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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Generator, optional.

Customer with 400 amp and (new) 600 amp manual transfer switches. SE rated. We were originally going to limit the load to essential use and feed both with the small genset used for the 400. Customer comes home with a 1200 amp genset he bought on an auction. It will be sitting outside under a large carport. Not a SDS. The calculated load is around 750. We used 3 sets of 350 Al for a feed from the utility. What size do I need to use from the new genset? Equal to my 350s? The 1000 amp to a gutter and tap off from there? Or the 1200?
 
The key would be if the generator has an overcurrent protective device.
You need to protect the conductors from the generator to your ATS at their ampacity.
It is generally accepted that 445.13 references the conductors to the 1st OCP device which is often on the generator.
If you ATS's have overcurrent protection then you should be able to install conductors based on the generator OCP device and follow the tap rules to feed your two ATS s
 
augie47 said:
The key would be if the generator has an overcurrent protective device.
You need to protect the conductors from the generator to your ATS at their ampacity.
It is generally accepted that 445.13 references the conductors to the 1st OCP device which is often on the generator.
If you ATS's have overcurrent protection then you should be able to install conductors based on the generator OCP device and follow the tap rules to feed your two ATS s
Click to expand...

The Gen has 1200 amp CB. Gen is rated @ 549 amps. There is no neutral load. Manual transfer switches.

The conductors from the Gen to the line side of the CB are parallel 1/0. I know they have different ampacity rating and I have no control of those wires so 445.13 is moot for me, if those are what 445.13 refers to.

Seems a bit off kilter to size my conductors from the generator to the transfer switches @ 1200 amps when I have only 3 sets of 350 Al's to the POCO xfmr bank for the identical load.
 
Is it possible the 1200 amp breaker has a lower ampere rating plug & it;s simply 1200 amp frame ?
Is it possible to install a rating plug ?
I ask as it does indeed seem unusual for a 1200 amp breaker on a 549 amp generator.
Are the 350AL POCO wiring ?
If so there is little need in discussing them as they are under a different Code and mindset :D
If your genset has a 549 amp capacity does the customer understand he didn't purchase a 1200 amp generator ?\
Sounds like you may still need to watch the load closely.
My thinking would be to arrange for the gen-set to have 600 amp protection and size your conductors accordingly.
 
augie47 said:
Is it possible the 1200 amp breaker has a lower ampere rating plug & it;s simply 1200 amp frame ?
Is it possible to install a rating plug ?
I ask as it does indeed seem unusual for a 1200 amp breaker on a 549 amp generator.
Are the 350AL POCO wiring ?
If so there is little need in discussing them as they are under a different Code and mindset :D
If your genset has a 549 amp capacity does the customer understand he didn't purchase a 1200 amp generator ?\
Sounds like you may still need to watch the load closely.
My thinking would be to arrange for the gen-set to have 600 amp protection and size your conductors accordingly.
Click to expand...
Looks like 1200 amp plug On the pictures i have. Tests results on the rebuilt breaker indicate a 1200.

We used a current monitor on the existing to warn of overload. We will continue. The 549 will most likely run everything that is needed.
 
In most every case the conductors must be sized to carry the load and protected per 240.4.
This situation, to me, is muddied somewhat by 445.13 Exception although that only applies to the 1st overcurrent device.
To me the simple solution would be to reduce the generator breaker to the 600 amp range but someone may well have a better solution.
 
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