They will run everything like normal then blame you when it trips the generator off line.
They won’t remember to only run critical loads during an outage.

 

Fuel source, diesel, LP or NG? How large are the electrical loads, ie well, ovens, dryers, cooktops/ranges, condensers/heat pumps, hot tubs? Lights and receptacles, small appliances, I'm less concerned about. I'd prefer large enough to not get into load management. Using NG, you usually lose some output.

 

At the risk of being somewhat pedantic Let me expand on the relative energy output of the non diesel fuels. Internal Combustion Engines that burn gasoline, liquified petroleum gas (LPG), or natural gas as fuel all start life as Gasoline engines. There best power output will be when burning gasoline. When fueled with LPG the power output is reduced 10%. When fueled with natural gas the output power is reduced by 18%. That means that the generator should be sized for the fuel it will actually be fueled with. For maximum flexibility the generator should be sized at 1.2 times it's calculated load so that it will be able to carry it's load with any of the 3 fuels.

Tom Horne

 

What addition of the US National Electrical Code (NEC) is enforce by the Authority Having Jurisdiction in your location enforce. That is very important for how the Service Disconnecting Means is arranged. Do you already know if the Transfer Switch will be listed and marked as "Suitable For Use As Service Equipment?" That also has a large effect on how it can be placed in relationship to the Service Disconnecting Means (Main Breaker).

My first suggestion would be to do a load calculation as if you were sizing a feeder. Put the loads that the homeowners consider critical into the calculation to come out with the minimum size of Generator; "Engine Alternator Set" if your an ancient power production guy as I am; that will be needed to carry that load. Remember to include only the larger of the Heating and Air Conditioning Loads and not both. Use the load figures off of the actual manufacturers labels on the critical loads. Find out if the client wants an Automatic or Manual transfer switch. Because of the size of the generator that you have started with I will guess that the transfer switch will be automatic. Based on your impression about whether the clients, their "Know it all" teenage children, or other likely non technician person who may intervene with the load management decide whether you will need to segregate the critical from the optional loads.

If undisciplined load management seems at all likely you must segregate the optional loads from the critical loads. How I used to do that was to shift the optional loads to a separate panel. Unlike the more common approach I moved the loads that the generator is not able to carry into the second panel and leave the critical loads in the existing Service Equipment panel. The optional loads; especially those that the generator is incapable of carrying; will be fewer than the critical loads and many of them will be 240 volt and supplied from a 2 pole breaker. A Breaker that is fitted with a "Shunt Trip" will control power to the optional loads. A "Shunt Trip" is an electromagnetic solenoid that opens the circuit breaker it has been added to when it is energized. The transfer switch can be wired to energize the shunt trip thus disconnecting the optional loads panel when the power fails. Find out in advance if the transfer switch's control circuitry is 12 volt DC or 120 volt AC. 12 Volt DC is the preferred choice. 12 volt DC control power can be supplied by the Starting and ignition battery of the generator. That is preferable because it allows some of the control functions to happen prior to the transfer switch being thrown and the generator starting. One of those control functions is the disconnecting of the optional loads panel from the critical loads. Unless the Automatic Transfer Switch is an exotic type with control circuits that run on 120 volt AC you will want a shunt trip breaker with a 12 volt DC electromagnetic coil.

To supply the added optional loads panel see if you can obtain feed through lugs for the existing main panel. If those are available you can use them to supply the optional loads panel. If feed through lugs are not available for the existing panel then you will have to install a breaker in the existing panel to supply the added optional loads panel. Either way there will have to be a circuit breaker that will supply the loads in the optional loads panel unless it is the same ampacity as the existing Service Equipment Panel.

The type of panel that you select for the added optional loads panel is important. If you can find one for which the main breaker is available as a Shunt Trip Breaker then that is one good choice. If you can get a feeder breaker for the existing Service Equipment panel sized for supplying the optional load panel that is a Shunt Trip type that is also a good choice.

Depending on the ampacity and the number of breaker spaces in the existing panel you can select the optional loads panel to add additional breaker spaces, ampacity or both if the client will need more. The additional ampacity would involve doing a heavy up so plan ahead for how the 2 panels will be supplied when that gets done if you judge that it is likely. Do a whole house load calculation and add on any highly likely future loads such as Electric Vehicle Charging. There are many factors which effect how much amperage to add in for charging. The way they use there existing vehicles can be a pretty good indication of how they would use electric ones. The amount of daily use will effect whether one or more of the electric vehicles will need to be recharged overnight. That is just one factor in how much current the vehicle chargers will draw.

Tom Horne

 

What addition of the US National Electrical Code (NEC) is enforce by the Authority Having Jurisdiction in your location enforce. That is very important for how the Service Disconnecting Means is arranged. Do you already know if the Transfer Switch will be listed and marked as "Suitable For Use As Service Equipment?" That also has a large effect on how it can be placed in relationship to the Service Disconnecting Means (Main Breaker).

My first suggestion would be to do a load calculation as if you were sizing a feeder. Put the loads that the homeowners consider critical into the calculation to come out with the minimum size of Generator; "Engine Alternator Set" if your an ancient power production guy as I am; that will be needed to carry that load. Remember to include only the larger of the Heating and Air Conditioning Loads and not both. Use the load figures off of the actual manufacturers labels on the critical loads. Find out if the client wants an Automatic or Manual transfer switch. Because of the size of the generator that you have started with I will guess that the transfer switch will be automatic. Based on your impression about whether the clients, their "Know it all" teenage children, or other likely non technician person who may intervene with the load management decide whether you will need to segregate the critical from the optional loads.

If undisciplined load management seems at all likely you must segregate the optional loads from the critical loads. How I used to do that was to shift the optional loads to a separate panel. Unlike the more common approach I moved the loads that the generator is not able to carry into the second panel and leave the critical loads in the existing Service Equipment panel. The optional loads; especially those that the generator is incapable of carrying; will be fewer than the critical loads and many of them will be 240 volt and supplied from a 2 pole breaker. A Breaker that is fitted with a "Shunt Trip" will control power to the optional loads. A "Shunt Trip" is an electromagnetic solenoid that opens the circuit breaker it has been added to when it is energized. The transfer switch can be wired to energize the shunt trip thus disconnecting the optional loads panel when the power fails. Find out in advance if the transfer switch's control circuitry is 12 volt DC or 120 volt AC. 12 Volt DC is the preferred choice. 12 volt DC control power can be supplied by the Starting and ignition battery of the generator. That is preferable because it allows some of the control functions to happen prior to the transfer switch being thrown and the generator starting. One of those control functions is the disconnecting of the optional loads panel from the critical loads. Unless the Automatic Transfer Switch is an exotic type with control circuits that run on 120 volt AC you will want a shunt trip breaker with a 12 volt DC electromagnetic coil.

To supply the added optional loads panel see if you can obtain feed through lugs for the existing main panel. If those are available you can use them to supply the optional loads panel. If feed through lugs are not available for the existing panel then you will have to install a breaker in the existing panel to supply the added optional loads panel. Either way there will have to be a circuit breaker that will supply the loads in the optional loads panel unless it is the same ampacity as the existing Service Equipment Panel.

The type of panel that you select for the added optional loads panel is important. If you can find one for which the main breaker is available as a Shunt Trip Breaker then that is one good choice. If you can get a feeder breaker for the existing Service Equipment panel sized for supplying the optional load panel that is a Shunt Trip type that is also a good choice.

Depending on the ampacity and the number of breaker spaces in the existing panel you can select the optional loads panel to add additional breaker spaces, ampacity or both if the client will need more. The additional ampacity would involve doing a heavy up so plan ahead for how the 2 panels will be supplied when that gets done if you judge that it is likely. Do a whole house load calculation and add on any highly likely future loads such as Electric Vehicle Charging. There are many factors which effect how much amperage to add in for charging. The way they use there existing vehicles can be a pretty good indication of how they would use electric ones. The amount of daily use will effect whether one or more of the electric vehicles will need to be recharged overnight. That is just one factor in how much current the vehicle chargers will draw.

Tom Horne

It will be Natural Gas.

 

Put your 18kW generator in with a sub panel that has the transfer switch built in. More the loads the customer want to that panel, simple.

 

By putting your optional loads after the essential loads it is easier to automatically shed the optional loads. The whole reason for separating them at all is that the generator cannot carry them all let alone start them all at the same time. Optional load gets shed first, then the generator starts and comes up to it's operational speed, and then the transfer switch connects the generator to only the selected critical loads.

It is also generally less work to just add a panel for the optional loads. The obvious advantage of fully dividing the loads is cost reduction because you can use a smaller transfer switch. I like giving them the flexibility to use optional loads with great care and one at a time if I don't think the family are chowder heads. All that takes is one more jumper in the control wiring.

Tom Horne

 

I think that went out with the 2008 code. It either can support the full load connected to it, or manage less important loads. Portables, the end user is allowed to manage it, because they are there to start, run and connect the portable.

 

Hello,
I do not have any experience with sizing a generator, well I know how to size it for the load but not sure how it is typically done and what is NEC code compliant.
Here is my situation....
I have customer that has a 200-amp, single phase service to a dwelling and they would like a generator to back up some what they consider critical loads.
Such as the furnace, AC, well, & some kitchen appliances circuits.
My thought was I could get an 18KW generator, which would provide 80-amps and back up the entire 200-amp panel.
Then I would let the customer know that you cant run non critical loads such as a welder, dryer, etc etc.
Its obvious that 80-amps would be plenty to back up the loads they want to back up, but would that be NEC compliant?
It would elimate having to set another panel and relocated circuits.

Don't let these guys get you all off track with this and that. An 18KW will be just fine. Millions of them out there right now. Put in a service rated TS and let them know no cooking, minimal AC and definitely no electric heat. .

 

personally i let the customer decide how much money to spend
i give them choices of sizes and costs
if it is portable i tell them to buy it

this way i am not to blame when it doesnt go the way they want

 

An 18kw might be just fine, I just put one in. I don't know how large a home, what the loads are, electric or otherwise. Might be plenty with no load management, I can't tell without seeing it. I prefer to err on the larger size generator than less.

 

You might be putting the cart before the horse here. Where are you buying the generator from? They should be able to tell you what to use. There are several online sites that have a generator sizing app that you can use. Is this for a friend or just a customer? Be prepared to be married to it if things go wrong. Today's generators are like cars in that not everybody can fix them. Many times for installation and repairs you have to be factory certified. I deal with several generator sales shops that like to do the sales and service work. I only do the install. If any problems arise during a storm then it is between the homeowner and the generator people. I do not want a call at 1:00 in the morning.

 

Where are you buying the generator from? They should be able to tell you what to use.

Exercise caution on this. The larger the generator they sell you is the more money they will make on the sale. It might be wiser to get the electrical contractor that did prior work on your home with a good outcome to do the load calculation for you.

yes i know there is the least amount of energy per unit in NAT, size it for that and no more worries

When dealing with with an installation that would use Natural Gas as the fuel I would multiply the entire calculated load by 1.25. That way the generator's capacity when fueled with natural gas would match the load.

When we installed the new generator for my fire department I sized it for Natural Gas fuel and used a 500 pound capacity propane tank as the back up. That way we could be confident that either fuel would carry the load.

Then we got an ice storm and, because it was policy, we called for a refill of our propane tank as a hedge against any failure of the natural gas supply. Our supplier never returned our voice messages because the device that would call their pagers had been connected to the non emergency receptacle a foot away instead of to the emergency receptacle which was installed right next to it. The dispatcher had unplugged it from the receptacle with the RED outlet cover marked EMERGENCY POWER when she was cleaning and plugged it into the wrong receptacle when she was done. We had the fire station, which served the area the propane supplier is located in, send a unit to see if they could find anyone on the site. All of the drivers and the manager were out making deliveries to clients that were afraid that they would run out of propane for heat. That unit's crew left a large piece of cardboard on their office door asking that they call us. Instead they sent a tank delivery truck with another 500 pound propane tank, a technician to connect it in parallel to the first tank and a propane tanker to fill them both.

10 days later, when power was fully restored, I went over to their office and had a look at their arrangements. Since I was there as an emergency service customer's representative they were very cooperative. I went out and found a lockable metal in use cover for the receptacle and had a Micarta label made for it which said "Power failure communications equipment supply. DO NOT DISCONNECT. I changed the receptacle from duplex to single, painted the cover red, and applied the new label. Once I had plugged it back in and put the new cover on it I gave the manager the key to the padlock. The padlock I used has what is called a "Frangible Shackle." It could be broken with any hammer, if they had a true emergency themselves, without damaging anything else. I talked them into obtaining telephone forwarding service from the telephone service supplier that would send their voice messages directly to their paging carrier after 1/2 hour with no one acknowledging the message. During a subsequent ice storm, a tropical storm, and the aftermath of a Derecho those all worked very well.

The propane company later added, on there own initiative, stationary cellular service, for their office and the managers home, so that people could reach them if the phone lines actually went down. They also had their unused business band radio system recommissioned and renewed their radio license. That allowed them to use direct paging and 2 way radio as a backup. When our fire chief pointed this out to the local all news radio station they broadcast a nice story about them and the State's Office of Emergency Management got them a State award as a fully disaster ready business. 2 doses of free publicity suited them right down to the ground.

Motto: try to remember to say thank you. It never hurts and often helps.

Tom Horne

 

Hello,
I do not have any experience with sizing a generator, well I know how to size it for the load but not sure how it is typically done and what is NEC code compliant.
Here is my situation....
I have customer that has a 200-amp, single phase service to a dwelling and they would like a generator to back up some what they consider critical loads.
Such as the furnace, AC, well, & some kitchen appliances circuits.
My thought was I could get an 18KW generator, which would provide 80-amps and back up the entire 200-amp panel.
Then I would let the customer know that you cant run non critical loads such as a welder, dryer, etc etc.
Its obvious that 80-amps would be plenty to back up the loads they want to back up, but would that be NEC compliant?
It would elimate having to set another panel and relocated circuits.

Do a load calculation and put a load shed on appliances until you get where you need to be.
My 2000 sf all electric house has a 150amp service. My load rarely goes above 4kw.
I have a 22kw generator with a 100amp breaker.
I would go with an 18kw or 11kw. Im in that biz. I know the difference.
Ideally, I would have had a liquid cooled unit, preferably diesel.

 

i disagree with diesel because it will not last indefinitely
not to mention the refilling process
NAT and LPG will last indefinitely

my personal preference would be a utility line with NAT
no delivery trucks required when weather is bad and roads closed

yes i know there is the least amount of energy per unit in NAT, size it for that and no more worries

 

The industrial service providers offer fuel polishing to help maintain your diesel supply. It becomes part of regular maintenance along fuel filters, air filters and maybe load banking for keeping the exhaust clean.

lack of maintenance will cause problems regardless of fuel type.

 

My diesel fuel question is aimed towards residential customers. Nobody wants to deliver small quantities of diesel to a residence unless they charge a lot for the delivery. One customer has a 1000 gallon heating fuel tank and the other has a 500 gallon tank.

 

Watch with running your generator on home heating oil. It does not have as much luberciticy added like off road fuel oil. Used to deliver it for a few years picking it up at the fuel racks in the port.

18kw makes me think propane or nat gas genny. How big is the well pump? How is the waste water system ex septic does it have a pump tank or grinder/boost pump? Electric for heat?

It will work till it don't.

 

Is there a good generator contractor in the area? This is what I do. Assist electricians and homeowners get the right size and fuel. Just like anything, you go to the internet, you get what you get.

 

It’s what I do too.

 

You can turn over your own diesel fuel if you use it in your vehicles or equipment.

An upgraded-size natural gas line may be needed for a larger backup gen. That was the case the last time I sized a gen for a full 200A backup.

 

The fuel thing is a big deal, some areas don't have the natural gas pressure or won't allow it because the infrastructure is old. I work with a lot of propane installs because natural gas isn't everywhere. Does this install have the room for tanks, is there enough room for at least 2 120 gallon tanks, how cold does it get there? If you have existing tanks, how large and what is the current usage? Diesel is fine too, but fuel maintenance, and smaller capacity in base tanks and shorter run time and or the complexity of additional tanks or the ability to get refills in a timely manner, are questions to be answered. Any of these fuel types are likely more than up to the task provided they are set up properly.

 

Be careful to check your fuel choice with the local fire code enforcement authority. Some forbid any propane tank greater than 100 pounds capacity that is not buried or encased in fire proofing. That is especially likely in wildland fire prone areas. Do not assume that does not include your area because your not in the west. CHECK! Many local fire codes forbid the storage or flammable liquids such as Gasoline in large quantities. Some limit the total volume of gasoline stored without a permit to 25 Gallons. In order to get the permit the storage will have to meet the requirements of the NFPA 30: Flammable and Combustible Liquids Code. The installation of a stationary propane storage will have to meet the requirements of the NFPA 58: Liquefied Petroleum Gas Code. The entire gaseous fuel system has to meet the requirements of NFPA 54, National Fuel Gas Code. Requirements can include marking of the building and enclosures in which the fuel is stored, the use of Nationally Recognized Testing Laboratory (NRTL) listed containers and listed enclosures for containers which hold fuel above a code prescribed amount in the aggregate of portable containers. The requirements for Combustible liquids are generally less demanding to meet than those for the more readily ignited flammable gasses and liquids.

As one of the things to look out for your existing fuel oil tank may not be subject to the latest regulations because of the date of it's installation. No regulatory change made after that date can be applied to the tank involuntarily because of the US Constitutional prohibition on applying law adopted after the act that the new law would be applied to. Such laws are referred to by the legal phrase "ex post facto." The literal translation into English is "after the fact." Thus a law adopted after the act it is to forbid or regulate is an ex post facto law. But when you change the use of that installation substantially that could bring the entire installation under regulations adopted prior to the modification. A Liquefied Petroleum Gas tank may be required to be anchored in place if it is located in a particular classification of risk on your Community's Flood Map.

You'll want to know which if any of these regulations apply to your fuel storage installation before you build or modify it.

Tom Horne

 

A grid tied inverter can’t sell back to a dead grid. 25 years ago inverters were configured to function that way. Far more generators are probably connected without and interlock and I haven’t heard of a lineman being killed by one. Might have happened, but I haven’t heard of one.

 

Solar grid tie inverters are synchronized to the power grid so that when the utility power is lost they automatically shut down in less than a second. That is a to safeguard the lineman working to restore service. The same transformer that lowers the distribution voltage to 120/240 for your home will take any 120/240 coming from your generator, through any form of back feed, up to the distribution voltage so it can travel very away on the distribution line and kill a lineman. It only takes 30 Milliamperes to stop a persons heart and kill them. In many states that could be charged as Depraved Indifference which prescribes greater penalties than manslaughter.

The International Brotherhood of Electrical Workers has committed to seeking the highest possible penalty allowed by law for anyone who injures or electrocutes an Electrical Worker by back-feeding power into the distribution system regardless of membership in the union. They will become aware of the incident because the local union will inform them at once of any such occurrence.

Tom Horne

Diesel Fuel can be stored for years if it is treated with a fungicide to prevent the growth of fungus in the fuel. Manufactured Gas (Propane) can be stored for years without any treatment at all. It is generally less expensive to store propane than diesel because a diesel fuel tank must be encased in concrete or buried in a completely contained vault to prevent leakage into ground water and the possibility of a Boiling Liquid Expanding Vapor Explosion (BLEVE) if an unprotected tank were exposed to fire.

Tom Horne

Uhhh, you should come north and see all the above ground diesel tanks, 1000’s.

 

double post

 

I look at this way, I make mistakes about testing what I'm working on especially if I'm tired and I want to get home or distracted by any number of things. I'd just rather do it so there's little to no chance of someone else being tired out in that crappy weather getting hurt.

 

I hate to agree with Hack, but can you find a documented case of lineman injury from backfeeding an inverter or a generator?

 

I do not know of any injuries but in my town and the next town over there were three house fires over the years since Storm Sandy because the generator was not isolated and when the utility came back on the was an argument between the generator and the utility.

 

Crewman's electrocution blamed on generator
Staff Writer
The Gadsden Times

A generator near a power line where a utility worker was electrocuted during Hurricane Dennis repairs may have been improperly installed, authorities said.
Ronnie Allen Adams Jr., 41,of Winterville, Ga., died Tuesday when he came in contact with a charged power line. A spokesman for Adams'

 

This is what I was talking about when I said “stories”. The generator “may have been the cause”, but it may not have been the cause as well. Everything with this article is gossip, there’s no documentation from a thorough investigation citing the generator as the cause.

A spokesman for the employer said all this, because it was definitely not anything to do with the employers lack of safety practices and constant push to get work done quicker, it had to have been a generator that was conveniently running at the time.

 

I was surprised how hard to Google examples rather than warnings, took longer than I expected to find a real life story

I remember lineman electrocuted a few counties away from backfed genny, but don't think this was the one

So it has happened, really most safety rules are to avoid catastrophe occurring from unusual chain of events

 

https://www.oshrc.gov/assets/1/6/06-0166.pdf