Generators

[Cavie]

It has been determinded by my AHJ that generators installed with ATS shall be sized to supply 100% of the connected load. MTS systems need not be sized to total load but individual circuit breakers in the panal must be marked as Generator circuits. This decision was made after addending a Emergancy Generator Seminar shich I did not attend. Demand calcs are required for the sizing of the Generator, ATS, Feeders that feed the panel being used. I think this is a wonderful idea as when the 15KW gen starts up and feeds a loaded 200 amp panel, the 70 amp breaker will trip and therefor no power. Most of these homes are not occupied durning the summer months when it is likley to be needed therefor no body to reset and turn off unnessary circuits. A/C, Refridgeration, pool pumps, security systems, etc will be out. Any thoughts or code referances to justify this requirement?

 

[iwire]

I think it is a lousy uncalled for requirement but I also believe the 2008 NEC is moving that way as well.

 

[benaround]

Cavie,

What code art. is being used to enforce this ?

 

[Cavie]

benaround. He sited a few code numbers this morning but I can't rember all of them but one I do is art 220.40 General. For non residential, he is quoting 700.1 and 700.5. This matter will be discussed ini detail at a meeting on Monday morning. I thought it would be good to know how it is being delt with around the country.

 

[dbuckley]

I dont know about the code refs, but if you're installing a genny that is incapable of supplying the realistic power required then its back to the old school with split distribution, essential and non-essential power, and making sure the essential load is reasonably within the capability of the genset. Which is another way of saying "generators installed with ATS shall be sized to supply 100% of the connected load.", where the connected load is not the entire load of the home.

 

[chris kennedy]

Cavie, I see SW Florida. Broward and Miami Dade both issued similar requirements I believe in November of 06.

 

[Cavie]

dbuckley. That is what he is saying. Size the Feeders and ATS and gen to the total connected load. In the case of a 15kw gen, this would require a small subpanel. A way around this is to install a "Future" gen hookup with feeders sized to the 200 amp and do not install the gen untill after the inspection.

 

[Cavie]

chris, what are they using for code requirements? art. #'s?

 

[George Stolz]

I think it is a lousy uncalled for requirement...

I don't think it ranks in the top ten, but I would not have supported the change.

... but I also believe the 2008 NEC is moving that way as well.

Agreed. The proposal to require ATS-supplied Optional Standby Systems to have a rating equivalent to the connected load (or use load shedding) passed in the ROP stages, and sailed unchallenged through the ROC.

Cavie, knowing this, perhaps it would be more appropriate to advise to wait for the adoption of the 2008 code, as opposed to the AHJ making something up in the meantime?

Article 700 does not apply to most backup systems, generally they are governed by the far less restrictive 702.

 

[chris kennedy]

chris, what are they using for code requirements? art. #'s?

I really never had to ask. 702.5 would be my guess. These requirements were short lived I believe because of the quantity and variety of generator installs here. We have been slowly getting out of gen installs.

 

[benaround]

Cavie,

The 700.1 and 700.5 require the gen for full load already, no problem there.

It's the 702.5 OSS where I see the problem, the user of the optional

standby system shall be permitted to select the load connected to the

system.

 

[360Youth]

I dont know about the code refs, but if you're installing a genny that is incapable of supplying the realistic power required then its back to the old school with split distribution, essential and non-essential power, and making sure the essential load is reasonably within the capability of the genset. Which is another way of saying "generators installed with ATS shall be sized to supply 100% of the connected load.", where the connected load is not the entire load of the home.

Well put. I don't know of any specific ref., but common sense says not to load a generator beyound its kw rating and OCP. It is surprising how many customers and even ECs have wanted a 100 amp ATS for a service because the genset was only a 15 or 20 kw. The switch needs to be rated for the service or sub-panel but the genset can be sized for the selected loads (provoding they are separted from the remaing connected load at time of standby). I'm not sure anything in NEC prevents a 15kw installed on a 400 amp service, but the first time it tries to start up and run, it is not the AHJ you will have to worry about, it is the HO.:grin:

 

[dezwitinc]

Gen Sizing

Gen Sizing

Over here on the east coast of Florida, we are required to size a generator with an automatic transfer switch to be of sufficient capacity to provide for a load calculated using 220.82.
I was told by an inspector that I should imagine that it is Thanksgiving Day, all the kids are home washing and drying clothes, the range, wall oven, and microwave are all cranking, the pool pump and 8kW heater are running, it is unusually cold in Florida so all the air handlers are cranking heat, and all of a sudden, we lose FPL.
The unfortunate part of this is that many of these homes have 2 dishwashers, 3 disposals, 2 dryers, 3 or 4 air handlers with 10 kW heat each, etc. and only two people living in them.
You end up with some ridiculously large generators that develop problems like wet stacking because they never see a fraction of the load that was calculated.
Our normal solution for this is either subpanels or manual transfer switches which are not bound by these requirements.
But as you can imagine, people with 2 dishwashers, 3 disposals, etc. are usually not too keen on operating a manual transfer switch so they spend the money and then buy a maintenance contract.

 

[360Youth]

Over here on the east coast of Florida, we are required to size a generator with an automatic transfer switch to be of sufficient capacity to provide for a load calculated using 220.82.
I was told by an inspector that I should imagine that it is Thanksgiving Day, all the kids are home washing and drying clothes, the range, wall oven, and microwave are all cranking, the pool pump and 8kW heater are running, it is unusually cold in Florida so all the air handlers are cranking heat, and all of a sudden, we lose FPL.
The unfortunate part of this is that many of these homes have 2 dishwashers, 3 disposals, 2 dryers, 3 or 4 air handlers with 10 kW heat each, etc. and only two people living in them.
You end up with some ridiculously large generators that develop problems like wet stacking because they never see a fraction of the load that was calculated.
Our normal solution for this is either subpanels or manual transfer switches which are not bound by these requirements.
But as you can imagine, people with 2 dishwashers, 3 disposals, etc. are usually not too keen on operating a manual transfer switch so they spend the money and then buy a maintenance contract.

I am not sure I understand the requirement. Are they saying that if a generator with ATS is installed it must be able to carry a certain portion of the calculated load in order to live comfortably? Around here, you can have a 5kw on ATS to run the fridge if that is all they want, you just ahve to make sure the deign is such that that is all the generator will take on under loss of power (sub-panel and smaller ATS, etc.) We have a lot of disappointed customers when we tell them taht a 16kw or even 25kw will not run their whole house on an ATS because it doesn't matter that they have no intention on using the upstairs a/c, it only matters that they may lose power while grocerry shopping and the generator must be sized to run the potential connected load. That is about the time sub-panel discussions come into play. But I have never had an AHJ tell me the size generator that needs to be put in. They are just looking for proper install and connections. The customer is the one I have to answer to if the generator we sold them faults out because of poor design on our part.

 

[LawnGuyLandSparky]

I think the issue here is that often a 100a sub is installed, and every conceviably needed or useful circuit is tied to this generator panel, even though the genset is incapable of providing every one of these loads simultaniously. The "automatic" part of the operation isn't really automatic, as in the event of a power failure when no one is present or knowedgable, there's no one to shed the nonessencial loads, causing the genset OCPD to trip, rendering the entire installation useless.

 

[dezwitinc]

Generator Sizing

Generator Sizing

What they require is that under automatic operation for a whole house application, the generator must be sized to carry the entire calculated load.
As we know, very seldom if ever would you be able to put a meter on a service and see as many amps as the calculation shows.
Example:
I have a neighbor that we did an install for. Two people living in a 4200 square foot house. Two dishwashers (Kosher kitchen), 2 disposals, 2 water heaters, two dryers, 24kW of heat strips (we live in Florida), pool pump, 3 small appliance circuits, etc. The way that we are required to size here, they had to have a 60kW unit. Do you see any possible way that they would ever see 60kW on their service? Not in a million years.
Generators don't like being run at 20 or 30 percent load (if they see that).
This then leads to nothing but high cost of operation and maintenance.
I'm not saying that we should be able to put their house on a 15kW but let's have some diversity factors to apply so we can install a realistic unit.
I understand that there are some municipalities up in central and northern Florida that allow for some specific equipment exclusions when doing the load calc.
These types of exceptions lead to more affordable installations.
This means more work for us and more people protected when the next big one hits us.

 

[LarryFine]

It's not very difficult to use auxiliary contacts to disable 24v controls for HVAC systems. Power goes off, AC and heat contactors drop out, generator comes on, no HVAC loads.

If desired, when homeowner returns to find the power off and generator running, he can manually switch off non-essential loads and bypass auxiliary controls to restore HVAC.

 

[bphgravity]

I did attend that course presented by Mark Ode and John Minick that Cavie is refering to. All Mark did was describe what the 2008 section will likely require for capacity and rating of optional standby systems.

However we have similar requirements as posted by Cavie.

Application Permit Requirements
A standard City of North Port permit application for installing a generator connected to a home’s electrical service costs $40.00, plus any applicable surcharges. Documents required at time of application include:
1. A site plan showing the generator’s location;
2. The location of the generator’s fuel source and the type of fuel to be used;
3. Manufacturer’s specifications;
4. An itemized list of the electrical loads to be served, including any motor loads using motor startup current;
5. Diagrams of feeders, including the size and type of conductors to be used.

Contact Florida Power and Light before installation
If it is necessary for the electrical service to be turned off, or if access is required inside the meter enclosure, the homeowner or installer must contact to arrange for disconnection of the electrical service. The toll-free telephone number for FPL is 1-800-226-3545.
After the installation
After installation, contact the North Port Building Department at 423-3186 for the required final inspection of the work. PLEASE NOTE that the City must approve the work before FPL will restore power to the premises.

Guidelines for Portable Generators with Manual Transfer Equipment:

Permanently installed equipment for the connection of a portable generator must comply with Section 702.6 of the 2002 National Electrical Code (NEC). The manual transfer equipment will require an interlock device suitable for the intended use. This device must be installed to prevent the inadvertent interconnection of the normal and the optional system supply. The connection device must be a UL Standard 231 Listed Power Outlet. The back-feeding of electrical outlets within the home is not permitted.

Guidelines for Permanent Generators with Manual Transfer Switches:

Permanently installed generators with permanently installed manual transfer equipment must comply with the provisions for portable generators or use a Listed Transfer Switch or Panel Board. The equipment must be installed so as to allow the user to select the connected loads upon manual transfer.
Guidelines for Permanent Generators with Automatic Transfer Equipment:
Permanently installed generators with automatic transfer equipment must comply with the provisions of Section 702.5 of the 2002 National Electrical Code. The calculated load as determined by Article 220 of the 2002 NEC must not exceed the rating of the generator output. Please note that a “Demand Load” will not be accepted in lieu of the calculated load.
ALL load calculations must be included with the approved permit documents and must be available on site with the permit placard at the time of the inspection. All transfer equipment must be listed. Automatic transfer equipment installed on the supply side of the method of disconnecting the service must be listed as suitable for use as service equipment.

Required permanent signs for all installations

Permanent signs must be posted at all of the above-described installations that comply with Section 702.8 of the 2002 National Electrical Code. The required signs must indicate the type and location of the on-site optional standby power source, and must be permanently installed and located at the service disconnection point and at the meter enclosure.

All equipment must be installed according to the manufacturer’s instructions.

Portable generators with built-in power receptacles

Generators that supply power to connected equipment through built-in receptacles mounted on the generator DO NOT REQUIRE PERMITS OR INSPECTIONS.
However, they must be placed well away from a home or any air intake to prevent the danger of carbon monoxide poisoning.
As with any of the equipment listed above, be sure to read and follow all safety precautions in your user’s manual.

 

[SurfSide EC]

It's not very difficult to use auxiliary contacts to disable 24v controls for HVAC systems. Power goes off, AC and heat contactors drop out, generator comes on, no HVAC loads.

If desired, when homeowner returns to find the power off and generator running, he can manually switch off non-essential loads and bypass auxiliary controls to restore HVAC.

But if it is capable to run the HVAC when they return home, why not leave it on to begin with? Unless you are talking of spacing out the start-up loads, which is really one of the big dangers in ATS. That install does come in handy. We have used that technique a few times. Never to the point though where the HO had the power to override the lockout.

Edit: Sorry, I missed the part of shedding non-essential loads. Most of our installs are sized where if it could take on the HVAC, the remaining non-essential loads wouldn't make that much of difference. It is typically that HVAC that drasticlly changes the size of the generator.

The "automatic" part of the operation isn't really automatic,

I'm not sure I understand how it is not automatic. The last part you said was true, defeating the whole purpose of the install by trying to take on more laod than the genset OCP will handle. Automatic simply means the generator must be able take on any potential load, not matter how unlikely.

 

[LawnGuyLandSparky]

I supose I'm trying to put the intent in perspective - to rationalize it. I agree with the rationalization.

As I read the article that pertains only to permanently connected loads to permanently connected gensets with automatic transfer switches:

Guidelines for Permanent Generators with Automatic Transfer Equipment:
Permanently installed generators with automatic transfer equipment must comply with the provisions of Section 702.5 of the 2002 National Electrical Code. The calculated load as determined by Article 220 of the 2002 NEC must not exceed the rating of the generator output. Please note that a “Demand Load” will not be accepted in lieu of the calculated load.

This is not true of portable or permanent gensets with manual transfer switches.

Typically, a genset panel with a manual transfer switch will be overloaded (for the genset's output, not the panel's normal utility feeder) intentionally with the understanding that the user will manually select the desired loads to be powered.

If this is done with a fully automatic genset and a fully automatic transfer switch, it's likely that in the absense of someone who knows, the entire installation which is exected to work, won't work at all.