gen ocpd
- Thread starter jes25
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hurk27
Senior Member
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- Portage, Indiana NEC: 2008
Re: gen ocpd
Re: gen ocpd
Is this a 2-pole breaker or is this a single pole breaker just for the 120 volt twist-loc receptacle? 5500 watts is 45.8 amps at 120 volts so it will protect the generator. But it is only 22.9 at 240 volts so any 240 volt receptacles should only have 20 amp 2-pole breaker on them. Also there might be another auto-resetting breaker on each leg inside of the panel on the generator that protects the generator from overloads and this breaker will protect for short circuits.
Re: gen ocpd
Is this a 2-pole breaker or is this a single pole breaker just for the 120 volt twist-loc receptacle? 5500 watts is 45.8 amps at 120 volts so it will protect the generator. But it is only 22.9 at 240 volts so any 240 volt receptacles should only have 20 amp 2-pole breaker on them. Also there might be another auto-resetting breaker on each leg inside of the panel on the generator that protects the generator from overloads and this breaker will protect for short circuits.
- Location
- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: gen ocpd
Re: gen ocpd
Or perhaps this is one of those newfangled 183 volt generating systems I keep hearing about?
Re: gen ocpd
Or perhaps this is one of those newfangled 183 volt generating systems I keep hearing about?
petersonra
Senior Member
- Location
- Northern illinois
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- Semi-retired engineer
Re: gen ocpd
Re: gen ocpd
The generator is rated in watts but it also has a VA rating which allows for a higher current then the wattage rating would seem to allow since your PF will never be unity.
They probably sized the breaker at the next convenient size.
Re: gen ocpd
The generator is rated in watts but it also has a VA rating which allows for a higher current then the wattage rating would seem to allow since your PF will never be unity.
They probably sized the breaker at the next convenient size.
- Location
- Mission Viejo, CA
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- Professional Electrical Engineer
Re: gen ocpd
Re: gen ocpd
Most small induction generators in that class are rated based on a power factor of 0.8;i.e., the rated output current at 240V is 28.6A.
Overload protection is often by "inherent design." Usually this means the "governor," whether electronic or mechanical. The onboard OCPD is primarily for SC/GF protection.
Re: gen ocpd
Most small induction generators in that class are rated based on a power factor of 0.8;i.e., the rated output current at 240V is 28.6A.
Overload protection is often by "inherent design." Usually this means the "governor," whether electronic or mechanical. The onboard OCPD is primarily for SC/GF protection.
Re: gen ocpd
Re: gen ocpd
Overload protection for a generator is difficult at best to provide.
In one takes a look at a common thermal magnetic breaker the I2t, time current curve, you will find that the generator doesn't have the overload capability to sustain a current long enough in duration in order to trip the breaker. There have been special generator breakers available by one manufacturer that provided a much lower magnetic (instantaneous) pick up caliberation which is more in line with the over current capabilities of a generator.
Should an overload breaker be provided by the gen set manufacturer if may more like a breaker with a low magnetic trip and not one which is thermal.
Re: gen ocpd
Overload protection for a generator is difficult at best to provide.
In one takes a look at a common thermal magnetic breaker the I2t, time current curve, you will find that the generator doesn't have the overload capability to sustain a current long enough in duration in order to trip the breaker. There have been special generator breakers available by one manufacturer that provided a much lower magnetic (instantaneous) pick up caliberation which is more in line with the over current capabilities of a generator.
Should an overload breaker be provided by the gen set manufacturer if may more like a breaker with a low magnetic trip and not one which is thermal.
Re: gen ocpd
Re: gen ocpd
I am going to install a sub panel for the emergency power. The panel I am going to use is a ITE 60a/30a with a breaker interlock so they cant be on at the same time. The gen has a single phase 30a four wire twist lock on it with a 30a breaker. It just seems like something is wrong since the generator cant supply enough power to trip the breaker. What will happen if they attempt to use 29a of power which could be possible if the well pump, sump pump and micro etc are all ran at the same time. How can I protect against this or is this common with generator panels. Is there a safety concern?
Re: gen ocpd
I am going to install a sub panel for the emergency power. The panel I am going to use is a ITE 60a/30a with a breaker interlock so they cant be on at the same time. The gen has a single phase 30a four wire twist lock on it with a 30a breaker. It just seems like something is wrong since the generator cant supply enough power to trip the breaker. What will happen if they attempt to use 29a of power which could be possible if the well pump, sump pump and micro etc are all ran at the same time. How can I protect against this or is this common with generator panels. Is there a safety concern?
physis
Senior Member
Re: gen ocpd
Re: gen ocpd
Don't generators usually have a peak output rating as well as a continuous output rating? I'll bet that generator (not counting the engine) is capabable of quite a bit more than 5500 watts for at least a short time.
At 746 watts per horse power (at 100% efficiency) is there enough horse power that it wont stall if overloaded?
How many HP is the motor?
Re: gen ocpd
Don't generators usually have a peak output rating as well as a continuous output rating? I'll bet that generator (not counting the engine) is capabable of quite a bit more than 5500 watts for at least a short time.
At 746 watts per horse power (at 100% efficiency) is there enough horse power that it wont stall if overloaded?
How many HP is the motor?
Re: gen ocpd
Re: gen ocpd
You may want to ignore this if you want but to put the thermal inverse time current characteristic in somewhat of a perspective NEMA AB4, Guidelines for Inspection and preventive Maintenance of Molded Case Circuit Breakers Used In Commercial and Industrial Applications, at 300% rated current breakers rated 0-30a and 250 and less must trip in 50sec of less. (Residential breakers have the same thermal trip curve.)
Remember that this is a single point in the I2t curve. The question then becomes how much over current can the gen set provide for the duration of time needed to trip the breaker.
thermally.
With regards to short circuit protection the same issue exists. Residential breaker may have an instantaneous trip calibration of as low as 6x the rating of the breaker to as much as 10x. Can the gen set produce enough fault current to trip the breaker magnetically.
With gen sets one doesn't have the luxury of have backbone of a utility power grid to sustain currents of high enough magnitude for a long enough period of time in order to trip an OCPD.
To oversize a generator would be just too expensive. They are generally sized to service a specific load.
Re: gen ocpd
You may want to ignore this if you want but to put the thermal inverse time current characteristic in somewhat of a perspective NEMA AB4, Guidelines for Inspection and preventive Maintenance of Molded Case Circuit Breakers Used In Commercial and Industrial Applications, at 300% rated current breakers rated 0-30a and 250 and less must trip in 50sec of less. (Residential breakers have the same thermal trip curve.)
Remember that this is a single point in the I2t curve. The question then becomes how much over current can the gen set provide for the duration of time needed to trip the breaker.
thermally.
With regards to short circuit protection the same issue exists. Residential breaker may have an instantaneous trip calibration of as low as 6x the rating of the breaker to as much as 10x. Can the gen set produce enough fault current to trip the breaker magnetically.
With gen sets one doesn't have the luxury of have backbone of a utility power grid to sustain currents of high enough magnitude for a long enough period of time in order to trip an OCPD.
To oversize a generator would be just too expensive. They are generally sized to service a specific load.
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