We're making steady, if slow, progress getting our RV site set up at our airstrip property in Lenoir City, TN.
We got our temp pole inspected and powered up:
(https://c1.staticflickr.com/3/2824/33236623484_6c9bfaebce_z.jpg)
(water is also running to the frostproof spigot)
This setups for just until we have our hangar built - at that point the wiring will run from the hangar panel back to the RV pedestals at whatever amperage we choose.
The utility company would not approve more than two 20A circuits, so that's what we're having to live with for now. The box cannot be modified or hard-wired.
The plug seen is underground ROMEX running to lights and outlets to my shed.
Yesterday I installed a junction box and a similar 20A plug to connect to the wiring run into the underground conduit seen in the above photo.
Got the RV panel wired yesterday:
(https://c1.staticflickr.com/3/2882/33333009634_6d64dfa2f8_z.jpg)
(https://c1.staticflickr.com/3/2854/33333010614_eda6578b93_z.jpg)
Questions...
1) Would it enhance safety to install a ground rod at the pedestal?
2) It appears as though the 30A outlet will be "hot" if I throw the breaker. I know more than a 30A draw will pop the breaker at the temp pole, but otherwise is it feasible to just plug my 30A cable into that? I'm hoping the gauge of the wire and relatively short (125') run may allow us to run the air conditioning. If not we can always power up our generator in the heat of the day.
Thoughts?
As an aside, we got the gravel down:
(https://c1.staticflickr.com/3/2805/33645008260_eb682479e0_z.jpg)
Next priority is getting topsoil and grass seed down - the ungraveled areas turn into a muddy mess in the rain!
Eddie:
The power company installed a ground rod at your incoming power panel, right? Then that is the only ground you should have. The NEC requires one ground at the power source and only one ground to prevent ground loops.
I had a hard time following your description, but I think you will be able to run A/C from your new power supply as long as the wire size is big enough. I suspect it is at least 10 gauge which should work ok. A two hundred fifty foot round trip with 10 gauge and 20 amps results in a bit more than 5 volts drop. High but usable. #8 would be better.
David
Thanks!
Yes, there's a ground rod at the temp pole.
So, one at the pedestal is actually a bad idea? I ask because I installed one at the pedestal at our N GA home, thinking "belt and suspenders". It's about 225' from the main panel. There we used 4ga aluminum wire.
Sorry, not sure of the wire gauge on the property, though you can get an idea from the open panel photo. I'd guess 8ga - it's larger than the wires running from the buss to the 20A and 30A outlets, for comparison purposes. I'll verify next time up!
Yes, a second ground is a bad idea.
It looks like you've got 240AC at 50 amps in your RV box. Wow! What's that for?
To your previous question; yes, you can power your new RV box with your temp 20 amp supply. The temp box breakers are the controlling limiter, but it's fine to use that arrangement. If you draw more than 20 amps, the breaker will flip, but no big deal.
Quote from: Merlin on April 21, 2017, 09:42:02 AM
Yes, a second ground is a bad idea.
Then maybe I should disconnect the one I put in at home?
Can you clarify why it's a bad idea? On the surface it seemed like a safety measure.
QuoteIt looks like you've got 240AC at 50 amps in your RV box. Wow! What's that for?
Nothing, right now. It's just how the RV boxes came configured.
Ultimately, we'll have two pedestals. The idea was to have 50A available in case someone with a large RV that required it were to visit.
This seems to be how they're wired:
(http://rvtravel.com/uploads/1/50_Amp_240V_metered.JPG)
Seems like we'd have to pull a second hot lead for that to work.
Eddie:
The National Electric Code requires one and only one ground located at the power source, which in your case is the power company supplied power panel. You will not be in compliance if you install another ground rod downstream of that one. 'Nuff said.
Now if you just added a second ground at a secondary panel AND DID NOT TIE THE NEUTRALS TO IT, and just made it another ground in parallel with the primary one, then I can't see anything particularly bad about that practice. But why do it if the NEC says not to?
Some years ago I installed an outdoor hot tub at the back of our house and the main panel was in the front. The NEC requires a disconnect and a GFCI within 10' of the hot tub. So it was a similar situation to yours and I did not install a separate ground rod. The building inspector approved that installation.
David
Here is the reason for one, and only one, ground point in an electrical system:
"The common ground point—installed in the service disconnect panel—is connected via a grounding electrode conductor to the common ground reference, such as a ground rod. This connection to earth is made at only one point in each electrical system; otherwise, parallel paths will exist for the currents to flow. These parallel current paths would represent a safety hazard and are not allowed in installations wired per the NEC/CEC."
Also, I see now that the big 240VAC/50A breaker in the RV panel is not wired up yet (although one leg of it may be hot per the photo, so be careful). If you ever have "friends" camping there that need that kind of power, be prepared for an increase in your electric bill!
My Saturday morning two cents' worth:
It seems the operative distinction is whether the added ground rod is connected to the system neutral. There must be only one intentional N-G connection. In any installation involving long wire runs there will be a voltage developed between the system ground point and the neutral at the remote point. Any appliances connected to that neutral will develop a voltage on the case due to capacitive and/or other high impedance paths. Eliminating these voltages, and accidental shorts, is the purpose of the safety ground. Connecting the trailer frame to the system safety ground, i.e. the ground wire in the 3 wire service line as it should be, will eliminate most but maybe not all of this voltage. Connecting the trailer frame, NOT the system neutral, to an added ground stake will further reduce the potential referenced to the physical ground at the specific trailer location. This is OK. Recognize that additional parallel ground paths between the trailer frame and earth ground are impossible to eliminate, but they may be through leveling jacks, the tongue jack, or even people. Bottom line: If voltage exists between the trailer and local ground, first verify the system safety ground is intact and no direct N-G connection exists in the trailer or local power pedestal. If OK, an additional ground stake is appropriate if not connected to system neutral.
Eddie you have a nice property! Before going seasonal in a campground I had considered buying a property instead. I might do it sometime
Thanks for all the input!
Who knew health insurance electricity could be so complicated?
To be clear, I think I understand that ground and neutral should not be bonded anywhere but at the main panel/source. The question is just: does an earth ground at an RV pedestal benefit in any way from having its own earth ground?
I did a Google search to try to find a clear explanation and the amount of conflicting information is astounding! And much of it seems quite authoritative, listing and quoting pertinent NEC codes. It seems like a lot depends on definitions of things such as "structure" and "branch". It also seems like the need for an earth ground at pedestals may vary with location, and maybe even the inspector involved.
I ended up on Mke Sokols's NoShockZone page: http://noshockzone.org (http://noshockzone.org)
Others have recommended him and his site as a "go to" source for all things electrical. I'm going to email him with my exact situation and see what his take is. I'll post his answer here (with permission, of course).
I don't want to seem argumentative or ungrateful for the advice so far, and I really do appreciate it.
Good move. I hope he will help out.
Quote from: Merlin on April 23, 2017, 09:14:37 PM
Good move. I hope he will help out.
He emailed me from Rotterdam(!) and said he'd try to answer my question tomorrow.
I'll keep you guys updated.
For those interested, the text of my email to him:
Here are the particulars:
We bought some property on an airstrip in Lenoir City, TN. We've made a fenced area to park our 21' CampLite travel trailer in. The idea is to give us a base of operations while a hangar and efficiency apartment are built over the next year or so.
The utility company so far will only allow a temp pole to have two 20A circuits. We had one installed and it passed inspection and is powered up:
<IMG_5083.jpeg>
That ROMEX is running underground to a nearby shed. The conduit is running about 125' to where we've put an RV pedestal. I have since wired a 20A plug and attached its leads to the three pulled wires in a waterproof junction box. The temp pole has an earth ground.
I wired the other end thusly:
<IMG_5095.jpeg><IMG_5097.jpeg>
I think I know enough to leave the bare copper wire on the right unbonded to neutral. For now we can live with 20A service to our trailer, since the utility company forbids any modifications to the temp pole once installed and inspected. They've apparently had issues with customers getting larger capacity feeds - for boats mainly - and then using it as a semi-permanent installation. Ultimately, once the hangar is built, 100A service will run from the transformer to a main panel and meter at the hangar and then run from there back to the RV pedestals (there will ultimately be two) using the existing conduit and wire. I think I see that if we ever wanted to use the 50A outlet, a fourth wire would have to be pulled.
Anyway, my inclination was to install a ground rod at the RV pedestal to provide some additional level of safety if the ground from the temp pole was ever compromised. Or maybe just lightning protection. Others have suggested that's either unnecessary or a bad idea in general.
Would you mind sharing your thoughts, and would you mind me posting them to the forum?
As an aside, I have a similar setup at my N GA home, but using 4GA aluminum wire over a 225' run. I did install a ground rod at the RV panel there.
As a further aside, I have had a "hot skin" of a full 110V once, due to a mis-wired pump house outlet combined with accidentally shorted ground and neutral circuits on my trailer. So count me in the camp of those to whom it has happened! It's especially scary when a grandchild asks, "Why is the trailer shocking me?"
Thanks in advance, and enjoy your Sunday!
Fast Eddie
As an aside, as I wait for a fuller response from Mike, here's the final 20A outlet to underground wiring interface at my temp pole:
(https://c1.staticflickr.com/5/4192/34169921911_bb7bd94e36_c.jpg)
We turn off the breakers and unplug when we leave and padlock the panel.
When permanently burying wiring in that plastic conduit, how deep did you have to go with the trench?
Quote from: Merlin on April 27, 2017, 12:49:28 PM
When permanently burying wiring in that plastic conduit, how deep did you have to go with the trench?
I wasn't there, so I'm not sure.
I'll ask.
As I recall the National Electrical Code (NEC) requires 18" unless under rock or concrete. Used to be you could bury a 30A or less circuit 12" but I didn't see that exception last time I looked.
He just messaged me back - 24" to 36".
OK, Mike Sokol got back to me.
First, it would never, ever have occurred to me that the underground ROMEX I had on hand would be improper for the short run to my 20A outlets, but he replied in response to my photo:
Ed,
So there's three reasons I can think of to replace that short run of underground Romex with the proper cable:
#1) The plug you've connected it to is probably (almost certainly) not rated for solid wire. It really needs to be stranded wire.
#2) Solid wire Romex isn't rated for use where I can be continuously flexed. That will eventually cause work-hardening and breakable. Sure it would take thousands of flexes to make that happen, but when it does there can be a real fire hazard.
#3) The sheath of this Romex cable isn't rated for abrasion, so something rubbing against it will eventually break though the insulation and cause a potential shock hazard.
To be 100% code compliant, this piece of exposed Romex really should be replaced with a length of 12-gauge SOOW rubberized extension cable. At least that's how the latest code is interpreted. It's not expensive and rated for up to 600 volts, plus it's a hard-serivce cable that can withstand abrasion, oil, immersion in water, and flexing at cold temperatures. You might be able to get by with SJOOW (Junior Hard Service Cable) which is similar but rated for up to 300 volts with a thinner jacket. It's likely that using a piece of SJOOW (available for may 50 cents a foot at any Lowe's or Home Depot) would satisfy most any inspector who takes a peak. That piece of exposed Romex wold raise a red flag with any inspector I know and could cause all kinds of other questions to be asked.
You'll want to confirm the continuity of the ground bond on the far end of this run by measuring between the neutral and ground wires. It should measure maybe a volt or two with any substantial load. If it measures 5 to 100 volts, then the ground is floating. If it measures zero volts (with a load) then you have a bootleg ground. But a volt or two (half of the total voltage drop over that length of wire) is what you should expect to measure.
Yes, you can post this on your forum as long as you send me a link so I can confirm you've included all the facts. And please send me a picture of your final solution.
I replied that I would swap the correct rubberized cable for the ROMEX I used next time I was up.
Secondly, he said this about my original query about a ground rod at the pedestal:
And you can certainly add your own ground rod at the secondary end of your system. That may be required in some localities and would look good to any inspector <who> takes a look.
While SOOW cable may be suitable for underground direct burial, that is not what the industry uses. They use UF (underground feeder) cable for this purpose. It is available at Home Depot or Lowes for $19 for a 25' roll of 12/2 cable, which is what you need for your 20 amp circuit.
Most codes require it to be buried 18" deep. It is also a good idea to cover the first 6" inches or so with a contrasting sand to warn a future digger that something is there.
David
We were not talking about any of the underground runs, just the final bit connecting the underground ROMEX or wires in conduit to the 20A receptacles on the temp pole.
OK, sorry I thought this was underground. Yes SOOW would be the right thing for exposed, above ground cabling.
David
Thanks for posting the info. Sokol's an experienced source for electrical safety in RVs.
Now if you could just find that extra N-G bond in your camper...........
Quote from: FastEddieB on April 21, 2017, 08:36:38 AM
2) It appears as though the 30A outlet will be "hot" if I throw the breaker. I know more than a 30A draw will pop the breaker at the temp pole, but otherwise is it feasible to just plug my 30A cable into that? I'm hoping the gauge of the wire and relatively short (125') run may allow us to run the air conditioning. If not we can always power up our generator in the heat of the day.
Yes, the way this is wired will allow the 30-amp outlet to be powered up, but only with 20 amperes of current available. That's not dangerous and not even a code violation as long as you make it with a +20-amp service" sticker in some locations. The upstream 20-amp circuit breaker will protect the 12-gauge wire run from over-current, so that's perfectly safe. However, 125 ft of wire is a really long run (code calculations are based on 100 ft), so it's doubtful you'll be able to start an air conditioner on that circuit. You'll want to listen carefully when starting the HVAC to make sure it's not going into locked-rotor mode (humming but not starting up) since you can destroy an HVAC compressor pretty quickly with undervoltage.
Mike Sokol
No~Shock~Zone
Thanks! And welcome!
When I was up last time, I tested and the 30A service is wired to be on a different "leg". It would take a jumper between the two screws on the upper left to energize it.
(https://c1.staticflickr.com/3/2882/33333009634_6d64dfa2f8_c.jpg)[/
That would also energize both sides of the 50A breaker. If I went this way I could either disconnect the hot leads out from the 50A breaker or just leave the 50A breaker off and mark it INOP. I had already thought about marking the 30A outlet "20A SERVICE ONLY".
I forgot to check the gauge of the cable in the underground run. From the photo, it looks to me like the runs to the outlets in the cover is 12GA, and the cable coming into the box is clearly larger - 10 GA? I will check next time up.
As an aside, I also painted the ground wire a much brighter green to avoid possible confusion.
Thanks again for your expertise - please don't be a stranger!
Quote from: FastEddieB on April 29, 2017, 08:46:07 AM
That would also energize both sides of the 50A breaker. If I went this way I could either disconnect the hot leads out from the 50A breaker or just leave the 50A breaker off and mark it INOP. I had already thought about marking the 30A outlet "20A SERVICE ONLY".
Actually, every dogbone adapter you see with 15/20 to 50 amp converter plugs does a jumper between the two hot legs on the 50-amp side, and connects it to the single hot leg on the 15/20-amp side. So you can make the jumper yourself and save someone from needing an adapter. Same for the 30-amp outlet adapters. Of course, you'll still have only 20 amps available, but if you go over the limit the circuit breaker will trip, so no big deal.
QuoteI forgot to check the gauge of the cable in the underground run. From the photo, it looks to me like the runs to the outlets in the cover is 12GA, and the cable coming into the box is clearly larger - 10 GA? I will check next time up.
If it's 10 gauge that's great since that will reduce the voltage drop on 125 of wire significantly. In fact I generally oversize the wire gauge on any run that's going to be over 100 ft, and even for 50 ft runs.
QuoteAs an aside, I also painted the ground wire a much brighter green to avoid possible confusion.
Just be as obvious as you can be. We generally use green PCV electrical tape.
Mike Sokol
The No~Shock~Zone
Thanks for joining and posting, Mike.
Quote from: jmsokol on April 29, 2017, 01:03:03 PM
Actually, every dogbone adapter you see with 15/20 to 50 amp converter plugs does a jumper between the two hot legs on the 50-amp side, and connects it to the single hot leg on the 15/20-amp side.
Mike Sokol
The No~Shock~Zone
Mike,
I know you really didn't mean what you said. A jumper between the two hot legs on the 50A side would be very exciting....for a millisecond or so. The dogbone adapters connect ONE 50A hot to the 15/20/30A socket.
Quote from: charliem on April 29, 2017, 01:26:29 PM
Quote from: jmsokol on April 29, 2017, 01:03:03 PM
Actually, every dogbone adapter you see with 15/20 to 50 amp converter plugs does a jumper between the two hot legs on the 50-amp side, and connects it to the single hot leg on the 15/20-amp side.
Mike Sokol
The No~Shock~Zone
Mike,
I know you really didn't mean what you said. A jumper between the two hot legs on the 50A side would be very exciting....for a millisecond or so. The dogbone adapters connect ONE 50A hot to the 15/20/30A socket.
Actually, I did mean what I said, but let's make sure I'm being clear about what I'm saying. On a 15-amp male to 30-amp female adapter there's one-to-one connections between the hot, neutral and ground contacts. That is, Hot-to-Hot, Neutral-to-Neutral, and Ground-to-Ground. On a 30-amp male to 50-amp female adapter there's a slightly different connection setup. While there's a Ground-to-Ground connection and Neutral-to-Neutral connection from the 30-amp male plug to 50-amp female outlet, there's also a Hot-to-Hot-to-Hot connection from the 30-amp male plug to the 50-amp female outlet. That is, both hot legs of the 50-amp outlet are indeed bonded together and connected to the single hot leg of the 30-amp plug. That being the case, a single 20-amp male plug to 50-amp female outlet does have the two hot legs bonded together on the 50-amp outlet side. Of course, you can't bond the two hot legs together on the incoming power side as that would be a spectacular short as you noted.
I think why there's confusion is that I'm an EE and always talk about power from the source to the load. That is, I start on the end that plugs into the pedestal or home outlet and finish with the end you plug your RV into. So while I will call something a 15 to 30 amp dog-bone adapter, I have noticed that a lot of RV owners talk about adapters the opposite way. That is, you'll call the same thing a 30 to 15 amp adapter to plug your 30-amp RV into a 15-amp outlet in your home. Hard for me to get out of that habit after 50 years of going from power source to load.
Also note that it's hard for me to call any of this an outlet. In the NEC it's referred to as a receptacle, NOT an outlet, even though outlet makes more sense.
So please sound out if what I'm saying is confusing. I'm trying to be as exact as I can while still using as much layman slang as possible. If you need more clarification you'll need to wait until I get back from Paris next week. I have a bunch of diagrams on my home computer I can post later.
OK, I agree. The way I first read it you were adapting between the 50A pedestal mounted receptacle and a 15/20A cable mounted plug from the trailer. 'Nuff said. We EEs are on the same page. Glad to have you on the forum.
BTW, in the world I come from anything above 0dBm is high power ;)
Quote from: charliem on April 29, 2017, 04:17:01 PM
BTW, in the world I come from anything above 0dBm is high power ;)
How about +4 dBu ;)
BTW: I might have a sponsor that will allow me do a few seminars about RV electrical safety and hookups at campgrounds on the mid-atlantic coast. Do you guys have any rallies or meets this summer or fall? I'm in Maryland and normally do seminars as far south as SC and as far north as NY. And I go as far west as Ohio and Indiana. Any suggestions?
Quote from: jmsokol on April 30, 2017, 11:52:26 AM
[
How about +4 dBu ;)
Never heard of dBu so I looked it up. Open circuit voltage into an unspecified impedance? Real men work at 50 ohms ;)
Quote from: jmsokol on April 30, 2017, 11:52:26 AM
Quote from: charliem on April 29, 2017, 04:17:01 PM
BTW, in the world I come from anything above 0dBm is high power ;)
How about +4 dBu ;)
BTW: I might have a sponsor that will allow me do a few seminars about RV electrical safety and hookups at campgrounds on the mid-atlantic coast. Do you guys have any rallies or meets this summer or fall? I'm in Maryland and normally do seminars as far south as SC and as far north as NY. And I go as far west as Ohio and Indiana. Any suggestions?
Mike, We do have meetups that are great fun. It's a good crew on here. However, our meet ups are relatively small affairs. The one last summer in OR was about 40 people total and the one this summer in ME is about half that. We keep track of those in a separate thread on this forum: Aluminum Camper Gatherings. If ME is not too far, check out the details of the August 5-6 meetup on that thread. I may try to organize one in the Midwest at a campground on the Great Lakes in 2018. I'm sure there would be lots of interest in RV electrical safety wherever you go!
I had some time today and replaced the ROMEX with 10GA SOOW on the temp pole run. Will take care of the shed lead next time up.
(https://c1.staticflickr.com/5/4182/33674762974_2512e55d5c_c.jpg)
Also jumped the two 50A legs, which did energize the 30A receptacle and I confirmed the correct voltage across each lug. Will mark it "20A MAX" when I have my labelmaker with me.
(https://c1.staticflickr.com/5/4184/34475808926_748a20b919_z.jpg)
(https://c1.staticflickr.com/5/4164/34475808756_77a926e63d_c.jpg)
Ran the ground wire out from the ground bus, but waiting to sink the ground rod to hear back from the contractor to verify there's nothing running underground where I plan on putting it.
(https://c1.staticflickr.com/5/4178/34356237032_2bef1c7da8_c.jpg)
Mike says it should now pass muster if an inspector happens to wander by!
Flew up today for the finishing touches:
(https://c1.staticflickr.com/5/4193/33864708544_b5e8006dd7_b.jpg)
Done!
Your place looks like a slice of heaven.
I bet it is hard to leave!
Quote from: Diversteve on May 17, 2017, 08:13:32 AM
Your place looks like a slice of heaven.
I bet it is hard to leave!
It's very nice, but our home in N GA is a little slice of heaven as well!
Have not had a chance to power the RV from our RV pedestal yet. Should have a good solid 20A at the 30A connector, with large gauge wires running from the temp pole to the pedestal. That should be enough to power the air conditioning if nothing else is running, and its easy to throw the breaker for the RV's converter to take that load off as well.
Question...
If someone snuck in at night and swapped a 30A breaker for one of the 20A breakers at the temp pole, would that present a problem? The only "bottleneck" I can see would be the 20A outlet and 20A plug at the temp pole. The rest of the wiring is certainly up to 30A service with no problem, and the temp pole is fed with 100W service.
If someone were to wear black clothing and use night vision goggles so a flashlight was not needed, it seems doable. You've ID'd the "bottlenecks".
Quote from: Merlin on June 05, 2017, 10:18:03 AM
If someone were to wear black clothing and use night vision goggles so a flashlight was not needed, it seems doable. You've ID'd the "bottlenecks".
Thanks. I just contacted NinjasRUs for their rates.
I don't anticipate the bottlenecks being an issue if I try to keep the draw anywhere near 20A, which I think I can do.
You should be entirely legal, code wise with a 20A breaker feeding properly sized wire and a 20A outlet at the far end. Lot's of things can happen to make legal electrical stuff illegal, but i wouldn't worry about it.
David
Update:
Camped at the property Thursday night, first time with power to the pedestal.
A friend suggested that I just remove the 50A breaker and move the 30A over one slot:
(https://c1.staticflickr.com/5/4209/35361461115_5f70f6edcc_c.jpg)
Both share the same leg now, so jumper required.
After testing the 30A outlet, plugged in and viola! - works as intended.
(https://c1.staticflickr.com/5/4285/34518542694_3c08ae9736_c.jpg)
Did not need air conditioning, but meant to try it out and forgot. If the 20A breaker at the temp pole trips, I'll consider replacing it with a 30A single-pole breaker.
Also drove in and hooked up an 8' ground rod at the RV pedestal.
I now just need to install blanking plates for the two empty slots. Thanks again for all the input.
Good news!
We drove from Kitty Hawk to our TN property yesterday and camped last night. We were tired and waited until this morning to hook up to our pedestal.
Air conditioner started up and ran just fine. As an experiment I also ran the microwave at the same time and nothing tripped. We may be at the limits of 20A sevice to our 30A receptacle, but not overtaxing it as long as we don't run everything at once.
Thanks again for the guidance!
Quote from: DavidM on April 21, 2017, 11:15:38 AMThe National Electric Code requires one and only one ground located at the power source, which in your case is the power company supplied power panel. You will not be in compliance if you install another ground rod downstream of that one.
Close! What you're thinking of is NEC 250.24(A)(1) where only one
neutral to ground bond is allowed. You indeed can have multiple ground rods or GEC's in a system per that section and NEC 250.32 which outlines requirements for a grounding electrode system and bonding of grounding electrodes.
Ground loops cause hell for low voltage systems like paging amplifiers, but the point of a ground is strictly for safety of life and property when something goes wrong.
It's absolutely OK to install a ground rod at an RV pedestal, an automatic standby generator (if neutral is bonded to frame, check installation guide), a telco demarc, hot tub - anything like that. Give that fault current a short path ground.
Then also remember the amount of current flowing through the line leg should equal the amount of current flowing through the neutral wire for your load (true for line to line but let's focus on N and G) - this is where the single Neutral to Ground bond rule comes into play. If that current finds another path in your system to flow, best case you have weird problems, worst case a fire.
There's a fantastic video on Youtube from Dave Gordon called Open Neutral that helps visualize where the current is going in a two leg + neutral system. The video ID is LJvyb_WujZg.
Also countless Youtube videos about the N-G bong and why it's important, what is a loaded neutral, etc.