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Author Topic: neutral ground bonding - using coach to power the house  (Read 15838 times)
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« Reply #75 on: February 08, 2011, 12:35:21 PM »



I think this is what we're getting at (all contained in the structure to be powered by the bus - not on the bus)

  Okay, but you left out whether the RV Generator has the ground and neutrals bonded or not.

  In my case I intend to have a transfer switch that delivers generator power directly to the main panel, and will disconnect un-needed circuits to keep from overloading the generator. i notice in your drawing you are switching the neutal. I need to call the place I bought the TS as supposedly there is a kit to switch the neutral.
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Tim Strommen
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« Reply #76 on: February 08, 2011, 01:20:13 PM »

...Okay, but you left out whether the RV Generator has the ground and neutrals bonded or not...


Sorry, should have used a bigger font...  You would need to actually have that warning label on the input plug.



In your case where you wish to power the entire main panel, the same general concept applies - you'd need to have the switch before the main pannel, and would need a main-breaker after the meter but before the main panel and transfer switch to protect the main entry conductors and transfer switch.  The neutral would have to be bonded at that new main service entry breaker, and that main entry neutral separated by the transfer switch.

Like this:




-Tim
« Last Edit: February 08, 2011, 06:29:59 PM by Tim Strommen » Logged

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« Reply #77 on: February 08, 2011, 07:42:23 PM »

This discussion has got me re-examining my generator setup in the bus as well as how it connects to the house.

I have a 6500 Onan Generator that was a construction type generator (i.e. non RV type) It originally was connected for 120 V but I changed the wiring connections a few years ago to put out 220 so I could hook it up to the house and run out well water pump(its 220V) I then took off 120 from one leg for the bus. I realize this unbalances the generator but we don't use the generator very much and it has worked well for what we use it for. I can't see any labelling suggesting whether the neutral and ground are bonded or not. I have 2 hots and a neutral going to a "welder plug" that I use to run to the house. There is no ground wire and I'm not sure if the generator is grounded to the bus chassis. At the house I feed into the main panel through a breaker with a mechanical interlock which only allows EITHER the main breaker or the "bus" breaker to be on. In other words the main breaker can't be on at the same time as the "bus" breaker.

So first of all I'm wondering if the connection between the generator and the bus is safe and secondly what do I have to do to ensure the connection to the house is SAFE.

Thanks

Fred Mc.
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Tim Strommen
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« Reply #78 on: February 08, 2011, 08:10:15 PM »

...I have a 6500 Onan Generator that was a construction type generator (i.e. non RV type)...

Generally - standalone "portable" generators (like yours) are internally bonded at the generator head (while it's powered off of course...).  You can verify visually by pulling off the service panel at the head (there should be a jumper wire from ground (case) to some other pole.


...There is no ground wire and I'm not sure if the generator is grounded to the bus chassis...

Use a multi-meter to verfiy that there is no connection to ground (chassis) on your bus.  If it measures "open", you'll need to fix that first.  If you get continuity, then you probably have a ground connection somewhere and you may want to hunt it down and relocate it to make it more obvious (ground should follow the hot/neutral lines - always).


...So first of all I'm wondering if the connection between the generator and the bus is safe and secondly what do I have to do to ensure the connection to the house is SAFE...

You should have a ground to the house, that's for safety.  Since the generator is vehicular mounted, it needs to retain its bond internally - this means that you must disconnect the neutral from the main power comany's service entry when you transfer your house loads as illustrated in the previously posted diagrams.  You can verify that the bond is broken by not plugging in your generator and flipping the transfer switch to the Generator input.  Then with a multimeter - check for continuity between the ground and neutral.  If it's open - you're good.  If there is still continuity, there is a double bond - and that's bad...

-Tim
« Last Edit: February 09, 2011, 02:54:49 PM by Tim Strommen » Logged

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« Reply #79 on: February 08, 2011, 09:10:05 PM »

  I spoke to Katolight in Mankato MN, they are the generator company I bought the transfer switch from. I bought it several years ago for another house Iowned and never used it. I would have talked to them before I hooked it up, but this discussion really bugged me to want to know what I'm doing.

  As has been discussed here, all portable and RV Gensets have neutral and grounds bonded, and that is NEC code for those type gensets. When you connect your house to a portable generator or RV however, it is no longer under the same code as a portable, you do not want the generator ground and neutral bonded in this situation.

  While the man I spoke to said that many people connecting bonded RV generators to their homes get away with it, and that in most cases there isnt a problem, he also warned that just because you havent noticed anything, doesnt mean the problem isnt there. He said in one particular case, he measured 197 volts between a campers skin, and ground, when it was hooked up to a house and power was backfeeding into the ground.

  His recommedation was to install a knife switch between the ground and neutral at the generator, so the switch becomes you bonding mechanism. On to bond, as when your running your rig, and off off to de-bond, when your powering your house. He said there really is no need to switch the neutral in a non critical system.
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« Reply #80 on: February 08, 2011, 10:57:18 PM »

Fred Said"
"So in a standard 200 amp house main panel does the main disconnect (which is 240v) shut off the hots and neutral when it is shut off? How can you tell if it disconnects the hot and neutral?"

and Gary Said
"No it doesn't, it just shuts off the two hots. Even the main breaker at the meter loop only disconnects the two hots."

What confuses me is the fact that I can buy this product (http://www.interlockkit.com/) which, as I see it, simply prevents the main breaker from being "on" while the generator breaker is "on" and does nothing to disconnect the neutral which, apparently is dangerous. What am I missing here as I gather from these discussions that unless both hots AND the neutral are disconnected from the utility you can still electrocute someone down the line. How do they get away with selling a product that can be "lethal".

Fred Mc.
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« Reply #81 on: February 09, 2011, 07:04:47 AM »

Artvonne sed :

"As has been discussed here, all portable and RV Gensets have neutral and grounds bonded, and that is NEC code for those type gensets. When you connect your house to a portable generator or RV however, it is no longer under the same code as a portable, you do not want the generator ground and neutral bonded in this situation."

And I thought I'd point out that my newish Yamaha EF3000iSEB (what a dumb name) inverter generator has floating neutral.  I have never been able to figure out why, but portable generators with floating neutral are indeed common.

Brian
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« Reply #82 on: February 09, 2011, 08:56:42 AM »

...What confuses me is the fact that I can buy this product (http://www.interlockkit.com) which, as I see it, simply prevents the main breaker from being "on" while the generator breaker is "on" and does nothing to disconnect the neutral which, apparently is dangerous...


So there are two distinct configurations discussed here in this thread:

  • Standby, permanent fixed-installation (hardwire, dedicated to the house - neutral not bonded)
  • Portable, temporary installation (use a flexible power-cord to hook it up then put it away when you're done, take it with you to another jobsite, or vehicle mounted - neutral is bonded)

The "Interlockkit" device is designed to work in the first case since it just switches the hots, but you need a different setup if your generator is a temporary/portable type.


...I spoke to Katolight in Mankato MN...  ...His recommendation was to install a knife switch between the ground and neutral at the generator, so the switch becomes you bonding mechanism. On to bond, as when your running your rig, and off to de-bond, when your powering your house. He said there really is no need to switch the neutral in a non critical system...


They say that, but possibly without context/pretext of this thread (I have no idea).  I actually take issue with their recommendation to install a knife switch at the generator, and here's why:  You will now have to switch things at two locations (one at the transfer switch, one at the generator - possibly with tens of feet between the two devices).  The point of an interlocked transfer switch is to ensure that the system is safe to operate before power is applied.  Two switches that are not directly interlocked adds a significant risk, and operation complexity.

Will you always remember to flip both switches?  What if you're in a hurry one time and forget to de-bond it?  Also, what if you meant to re-bond it and while you were putting away the cord you got side tracked in a conversation and never remembered to re-bond it?  What if you're not the one to hook it up or take it back down, will the operator know that they need to de-bond it or re-bond it?  What happens if someone messes with the state of the bond/de-bond switch separately from the transfer?  How can you prevent independant operation of the device when it's in-use?


It is solely for the advocation of safety that I recommend that if you are really planning on using your bus generator as a house back-up and you are conscious of this in advance (for instance planning to put in an input-plug in a box), why wouldn't you put everything in one device (i.e. the transfer switch)?  This way the circuits are set up correctly by hard-wiring them appropriately for each power source, and any idiot can run the system safely (safe by design is better than safe by memory).

My opinion.

-Tim
« Last Edit: February 09, 2011, 04:06:20 PM by Tim Strommen » Logged

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« Reply #83 on: February 09, 2011, 01:09:39 PM »

I must apologize for being away from this thread, as I see some folks have asked me direct questions.  I am away on a Red Cross training exercise and really have not had time to even read, let alone respond to, this board.  I have a short break here but will again be tied up through the end of the week.

I note that in my absence, Tim has done a great job of elaborating on the issues.

I am very concerned about a recurring theme in this thread that I think needs to be addressed.  Specifically, a number of folks have asked "Why would they sell Device X in hardware stores if connecting it to my house and generator is dangerous?"  This is a lot like asking "Why do they sell matches if they can set my house on fire?"  Neither matches nor non-neutral-switching transfer switches are dangerous by themselves, but they each can be used in dangerous ways.

As an example, both ungrounded, two-wire cable and grounded three-wire receptacles are available (and listed), but using them together is dangerous.  Metal cable and plastic junction boxes are listed and are widely available but they can not be used together.  Listing of a device, by UL, CSA, or any other lab, means the device is safe and approved to be used as designed -- it does NOT automatically make any installation of that device safe.

Household transfer switches (or interlocking breakers) are perfectly safe when used with a fixed-base, household backup generator, because such generators have floating neutrals.  Likewise many portable generators intended for this purpose have floating neutrals and can be connected in this way.  I would dare say that 99.999% of backup generator installations simply do not have the issue that we will have with our coaches, which is why the vast majority of transfer switches are designed without provision for switching the neutral.

On the flip side, RV's always have this issue:  if an RV is equipped for both shore power and a generator, any internal transfer switch must always switch the neutral.  Manufacturers of transfer switches explicitly for RV use make their switches with neutral switching included.

What we have been discussing in this thread is doing something that almost no homeowner and even very few RVers would ever do: using an RV generator as a backup power source for a fixed house.  BECAUSE IT IS NOT COMMONLY DONE -- ALMOST NO ONE EVER DOES IT -- YOU WILL NOT FIND INFORMATION, PARTS, DIAGRAMS, ADVICE, OR ANY OTHER MATERIALS ABOUT HOW TO DO IT CORRECTLY.

Now, I am sorry (just a little) for shouting, but this stuff is important.  Doing this incorrectly can kill you, or someone else.

IF you propose to use your bus to power your house, you will be doing something that has probably not been discussed anywhere else on the Internet than right here in this forum more than a half dozen times.  And you had better be sure you know how to do it right.  I would bet real money that if you called a dozen professional, licensed electricians in your area, ten of them would get it wrong -- which is another reason it is so important for you to know what you are doing.  There is no manual for it, and it is not explicitly covered in the code -- you need to know how to integrate the relevant parts of the code and apply them yourself.

The generator in your coach has neutral and ground bonded together.  It is dangerous and unlawful to install a means, such as a switch, to unbond them.  So in order to safely power your house from your coach, the neutrals in the house must be isolated and the transfer arrangement, whether that is a manual switch, automatic switch, interlocked breakers, or a temporary pigtail MUST SWITCH THE NEUTRAL.

...
That was my suggestion at the beginning of the thread --- simple straight forward and yes code compliant as a TEMPORARY use panel.
...

Only if it is lying around loose.  Having it permanently attached or wired to anything is not TEMPORARY and is therefore not allowed, which is what I originally wrote in response.  I read your original post as proposing a built-in sub-panel with built-in receptacles for this purpose, which is against code.  I read Bob's suggestion as for a loose, rolled-up and stored system of panels and cables which would be deployed as needed.  This is permitted, but I would point out that it is not different from the very first thing I wrote on this subject: power your loads with extension cords run back to the bus.  Some folks felt that having extension cords (or temporary cables from a loose temporary panel) running all over the house was not what they wanted.

Now I have a question for [Sean]. If you are wired like I explained, then your breaker panel in your house is considered a sub panel correct? And in that sub panel all your grounds and neutrals are isolated. This means nothing in the house is bonded.

Just because the bond is not in that panel does not mean it does not exist.  The bond is somewhere upstream.  There MUST be a bond at the service entrance.

Quote
If I connect a standard 2wire transfer switch before this panel, and my generator is still bonded.
How am I getting a double bond?

Because the neutral and ground from the bus generator are connected all the way back to the neutral/ground bond at the service entrance.

...
What confuses me is the fact that I can buy this product (http://www.interlockkit.com/) which, as I see it, simply prevents the main breaker from being "on" while the generator breaker is "on" and does nothing to disconnect the neutral which, apparently is dangerous. What am I missing here as I gather from these discussions that unless both hots AND the neutral are disconnected from the utility you can still electrocute someone down the line.

I think we are confusing issues here.  You will not electrocute someone working on the lines with the double bond.  You are, instead, creating a dangerous situation in your own house/bus.  Only a single line runs from the transformer to your house for the neutral (there is no separate ground) and any double-bond issue will not affect the power company.  As long as the hots are disconnected by the transfer gear, such as the interlocked breakers you linked, the power company is happy.  It is your own premise that is in danger from the double bond.

Quote
How do they get away with selling a product that can be "lethal".

The product is not lethal by itself, it is the way it is used, or misused.  Many products that can be lethal are sold every day, including handguns.  The manufacturer is not responsible for how the product is used, only that it is safe when used as designed.

The product you linked is designed to be used with household backup generators, not RVs.

Hope that clears some things up.

-Sean
http://OurOdyssey.BlogSpot.com

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« Reply #84 on: February 09, 2011, 09:02:46 PM »

  I was trying to get around having two generators, but I think thats really the safest bet when everything is considered, not worth killing anyone through a stupid mistake. Does seem odd though, that a company that builds, sells and services generators from 15KW to 3000 KW wouldnt know code.
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« Reply #85 on: February 10, 2011, 06:15:55 AM »

Whether or not it would meet code, I still think you would be safe under any circumstance by SECURELY bonding the generator frame, thus the bus frame to the house ground, using at least a #2 cable.
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« Reply #86 on: February 10, 2011, 09:10:27 PM »

Whether or not it would meet code, I still think you would be safe under any circumstance by SECURELY bonding the generator frame, thus the bus frame to the house ground, using at least a #2 cable.

I don't really belive that's a question we've been discussing here - grounding is grounding - everything that is metal (and not part of the neutral/hot power transmission) should be grounded and connected to the same ultimate ground point (i.e. a ground rid driven into earth) in a daisy-chain/star fashion and not include loops of ground.  This includes the boxes, metal conduit, bus chassis - both in the house and on the bus...

Inconveniently NEC also calls the interconnection of metalic enclosures "bonding" and this unfortunate cross-terminology can create a heck of a lot of confusion for laypeople!  Interconnecting the conduit, metal encolsures is "bonding to ground" but there should only be one "ground to neutral bond" in a system - ever! (have we gotten that point across yet? Grin)

Best,

-Tim
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« Reply #87 on: February 10, 2011, 10:07:36 PM »

  Just get another generator and hook it up to your house as a genuine standby genset. Obviously this is something thats not meant to be done, very few professionals have a handle on it, and a mistake could kill someone. That isnt a joke either. I know a lot of people play around with 120 volt and think its just a lil shock. That lil shock can become deadly if it has some wattage going through it. I know for a fact that 60 watts will throw a 220 pound man across a room and stun him (me). 8KW will light you up like the 4th of July and leave you smokin dead. Beleive it.
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« Reply #88 on: February 11, 2011, 06:27:32 AM »

One of the inspirations for this thread is that many busnuts can barely justify the ca$h for the one used generator they have now. Some can only afford the one size fits all.

Powering the house during a power failure is not a luxury, depending on your climate or situation, it is a necessity. Further economic disaster, which cannot be afforded, will result if the house doesn't regain some power for critical systems like heat, pumps, refrigeration, etc, as the case may be.

The economic losses are more easily seen than the confusing electrical safety theory that is difficult to prove via simulation.

I started the thread to get the collective experience in one place, focused on the specifics of this challenging project, and hopefully, folks realize there are very few professionals out there that will be able to complete a safe install, and that those of us that might do this, need to go back and check what we think we know.

With these sorts of things, unfortunately, or fortunately, we never get to know that we saved a life.

happy coaching!
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« Reply #89 on: February 11, 2011, 08:20:36 AM »

  All I can say, is that if after almost 7 pages we dont have a CLEAR and SIMPLE answer.... If a company that has been in business for 53 years and builds generators from 15KW to 3000KW cant answer it properly.... If Elecrical inspectors dont want to touch it.... If Firefighters are warned to avoid it.... If power company linemen are scared to death of it....

  Maybe we should be extremely careful how we approach it? Seriously, if highly trained electricians have a problem with it, and just plain say we shouldnt do it, then its something to really consider leaving alone.

  The neutral is connected to the ground connection inside your main house panel to a ground rod buried in the ground. Ideally, current will always flow from hot to neutral, and any short will be directed to ground.

  Your Bus generator has the neutral and ground connected together in the main panel too, but it is NOT grounded to earth, its grounded back to itself. Connecting your Bus generator to the main panel in your house, the Bus is now putting hot current potential into the earth, something that wouldnt happen "inside" the Bus. Now, when you step up to the Bus, or come out and step down to the ground, you could potentially offer a better neutral current path THROUGH THE EARTH, back to the main panel, than the neutral running back to your main panel. It is very important everyone understands this point.

  The only safe way to do it, is to have the neutral and ground seperated in the Bus when generating power to your home and have the generator completely isolated, retaining the bond in the house main panel. But you have to have the neutral and ground bonded again when generating power "inside" the Bus. As others have said, one mistake, one time when you forget to make the switch one way, or the other, could kill. Its fine if it kills me. Not so fine if it kills my kid, or my grandchild, or anyone else. A knife switch would certainly work to BOND and DE-BOND the generator connection, but one mistake, one way or the other, could be deadly. The bond connection needs to be physical and permanent.

  I know many are trying to get by on a shoestring, and I know many of us dont always feel we need a lot of oversight over so many things. But a life is pretty valuable these days, a lot more than a dumb generator. Another thing to consider is what would happen if you were absent and someone else had to unhook your rig, you wife, your son, a friend. Would they reconnect things back the correct way? Ive read enough here to decide its just plain not worth messing with. 
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