backfeeding utility? okay/illegal/or just a bad idea?

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MIEngineer

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Hello All,

Is anyone aware of a code reference indicating that a transfer switch or some other means is required to prevent back-feeding of utility by way of a generator or renewable system (solar array or wind turbines)?

I ask because I was at a building equipped with solar modules and wind turbines. The output of the inverter was installed so that it would backfeed a panelboard through a breaker. In the same panelboard the utility feed was terminated on the main lugs of the MLO panel. The inverter has the capability to accept utility power but the system was not installed that way.

I understand that part of the interest in to backfeed the utility to make your meter spin "backwards." But this should only happen if there is utility voltage present.

Does this application differ from someone installing a generator directly into their main panel of their home?

I know the utility does not like this but is it a code violation or just a bad idea?

Thanks,
 
It is highly illegal and highly dangerous, code prohibition or not.

There are grid-tie inverters that automatically remove the output upon loss of utility power.

Otherwise, an automatic or manual transfer switch is required.
 
Here is your code art for a 690 install.

690.61 Loss of Interactive System Power.
An inverter or an ac module in an interactive solar photovoltaic system shall automatically de-energize its output to the connected electrical production and distribution network upon loss of voltage in that system and shall remain in that state until the electrical production and distribution network voltage has been restored.
A normally interactive solar photovoltaic system shall be permitted to operate as a stand-alone system to supply loads that have been disconnected from electrical production and distribution network sources.
Click to expand...

And the HB commentary that follows.

The requirement of 690.61 prevents energizing of otherwise de-energized system conductors or output conductors of other off-site sources (e.g., an electrical utility) and is intended to prevent electric shock. This feature normally is provided as part of the utility-interactive inverter.
Click to expand...
 
So your answer is, while there is no code requirement for a transfer switch, there is a code requirement for the alternate energy source to be disconnected from the utility upon loss of voltage on the utility side.

In some inverter systems, that is accomplished by the use of a DC contactor on the PV array input side that is held in by the utility power only. If the utility fails, the contactor coil drops out and isolates the power source. That is what makes it a "grid-tie" inverter, because it is only intended to be used to supplement utility power (and / or run the meter backwards). It cannot operate in "island mode" unless you add a transfer switch and change the circuitry inside (some have a simple selector switch to do that part of it).

So your observation may not be picking up the whole story. However, you are right to question it.
 
Could be that article 705 covers this matter.

ARTICLE 705 Interconnected Electric Power Production Sources
 
Jraef said:
So your answer is, while there is no code requirement for a transfer switch, there is a code requirement for the alternate energy source to be disconnected from the utility upon loss of voltage on the utility side.

In some inverter systems, that is accomplished by the use of a DC contactor on the PV array input side that is held in by the utility power only. If the utility fails, the contactor coil drops out and isolates the power source. That is what makes it a "grid-tie" inverter, because it is only intended to be used to supplement utility power (and / or run the meter backwards). It cannot operate in "island mode" unless you add a transfer switch and change the circuitry inside (some have a simple selector switch to do that part of it).

So your observation may not be picking up the whole story. However, you are right to question it.
Click to expand...


Thank you all for the prompt responses. There is a grid-tie inverter in place that has AC input, DC input and AC output. Everyone's responses go to solidify my limited understanding. The proper equipment is in place there is just a mis-application and/or wiring error.

The fact that transformer feed backwards is actually what brought light to this whole matter. Theis is a testing area working closely with the utility. There was a primary line fuse that opened due to storms. Before replacing it the utility lineman noticed there was volatge on the load side of the open fuse, hence the inquiry into the backfeeding.

I will press that this be replaced with everyone's input.

Thank you.
 
MIEngineer said:
There was a primary line fuse that opened due to storms. Before replacing it the utility lineman noticed there was volatge on the load side of the open fuse, hence the inquiry into the backfeeding
Click to expand...

That was a good catch. I often work around the POCO guys, and have yet to see one test a cut-out or fuse link for voltage before closing it.
 
chris kennedy said:
That was a good catch. I often work around the POCO guys, and have yet to see one test a cut-out or fuse link for voltage before closing it.
Click to expand...
Same here. I was at my mom's (near one end of a townhouse neighborhood) one evening, the power went out, and we heard a boom about 1 second later. We called the POCO, and I watched for the truck, which went to the other end of the property.

Naturally (:cool:), I went out there to watch/chat/help/annoy the guy. The cutout feeding the underground 1-phase line had blown and sprung. He used the hot-stick, brought down the tube, and replaced the link. Hung it back on, flipped it up, and BOOM!

Then, he went to look for the cause. It ended up being an unidentifiable animal gnawing on the termination of the MV cable in the last pad-mounted transformer, behind my mom's place. I held the lantern while he redid the termination. (I got to help. Yay! :D)

That fuse blowing when I was standing next to the truck was quite the chest-thumper. The flash was rather bright, too. It was fun talking about wiring and stuff while he worked. I wonder why we didn't hear the critter vaporize?
 
LarryFine said:
WHAT?!

I meant the first one, when the lights went out. The transformer is behind her building.
Click to expand...



Coorination did its job.

In using an extension stick to refuse a cutout we don't normally check for backfeeding voltage either. You are not exposed to the voltage at the end of the stick.
 
MIE,

One consequence of Back Feeding into the POCO system
is that in an emergency the lineman will pull the fuse and work on the system.
:smile:
If you backfeeding 120V ac, then the transformer will boost up to maybe 1200V
and that places 1200V back onto an "unfused" POCO line.
:mad:
You have violated the 'lock-out' concept and place the lineman in jeapardy.
:mad:

I am sure you will correct this situation. :smile:
 
Reminds me of a story I heard at a seminar about a hospital that had a co-generation plant that ran the entire hospital.

They convinced every electrical inspector that they didn't need seprate branches for emergency power that the NEC requires because they had a unique situation where the entire hospital was backed up by the co-gen plant.

One day the utility lost power. Something went wrong in the cogen controls, and for a few seconds, that cogen plant tried to backfeed every house, gas station, and walmart in the entire neighborhood.

Needless to say, the cogen plant suffered major damage, and they wound up having to evacuate the entire hospital.
 
MIEngineer said:
Hello All,

Is anyone aware of a code reference indicating that a transfer switch or some other means is required to prevent back-feeding of utility by way of a generator or renewable system (solar array or wind turbines)?

I ask because I was at a building equipped with solar modules and wind turbines. The output of the inverter was installed so that it would backfeed a panelboard through a breaker. In the same panelboard the utility feed was terminated on the main lugs of the MLO panel. The inverter has the capability to accept utility power but the system was not installed that way.

I understand that part of the interest in to backfeed the utility to make your meter spin "backwards." But this should only happen if there is utility voltage present.

Does this application differ from someone installing a generator directly into their main panel of their home?

I know the utility does not like this but is it a code violation or just a bad idea?

Thanks,
Click to expand...
usually the backfeeding from PV arrays or wind turbines is through a UL listed grid tie inverter. it senses whether utility power is present and only backfeeds then.

its not a bad idea nor is it a code violation. its not real cost effective.
 
glene77is said:
MIE,

One consequence of Back Feeding into the POCO system
is that in an emergency the lineman will pull the fuse and work on the system.
:smile:
If you backfeeding 120V ac, then the transformer will boost up to maybe 1200V
and that places 1200V back onto an "unfused" POCO line.
:mad:
You have violated the 'lock-out' concept and place the lineman in jeapardy.
:mad:

I am sure you will correct this situation. :smile:
Click to expand...


It appears as if all the correct equipment is in place just not wired properly. Luckily this building is in a testing set-up and at the moment every diconnect available is open. But yes, what you describe happened, the 120V backfeed energized the 4.8 kV line lighting up some nearby 277V parking lot lights.

I knew it was dangerous and not a bad idea and by reading the comments 690.61 is my citation for a code violation.
 
MIEngineer said:
Hello All,

Is anyone aware of a code reference indicating that a transfer switch or some other means is required to prevent back-feeding of utility by way of a generator or renewable system (solar array or wind turbines)?

I ask because I was at a building equipped with solar modules and wind turbines. The output of the inverter was installed so that it would backfeed a panelboard through a breaker. In the same panelboard the utility feed was terminated on the main lugs of the MLO panel. The inverter has the capability to accept utility power but the system was not installed that way.

I understand that part of the interest in to backfeed the utility to make your meter spin "backwards." But this should only happen if there is utility voltage present.

Does this application differ from someone installing a generator directly into their main panel of their home?

I know the utility does not like this but is it a code violation or just a bad idea?

Thanks,
Click to expand...
Utility has rules how these connections to be made. As I understand how it works is that the system is only allowed to feed onto the Utility line if the system is UP, in other words it can-not feed onto a dead line.
 
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