New 2008 requirements for whole house generators

[aelectricalman]

I was told by an EC from who im bidding againt that there is a new code for the install of Automatic transfere switches. He says that you can not just place an automatic transfere switch in line between the meter and a main for the purposes of having "Whole house capability". He said that you have to have a load shedding device to shed the power from the heavier load equipment. I cant find that in the code but maybe he was mistaken and/or confused. He said the reason has something to do with "when the utility power comes back on", its safe. I thought all those transfere switches id been buying was for that. What does load shed have to do with anything from a code standpoint?

 

[480sparky]

Just about everything in 702.5 has been changed. What you're asking about is in 702.5(B)(2)(a) and (b).

In short, it means you need a genny that can power the entire load the service can demand from it, or else automatically remove loads down to the point the genny can supply them adequately. In other words, you don't put a 5kw generator on a 400a service with an ATS.

 

[aelectricalman]

OK, I see

OK, I see

Yeah code can be a pain in the ass. I feel like the Main on the transfer switch should sufice as an overcurrent protection device. With that in mind, the homeowner would just use precaution and at worst case trip the main. I guess it boils down to not trusting a main to trip.

So by this method, either up the Generator size or use a loadshed Xfer switch.

 

[mikeames]

Yeah code can be a pain in the ass. I feel like the Main on the transfer switch should sufice as an overcurrent protection device. With that in mind, the homeowner would just use precaution and at worst case trip the main. I guess it boils down to not trusting a main to trip.

So by this method, either up the Generator size or use a loadshed Xfer switch.

No thats not the point. A 400 amp transfer switch with a main as you stated would not trip before a 5kw generator dies. The problem lies with an undersized generator.



Now I agree that the code does not make sense some times IMHO. For example if I have a house with a 400A service and I want to installa 400 a XFER switch fine. Now if I am the home owner why cant I hook a 5KW generator up to it????? If I use more than 5k of power THE MAIN IN THE GENERATOR SHOULD TRIP.
For residential applications I dont agree with the changes. For comercial I totally agree.

 

[augie47]

I have to say that to me the requirement is sensible. Note that in the case of manual transfer switches, the user can select the load connected to the system, so as I read it, if you wanted to install a 5 kw generator on a 400 amp service with a manual transfer switch it is still permissible. When transferring, the homeowner can turn off loads at their discretion.

With an automatic transfer, it does little good to transfer a load only to have the generator overload and stop. Proper selection of the load is vital in selecting a generator for automatic use and 702.5 just requires that to be done.

 

[hillbilly1]

With the automatic t-switches, I fully agree with the requirement of load shedding. If power is lost, and nobody is around to turn off loads, temporary undervoltage conditions could exsist until the generator shuts off or trips. The small residental units seem to take longer to shut down on an overload situation. As for the manual switches, loads are manually selected, and if the homeowner overloads the generator, it is their fault for being a DA.

 

[mikeames]

I have to say that to me the requirement is sensible. Note that in the case of manual transfer switches, the user can select the load connected to the system, so as I read it, if you wanted to install a 5 kw generator on a 400 amp service with a manual transfer switch it is still permissible. When transferring, the homeowner can turn off loads at their discretion.

With an automatic transfer, it does little good to transfer a load only to have the generator overload and stop. Proper selection of the load is vital in selecting a generator for automatic use and 702.5 just requires that to be done.

Good point I didn't think it through with the manual option.

 

[C3PO]

You could also consider adding a subpanel with the loads you want the generator to run and size the ATS and generator to handle just the subpanel.

 

[richxtlc]

Last year I had a 20kW whole house generator installed with a TOS. This inspector had the electrician install a disconnect device between the Gen and TOS and he had to install a CT for the central air conditioner. This CT was placed in the sensing circuit of the TOS and would prevent the air conditioner from coming on if the load on the gen was too high to allow the air conditioner to start.

 

[Power Tech]

Did somebody die for this to come into code?

I would like to audit the stock portfolio of the creators and yes voters on the code and see if they invested in the generator manufacturers.

 

[C3PO]

Did somebody die for this to come into code?

I would like to audit the stock portfolio of the creators and yes voters on the code and see if they invested in the generator manufacturers.

The change is really not a big deal. It would be a very poor installation if every time the ATS switched to generator that the gen main tripped. The code change has not effected the way I put in generators at all.

 

[480sparky]

Did somebody die for this to come into code?

I would like to audit the stock portfolio of the creators and yes voters on the code and see if they invested in the generator manufacturers.

Probably it was brought about by the number if installs where they gennies were far too small to carry the load if the utility drops out and the ATS fires up and switches over.

I've seen many installations where the electrician installing the generator basically thought, "Well, the unit has a breaker on the out put, so it cannot be overloaded."

But still, how do you justify installing something that will automatically be overloaded?

 

[partimer31]

Tos what?

Tos what?

20 Kw generator with a; TOS

I should know what, TOS stand for, but could someone please
refresh my memory.


THANKS

 

[mikeames]

It would be a very poor installation

I agree but the code is min. There are a lot of situations that would be poor but legal. I agree with the code but it goes against my view of the code. I see the code as a document that prevents unsafe work whith as little restriction as possible to allow for design consideration. Case in point is not having a maximum receptical count on a general purpose resi circuit. Someone could put 90 receps on one circuit and be legal. No a good idea but legal. Someone could very well put 90 receps in and load them all to 100% of the max circuit rating and it would be legal because it was installed as a general purpose circuit and abused after the fact.

I see the generator issue for Residential use the same way. Poor ides YES but why prohibit that and not change the recep issue? There just see to be others issues why was this singled out for no apparent safety reason. If I had to write it I would keep the code and add an exception for single family residential dwelings.

 

[skeshesh]

Code

Code

I see the code as a document that prevents unsafe work whith as little restriction as possible to allow for design consideration.

NEC 90.1 Purpose - (A) Practical Safeguarding The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.

I have to say that I agree with the change. Although the generator's OCPD will provide protection, it is well within the purpose of the code to provide guidelines to avoid overloading of the genset. This is a specific issue which does result in overload conditions frequently, whereas your example with the receptacles is a scenario that is both exaggerated and incorrectly used since no electrician would put anywhere close to 90 rec. on a circuit and general purpose receptacles ARE actually used in such a variety of applications that it's not very predictable. Finally the code has also allowed leeway for pragmatism since using a manual TS in a residence will allow for a range of practices.

 

[mikeames]

Thanks for the 90.1 reference but I have that book as well.

both exaggerated and incorrectly used since no electrician would put anywhere close to 90 rec

No kidding but still legal.

You missed to point of my post.

 

[skeshesh]

Didn't mean to offend Mike. I'm just saying that the changes to the section definitly do accomplish preventing "unsafe work whith as little restriction as possible to allow for design consideration", as you put it as well as accomplishing the code's purpose of protecting property (generator). I don't see not being able to use the ATS in certain situations in a residence as being a restriction on design. The changes accomplish the goal of addressing genset overloads in residentials which does happen decently often as opposed to the receptacle issue you bring up does not happen often enough to warrent a code change, IMO. So I don't see what point it is that I missed?

 

[aelectricalman]

Interesting questions

Interesting questions

Ok, I now understand the new code and understand the reasoning. I spoke to the inspector and determined that there were 2 options for using a whole house (200 amp) Automatic Transfer Switch (ATS) with a 20KW Generator. The first would be to by a load shedding ATS with a power manager (Price tag = $1500) or do a load calculation on the home to determine if you are below the peak load requirement with the load calculation. If you are a little above the requirement of 83.3Amps, say 100Amps, then use a power master style single circuit load shedder to help regulate individual items, so they will not come on until load fulfillment is met. This power master could be placed on 2 water heaters so that they alternate every so otfen and are not on at the same time. Another example would be a Range oven and clothes dryer on one power master. Once demand is met on one circuit, you can switch to use the other. My question I am deriving at is this. Can you place a load shedding device such as Generacs Power Master, on two heat strips of an emergency back up system so that both strips will never be on at the same time during generator usage. The custome has 2 60amp rated breakers in the panel for the heat strips. My assumption is that (and its not important to know exactly yet) each 60 amp breaker is pulling 10K max. With these tentative figures and not knowing the method of the madness is this the best way to do this or are there other ways to stop the 2nd and 3rd and 4th heat strip from coming on (Automatically) so that it resumes normal function when the power is restored. All of this without having to make a manual change to restore POCO power?

 

[augie47]

In my opinion, if you can get the Homeowner to agree, the easiest/least expensive solution would be to add a subpanel supplied by the transfer switch leaving certain non-essential heavy loads (such as one of the water heaters or one heat unit) in the main panel.
If the homeowner is not agreeable to loosing any loads, then your loadmaster would be my "plan B"

 

[Power Tech]

Probably it was brought about by the number if installs where they gennies were far too small to carry the load if the utility drops out and the ATS fires up and switches over.

I've seen many installations where the electrician installing the generator basically thought, "Well, the unit has a breaker on the out put, so it cannot be overloaded."

But still, how do you justify installing something that will automatically be overloaded?

Like this: The customer pays me. I tell them what they need. I do the load calc. and inform them in writing that there is an overload possibility.

They make the final decision.

They issue me a PO with a directive to do the work and that they are aware of the overload possibility. They will shut off all non critical loads in an outage.

The code assumes somebody is going to turn on the electric range, all the lights, and jump in the spa.

They give the public no credit for common sense.

I have not investigated the code, it just seems the Gov't is getting out of hand.

Let's face it. Laws are made with boxes of money.

I will now duck and cover.