disconnect for a generator

[Energy-Miser]

35 kw generator, 200 amp auto transfer switch, 800 amp service. Per NEC, does the feed coming to the transfer switch from the CT cabinet have to go through a disconnect? I get contradictory advice from different people who are involved in the project. Thanks,

 

[suemarkp]

I take it the CT cabinet is the utility service. If so, is your ATS stamped "Suitable for use as Service Equipment"?

Does the ATS have built in fuses or breakers, or if not is it connected to an immediately adjacent main disconnect breaker/fuse of 200A rating or less?

Does your install meet exceptions 1,2,3,4 or 5 of 230.40? Are all the disconnects compliant with 230.71?

 

[LarryFine]

Per NEC, does the feed coming to the transfer switch from the CT cabinet have to go through a disconnect?

Simple answer: yes.

I sure hope you're not attempting to supply the entire 800a service through the 200a T/S.

 

[bigsid]

35 kw generator, 200 amp auto transfer switch, 800 amp service. Per NEC, does the feed coming to the transfer switch from the CT cabinet have to go through a disconnect? I get contradictory advice from different people who are involved in the project. Thanks,

Don't try and feed the whole building with that generator because, the rated amps should be about 121amps for 120/208volts or 52amps for 277/480volts and 60amps for 240/416volts 3 phase. But, yes it has to go thru a disconnect.

 

[iwire]

Simple answer: yes.

I have to disagree here Larry

But, yes it has to go thru a disconnect.

As well as here.

IF the transfer switch is in fact 'Service Rated' no other disconnecting means is required.

As far as the loading that is a problem.

 

[nakulak]

If the transfer switch was rated 800 I think it would be ok, but since its a 200A transfer switch I would assume that the equipment was not listed to handle the maximum fault current, and therefore it would seem to me that this would require a 200A fused disco prior to the ATS ? (230.82 5 says its ok to have the ATS ahead of service disconnecting means if listed as service equip (as pointed out above), but it must "be installed in accordance with requirements for service entrance conductors" - 230.42 A - max current of busways shall be the value for which the busway was rated")

 

[iwire]

I think we are saying the same things in different ways.

If he intends to run the entire buildings load through a 200 amp switch there are many issues.

But let me suggest this.

If he intends to tap the 800 service disconnect on the load side then an overcurrent device will be needed.

If he intends to tap the 800 service disconnect on the line side then an overcurrent device will be not be needed.

However the transfer switch would have to be service rated and of course have a fault current rating that would exceed the available current.

Without more input from Energy-Miser we are just guessing.

 

[LarryFine]

Simple answer: yes.

I have to disagree here Larry

But, yes it has to go thru a disconnect.

As well as here.

IF the transfer switch is in fact 'Service Rated' no other disconnecting means is required.

I can't be sure I speak for Sid, but I believe I do . . .

I included a service-rated T/S in my use of the word disconnect. After all, the first terminals the line conductors land on in such as T/S would, in fact, be the service disconnect.

So, I stand by my simple yes. A complicated yes would have included the compliant options.

 

[iwire]

I included a service-rated T/S in my use of the word disconnect. After all, the first terminals the line conductors land on in such as T/S would, in fact, be the service disconnect.

As true as that is your 'yes' answer was IMO misleading.

 

[Energy-Miser]

Sorry should have been more clear

Sorry should have been more clear

Simple answer: yes.

I sure hope you're not attempting to supply the entire 800a service through the 200a T/S.

No, of course not. The generator will be feeding a 200 amp panel box for the selected load throughout the house. Energy-Miser.

 

[Energy-Miser]

I have to disagree here Larry



As well as here.

IF the transfer switch is in fact 'Service Rated' no other disconnecting means is required.

As far as the loading that is a problem.

Thanks for your response. I will have to check and see if the 200 amp T/S is service rated or not. I must mention that there is a 150 amp disconnect on the generator itself, but that probably does not make any difference regarding my original quesion.

 

[Energy-Miser]

Well, let's see...

Well, let's see...

Thank you for your responses. To clarify some of the issues, yes the CT is a utility cabinet and no the generator is not configured to supply the whole house, only to supply one of the four 200 amp panels in the house (two other are subpanels fed through 200 amp disocnnects each, and the third one is a 200 amp main disconnect panel).

 

[Energy-Miser]

A couple of things

A couple of things

I take it the CT cabinet is the utility service. If so, is your ATS stamped "Suitable for use as Service Equipment"?

Does the ATS have built in fuses or breakers, or if not is it connected to an immediately adjacent main disconnect breaker/fuse of 200A rating or less?

Does your install meet exceptions 1,2,3,4 or 5 of 230.40? Are all the disconnects compliant with 230.71?

Thanks suemarkp. The CT cabinet is the utility service, and I will need to look into whether the ATS is stamped with "Suitable for use as Service Equipment". It seems there might be a place inside it to install special disconnect breaker, once your remove the cover, but I can't be sure. It is a Caterpillar Geneartor/ATS unit, and I will mention its model number and include a picture of it next chance I have. There is a 2 pole 150 amp breaker on the generator itself, but of course that protects the generator leg and not the utility leg, which may become an inpection issue for us if not addressed. Thanks again, Energy-Miser.

 

[Energy-Miser]

Whole house??

Whole house??

Don't try and feed the whole building with that generator because, the rated amps should be about 121amps for 120/208volts or 52amps for 277/480volts and 60amps for 240/416volts 3 phase. But, yes it has to go thru a disconnect.

No, just a 200 amp panel, feeding selected loads. Energy-Miser.

 

[Energy-Miser]

I sure hope...

I sure hope...

I have to disagree here Larry



As well as here.

IF the transfer switch is in fact 'Service Rated' no other disconnecting means is required.

As far as the loading that is a problem.

Thanks IWIRE, your comments are encouraging. I sure hope that it is service rated, I will find out next time I am on that job site. That would sure solve my headache of inserting a disconnect (the connection from CT cabinet to the T/S is already made, through PVC piping and very little clearance to insert a disconnect the way the layout is, but we probably can work it in if it comes to that). E-M.

 

[Energy-Miser]

I will have more inforamtion on the T/S next time I log on, and hopefully some of the questions raised here will be answered. e/m.

 

[Energy-Miser]

I have to disagree here Larry



As well as here.

IF the transfer switch is in fact 'Service Rated' no other disconnecting means is required.

As far as the loading that is a problem.

We could not find a label saying that the ATS is service rated. But I thougth I will post its picture, maybe somone has worked with it before and will recognize it.

 

[LarryFine]

Nope, it's not. There's no disconnect mechanism ahead of the transfer switch itself.

 

[iwire]

Nope, it's not.

I agree.

Part of the service rating is externally operable manual controls to open both sources simultaneously.

 

[Energy-Miser]

Nope, it's not. There's no disconnect mechanism ahead of the transfer switch itself.

Thanks. I was hoping that you could point out that perhaps there is a place inside where a CB could be installed to work as a disconnect, but I guess that is not the case. Thank you for your reply. e/m