In preparation for Isabel and frequent thunder storms I purchased an old Dayton 15 kw PTO generator. This is a strictly portable installation. The neutral is clearly bonded to the generator frame and I can't see any way to separate the two with this generator design. The generator has a 50 amp 3 connector plug. I intend to backfeed my 200 amp main distribution panel through a 50 amp breaker and selectively power the circuits I need. Do I need to worry about grounding the generator and if so how should I do it? I do intend to install the Square D generator safety interlock in the future. Thanks for any insight.
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portable generator
- Thread starter dgwilson
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Ed MacLaren
Senior Member
Re: portable generator
If this generator is connected to your building wiring system as you describe, it should be done through a transfer switch that switches the grounded (neutral) conductor, and the generator neutral would be required to be connected to an acceptable grounding electrode.
It seems that you are already aware that backfeeding without the transfer switch is illegal and dangerous.
Ed
If this generator is connected to your building wiring system as you describe, it should be done through a transfer switch that switches the grounded (neutral) conductor, and the generator neutral would be required to be connected to an acceptable grounding electrode.
It seems that you are already aware that backfeeding without the transfer switch is illegal and dangerous.
Ed
Re: portable generator
I can't afford a $1600+ 3 pole double throw transfer switch. Because of livestock I also can't afford to be without power for an extended period of time as the power company has left me several times before. What is the concern as I'll have the main shutoff disconnected from the utility when operating the generator? Why would Square D make just such a interlock device? I would welcome any suggestions. Don't get me wrong, I want to be safe for my family and utility workers but I also have a limited budget.
I can't afford a $1600+ 3 pole double throw transfer switch. Because of livestock I also can't afford to be without power for an extended period of time as the power company has left me several times before. What is the concern as I'll have the main shutoff disconnected from the utility when operating the generator? Why would Square D make just such a interlock device? I would welcome any suggestions. Don't get me wrong, I want to be safe for my family and utility workers but I also have a limited budget.
Re: portable generator
You should have a switch that disconnects the utility neutral. The premises system then becomes a separately derived system. The earth grounding can be at the source or the first switch, or both.
The premises neutral should not be re-grounded after the first switch.
The generator should have the neutral bonded to the core and frame. This will contain a winding to core fault. The under voltage relay will then dump the exciter. This action is much quicker than any overcurrent device.
There should not be an equipment ground conductor from the first switch to the generator. The neutral conductor will perform fault detection.
The UV relay, in the generator control panel, will detect and react to a fault, and immediately dump the exciter.
This is exactly how the main generators in all power houses are connected. This method works correctly regardless of the size of the generator unit.
Many believe that a generator requires an equipment ground conductor for carrying fault current. This is not true.
This will bring out a lot of controversy and a rush to prove me wrong. Please do so, but show the math and white papers to contradict this opinion.
You should have a switch that disconnects the utility neutral. The premises system then becomes a separately derived system. The earth grounding can be at the source or the first switch, or both.
The premises neutral should not be re-grounded after the first switch.
The generator should have the neutral bonded to the core and frame. This will contain a winding to core fault. The under voltage relay will then dump the exciter. This action is much quicker than any overcurrent device.
There should not be an equipment ground conductor from the first switch to the generator. The neutral conductor will perform fault detection.
The UV relay, in the generator control panel, will detect and react to a fault, and immediately dump the exciter.
This is exactly how the main generators in all power houses are connected. This method works correctly regardless of the size of the generator unit.
Many believe that a generator requires an equipment ground conductor for carrying fault current. This is not true.
This will bring out a lot of controversy and a rush to prove me wrong. Please do so, but show the math and white papers to contradict this opinion.
Re: portable generator
Bennie
I have a question about the UV relay used to dump the exciter voltage. How would you build voltage to the generator on start up. If you have more than one generator on line and you lose your exciter voltage on one, you will get a large current flow from the other generator(s)to provide excitation to the one that lost it's exciter voltage. If this current flow isn't large enough to trip the breaker the generator that lost it's excitation will stay on line. Our UV's trip the main generator breaker.
Bennie
I have a question about the UV relay used to dump the exciter voltage. How would you build voltage to the generator on start up. If you have more than one generator on line and you lose your exciter voltage on one, you will get a large current flow from the other generator(s)to provide excitation to the one that lost it's exciter voltage. If this current flow isn't large enough to trip the breaker the generator that lost it's excitation will stay on line. Our UV's trip the main generator breaker.
Re: portable generator
I will have to review some of my generator information. So most of what I am writing is off the top of my memory bank.
Some UV relays will sense a fault and a phase failure. Dumping the exciter is easier than the main load switch, due to the amount of current involved. When the exciter is dumped the load transfers to other generators or dies from power loss.
When a generator is on line with other sources, the UV will dump the exciter, then the reverse power relay will open the power circuit breaker after the load is removed.
On very large generators, there is never any load switching between the generator and the primary of the main transformer. The connections are all solid. Off and on line switching is done on the high voltage secondary side.
I will have to review some of my generator information. So most of what I am writing is off the top of my memory bank.
Some UV relays will sense a fault and a phase failure. Dumping the exciter is easier than the main load switch, due to the amount of current involved. When the exciter is dumped the load transfers to other generators or dies from power loss.
When a generator is on line with other sources, the UV will dump the exciter, then the reverse power relay will open the power circuit breaker after the load is removed.
On very large generators, there is never any load switching between the generator and the primary of the main transformer. The connections are all solid. Off and on line switching is done on the high voltage secondary side.
Re: portable generator
Bennie
I am getting off topic and getting more into generator control than what was originally asked. I would make the statement that a generator will not reverse power trip if it looses excitation. A strong excitation current will flow from the other generators on line to provide excitation. This flow of current can result in over current tripping of the generator main power circuit breaker.
Bennie
I am getting off topic and getting more into generator control than what was originally asked. I would make the statement that a generator will not reverse power trip if it looses excitation. A strong excitation current will flow from the other generators on line to provide excitation. This flow of current can result in over current tripping of the generator main power circuit breaker.
Re: portable generator
Generators are separately excited. The loss of excitation makes the generator an induction motor. The reverse power relay will detect the reversal and open the main power breaker.
Somewhat like the old reverse current relay on a Ford. It prevents the generator from becoming a motor.
Generators are separately excited. The loss of excitation makes the generator an induction motor. The reverse power relay will detect the reversal and open the main power breaker.
Somewhat like the old reverse current relay on a Ford. It prevents the generator from becoming a motor.
Re: portable generator
Bennie
A generator will only reverse power trip when you have a flow of power into the generator. If you loose excitation you will get a current flow from the other generators that are on line into the generator that lost it?s excitation, this is called a magnetizing current. The generator will not reverse power since it is still providing power to the common buss. Now with that said if you loose engine power and the reverse power relay fails to operate, the generator can be driven in a reverse direction by the other generators. I have seen this happen only once. It isn?t good to have your engine being driven backward at a high rate of speed since the oil pump doesn?t work in reverse.
Bennie
A generator will only reverse power trip when you have a flow of power into the generator. If you loose excitation you will get a current flow from the other generators that are on line into the generator that lost it?s excitation, this is called a magnetizing current. The generator will not reverse power since it is still providing power to the common buss. Now with that said if you loose engine power and the reverse power relay fails to operate, the generator can be driven in a reverse direction by the other generators. I have seen this happen only once. It isn?t good to have your engine being driven backward at a high rate of speed since the oil pump doesn?t work in reverse.
G
Guest
Guest
Re: portable generator
Call your POCO and ask for an onsite consult. They will tell you what you need to keep their wo/men and your family and cows safe. Tell them you have a limited budget. Put some honey on it. Follow the NEC and the POCO rules, guidelines, and suggestions.
Here are some code sections to chew on:
445.10, 110.3(B), 445.13, 445.14, 250.30(A)(2), 702.5, 250.24(A)(5), 702.8(A, B) and very important: 702.6
Once you put a transfer switch on your portable generator your portable generator falls under the rules of a permanently installed generator-- regardless of its original function. If you want to connect your generator to your service you must install a transfer switch per 702.6 and your portable generator becomes a permanent generator and subject to those rules.
[ September 18, 2003, 01:57 PM: Message edited by: awwt ]
Call your POCO and ask for an onsite consult. They will tell you what you need to keep their wo/men and your family and cows safe. Tell them you have a limited budget. Put some honey on it. Follow the NEC and the POCO rules, guidelines, and suggestions.
Here are some code sections to chew on:
445.10, 110.3(B), 445.13, 445.14, 250.30(A)(2), 702.5, 250.24(A)(5), 702.8(A, B) and very important: 702.6
Once you put a transfer switch on your portable generator your portable generator falls under the rules of a permanently installed generator-- regardless of its original function. If you want to connect your generator to your service you must install a transfer switch per 702.6 and your portable generator becomes a permanent generator and subject to those rules.
[ September 18, 2003, 01:57 PM: Message edited by: awwt ]
Re: portable generator
This is my first post. I just joined this site. I wish I knew about it years ago and did not have to try to figure out these frustrating questions on my own or with limited help-(interpretations) from local inspectors or opinions from my fellow electricians.
Thousands of portable generators went out the doors of Home Depots and Lowes on the East Coast before, during and after hurricaine ISABEL.
I bought one from Lowes, a (5550 Watt Troy Bilt) and powered my house for two days from it's 30 Amp 4 pole 120/240 Volt twistlock receptacle into my 30 Amp male Inlet that fed my Optional Standby Panel that I had installed for Y2K.
Troy Bilt mentioned the NEC when they suggested that I ground the frame of the generator using of all things a #12 ground wire!
My interpretation of this question is that the neutral current is trying to return to it's point of origin, the generator. The generator is grounded to the Standby Panel (a sub panel with a bonded ground bar) through the 25 foot long 10/4 cable that connects it through the twistlocks.
An Amprobe reading revealed that the neutral was carrying 4 Amps and the Grounding conductor was carrying 2 Amps (probably because the Standby panel is mounted right below the Service panel with a 2 inch steel nipple and #10 Ground and #4 Neutral so the current can't tell the difference between the neutral and the grounding conductor which are bonded together less than two feet away in the Service Panel).(And according to the Troy Bilt schematic are common in the Generator).
Thinking I knew more than those (greenhorns) at Troy Bilt I connected the generator frame to the #6 ground wire that led to the Service ground rod using a #6 stranded. I did not take an Amprobe reading on the #6 but I would not be surprised to see a substancial reading.
I think Troy Bilt and all the other generator manufactirers are trying to cover themselves as best they can by suggestin that a ground wire be run to a rod. And suggesting a #12 may reveal a method to their madness because it would not interfere with the #10 ground and neutral in the cable feed. Am I too suspicious?
This is a portable generator connected by a receptacle and the house ground should provide the ground. A ground rod may not hurt if it is driven at the generator site and is not connected like I did it to the house ground which gave the neutral a total of three paths back to the generator. Remember that this generator is only temporary but when the Utility Power comes back the Service Panel becomes hot (although it is isolated by the transfer switch in the Standby Panel and the rod driven at the generator is now part of the Utility Neutral/Ground bond! Around and round we go. I say don't ground the generator frame. That's my opinion.
As far as lightning, a lightning arrestor could be installed in the Standby Panel. Or perhaps in my case in the Service Panel which is right above the Standby Panel. I don't think a ground rod would be a sure fire cure for a lightning strike anyway and imagine being in a pool of water next to your portable generator with a ground rod that is now common through the water to the ground rod at the house that is common to the generator ground and neutral through the Standby Panel.
I wanted to mention some Code rules to back up my opinion but I am very tired from reading the all the posts (I'm impressed). The majority of the posts seem to back up my opinion because this is a portable generator connecting the house through the receptacle mounted on the generator.
This is my first post. I just joined this site. I wish I knew about it years ago and did not have to try to figure out these frustrating questions on my own or with limited help-(interpretations) from local inspectors or opinions from my fellow electricians.
Thousands of portable generators went out the doors of Home Depots and Lowes on the East Coast before, during and after hurricaine ISABEL.
I bought one from Lowes, a (5550 Watt Troy Bilt) and powered my house for two days from it's 30 Amp 4 pole 120/240 Volt twistlock receptacle into my 30 Amp male Inlet that fed my Optional Standby Panel that I had installed for Y2K.
Troy Bilt mentioned the NEC when they suggested that I ground the frame of the generator using of all things a #12 ground wire!
My interpretation of this question is that the neutral current is trying to return to it's point of origin, the generator. The generator is grounded to the Standby Panel (a sub panel with a bonded ground bar) through the 25 foot long 10/4 cable that connects it through the twistlocks.
An Amprobe reading revealed that the neutral was carrying 4 Amps and the Grounding conductor was carrying 2 Amps (probably because the Standby panel is mounted right below the Service panel with a 2 inch steel nipple and #10 Ground and #4 Neutral so the current can't tell the difference between the neutral and the grounding conductor which are bonded together less than two feet away in the Service Panel).(And according to the Troy Bilt schematic are common in the Generator).
Thinking I knew more than those (greenhorns) at Troy Bilt I connected the generator frame to the #6 ground wire that led to the Service ground rod using a #6 stranded. I did not take an Amprobe reading on the #6 but I would not be surprised to see a substancial reading.
I think Troy Bilt and all the other generator manufactirers are trying to cover themselves as best they can by suggestin that a ground wire be run to a rod. And suggesting a #12 may reveal a method to their madness because it would not interfere with the #10 ground and neutral in the cable feed. Am I too suspicious?
This is a portable generator connected by a receptacle and the house ground should provide the ground. A ground rod may not hurt if it is driven at the generator site and is not connected like I did it to the house ground which gave the neutral a total of three paths back to the generator. Remember that this generator is only temporary but when the Utility Power comes back the Service Panel becomes hot (although it is isolated by the transfer switch in the Standby Panel and the rod driven at the generator is now part of the Utility Neutral/Ground bond! Around and round we go. I say don't ground the generator frame. That's my opinion.
As far as lightning, a lightning arrestor could be installed in the Standby Panel. Or perhaps in my case in the Service Panel which is right above the Standby Panel. I don't think a ground rod would be a sure fire cure for a lightning strike anyway and imagine being in a pool of water next to your portable generator with a ground rod that is now common through the water to the ground rod at the house that is common to the generator ground and neutral through the Standby Panel.
I wanted to mention some Code rules to back up my opinion but I am very tired from reading the all the posts (I'm impressed). The majority of the posts seem to back up my opinion because this is a portable generator connecting the house through the receptacle mounted on the generator.
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