Generators

[comjos]

I just purchased a 5500W generator for my home. I have a double wide manufactured home with its own service pole and 200A disconnect on the pole then the service entrance is ran into the service panel inside the home. I know the code states that all the branch circuits fed by the generator are to be completely disconnected from the homes service. This is what I would like to do to connect my generator to my home.


I have an outbuilding that I ran a #10 - 120/240V feeder to which supplies a 100A distribution panel. This is a very small outbuilding with a freezer and refrigerator and a small air compressor.
I would like to connect my generator's 120/240-30A supply to a vacant 30A 2pole breaker in my outbuilding and backfeed the power to my house service panel. I would make certain that the main disconnect was turned off in the event of a power outage.

My biggest question is this. According to the code, would I have to disconnect the neutral and the current carrying conductors or would it be acceptable to only use the main breaker to isolate the utility companies service from my generator service?

 

[don_resqcapt19]

Re: Generators

I would like to connect my generator's 120/240-30A supply to a vacant 30A 2pole breaker in my outbuilding and backfeed the power to my house service panel. I would make certain that the main disconnect was turned off in the event of a power outage.

That would be a code violation. A transfer switch it required.

702.6 Transfer Equipment.
Transfer equipment shall be suitable for the intended use and designed and installed so as to prevent the inadvertent interconnection of normal and alternate sources of supply in any operation of the transfer equipment. Transfer equipment and electric power production systems installed to permit operation in parallel with the normal source shall meet the requirements of Article 705.
Transfer equipment, located on the load side of branch circuit protection, shall be permitted to contain supplementary overcurrent protection having an interrupting rating sufficient for the available fault current that the generator can deliver. The supplementary overcurrent protection devices shall be part of a listed transfer equipment.
Transfer equipment shall be required for all standby systems subject to the provisions of this article and for which an electric-utility supply is either the normal or standby source.

Don

[ September 05, 2005, 12:29 AM: Message edited by: don_resqcapt19 ]

 

[comjos]

Re: Generators

I expected this would be my answer but the cost of a transfer switch is almost half the cost of the generator. I certainly am not wanting an unsafe condition. I worked 15 years for a power company in KY as an Engineering Technician, I know how important it is not to backfeed the transformer's secondary. Some of the distribution lines have a 19,900 Volt primary instead of a 7200 Volt one.

Does the NEC actually state that you must open/isolate the nutral in this transfer switch? The secondary of the power company's transformer has the neutral bonded to the case of the transformer and then the case is grounded to the grounding conductor then to the grounding electrode at the pole.

Thanks for your help with this.

 

[don_resqcapt19]

Re: Generators

Opening the grounded conductor is a design issue and not a code issue, although it does have an impact on how the system is grounded. The use of a transfer switch for the ungrounded conductors is not an option...it is required. There is no requirement that this be an automatic transfer switch and there are ways to make this installation code compliant without spending a lot of money.
Don

 

[petersonra]

Re: Generators

Originally posted by comjos:
I expected this would be my answer but the cost of a transfer switch is almost half the cost of the generator. I certainly am not wanting an unsafe condition. I worked 15 years for a power company in KY as an Engineering Technician, I know how important it is not to backfeed the transformer's secondary. Some of the distribution lines have a 19,900 Volt primary instead of a 7200 Volt one.

Does the NEC actually state that you must open/isolate the nutral in this transfer switch? The secondary of the power company's transformer has the neutral bonded to the case of the transformer and then the case is grounded to the grounding conductor then to the grounding electrode at the pole.

Thanks for your help with this.

it really does not matter what the utility primary voltage is. you need some means of making sure you do not backfeed that does not involve human intervention.

the action of connecting your generator to your homes electrical system must also disconnect the utility from your house wiring.

you would feel really bad if you killed someone because you wanted to save a few bucks.

and don is right. you do not need an expensive ats. there are more cost effective ways to switch between your two power sources.

you may or may not need to switch the neutral.

best advise I can give you is be carefull of the other guy and do it right and keep him alive.

 

[pierre]

Re: Generators

Depending on your load the 10 AWG conductors may be inadequate.

You should thank these guys for quick and accurate info, and purchase the ATS, as there are relatively inexpensive units that you can purchase - do a google for one.

 

[comjos]

Re: Generators

Thanks for all of your inputs on this. I had previously done a search for a transfer switch and boy did I find a lot of different techniques. Almost everything I found was a DPDT switch or a non-interlocking breaker system. You answered my question above about the neutral being disconnected. Since the neutral carries the unballanced load, I thought their might be a problem with not disconnecting it but actually the reasoning is that the current returns to its source not necessarly to the grounding means.
As far as what I was saying about the primary voltage,if you backfeed the transformer you could inadvertently step up the primary side of the transformer to whatever the distribution live voltage is. VERY VERY?DANGEROUS

This is a great forum and I believe you guys sure do know what your talking about.

Thanks in advance for your help and I look forward to talking to you on other topics.