are. The main point of my question was if I could use three wire cable (two hots and the combined ground/neutral) and tie the neutral and ground connectors together on the outlets, or if I had to use four wires to carry the two hots, neutral and ground and not tie anything together on the outlets. I know that the 3-wire scenario isn’t allowed in home wiring - it’s the equivalent of trying to retrofit a 2-slot outlet to a grounded by tying the outlet’s ground and neutral together and living on the assumption that the ground and neutral are and forever shall remain perfectly bonded together. As this is a generator sitting on rubber tires, earth ground doesn’t exist unless I intentionally connect the generator’s frame to an earth ground, so “ground” on the outlets - whether the ones built into the generator, or remotely at the end of a long extension cord - really doesn’t exist. As \*\*danceswithcats’ \*\* experience indicates that I’m better off leaving the generator ungrounded, I’ll do just that. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [May 3, 2004, 2:11am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/26 "2004-05-03T02:11:52Z")
> [@Q.E.D.](#): > > 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. Gotta agree with you on that! 120 just kinda hurts. Sort of a “bzzt! Ow!” The CRT anode stings like hell and kicks like a mule, but ignition just \*\*gnaws \*\* on you and rips at every nerve. I’ve never really thought about it before, but I’m guessing it’s because it’s a DC pulse and you just can’t let go of it because it’s DC. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [May 3, 2004, 3:03am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/27 "2004-05-03T03:03:28Z")
> [@Crafter\_Man](#): > > GFI’s offer the most benefit & protection for grounded systems. For a floating system, the fact that it is floating offers a lot of protection. One could even argue that GFI’s are not necessary on a floating system. _ **Excuse me?!** _ A ground fault circuit interrupter does not depend on any ground for effecacy. It is perfectly permissible to install them in indicated locations of 1 and 2 family dwellings without a ground so long as the appropriate sticker is applied to receptacles indicating that no ground is present. The circuitry of a GFCI is quite simple in that current out (hot) and current in (neutral) are compared using a coil. So long as that which goes out is equal to what returns, the coil measures zero. Failure in cordsets, tools, appliances, etc. which allow current flow to any other place causing an imbalance above the trip threshold will cause the device to operate. They will do so without a grounding conductor. ---
**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 3, 2004, 3:21am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/28 "2004-05-03T03:21:39Z")
> [@danceswithcats](#): > > _ **Excuse me?!** _ A ground fault circuit interrupter does not depend on any ground for effecacy. It is perfectly permissible to install them in indicated locations of 1 and 2 family dwellings without a ground so long as the appropriate sticker is applied to receptacles indicating that no ground is present. > > The circuitry of a GFCI is quite simple in that current out (hot) and current in (neutral) are compared using a coil. So long as that which goes out is equal to what returns, the coil measures zero. Failure in cordsets, tools, appliances, etc. which allow current flow to any other place causing an imbalance above the trip threshold will cause the device to operate. They will do so without a grounding conductor. **danceswithcats** : I’m very well aware of how a GFI works, and that an earth ground is not necessary for them to work. (For the record, a GFI uses a differential transformer to sense the difference in current between the hot and neutral lines. If it detects a difference in excess of 4 to 6 mA, it assumes the current is going elsewhere via a ground path, and trips a relay.) Where did I say it needed a ground to work? What we’re talking about here is the use of GFI’s on a _floating_ system. My point was that, while the use of a GFI on a floating system couldn’t hurt, a person could argue that it’s not really needed. I further gave my opinion that I would go ahead and use them. ---
**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 3, 2004, 3:23am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/29 "2004-05-03T03:23:22Z")
**gotpasswords** : O.K., I see what you’re saying. If you’re 100% certain the entire system will remain floating, then there’s probably not much harm in connecting the neutral & ground conductors together at the outlet and running one conductor back to the generator. But here’s the thing: Let’s say you plug a 120 VAC appliance into the outlet. Let’s say the appliance has a 3-conductor power cord and plug (hot, neutral, ground). Finally, let’s say the appliance has a metal frame or chassis. Are you going to guarantee the appliance’s frame or chassis never comes in contact with earth ground? Because if it does come in contact with earth ground, then you have grounded the entire system. If this happens it will be an interesting situation, in that there will be a voltage between earth ground and the generator’s frame due to V = IR. And of course, if there’s a break anywhere along the conductor that goes back to the generator, and the appliance is grounded, then someone touching the generator will receive a jolt. If it were me, I’d run 4 wires. ---
**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 3, 2004, 3:33am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/30 "2004-05-03T03:33:31Z")
**danceswithcats** : I reread your reply to me. Perhaps there’s some confusion here… when I say a “grounded system,” I mean an electrical system that is _ground-referenced_ as opposed to _floating_. (Your home wiring is the former.) I am _not_ saying the appliance itself has to be “grounded.” Because your home wiring system is ground-referenced, there is a risk of shock if you sould ever happen to come in contact with the hot wire. This is because a person is often grounded, and the hot wire is 120 VAC with reference to earth ground. A GFI is most beneficial with _ground-referenced_ systems. My point was that a _floating_ electrical system is inherently safe against shock (assuming it’s not floating up to a very high voltage!), and thus GFI protection may not be needed. But to be safe, I’d have it anyway. It’s cheap insurance. ---
**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 3, 2004, 4:40am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/31 "2004-05-03T04:40:24Z")
> [@gotpasswords](#): > > I’ve never really thought about it before, but I’m guessing it’s because it’s a DC pulse and you just can’t let go of it because it’s DC. I’m thinking it’s because when you’re working on a car, you can’t help but make a pretty good connection to the system ground, i.e. the frame, body or chassis. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [May 3, 2004, 8:00am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/32 "2004-05-03T08:00:42Z")
> [@Crafter\_Man](#): > > My point was that a _floating_ electrical system is inherently safe against shock (assuming it’s not floating up to a very high voltage!), and thus GFI protection may not be needed. But to be safe, I’d have it anyway. It’s cheap insurance. Floating systems are only inherently safer if you can guarantee that there’ll only ever be a single fault anywhere on the system. As either the system gets larger, or time passes, the probability of a second fault somewhere increases and approaches unity. It’s not safe when there are multiple faults. For example, say your house is supplied by a generator and you keep the system floating. A fault between active and say, the casing of your toaster occurs. No fuse blows, no GFCI operates, and the toaster is safe to touch. Now lets say a second fault occurs somewhere else, between say neutral and a water pipe. Still no fuse blows, and no GFCI operates. But if you happen to touch the toaster and the kitchen sink, pow. That’s why the decision was made to use a multiple earth neutral system in most places. To enable fault detection and interruption. ---
**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 3, 2004, 10:57am UTC](https://boards.straightdope.com/t/portable-generators-and-grounding/242912/33 "2004-05-03T10:57:58Z")
**Desmostylus** : I agree with you about the multiple fault thing, but I still contend that a floating system is inherently safer. (But this does _not_ mean I advocate floating a _home_ system, as it could float up to the primary voltage. I’m talking about a _portable generator_ here. If you wanted to float a home system you’d have to use a whole-house transformer.) I just don’t see any advantage to _purposefully_ grounding a portable generator. (And when I say “grounding,” I mean connecting the neutral/ground conductor to earth ground.) [Previous page](https://boards.straightdope.com/t/portable-generators-and-grounding/242912.md?page=1)