generators

[amge]

i have a job to wire a 45kw generator with a auto transfer switch. the home is going to be upgrated to 300 amps. can i use an ats that is rated for 300 amps for the service disconnect because the meter pan can be located on adjacent wall or do i need to put a main disconnect in. can 45 kw be used to supply a home with a 300 amp service.

 

[bphgravity]

If the ATS is listed as suitable for use as service equipment, it can be used as the service disconnecting means. You are still required to provide overcurrent protection if not integral to the ATS.

The total calculated load as determined by Article 220 cannot exceed the rating of the generator. So in this case, a 45kW generator can be connected as the optional standby system for a 300A service if the load of the house does not exceed 185A or so.

 

[hillbilly]

i have a job to wire a 45kw generator with a auto transfer switch. the home is going to be upgrated to 300 amps. can i use an ats that is rated for 300 amps for the service disconnect because the meter pan can be located on adjacent wall or do i need to put a main disconnect in. can 45 kw be used to supply a home with a 300 amp service.

1... Is the transfer switch you speak of rated for use as service equipment and does it meet the requirements of Article 230? More specifically 230.70, 230.74,75,76 & 77 and 230.90,91,92 & 94? (2005 NEC)

2.... (IMO) You can use whatever size generator that you want. Will a 45KW generator supply a 300A service? Do you mean will it provide power to all of the connected loads? Maybe, maybe not. That depends on the number and size of the connected loads that will (or can) operate at the same time.

No offense ..but...Have you ever done a generator and ATS (or MTS)installation?

steve

 

[tlaidman]

Most ats will have dry contacts that can be used to disable AC systems to lower the house load so as not to overload the generator

 

[sceepe]

Most ats will have dry contacts that can be used to disable AC systems to lower the house load so as not to overload the generator

I'll betcha that the folks dishing out the big bucks for the 45 kw gen set and ats are planning on running the A/C when the power goes out. This does not sound like a set up for the "camp out aroud the fireplace crowd".

sorry for the B.S. post that really didn't help to answer your question, But I needed one more post to get to 200. Now I can get my gold star from Mr. Holt .

 

[iwire]

The total calculated load as determined by Article 220 cannot exceed the rating of the generator. So in this case, a 45kW generator can be connected as the optional standby system for a 300A service if the load of the house does not exceed 185A or so.

Byran I disagree with you here.

An optional standby system does not have to have the capacity to run all the load it is wired to.

702.5 relieves us of that burden.

If the homeowner tells us they only intend to operate 45 KW or less of equipment at any one time than a 45 KW is fine.

It is typical for optional standby by generators to be much smaller than the load that could be applied to them.

The owner gets to select what is running.

Think of all the 200 amp panels that sell with an interlocked 30 or 60 amp generator breaker.

Personally I think it would be out of line for the NEC to require a larger than needed 'optional' generator based on Article 220.

 

[bphgravity]

Bob, I generally agree. We are not mandating the size or rating of a generator that would be required for an optional standby system. However, we do not feel that an automatic transfer switch allows the "user" to select the loads to be served. If a whole house automatic transfer switch is installed, we conclude the user has selected all the loads of the home to be served. In this case, we request a load calculation not exceeding the rating of the generator output. As you are fully aware, a decent sized home has a relatively small calculated load as compared to the size of the typically installed service.

We are permitting certain loads to be eliminated from the calculation such as the 5kW for the dryer, and the typical 8kW for a range. The user must be aware that operating these loads may exceed the rating of the generator if use din conjunction with other house loads.

This issue has been discussed to death here in Florida and this is the general compromise as determined by a joint effort of the IAEI and BOAF.

 

[DGrant041]

We are permitting certain loads to be eliminated from the calculation such as the 5kW for the dryer, and the typical 8kW for a range. The user must be aware that operating these loads may exceed the rating of the generator if use din conjunction with other house loads.

As long as the HO is aware of the cost-to-limitation ratio, it's all good. My mom found out after the fact that you shouldn't run the electric dryer on the generator. But she know's now.

 

[LarryFine]

To me, the biggest concern here is loads that are automatic. What happens in the peak of cooling (or heating, with heat-pumps) season, nobody is home, and the power goes out?

An interlock interrupting the 24v relay control wire is needed. It would be easy to wire with any ATS that has auxilliary contacts, and a manual bypass could be added for tended use.

 

[bphgravity]

Yes Larry, that is the basis of our concerns. I have discussed this very issue with Tarry Baker from the Broward County Board of Rules and Appeals whom also sits on CMP 13 and 20. Our generator installation guidelines and requirements are right in line with his interpretation of Article 702 provisions.

 

[LarryFine]

Our generator installation guidelines and requirements are right in line with his interpretation of Article 702 provisions.

Does that mean every generator must be sized to support HVAC as well as all other non-supervised loads? Or will they allow load shedding as I described?

 

[iwire]

However, we do not feel that an automatic transfer switch allows the "user" to select the loads to be served. If a whole house automatic transfer switch is installed, we conclude the user has selected all the loads of the home to be served.............This issue has been discussed to death here in Florida and this is the general compromise as determined by a joint effort of the IAEI and BOAF.

Respectfully I do not feel that is in line with the NECs intent.

Perhaps you should say in FL that is the requirement?

I see no safety issue (electrical safety hazard 90.2) in an overloaded optional standby generator.

If the CMP really feels that way IMO they should change the wording in 702.5

IMO it is a design issue not a code one.

JMO,

 

[bphgravity]

Again, I agree with you Bob. One thing that I have and am still learning about building construction enforcement is that "consumer protection" has multiple levels. Not all statues and laws created are for the physical safety and welfare of the public and their property. Some things are meant to protect person’s form being deceived or victims of fraud by contractors misrepresenting their services or products.

It would be nice if lines were bold and distinct, but this is not the case.