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Old 05-03-2012, 07:43 AM   #1
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Generator Over Current and Fault Protection


I'm buying a 12 lead Stamford generator, engine driven, and have a question or two about over current protection and ground fault protection. I will normally have it wired for single phase 120 and 240 in the double delta configuration. I may occasionally rewire it for 3 phase 240 in the series delta configuration.

For the single phase setup, what I've read so far leads me to believe I should have a main circuit breaker of about 125% continuous ampacity; it's a 10 kw generator. Is that correct? What kind of breaker do I need? Should this main be a GFCI? Do I bond neutral and ground? This is a portable unit so I need to package a load center on the generator frame. Can I wire one 240 receptacle directly to the main and two or three 120 volt GFCI's on it as well? Or do I need another 240 breaker downstream of the main? What should I be thinking about for swithching back and forth between single phase and three phase? Alot of questions, trying to get smart and be safe. Thanks.

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Old 05-03-2012, 10:04 AM   #2
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Generator Over Current and Fault Protection


The generator needs breakers rated for the "starting load" or the load the generator can sustain for just several seconds for motors to start up. Better would be "slow trip" breakers rated for the continuous load. The generator may or may not have built in breakers.

For switching back and forth between single phase and 3 phase generator output you can use a 3 phase panel (load center) next to or attached to the generator (triple breaker up top).

A "lug panel" (no up top main breaker) can be used as your load center if the generator has built in breakers.

Suggest not having neutral and ground permanently bonded at the generator; such a bond is already at your house main panel. When the generator is disconnected from the house and taken somewhere you manually bond the neutral and ground in it.

For stand alone use you should have GFCI protection. This could be either a 3 phase GFCI breaker, or individual GFCI receptacles or GFCI branch circuit breakers.

Receptacles may not be wired directly to the generator unless the receptacles are rated for the entire generator output or any generator sub-output protected by a built in breaker. Use branch circuit breakers in your generator load center. You can position double wide double breakers within the load center to deliver 240 volts when the generator is in single phase mode. (some positions will be live only in 3 phase mode). Do not put any single breakers (for 120 volts) on the phase (certain panel positions) that is live only in 3 phase mode; for a 240 volt delta system this voltage will be way above 120 volts.

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Last edited by AllanJ; 05-03-2012 at 10:29 AM.
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Old 05-04-2012, 02:01 AM   #3
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Generator Over Current and Fault Protection


First of all let me post the link for wiring diagram

https://www.cumminsgeneratortechnolo...atingsBook.pdf

That part you will have to scroll down a little to see the wiring diagram to make sure you are on proper voltage.

Just be aware if you are running single phase only you may have to derate the generator a little

For the GFCI breaker they will have it but it will not be cheap espcally with three phase verison.

If you are using as perament portable unit IMO for myself I will just wired in star (WYE ) connection if you going to use the three phase from time to time and the other reason is that with Star connection I don't even have to worry about wild leg connection vs what Delta connection will be as someone mention about that and wild leg to netural is typically 190 to 208 volts range ( depending if generatour or standard power source { latter will be 208})

And the other thing you have to be aware with three phase is the rotation if you have any triphase motour hook up if you hook it inproper sequence the motour can run backward so to slove it you can swap either two leads to get it correct sequince.

Hope that help ya some of the question ya looking for.

Merci,
Marc
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Old 05-04-2012, 07:18 AM   #4
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Generator Over Current and Fault Protection


Thanks guys. If I wire in star configuration and and wire to a three phase load center with main breaker, does the same load center allow me to put in single phase 240 and single phase 120 circuits? For the three phase load, do I install a circuit breaker after the main for the conductors to the load? What are your thoughts about using surface mount breakers instead of a load center--I'll only have 4-5 circuits? Thanks.
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Old 05-05-2012, 01:22 AM   #5
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Generator Over Current and Fault Protection


Quote:
Originally Posted by Believer View Post
Thanks guys. If I wire in star configuration and and wire to a three phase load center with main breaker, does the same load center allow me to put in single phase 240 and single phase 120 circuits? For the three phase load, do I install a circuit breaker after the main for the conductors to the load? What are your thoughts about using surface mount breakers instead of a load center--I'll only have 4-5 circuits? Thanks.
If you understand the star ( Wye ) all three phase line to line is 208 volts and line to neutral is 120 volts that means you can use any one of the three phases.

However if you still want to use straight single phase plus three phase in 240 volts you can use the delta connection but you will have to be carefull with the wild leg as it was mention before the three phases are 240 volts line to line but there is a gotcha the two pairs from line to netural you will read 120 volts but the third phase the line to neutral will read 208 volts so if you wire up the panel and skip every third breaker if you need line to neutral loads ( 120 volts )

The wild leg can do alot of damage to your equiment if not watch out on connection

My best answer is install a small outdoor panel if you can find one in three phase verison and I am sure you may have to go electrique supply centre to get this due most of the big box store will not stock this size much at all.

So your connecton on the generator is pretty much your choice.

Just becarefull some of the 240 volts equiment may not run very well on 208 volts so just a head up with that ( Note: electrique heater types will work but it will be little less heat / wattage )

Electrique motours can run on 208 volts if they are labeled for it otherwise stick to 240 volts.

Merci,
Marc
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