LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
"I don't think so, Tim!"
Especially if you ask the POCO. A pair of those do not make a proper interlocked transfer switch.
Panel lock out vs. tran. switch
- Thread starter masselectrician
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Especially if you ask the POCO. A pair of those do not make a proper interlocked transfer switch.
I agree, it wouldn't be much different than expecting a home owner to use their widow maker cord correctly.
Roger
stew
Senior Member
- Location
- federal way,washington
I was trying to find in the code where it says that the devices have to meet manufacturers approval but havent been able to find it. It may just be a WAC requirement in washington. Havent located my copy of WAC but I am quite sure we cant use the Interlockit here anymore if an inspection is done.
comjos
Member
- Location
- Pikeville KY
Does the code actually state that you "must" use a transfer switch for optional standby generator?
comjos
Member
- Location
- Pikeville KY
I was looking at the Exception
I think "temporary connection of a portable generator" is one key here. I think this is a permenant type generator - one that is hardwired.
Also, if you refer to the definition of "qualified" in the front of the NEC, a homeowner would not meet that definiton. I believe NFPA 70E also has more info on what constitutes a qualified or trained individual.
Also, in a residential setting, even if the homeowner was qualified (say he is an electrician) there wouldn't be any way to ensure other people don't operate the switch. For example, the house could be sold to someone else.
Also, Larry's comment is very true. It is the POCO's linemen that are in danger when someone connnects a generator without turning off the main.
Steve
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Plus, it's not only the 120/240v that's a danger. Many people still don't get that transformers work both ways. If you feed the secondary voltage back into a transformer's secondary, the full primary voltage will be developed.
Imagine being a lineman working on power restoration after a storm, and finding 19.9kv (or whatever) on the load side of a broken primary line . . . the hard way. It's not just a possibility; linemen have actually died from this.
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Yep, a grand total of one.
After Katrina a lineman died because the homeowner connected a suicide cord at exactly the wrong time. The lineman had grounded the source side of the line going down a street. He cut the overhead line to take out some slack and that's the moment the homeowner turned on the generator he just bought. Had the homeowner turned it on 5 minutes earlier or later the generator would have just been shorted by the lineman's grounding jumper.
This pales in comparison to the number of linemen killed by delta bank back feeds and linemen hit when another lineman pushes in a cutout elsewhere on the system.
comjos
Member
- Location
- Pikeville KY
I am definitely not endorsing a homeowner to use a lockout and back feed the home with a portable generator. I worked 15 years in the engineering department with AEP in both the distribution and transmission design and know what a serious issue this is to back feed a distribution transformer that once stepped down from 19,900 volts to 120/240, it can cause death. We grounded everything during restoration of a downed power line but there is a time when the jumpers come off to power-up the line. Usually this is done with hot sticks but it's just too unsafe for a back feed possibility. I believe the code added this exception for standby generators for service work (by a qualified electrician) considering all the power outages that have been occurring. I would be interested to know if, as an electrician, is this exception good. Also, since this lockout of the main breaker does not open the neutral what happens if a tree contacts the ungrounded distribution line and also touches the neutral. This could feed high voltage spikes to the generator and home.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Only one ever? You know that to be a fact? Are you suggesting the concern is unwarranted, or even overrated?
I've had customers insist I install outlets (not inlets) and a 2p breaker for generators, and without any interlock or transfer whatever.
Sorry, but "It was like that on my last house" or "I'll remember to turn off the main first" or "I'll tape a note to the panel door" just don't cut it for me.
Pretty solidly, yes. At least any time in the last several decades.
Unwarranted, no. Overrated absolutely. I'd like to see some consistency.
Utilities do far more dangerous things during storm recovery. The SOP for most utilities is to throw a new fuse wire into any down cutout they see to see if it will hold rather than patrolling the entire line. If Mr. homeowner is clearing down trees to get in/out of their house they get fried. If a lineman isn't grounded out properly they'll get fried.
I won't do it nor would I recommend it. It is called a "suicide cord" for a reason. It is way too easy to have live exposed terminals from mis-operation.
There is a reason OSHA says that the grounds are supposed to be on both sides of the work and they have to come off using sticks rated for the voltage. It is because many linemen have died during this stage.
Most often happens during storm recovery via one of several ways:
Two way feeds where a crew doesn't realize they are sending power into another work crew or where they sectionalize wrong.
Y-Delta banks (common on irrigation around here) where a live phase back feeds the "dead" phase. This one is insidious because a ground jumper won't blow any fuses. If the crew only grounds the upstream side and then later cuts the phase wire, the line can become live enough to be deadly.
Customer 480-208Y120 step down transformers. Many utilities have worked hard to banish Y-Delta banks because of problems with ferroresonance. But customers can still have delta connected step downs and it can do exactly the same thing as the Y-delta banks.
The neutral is bonded at the main panel. If the neutral gains enough potential to hurt anything in the house than it can kill or damage equipment whether there is a generator or not.
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