Home Generator question:

[SRath]

I have an Elliot-Magnetek 12kw LP powered generator switched by a Cutler-Hammer 100amp fully-automatic transfer switch. The T. S. is mounted between a 200amp main breaker box and 100amp sub-panel. When the utility power goes out, the genset automatically senses it and switches the genset on and brings it online while disconnecting from the utility. The genset feeds the 100amp sub-panel which houses the critical circuits for my house.



Everything works well, but I have a question about the proper grounding of the setup.



Inside the genset is bridge wire from the neutral to the ground lug which the instructions say should be removed if you want an "insulated neutral". I am guessing that if it is removed, the genset grounding relies entirely upon the grounding of the main breaker box, transfer switch, and subpanel for it's ground.



How should it be? Do I want an "insulted neutral" or not and why or why not?



How should the overall grounding of the system be handled (generator, generator cabinet (equipped with grounding lug for connecting to ground rod), main breaker box, transfer switch, and sub-panel)?



Here is an schematic showing the optional bridge wire. I know it might hard to see, but the bridge wire is the dashed u-shaped line in lower center:

 

[Hoefler]

Check your local codes. In most residential construction, stick built, the ground and common are tied together either in the meter base or at the pole, or both. In mobile homes, manufactured housing, and RV's; the ground is separate from the common.

 

[KLauber]

Pretty Cool Scot. I was thinking about getting one of these also and maybe a solar panel to heat the water heater. Was this a boxed set or did you cobble it together?

 

[SRath]

eliminating dependency

It came, out of the box new when I bought it more than 10 years ago, with that ground loop wire disconnected and remains that way right now. Believe it or not, I only recently (successfully) hooked the automatic transfer switch up (yeah, I'm a little slow). I did some separate, direct, temporary wiring during the few times I really needed the generator until then, making sure nothing was still connected to the grid.



The generator served us well (cobbled like that) a few years ago when an ice storm left everyone here powerless (no heat or water or electricity, etc) for over a week. Bad things happen when it is that cold and you have no juice or heat or water for that long. Again in '08, the Great Flood wreaked havoc with energy supplies for a long time. But other than that schematic of the internals of the generator, there were no instructions for installing the automatic t-switch, and with the complex self-starting monitoring system and automatic switching, I felt a little overwhelmed figuring it out. I tried, and thought I had it right, but couldn't quite get it to all work together.



Motivated again after last week's power outage due to a storm, I renewed my efforts and voila': I found where a wire had not been tightened inside it's lug in the generator causing it to only produce 120v instead of 240v. I had everything hooked right all along after all, but some assembly worker had neglected to tighten one screw. Now, everything is hooked up, tightened, and works great!



The setup constantly monitors utility power. In the event of a black or brown out, it automatically fires the unit up, warms it up a little, checks that all is right with the genny output, motor, etc, and switches to gen power. When it senses proper utility power has been restored, it switches back to the utility, runs a short cool-down, and shuts the unit off. It charges and maintains its own battery at all times, and fires itself up to "exercise" on a regular basis. Pretty cool now that it all works right.



My inclination is to let the house system do the grounding since the generator is a part of it (leave that loop disconnected like it came). I do want to sink a separate ground rod and ground the genny cabinet, though. Why not? It has a ground lug welded on and all it takes is copper rod and a little wire.



I just don't know if I should tie the internal generator neutral to that ground using the optional loop. I think not since the genny neutral is always tied to the utility/house neutral, which has it own ground circuit. The breakers and transfer switch only affect the hot leads.



It's a cool system, Ken, and offers peace of mind. When we first bought this rural house, this area had frequent power supply problems due to age and overbuilding that had not been kept up with by the utility company. Mostly just a couple of hours, but you never knew... With the massive construction and growth boom of the past 10 years around here, and an updated grid, power outages have become less of a problem, but I still have the area's largest cottonwood tree next to which the utility company put the transformer pole for this neighborhood. That tree is giant water-filled lightning rod, and that transformer has been blown up at least 4 times in the past several years.



It was a fairly expensive investment, and one you seldom need. But when the power goes out for extended periods and it is sub-zero weather, or it is hot and you cannot keep your fridge and freezer running, or you just don't like sitting around in the dark, it is great to have a generator. In retrospect, a smaller, simpler setup would get the job done. Since my boys were very young then, and I was away a lot, I wanted an automatic system so my wife wouldn't have to do anything and even if we were all gone for the weekend or a week, it would do it's job. During the Ice Storm outage, I parked my camper at my neighbor's house and powered her essentials with its 5500w generator. Good thing, too, for some reason, it took the overworked utility company a week extra to get her house back online.



Our house was heated with LP when we bought it, and I have a 1000 gallon tank out back. Shortly after we bought the place, the utility company brought natural gas through this area, which was much cheaper, so we switched. But I now have 1000 gallons of LP dedicated to run that generator and I plan to also install an LP fireplace/heater as an auxillary heat source and for the asthetics. I have a small woodbuning stove to hook up this summer as I finish some remodeling, too. that will give me 4 different sources of heat: Electric space heaters (AC power is also needed for the furnace of course), wood heat, natural gas (for the furnace), and LP gas (for the fireplace and generator).



I have my own well, sunk less than 10 years ago to the very deep 2nd aquifer, and I have my own septic system. With that generator and LP supply, I can go off the grid for months if I had to and never miss a beat except for my internet connection. And I'm strongly considering a satellite or fiber-optic system for Internet and cable TV since the local cable provider is getting outrageously expensive.

 

[Skydiver]

I can't see a problem with the extra ground. If lightening hits your generator,,,nuff said.
In 2003 our hunting land (skinnin shed) needed a new power service installed. The utility company said we did not pass inspection because the meter panel was not grounded. This was new to me as I have installed about 8 meter panels before. Your state code will show if this in required.
By the way SRath, nice set up, real nice.
I love my LP.

 

[KLauber]

Ok, now I am sold, cause even though all our power lines are underground (subdivision built in 93), the areas outside our little burb often cause problems mostly in the winter.

Thanks Scott!

 

[SRath]

I have one hunting buddy who is a Journeyman electrician and another who has been a lineman for many, many years doing everything from local utility lines to massive cross-country high voltage towers. I'll have those guys come over for a couple cold ones and to check everything over. They are well aware of what Code requires and of what should be done for extra safety's sake. Not just mine, but the safety of linemen working to restore power, too. That part is absolutely safe, I'm sure, since the transfer switch will not allow one system to bleed into the other.

But like Skydiver said, I also don't want my system vulnerable to lightning or overload feedback damage.

 

[SRath]

Quote: The setup constantly monitors utility power. In the event of a black or brown out, it automatically fires the unit up, warms it up a little, checks that all is right with the genny output, motor, etc, and switches to gen power. When it senses proper utility power has been restored, it switches back to the utility, runs a short cool-down, and shuts the unit off. It charges and maintains its own battery at all times, and fires itself up to "exercise" on a regular basis. Pretty cool now that it all works right.

This is why the automatic transfer switch would not work for so long, even though it was hooked up right. The electronic brain unit did not agree with the missing output due to the loose power connection in the generator housing and refused to bring the genny online. That proves to me that it did its job well.

 

[Hoefler]

The panel in the gen-set as well as the cabinet need to have their own ground. Relying on the utility or meter ground can cause a back feed in the utility system, possibly electrocuting your lineman working on the system.

 

[SRath]

So are you saying that optional ground loop in the cabinet should be connected?

 

[CKelley1]

in your case, the way you have it connected you should bond the neutral to ground at the generator. this establishes the neutral at ground potential. you can not have any load current traveling on a ground. only at a source to establish witch conductor is to be the neutral is grounded. another example a transformer. there is no connection between primary and secondary therefore the secondary will have no voltage reading to ground. you must connect the lead you want to be the neutral to ground but from this point on the neutral can never touch ground again

 

[Dieselnut59]

When I first bought my rural house in 1998, I knew I would need a generator. When we started our business in 1999, I knew I would need a portable welder machine. I decided the best thing, since I would never need either all that often, but when I do need either, I NEED it, was to buy a welder/generator. I bought a Miller Bobcat diesel unit with 250 amp welding output and 10,500 watt generator output. My house's appliances (water heater, clothes dryer, stove and heat) are propane powered, so the only major things I need to run are the freezer, refrigerator, well pump and blower for the furnace. The furnace is a dual fuel unit (LPG/electric heat pump), so I can switch it to emergency heat mode and it will run strictly as a gas furnace, only requiring power to run the blower. The diesel welding machine with generator is similarly priced with diesel generator only units of similar output, so the welder/generator was an easy decision for me.

I know it is not the "code" way of doing it, but i have a 50 amp breaker for the generator input on the electrical panel and a 150 amp main disconnect by the electrical panel. I first switch off the 150 amp disconnect, then fire up the generator and turn on the 50 amp breaker on the generator and the house panel. I need to set up a transfer switch, but I want the type that is a "double throw" that turns off the utility's power and on the generator's power manually, since my machine is portable.

For the refrigerator and freezer and few little things in my shop, I have a 3500 watt Robin diesel generator that I simply plug the appliances into an extension cord to run. My shop has 3-phase power and there is nothing I "must" have during a power failure that the little generator can't handle. In there, I have a little Dearborn LPG heater that I can light to keep things from freezing and the water uses the same well as the house.

Ken, you are welcome to check out my machines if you would like. Best of all, they run on my 50% cooking oil/diesel blend, so they smell like our trucks when running!

 

[SRath]

CKelley, Assuming the power company grounded my 200amp service when they installed it, then from what you say about "you must connect the lead you want to be the neutral to ground but from this point on the neutral can never touch ground again" it would be wrong to ground it again at the generator, leaving me still confused.

Are you saying I must isolate the house neutral and ground and ground everything through the generator?

If it matters, I have no choice about which of the 3 leads from the generator, or from the utility company are the neutrals. They are already established and they connect together in the transfer switch with no switching being done between them. Only the hot leads are switched when the transfer switch does its thing.

 

[CKelley1]

no. the power company grounds the center leg of there transformer to establish the neutral. at the house the neutral is again bonded to ground before the first loads are connected. the generator is a new and different source and must be treated the same. you bond the center leg of the winding to establish the generator neutral at ground potential. from there the generator uses the same bonding strap in the first panel as power co. i am not very good at explaining things. but if you think about it it will make since. most houses only have one breaker box and the bond is made in the box, from that point on no ground is allowed to carry any load current. it is strictly for fault current only. bonding is hard to understand for the average person or even electricians, you even have to be careful not to loupe neutrals. each load has to have the exact current in the hot wire as the neutral between the load and breaker box for single pole circuits. back to your generator, just bond the neutral to ground at the generator and leave every thing else alone

 

[Dieselnut59]

no. the power company grounds the center leg of there transformer to establish the neutral. at the house the neutral is again bonded to ground before the first loads are connected. the generator is a new and different source and must be treated the same. you bond the center leg of the winding to establish the generator neutral at ground potential. from there the generator uses the same bonding strap in the first panel as power co. i am not very good at explaining things. but if you think about it it will make since. most houses only have one breaker box and the bond is made in the box, from that point on no ground is allowed to carry any load current. it is strictly for fault current only. bonding is hard to understand for the average person or even electricians, you even have to be careful not to loupe neutrals. each load has to have the exact current in the hot wire as the neutral between the load and breaker box for single pole circuits. back to your generator, just bond the neutral to ground at the generator and leave every thing else alone

So you are saying our generators need to be bonded (mine is) and have their own ground? As in their own ground rod when in use? Mine has a connection for a separate ground but I never figured I needed it as I have a #6 cable that has a red, black, white and green wire in it, so it is grounded at the panel. If it is better or safer to have an additional ground, I will do it, including driving another ground rod where I run the generator at.

 

[CKelley1]

you do not need a separate ground rod for the generator in your application. only if a generator is used in a stand alone configuration is a ground rod or grid wire needed. in your application the frame of the generator is connected to the ground wire that is connected to the house ground. if you did not run a ground wire between the generator and the panel and did not bond the center leg to the frame the entire generator could float to a 120 volts with any type of fault in the generator. i see this more around 480 volt generators used around rock crushing operations, they are temporary and set up by unqualified people.

 

[fest3er]

you do not need a separate ground rod for the generator in your application. only if a generator is used in a stand alone configuration is a ground rod or grid wire needed. in your application the frame of the generator is connected to the ground wire that is connected to the house ground. if you did not run a ground wire between the generator and the panel and did not bond the center leg to the frame the entire generator could float to a 120 volts with any type of fault in the generator. i see this more around 480 volt generators used around rock crushing operations, they are temporary and set up by unqualified people.

So, to state it as a rule of thumb, there should be one continuous ground circuit throughout an electrical 'site', all frames and chassis should be bonded to that ground and that ground should be bonded to a single effective ground rod. (The British use the word 'earth', which clarifies the purpose of the circuit. )



Going one step further, a wire sizing rule-of-thumb might be to select the gauge that matches the circuit breaker/fuse and add 2 AWG for each extra 50' in that run. (Refer to paragraph at end. )



And the final rules-of-thumb: connect safety ground wires properly and bond them to the neutral bus (bonding post) in the breaker box. Make sure all connections are properly snugged; if they are big enough, they'll have torque specs.



Armed with these and common sense, you should be able to plan and install solid and safe electrical circuits.



Wire has resistance which becomes measurable as the wire becomes long enough. The minimum wire gauge specified for a circuit of a specific maximum current is good for only 50 feet in order to maintain desired minimum voltage drop. That is, 12 ga. wire will carry 20A for 50' while maintaining acceptable voltage drop. This matters because the return neutral/ground will also have a voltage drop. If you tried to draw 20A across 500' of 12 ga. wire, you would likely find the neutral/ground at the far end of that circuit floating up measurably; you might also be lucky if there's enough voltage for your equipment to run in the first place.

 

[CKelley1]

i should have used the term earth ground. thanks. the wire size for length of run has always been in the nec code book expressed as a % drop. no one ever enforced it. that is why they rewrote the article to determine the size

 

[Dieselnut59]

So, to state it as a rule of thumb, there should be one continuous ground circuit throughout an electrical 'site', all frames and chassis should be bonded to that ground and that ground should be bonded to a single effective ground rod. (The British use the word 'earth', which clarifies the purpose of the circuit. )



Going one step further, a wire sizing rule-of-thumb might be to select the gauge that matches the circuit breaker/fuse and add 2 AWG for each extra 50' in that run. (Refer to paragraph at end. )



And the final rules-of-thumb: connect safety ground wires properly and bond them to the neutral bus (bonding post) in the breaker box. Make sure all connections are properly snugged; if they are big enough, they'll have torque specs.



Armed with these and common sense, you should be able to plan and install solid and safe electrical circuits.



Wire has resistance which becomes measurable as the wire becomes long enough. The minimum wire gauge specified for a circuit of a specific maximum current is good for only 50 feet in order to maintain desired minimum voltage drop. That is, 12 ga. wire will carry 20A for 50' while maintaining acceptable voltage drop. This matters because the return neutral/ground will also have a voltage drop. If you tried to draw 20A across 500' of 12 ga. wire, you would likely find the neutral/ground at the far end of that circuit floating up measurably; you might also be lucky if there's enough voltage for your equipment to run in the first place.

That is interesting about wire length. My electrical shed (where I store my electrical supplies) is about 250 feet from my barn and has a #10 wire powering it, with a little sub panel in it and a 30 amp 240v breaker in the barn. The barn is fed with 300 feet of #2/0 wire and has its own subpanel, with its own bonded ground. It is fed from a 100 amp 240v breaker in the house panel. So the shed is technically 550 ish feet away from the house. I still get 112 volts at the lights and receptacles there.

 

[Skydiver]

Dieselnut59, Is that 112 volts measured while you are using anything that consumes power? Reason I ask is electricity behaves much like water. We can have for example 50 psi in any length water pipe that remains constant untill the valve is open. As we know a smaller pipe or wire will deliver less water or power than a larger size. The #2/0 wire should be plenty big. If you check voltage at the shed with NO load in service then the house it should be very close to the same.