background................
the device to be powered is a rectifier shelf which has one 1'' k/o on the rear left & right which normally mandate non conductive whips with 90deg non conductive sealtite drops, one drop to each side of each shelf for ac inputs.
there is a terminal block on the rear left and right for farily universal AC input landings.
one terminal strip applies power to rectifier shelf 1 position 1, 2 and 3.
the other terminal strip applies power to rectifier shelf 1 position 4, 5 and 6.
the devices to power are 4kw rectifiers which can accept input of single or 3ph voltage from 120v-350vac.
output is nominal -54vdc & roughly 75A nominal.
the oem data sheets and standard ac input OCP for this rectifier has been a 30A 2pole for either 208v or 240v 1ph input.
you can also power a group of 3 rectifiers from one 3 pole ocp if the site has 3phase but that is not the application here.
the customer desires to have each rectifier on its own OCP to maximize redunduncy which i totally agree with.
I supplied the above background to lead into my opinion seeking mission here.
this has more to do with conduit fill, derating and the possibility of using the next size up rule.
the site happens to be a simple 240v single phase 400A 3wire build with dual gens, MTS and ATS & 400A MDP loaded down linear and non-linear to about 38% (2 wall mtd 5ton hvac, lighing , DC plant, ac circuits all inclusive). Our scope is to transition all thier smaller dc power system loads into a single -54v, 10ka capable DC plant, we are not adding any load, just transitioning from one source to another then demo/dispose the powered down dc power systems.
the sites are always enviromentally controlled for temp to nominal 74degF.
normally i would pipe in two 1''cdts from the MDP over to a 6'' x 6'' jbox in the overhead above the DC Plant (this one is 10kAmps at -54v)
from the jbox i would drop in 1) nonconductive sealtite whip to each side of each self.
next i would wire in 3) delta #8 30A 2pole circuits from the MDP home run to the rear left and right terminal strip of each shelf.
leading into to my question.... can i use #10 wire instead of #8?
reason i ask is the oem data sheet posts max ac ampacity draw is roughly 18amps per rectifier.
Customer standards are usually more strengent than the AHJ in many cases but they dont go to this level of detail.
Customer does mandate that all ckts AC or DC be copper built around 310.16 , 75degC column only.
#10 is good to 35A
#derate #10 to 28A for 4-6current carrying conductors in a single pipe.
NEC allows temp correction factor of 4% conductor ampacity capablity to add back on for a room kept at 70-77.
28A x 1.04= 29.12amps.
OEM states the rectifer can only draw at max approx 18amps.
this customer tends not to entertain the "thats close enogh" conversations, so that being said, is #10 a proper application to task?
thanks!
the device to be powered is a rectifier shelf which has one 1'' k/o on the rear left & right which normally mandate non conductive whips with 90deg non conductive sealtite drops, one drop to each side of each shelf for ac inputs.
there is a terminal block on the rear left and right for farily universal AC input landings.
one terminal strip applies power to rectifier shelf 1 position 1, 2 and 3.
the other terminal strip applies power to rectifier shelf 1 position 4, 5 and 6.
the devices to power are 4kw rectifiers which can accept input of single or 3ph voltage from 120v-350vac.
output is nominal -54vdc & roughly 75A nominal.
the oem data sheets and standard ac input OCP for this rectifier has been a 30A 2pole for either 208v or 240v 1ph input.
you can also power a group of 3 rectifiers from one 3 pole ocp if the site has 3phase but that is not the application here.
the customer desires to have each rectifier on its own OCP to maximize redunduncy which i totally agree with.
I supplied the above background to lead into my opinion seeking mission here.
this has more to do with conduit fill, derating and the possibility of using the next size up rule.
the site happens to be a simple 240v single phase 400A 3wire build with dual gens, MTS and ATS & 400A MDP loaded down linear and non-linear to about 38% (2 wall mtd 5ton hvac, lighing , DC plant, ac circuits all inclusive). Our scope is to transition all thier smaller dc power system loads into a single -54v, 10ka capable DC plant, we are not adding any load, just transitioning from one source to another then demo/dispose the powered down dc power systems.
the sites are always enviromentally controlled for temp to nominal 74degF.
normally i would pipe in two 1''cdts from the MDP over to a 6'' x 6'' jbox in the overhead above the DC Plant (this one is 10kAmps at -54v)
from the jbox i would drop in 1) nonconductive sealtite whip to each side of each self.
next i would wire in 3) delta #8 30A 2pole circuits from the MDP home run to the rear left and right terminal strip of each shelf.
leading into to my question.... can i use #10 wire instead of #8?
reason i ask is the oem data sheet posts max ac ampacity draw is roughly 18amps per rectifier.
Customer standards are usually more strengent than the AHJ in many cases but they dont go to this level of detail.
Customer does mandate that all ckts AC or DC be copper built around 310.16 , 75degC column only.
#10 is good to 35A
#derate #10 to 28A for 4-6current carrying conductors in a single pipe.
NEC allows temp correction factor of 4% conductor ampacity capablity to add back on for a room kept at 70-77.
28A x 1.04= 29.12amps.
OEM states the rectifer can only draw at max approx 18amps.
this customer tends not to entertain the "thats close enogh" conversations, so that being said, is #10 a proper application to task?
thanks!
