residential generator installations

[currentelectric]

Can you please clarify the purpose and intent of article 445.13/ ampacity of conductors. Is it ok to use a 4 conductor #2 SER aluminum cable for a feeder to a service entrance rated transfer switch from a 20 KW kohler RESAL generator which comes supplied with a 2 pole 100 amp breaker. The nameplate rating for this generator for natural gas is 75 amps. According to 445.13 115% of 75 amps is 86.25 amps. Since # 2 SER has a rating 90 amps is adequate for my application. Out of over 100 installations we have completed in the State of New Jersey with the Kohler 20 KW generator I have never had a problem passing electrical inspection. Unfortunately I have had one issue with an electrical inspector who has failed my installation because of the use of the # 2 SER wire from the generator to the transfer switch. I have provided him with a total load calculation for this particular house with the use of a Kohler Load Controll module which sheds 2 AC loads, 30 amp 240 volt oven, and a 30 amp hot water heater. The inherent design of the generator and the use of the load control module prevents and loads above 75 amps. Also does the exception in this article also dictate that the rating of the wire can be rated for 75 amps? Ralph Somma , Current Electric Of Colts Neck LLC.

 

[ceb58]

Can you please clarify the purpose and intent of article 445.13/ ampacity of conductors. Is it ok to use a 4 conductor #2 SER aluminum cable for a feeder to a service entrance rated transfer switch from a 20 KW kohler RESAL generator which comes supplied with a 2 pole 100 amp breaker. The nameplate rating for this generator for natural gas is 75 amps. According to 445.13 115% of 75 amps is 86.25 amps. Since # 2 SER has a rating 90 amps is adequate for my application. Out of over 100 installations we have completed in the State of New Jersey with the Kohler 20 KW generator I have never had a problem passing electrical inspection. Unfortunately I have had one issue with an electrical inspector who has failed my installation because of the use of the # 2 SER wire from the generator to the transfer switch. I have provided him with a total load calculation for this particular house with the use of a Kohler Load Controll module which sheds 2 AC loads, 30 amp 240 volt oven, and a 30 amp hot water heater. The inherent design of the generator and the use of the load control module prevents and loads above 75 amps. Also does the exception in this article also dictate that the rating of the wire can be rated for 75 amps? Ralph Somma , Current Electric Of Colts Neck LLC. 732 539 1987, currentelectriccn@gmail.com

Because the generator has a breaker built in it is the first distribution device so 445.13 is out of the window. It doesn't apply. Now the debate. There are some that have used and had accepted the #2 based on table 310.15(B)(7). But there are those that will go with the wiring must be sized to the OCD which would be #3Cu or # 1Al

 

[Gaffen99]

Ralph, I have done the same install. I read it the same way, size the wire to the nameplate. The generator OCP is based on the next available size breaker from the manufacturer. Ask him to cite article for failure, and cite your own reasoning. Sometimes the AHJ just needs a different perspective. Welcome to the forum, good luck.

 

[Gaffen99]

Would this be considered a feeder to apply 310-15 (b) 7?

 

[currentelectric]

residential generators

residential generators

So what is the intent of article 445.13 and the exception of 445.13. Article 445.1 identifies the scope for this article as the installation guidelines. Can anyone explain the purpose of article 445.13?

 

[Gaffen99]

I have seen some larger generators that don't have a OCD on the unit itself. I think that is the real purpose of the article.

 

[ceb58]

Ralph, I have done the same install. I read it the same way, size the wire to the nameplate. The generator OCP is based on the next available size breaker from the manufacturer. Ask him to cite article for failure, and cite your own reasoning. Sometimes the AHJ just needs a different perspective. Welcome to the forum, good luck.

You have failed to insert the word "standard". This is why Generac had to change their breakers from 100 back to 90 on the 20Kw units. Their pre wired whips contained #4Cu for the feeders. They tried to use 240.4(B). However, #4Cu is rated at 85 amps. The next standard OCD, as listed in 240.6, is 90 amps. So it was better to drop the breaker size than increase the wire size. Since the generator has a breaker installed 445.13 is a moot point because it is referring to the conductors between the generator and the first distribution device, which would be the breaker. I personally go with 240.4 and size the wire to the breaker size.

 

[iwire]

Would this be considered a feeder to apply 310-15 (b) 7?

It could apply only if the feeder carries the entire dwelling unit load.

 

[iwire]

So what is the intent of article 445.13 and the exception of 445.13. Article 445.1 identifies the scope for this article as the installation guidelines. Can anyone explain the purpose of article 445.13?

I have seen some larger generators that don't have a OCD on the unit itself. I think that is the real purpose of the article.

I agree.

 

[GoldDigger]

It could apply only if the feeder carries the entire dwelling unit load.

And this is not true because some loads are cut off by the load shedding relays?
While the generator is supplying the house, it is the sole supplier of power to the dwelling, and to all of the loads which factor into the calculated load of the house during that time.
Or would you assert that the POCO service wires also no longer supply the entire load of the house because the generator is sometimes used?

Tapatalk!

 

[augie47]

I would have to side with Iwire on this.
The provisions of 310.15(B)(6) take into account the load diversity of a complete residence thus the wording "all loads associated with the dwelling". If the generator supplies the entire house then I can see the Table applying, however, when your cherry-pick loads by a separate panel or load shedding you no longer have the "whole house diversity".
As with most Code things we discuss, we have opinions. Mine is the same as his.
Bob may not take offense at "this is not true", but I think an "IMO" would definitely be in order.
More importantly will be the opinion the OPs inspector has.

 

[HackElectric]

I love it. Back when you could put the whole house on an automatic generator you could use the smaller conductor. Now, you take that same house and shed many of the loads and you need a bigger conductor. Silly NEC.

 

[iwire]

I love it. Back when you could put the whole house on an automatic generator you could use the smaller conductor. Now, you take that same house and shed many of the loads and you need a bigger conductor. Silly NEC.

Only if the installer is just as silly.

If you shed just one or two small circuits you might in fact have to use a larger conductor.

But most people will shed some large loads like HVAC etc and in that case you would be using a smaller conductor as the load has dropped.

The real silliness is the fact that reduced conductor size situation even exists, just fix the service calculations and do away with the special table. (They have made changes in 2014 but the result is the same)

 

[HackElectric]

Only if the installer is just as silly.

If you shed just one or two small circuits you might in fact have to use a larger conductor.

But most people will shed some large loads like HVAC etc and in that case you would be using a smaller conductor as the load has dropped.

I don't see how you would use a smaller conductor, you size the conductor to the breaker on the generator.

 

[GoldDigger]

I don't see how you would use a smaller conductor, you size the conductor to the breaker on the generator.

Yes, you can size it according to the size of the generator breaker. But the question is which table you use to do that.


Tapatalk!

 

[iwire]

I don't see how you would use a smaller conductor, you size the conductor to the breaker on the generator.

You would be load shedding so you could use a smaller generator than you would have needed for the entire service.

 

[HackElectric]

You would be load shedding so you could use a smaller generator than you would have needed for the entire service.

No one was sizing the generator to the entire service.

In my experience, people weren?t using those extraneous loads when sizing the generator pre-2008, they were choosing the same size generator that they would choose today (enough to power what they want without worrying about the other stuff like HVAC or other large appliances). Heck, AFAIK, that?s the exact reason for the 2008 change requiring auto standby generators to be sized to the connected load.

In the end, the customer chooses the same 20kW generator today as he would have 7 years ago. The difference is that we have to use a larger conductor even tho we are decreasing the load connected to it.

Silly NEC.

 

[iwire]

No one was sizing the generator to the entire service.

In my experience, people weren?t using those extraneous loads when sizing the generator pre-2008, they were choosing the same size generator that they would choose today (enough to power what they want without worrying about the other stuff like HVAC or other large appliances). Heck, AFAIK, that?s the exact reason for the 2008 change requiring auto standby generators to be sized to the connected load.

In the end, the customer chooses the same 20kW generator today as he would have 7 years ago. The difference is that we have to use a larger conductor even tho we are decreasing the load connected to it.

Silly NEC.

I have no idea what kind of bull you are trying to sling. :lol:

If you are load shedding it is to use a smaller generator.

The rule has not changed for many many code cycles, the only thing that changed was the wording as many people where misunderstanding the rule.

 

[HackElectric]

I have no idea what kind of bull you are trying to sling. :lol:

I'm not trying to "sling any bull" and I'd appreciate you not trying to bring it down to that level.

If you are load shedding it is to use a smaller generator.

That's simply not true in all cases, especially when it comes to "residential generators" as we are discussing in this thread.

Much of today's load shedding in the application of this thread is for the purpose of adhering to the NEC. That's it, that's the only reason why we do it.

Before the 2008 code which required the generator to be sized to the connected load, load shedding was very rarely used. Certainly not to the extent it is used today. It was an expense that was added because the code required it.

As I mentioned, people bought the same smaller generator back then that they would buy today, they simply wouldn't turn the larger loads on. The fact that so many people bought smaller generators that couldn't handle the connected load is the reason why the 2008 code changed to require load shedding if the whole house was too much of a load for the generator.

The rule has not changed for many many code cycles, the only thing that changed was the wording as many people where misunderstanding the rule.

I don't know what you are saying here, but before the 2008 NEC a customer would decide they want a (for example) 20kW generator for their purpose and have it connected to their house that had a calculated load of let's say 120A. The code allowed that. When the 2008 came around, that same customer would ask for a 20kW generator to be installed, but they would have to pay for load shedding in order to bring the connected load down to under 83A, what the generator could supply.

Back to the subject, in the past when there was 120A connected load, you could use the smaller conductor. But if you load shed so there is only 83A or less, now you have to use a larger conductor.

 

[ceb58]

As I mentioned, people bought the same smaller generator back then that they would buy today, they simply wouldn't turn the larger loads on. The fact that so many people bought smaller generators that couldn't handle the connected load is the reason why the 2008 code changed to require load shedding if the whole house was too much of a load for the generator.

This was part of the reason the code was changed in the 2008 cycle. The other reason, and I'm too lazy to post the ROP, was installers were selling units to customer that were too small for the system. When the stand by system was needed it would trip out leaving them to figure out what was going on IF they were home. One of the proposals came from an inspector who ran into this type situation with a family who had medical needs. Then you have, if you can believe it, customers that were too cheep to have the properly sized unit installed. Then complain when the generator trips out leaving them in the dark.