Automatic Transfer Switch - Art 702

[Pierre C Belarge]

The contractor has installed a 15Kva generator. He has also installed a 200 amp overhead 120/240 volt service to the house. He has installed a service rated automatic transfer switch which is also rated at 200 amps.



Question:

Is this a permitted installation?
a) code wise?
b) 110.3(B) -manufacturer's requirements for the generator to be sized for automatic transfer switche to the load?

Is the generator sized properly?

 

[iwire]

Question:

Is this a permitted installation?
a) code wise?

Yes 702.5

b) 110.3(B) -manufacturer's requirements for the generator to be sized for automatic transfer switche to the load?

Need more info I don' t understand what you mean.

Is the generator sized properly?

Sure if the customer is happy, again 702.5.

 

[Pierre C Belarge]

Bob
For a manual transfer switch, I agree with you.

For an automatic transfer switch, I am not so sure.
" Shall have adequate capacity and rating for the supply of all equipment intended to be operated at one time."

With a manual transfer switch, that is controllable regardless of the load connected.

With an automatic switch, the power loss will close the switch for the generator and who knows what load will be available at that moment... especially when no one is available when it occurs.

Take a look at the proposed changes for the '08 code and the substantiations written there.
Page 782-783 in the ROP.

 

[George Stolz]

With an automatic switch, the power loss will close the switch for the generator and who knows what load will be available at that moment... especially when no one is available when it occurs.

Take a look at the proposed changes for the '08 code and the substantiations written there.
Page 782-783 in the ROP.

For the cheap seats:

TCC Action: It was the action of the Technical Correlating Committee that further consideration be given to the comment expressed in the voting and ?with a or b? should be revised to read ?with (a) or (b)?. The Technical Correlating Committee directs that the Action on this Proposal be rewritten to comply with 4.1.1 of the NEC Style Manual.
These actions will be considered by the Panel as a Public Comment.
Submitter: Jim Pauley, Square D Company
Recommendation: Revise NEC 702.5 as shown below.
702.5 Capacity and Rating.
(A) Available Short Circuit Current. Optional standby system equipment shall be suitable for the maximum available fault short-circuit current at its terminals.
(B) System Capacity. The calculations of load on the standby source shall be made in accordance with Article 220 of by another method that is acceptable to the authority having jurisdiction.
(1) Manual Transfer Equipment. Where manual transfer equipment is used an optional standby system shall have adequate capacity and rating for the supply of all equipment intended to be operated at one time. The user of the optional standby system shall be permitted to select the load connected to the system.
(2) Automatic Transfer Equipment. Where automatic transfer equipment is used, an optional standby system comply with a or b.
(a) Full Load. The standby source shall be capable of supplying the full load that is transferred by the automatic transfer equipment.
(b) Load Management. Where a system is employed that will automatically manage the connected load, the standby source shall have a capacity sufficient to supply the maximum load that will be connected by the load management system.

This reeks to me of a design issue.

Generators are protected against overcurrent, right? What is the safety danger from an optional generator kicking out due to poor design?

Smells like a Square-D sales proposal to me, JMO.

 

[iwire]

This reeks to me of a design issue.

Generators are protected against over current, right? What is the safety danger from an optional generator kicking out due to poor design?

Smells like a Square-D sales proposal to me, JMO.

I agree completely.

Any general purpose receptacle circuit can be overloaded and rely on an OCP to open to prevent damage.

In the case of a generator it protected against dangerous overheating by the breaker on it.

Forcing a generator to be sized per the NEC load calcs is IMO ridiculous.

The records the utility keeps prove that the NEC calcs are extremely Conservative which under normal circumstances is reasonable. Under utility failure the homeowner should be able to do whatever they want as long as proper over current protection is provided.

 

[cwsolo]

Depends, if the customer in out of town... what loads will go on that could potentially overload the generator?
1. the heat if electric or A/C
2. the refrigerator
3. the water heater
so if the heat is electric what we are required to do here is install a relay and run the heat portion of the thermostat wire through a normally closed contact that opens when the generator starts up,
if the customer if presumed to be at home and decides to manually overload the generator with other branch circuit loads or a dryer... how would this situation be any different than the customer overloading a manual tx switch?
the generator breaker tripping or manual tx switch breaker tripping equates to the same thing if the customer is home.
I don't see a problem as long as the thermostatically controlled loads do not overload the generator

 

[acrwc10]

two things I see here. most obvious 08' preposed changes are not yet code.
second having a 200 amp main means nothing to what load is actually in the house. I have seen lots of 200 amp panels on houses that could have had less then 100 amp mains,all gas appliances, minimal lighting loads. Thats the same logic as " there are 42-20amp breakers in the panel shouldn't it be a 800 amp panel?" Mabe the house has no large loads in it. With out all the load information the question is ambiguous, How long is a piece of string?No right or wrong answer. I would have seperated the "critical load" out into its own panel and only powered that from the ATS , not right not wrong.

 

[LarryFine]

Simplistically speaking, it's easy to use a T/S's aux. contacts to interrupt heat and AC 24v control lines. One of my jobs, we're going to use this method to eliminate problems when power is lost, especially when nobody is home, along with a bypass for when the occupant returns home and can do manual load shedding.

 

[tbonse]

Pierre,

I looked back over 702.5 and I feel a need to elaborate on Iwire's answer.

First if you are connecting the ATS before the main panel (either as or just after the main disconnect), with the entire house load after the ATS, then IMO you would be in violation of 702.5, unless the house uses less than 15kVA at all times. The chances of a structure with a 200A (48kVA on a 120/240 system) service only ever requiring 15kVA is extreemely low.

If instead you are connecting the ATS off of a supply from the main panel and then supplying a sub-panel where you have calculated the maximum load to be less than or equal to what can be supplied by the generator, then I would say that you are fully compliant.

 

[Pierre C Belarge]

My understanding of the rating of generators to the load they supply is an important issue with the manufacturer of the generator... not just SqD, but all manufacturers.
The overcurrent device is to protect the conductors that are on the load side of it.
Again my understanding from the manufacturers is that the overload can damage the generator...I am not exactly sure of the reason, this is what they say.
This is the reason for the proposal for the change in the '08.

This is also the reason for my original question. I have spoken with different manufacturers.

The automatic transfer switch in this case is also the service disconnecting means. The overcurrent device within it supplies the main house panel. (I would take an educated guess that the load to this house is about 100 - 115 amps during the summer...the summer is generally the larger demand times around here...remember the generator is 50 amps)

I have inspected the house this past Friday. I spoke with the contractor, and he is not connecting to the generator yet, as he is awaiting my decision.
I am trying to be as fair and correct in this matter as I can.
This is the real reason this forum has been set up. I am not looking for arguments, I am looking for what may be the correct answer.
The wording in 702.5 may not be properly worded at the moment, and hence the change to the '08.

This is a Generac generator, I will try and contact them this weekend as well.

Lets not get mad at what a homeowner's freedom of rights are here, that is not my goal... to take someones freedom of rights away... if that was so, I would have had the contractor change it and not made this a public situation.


One other question.
Why install an service rated, automatic transfer switch rated 200 amps supplying a panel with a chance to carry 100 amps in the summer and then install a 50 amp rated generator.

One other tidbit of info: this area has been losing power a lot lately, usually during the time of summer when the loads to the house/building is at its greatest... isn't this when this generator would be needed the most?

 

[iwire]

Well based on the current wording of the NEC, and the changes coming, the installation you are asking about is at this time complaint and will not be in the future.

If it is not compliant at this time than there would be no push from the manufactures for the change.

Now back to rant mode.

I sure would like to see some evidence to back up the claim a generator is not protected by the OCP provided on it.

I also would like to see some evidence of the current rules creating a dangerous conditions.

In other words can the manufactures provide any references to fires that have occurred?

And if the breaker does not protect the generator from overload why are they still willing to allow the manual selecting of loads buy the homeowner?

Without a doubt some homeowners will manually apply loads to the generator until the breaker trips.

I truly believe this is all about increasing sales of larger power plants.

 

[iwire]

One other tidbit of info: this area has been losing power a lot lately, usually during the time of summer when the loads to the house/building is at its greatest... isn't this when this generator would be needed the most?

A 702 generator is never "needed" it is an option.

Please consider what optional means, I am not being a smart ... I am serious.

If the homeowner wants to go cheap and that results in the power dropping out so be it.

 

[Pierre C Belarge]

You are correct in the fact that it is "optional", I never have disputed this.

What I am saying is two fold.
1. the customer depends on the contractor's knowledge to install a product that will work.

2. Not all optional standbys are installed in homes, some are for businesses and they do in some way depend on the optional standby to help keep them up and running... again falling back to they depend on the contractor to install a product that works as explained to them.


Now, back to my question.

Is it a proper/code installation to install a smaller rated generator than the load anticipated for an automatic transfer switch?

 

[iwire]

You are correct in the fact that it is "optional", I never have disputed this.

What I am saying is two fold.
1. the customer depends on the contractor's knowledge to install a product that will work.

2. Not all optional standbys are installed in homes, some are for businesses and they do in some way depend on the optional standby to help keep them up and running... again falling back to they depend on the contractor to install a product that works as explained to them.

all of the above is a design decision.

Of course, without a doubt I would communicate the problems to the customer and I would try to up sell the job to a high quality installation.

Now, back to my question.

Is it a proper/code installation to install a smaller rated generator than the load anticipated for an automatic transfer switch?

IMO yes it currently a NEC code complaint installation to use a smaller generator than the anticipated load connected to it.

If it was not we would not see the push for the change that is coming.

You do realize that if the change occurs in the NEC I will follow it as required but I will never agree that an optional generator should be sized per article 220.

My own home has a 100 amp 120/240 service or 24 KW.

Now for reasons of curiosity I ran everything in the house at the same time..window ACs, electric range, stove top, dryer lights, electronics, oil burner etc.

With all that on I had about 45 amps per leg at the meter using my true RMS Fluke 36 meter.

It is inconceivable to me that I if I chose to install a generator at all that the NEC would require me to buy a 24 KW or greater unit when it is not possible for the load to exceed 11 KW and that 11 KW is if I run everything at once.

Pierre can I ask you to address the safety difference in a generator being overloaded manually as compared to automatically?

Because the way this change is worded it appears the manufacturers believe there is a difference.

 

[George Stolz]

Is it a proper/code installation to install a smaller rated generator than the load anticipated for an automatic transfer switch?

Well, let's forget the 2008 for a moment and focus on the 2005. What may or may not happen in the next code cycle doesn't help you on the job you're inspecting next week. If you happen to be on the 2002 where you're at, same difference in this case.

702.5 Capacity and Rating. An optional standby system shall have adequate capacity and rating for the supply of all equipment intended to be operated at one time. Optional standby system equipment shall be suitable for the maximum available fault current at its terminals. The user of the optional standby system shall be permitted to select the load connected to the system.

The first sentence makes a case for your idea that an absent user would constitute a violation of the section. If the user is not present, then they would not be able to select the load connected manually.

However, does a user have to be present to select the load? How does the user select the load? By shutting off branch circuit breakers, or unplugging equipment, or switching equipment off at their disconnects.

Does a user have to be present to do this? No. They can select the load before they leave every day. When they return, they can turn the loads they didn't select back on. Is it a laughable design? Sure. Is it safe? I think so.

This is an optional system, for convenience to the user. The user can select how convenient they want it to be.

 

[iwire]

Nice points George.

Pierre I mean no offense what so ever here but IMHO it appears you want to use the NEC to regulate the 'quality' of an installation.

To me this is the same as people expecting a UL tag to ensure quality.

Neither the NECs or the NRTLs job is to regulate quality...only safety.

A optional generator shutting down due to to much applied load is not IMO a safety issue.

It may be a bad design but it is not unsafe assuming the rest of the NEC is applied.

 

[Pierre C Belarge]

Bob
You know how I feel about manufacturers using the NEC to sell their products. If anyone here was at the Eastern Sectional Meeting in Philadelphia, they heard my comments to that effect on Sunday when I got up in front of all the participants and expressed so at the microphone. So do not worry about that aspect of your post.


The safety concern I have is that the generator may be damaged by this type of setup. Again I say may as I am not 100% sure. I have spoken to some reps who say it can happen. I see the proposals for the '08 and not all of the proposals are by manufacturers.

Knowing what I now know (I did not know all of this 3 months ago), I am curious as to how this really should be installed.

In no means is what I am discussing taking any rights away from the homeowner.
This may, again I repeat may be an instance of where our industry has made installations in the past that were not necessarily correct and now has come to the forefront as many more of these types of installations are being made and the problems are coming up...I do not know the answer, otherwise I would not be asking the question.

 

[Pierre C Belarge]

Okay, from another angle.

If we can say for sure that the generator does get damaged from a load larger than it is designed to carry, would the example I have described be a code violation?

Remember now that 702.5 is broken down into three different sentences with three different meanings.


The user in my example has choosen for his whole house to be controlled by the transfer switch/generator. Should not the generator be sized to the calculated load of the house.
NOTE: a service size does not mean the load of the house is the same as the size of the overcurrent device protecting the service.

P.S. this is fun... it will be more fun if we can get to some sort of answer.

 

[peteo]

It seems, from an inspector's view, that the only issue would be whether the ATS is part of the 'system.' The 'user shall be permitted' means to me, that unless there's a local rule - the homeowner is the one who determines the sizing.

An undersized switch could suffer contact issues. If it's part of the 'system,' I agree with this article, (NFPA digest, June 2006,) that any liablility would be the homeowners. It seems that Broward County is the only exception, a jurisdiction which requires sizing to article 200 methods.

 

[LarryFine]

One other question.
Why install an service rated, automatic transfer switch rated 200 amps supplying a panel with a chance to carry 100 amps in the summer and then install a 50 amp rated generator.

Because the TS has to be sized for the current rating of whichever overcurrent device's current it will be switching, even if the generator is only 5Kw. If you want to use a 100a TS, it needs to be protected by a 100a device.