Residential Generators

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CharlesLindell

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Pittsburgh, Pennsylvania, USA
A customer of mine wants to install a basic generator for his home. I've never done one on my own before. Aside from the code book are there any suggestions, advice or things to consider that i might not know to think of. I put a call into the local ordinance office to see if they had any requirements (sound, location etc...) Thank you.

Chaz
 
Top of the list: Either install a transfer switch (manual or automatic) or tell the client to plan on using a couple extension cords to power specific items. Under no circumstances allow the generator to be connected directly to the house power system (e.g., by plugging it into the dryer outlet). I know someone who used that method to connect the generator of his RV to his house during power outages. I could not talk him out of it. In his case, nothing bad ever happened. That means luck was involved: not his good luck but the good luck of the linemen working to restore power.

I would start asking questions. Examples:
  1. Are there specific items they wish to have power during a utility outage?
  2. Do they want the generator to start and take load automatically?
  3. Pertaining to question 2, what if the utility outage happens when they are not at home (i.e., either at work or on vacation)?
  4. For an extended outage, will they leave the generator running all night, or will they restart it each morning?
  5. Also for an extended outage, how will they make sure they have enough fuel to keep the generator going?
  6. Pertaining to question 5, is natural gas an option for the generator fuel?

Welcome to the forum.
 
CharlesLindell said:
A customer of mine wants to install a basic generator for his home. I've never done one on my own before. Aside from the code book are there any suggestions, advice or things to consider that i might not know to think of. I put a call into the local ordinance office to see if they had any requirements (sound, location etc...) Thank you.

Chaz
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I don't know what the outcome was here in Florida, but at one time they were making you size the generator to the service size, no load shedding.

I would check or have the owner check with the AHJ in your area on how he/she is interpreting the code.

After that, the vendor or Generator people are the best to tell you how to install. They have a vested interest. They want to sell Generators!

Gary
 
the simplest cheapest way is to put a interlock on the main and the backfed generator breaker. Then put a inlet box to plug the generator into. most manufacturers sell an interlock kit for their loadcenters, and there are also "less listed" (;) )aftermarket ones. If it is manually controlled, you dont need to size the generator to the house loads.
 
Start by telling us what size generator you are talking about--whole house or portable. The answers above mostly pertain to one or the other.
 
Find out if the guy wants the whole house on during the outage. He will, but he doesn't want to pay for it.

Then, find out what load he would like to put on it after he hears the cost of the 100% duty.

Then, if he is cheap, he will go with a manual transfer switch. If not, go with an auto.

Then, does he want to haul gas or does he have propane or natural gas.

If he has natural gas, then you will have to de-rate the generator as opposed to Propane

Next, will his neigbor be pissed at the guy for the noise that is creates since its the only sound you will hear in a blackout.

I always had electrical plugs at the garage that everyone could plug their crap into. Makes better neighbors... And, it got a lot of neighbors meat in my freezer!
 
Basic generator is not enough information. As previously mentioned, you have to state whether it is a portable or a permanently installed unit. If I were to make an assumption, when you say "basic" I would think it is a portable. As previously mentioned, if it is a portable you'll need an interlock kit so that you don't back-feed to the utility grid and (probably) a 30A, 240V power inlet port connected to the generator breaker.

If you're talking about a permanently installed generator with an automatic transfer switch you are WAY beyond basic.
 
Gary11734 said:
I always had electrical plugs at the garage that everyone could plug their crap into.
Click to expand...

I don't have a generator, but I've installed a few. I've often wondered about neighbors expecting you to give them power in an outage. Sure, you would be a really good neighbor if you do, but did you account for the extra load when you purchased the generator? And the costs of having and running a generator are a lot. What happens when you say "It's costing me $50 an hour* to run this thing. I'd be glad to share my power if you help with the expense."


* A made-up number. I don't know what a real number would be, but if you consider all the permitting, material, installation, maintenance, and fuel costs over the useful life of a generator, it's got to be a lot.
 
Also need to find out where he wants it & how far from his LP or NG. Have seen units that wouldn't start because of not enough gas pressure. Usually too small of a gas line ran limiting the PSI at the gen set. Most of the manufacturers now have load shedding so you can offer that as an option. The load shed will kick out the AC or electric stove if the sump pump or fridge has to kick on. By doing it that way, you don't have to oversize the unit.
 
electrofelon said:
the simplest cheapest way is to put a interlock on the main and the backfed generator breaker. Then put a inlet box to plug the generator into. most manufacturers sell an interlock kit for their loadcenters, and there are also "less listed" (;) )aftermarket ones. If it is manually controlled, you dont need to size the generator to the house loads.
Click to expand...

+1
 
Just a thought (not an experiment), if one were to backfeed with say 5000 watt generator capability wouldn't it just bog down or pop a breaker rather than feeding the whole neighborhood plus the line fault? In my case an outage usually affects 520 customers.
 
Eddie_T said:
Just a thought (not an experiment), if one were to backfeed with say 5000-watt generator capability wouldn't it just bog down or pop a breaker rather than feeding the whole neighborhood plus the line fault? In my case an outage usually affects 520 customers.
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Usually, yes. But consider:

[1] Your house is probably fed from a ~35:1 step down transformer. (8K:240) Even if your generator bogs down to the point where it's putting out only 3 volts -- which, for all practical purposes on your side of the transformer, is functionally equivalent to "off" -- there will be a potentially-lethal voltage (~105 volts) present on the distribution side of the transformer. And you wouldn't be "feeding the whole neighborhood" because a lot of heavy consumers -- air conditioning and electric heat, for example -- won't have enough voltage to energize their contractors.

[2] "The whole neighborhood" extends only to the first blown fuse or broken wire. It might be 520 customers; it might be five.

[3] There's a life-threatening risk even before you get to "the whole neighborhood" -- the homeowner handling the exposed conductors of a male-to-male dryer cord, for example.

[4] Even if the odds of it ever happening are low, the failure mode is high -- a dead outdoor electrician. This is a circumstance where I want to hear "the design of the installation assures that it cannot and will not occur", not "likely to just bog down or pop a breaker". (and I'm not even an outdoor electrician with skin directly in the game)

Eddie_T said:
.. wouldn't it just bog down or pop a breaker ... ? ...
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If we were talking about a manual transfer switch or manual interlock on a residential load center, and the worst possible outcome would be burning out an air-conditioner compressor motor because the undersized generator can't provide enough oomph to start it, or leaving the whole house dark because the generator's main breaker popped, I'd be totally OK with that.
 
In my neighborhood if not 520 customers as the utility always tells me are out there are about 25 that I can almost see. Most with the normal electrical loads that don't have contactors such as heat, well pump, water heater, fridge, freezer, TV and lighting. I just can't see a generator powering it though I agree it shouldn't be attempted. Most who cite the hazard think the generator would be supplying 240v and do the math with that, I doubt even the 3v but wouldn't try it.
 
Coppersmith said:
I don't have a generator, but I've installed a few. I've often wondered about neighbors expecting you to give them power in an outage. Sure, you would be a really good neighbor if you do, but did you account for the extra load when you purchased the generator? And the costs of having and running a generator are a lot. What happens when you say "It's costing me $50 an hour* to run this thing. I'd be glad to share my power if you help with the expense."


* A made-up number. I don't know what a real number would be, but if you consider all the permitting, material, installation, maintenance, and fuel costs over the useful life of a generator, it's got to be a lot.
Click to expand...

They usually had a freezer in the garage and only one to two neighbors adjacent to the house.

A 200 Amp Generator is in the 18 to the 23K range now with installation? I had my guys at the shop put it in, so I have no idea what I paid for it back in 2006... I ran it off Natural Gas from the street.

In Florida, after a hurricane, you might as well get it where you can run the A/C or its not worth it.


I had a 5000 watt Honda before this. Took off the Range wires at the panel and back fed it. Made sure the meter was pulled so no back feed into the FPL line. I don't recommend this to anybody, and I will deny this thread if you ask me again! Then I bought a window shaker for one of the rooms. Load shed as needed at the panel. Worked fine until I got the permanent one.

During hurricanes, you had a bunch of guys tying to a Male 30 Amp to mate with the dryer outlet. The same thing, the meter is pulled so no back feed. Or, removed the main feeders to the meter so no chance of back feed. Again, DONT DO IT!
 
Gary11734 said:
In Florida, after a hurricane, you might as well get it where you can run the A/C or its not worth it.
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How about running the house on one generator and the AC compressor unit on another?

Hmmm. I wonder if a 5kw portable would start a compressor on a 30a breaker? :?
 
Gary11734 said:
I don't know what the outcome was here in Florida, but at one time they were making you size the generator to the service size, no load shedding.
Click to expand...

Maybe that was in one particular jurisdiction? I’ve installed many generators in Florida and that was never an issue. Even in Tallahassee, which is probably the strictest area of the southeastern US I’ve ever worked in outside of south Florida, they never restricted us from using load-shedding transfer switches.


Sent from my iPhone using Tapatalk
 
I'd start with asking the customer some questions.
List of requirements.
What to run...for how long.
Automatic or Manual.
Noise thresholds.
Generator operating environment (Rain, wind, snow, ice)
Maintenance expectations (vary significantly between portable and standby fixed)
Fuel supply.
CO considerations and mitigation.

Once you narrow down the above, it should narrow the technical solutions. Then the cost/requirements trade begins. As you modify the trades, different technical solutions enter or leave the range.

The cost/requirement trade range can be significant. For example, when I first looked at my needs, I was at a 22kW load shedding standby. But the costs skyrocketed when it came to fuel storage, connections, and efficiency. I eventually settled on a portable generator with a battery bank auxiliary at a tenth of the cost of the standby. I had to make some tough decisions, but that's why they're called tradeoffs. Everyone's needs are different. Finding the sweet spot between what you get, what you need, and what you can afford...that's the key. And it takes several iterations. Took me six months to a year..and about five different designs.
 
Back when Costco was selling those Coleman 5 kw rated units, they could start and run a 240 volt deep well pump, but not much else, like refrigerators and freezers at the same time. But at $499 each my friend thought it cheaper to buy two than one real 7.5 or more kw generator. Since his house had two panels (very common around here in heat pump large house land) I wired one generator to each panel with a Square D 6 pole space transfer panel. Start a 3 ton compressor, not going to happen with those small guys. But larger one, sized for the compressor, should work fine.

BTW, those small Honda inverter types can be paralleled for more kw.;)
 
brantmacga said:
Maybe that was in one particular jurisdiction? I’ve installed many generators in Florida and that was never an issue. Even in Tallahassee, which is probably the strictest area of the southeastern US I’ve ever worked in outside of south Florida, they never restricted us from using load-shedding transfer switches.


Sent from my iPhone using Tapatalk
Click to expand...

Mr. Danger, the cheif electrical inspector for Dade County at the time was saying this. I was in the Miami/Fort Lauderdale at the time. I'm thinking after Andrew. Glad to know there is sanity again in Florida.
 
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