I know how some hate zombie threads,, per below but i wanted to give an update.
http://forums.mikeholt.com/showthread.php?t=65776
Purpose is that in my projects, a lot of AC companies are attempting to get involved in DC power work and
there is a lot of information to gain in this area and not quickly learned over night.
The application for this drill will be a -48v power system such is the standard for Telco's and Cable Facilities
The formula is this...
K factor x Loop Lenght x OCP amps / voltage drop.
Choose either 10.8 or 11.1 for your copper K factor (ask your customer for thier standard)
Choose to use either full 100% amperage in your formula or 80% (ask your customer for thier standard)
Next, ask your customer what thier allowable voltage drop is "in between" the devices.
Typically and this is a very good "typical", the totall allowable loss across a "circuit" will be 2volts total.
Some customers like ATT will only allow a total loss of 1.75vdc across the entire circuit from power plant to load~!!
there can be several devices in a "full" dc circuit in order to achieve the proper voltage drop consideration.
here is a typical -48v DC power facility layout (amperage does not matter, it could be 200A capable or 20,000A , doesnt matter)
Battery
-can consist of various series parrallel 12v batteries such that the end result is a -48v system (very light weight)
-can consist of various 2volt cells in series such that the end result is a -48vdc (very heavy , can be up to 4tons each)
DC Power Plant
-can consist of any qty of rectifiers with + & - copper buss work bonded to the battery strings.
-can consist of any qty of rectifiers with large DC circuit breakers feeding a BDFB / BDCBB
-can consist of any qty of rectifiers with large or small DC breakers feeding a BDFB / BDCBB or small equipment loads
-can consist of any qty of rectiifers with small DC breakers feeding small equipment loads.
BDFB or BDCBB (Battery Distribution Fuse Bay or Battery Distruibution Circuit Breaker Bay)
~~think MDP or think Sub Panel distribution.
-can consist of any combination of individually fed panels which tyipcally power up small equipment loads at -48vdc
Equipment loads
-typically mount in a metal frame or equipment rack
-most commonly each "load" has a primary and secondary input power supply -48vdc
-*some* equipment power supplies can be programmed to "load share" at the same time.
-load sharing insures that if the "A" side dc input fails, the "B" side input is still there and picks up the additional KW.
-the above is called redunancy in that its very important for our communications systems to have this feature and even at the power plant or battery level.
example of a simple power system with battery back up, a power plant, a battery distribution center and a load.
some telcos or cable operators:
Battery >>> .25vdc>>>Power plant>>>.875vdc>>>BDFB/BDCBB>>>.875vdc>>>equipment load
AT&T
Battery >>> .25vdc>>>Power plant>>>.75vdc>>>BDFB/BDCBB>>>.75vdc>>>equipment load
Another good point to make is that as that most all dc power plants use switch mode power supplies.
while there is a utility outtage and the generator has failed, the batteries begin to discharge.
as the voltage goes down, the amperage Goes UP. A lot of customers require you to design your power cables around 42vdc tables and thats a different topic with respect to "volts per cell" in batteries,, see CD or Deka battery tables,, also GNB (all valve regulated lead acid)
now lets determine the wire size required for a 60A circuit using two very different distances.
You have to meet the greater of two considerations.
The typical dc power wire is usually :
RHH/RHW/Low Smoke Class I Flex cabling No Cloth Braid, Flex - Low smoke, No Halogen = List# 24194 L2
~to play it safe and as typical in commuinications facilities, the NEC table 310.16 in raceway 75*c column is observed.
--you will rarely ever get to set up your power cables in cable tray as shown in the "triangle" pattern / spacing the NEC illustrates so that benefit is typically not ever going to be your $ saving on your project.
in the below example, you are cabling from the BDFB/BDCBB using .875vd
A 60A circuit is 42 feet one way
~nec table 310.16 75* column says to use #6 awg.
GR1275 + other telcordia standards require a voltage drop CM cable determination.
we are going to use 11.1 k factor and 80% ocp for the below
11.1 x 84' x 48amps / .875 = 51148cmills of copper required
#6awg meets both the NEC and the GR1275
A 60A circuit is 84 feet one way:
~nec table 310.16 75* column says to use #6 awg.
GR1275 + other telcordia standards require a voltage drop CM cable determination.
we are going to use 11.1 k factor and 80% ocp for the below
11.1 x 168' x 48amps / .875 = 102298cmils of copper required
#6awg meets
#1/0 meets GR1275
In this case this 60A circuit must be wired with 1/0
If 1/0 lugs do not connect properly from the source end and to the load end, 1/0 to #6awg Htaps must be used.
http://forums.mikeholt.com/showthread.php?t=65776
Purpose is that in my projects, a lot of AC companies are attempting to get involved in DC power work and
there is a lot of information to gain in this area and not quickly learned over night.
The application for this drill will be a -48v power system such is the standard for Telco's and Cable Facilities
The formula is this...
K factor x Loop Lenght x OCP amps / voltage drop.
Choose either 10.8 or 11.1 for your copper K factor (ask your customer for thier standard)
Choose to use either full 100% amperage in your formula or 80% (ask your customer for thier standard)
Next, ask your customer what thier allowable voltage drop is "in between" the devices.
Typically and this is a very good "typical", the totall allowable loss across a "circuit" will be 2volts total.
Some customers like ATT will only allow a total loss of 1.75vdc across the entire circuit from power plant to load~!!
there can be several devices in a "full" dc circuit in order to achieve the proper voltage drop consideration.
here is a typical -48v DC power facility layout (amperage does not matter, it could be 200A capable or 20,000A , doesnt matter)
Battery
-can consist of various series parrallel 12v batteries such that the end result is a -48v system (very light weight)
-can consist of various 2volt cells in series such that the end result is a -48vdc (very heavy , can be up to 4tons each)
DC Power Plant
-can consist of any qty of rectifiers with + & - copper buss work bonded to the battery strings.
-can consist of any qty of rectifiers with large DC circuit breakers feeding a BDFB / BDCBB
-can consist of any qty of rectifiers with large or small DC breakers feeding a BDFB / BDCBB or small equipment loads
-can consist of any qty of rectiifers with small DC breakers feeding small equipment loads.
BDFB or BDCBB (Battery Distribution Fuse Bay or Battery Distruibution Circuit Breaker Bay)
~~think MDP or think Sub Panel distribution.
-can consist of any combination of individually fed panels which tyipcally power up small equipment loads at -48vdc
Equipment loads
-typically mount in a metal frame or equipment rack
-most commonly each "load" has a primary and secondary input power supply -48vdc
-*some* equipment power supplies can be programmed to "load share" at the same time.
-load sharing insures that if the "A" side dc input fails, the "B" side input is still there and picks up the additional KW.
-the above is called redunancy in that its very important for our communications systems to have this feature and even at the power plant or battery level.
example of a simple power system with battery back up, a power plant, a battery distribution center and a load.
some telcos or cable operators:
Battery >>> .25vdc>>>Power plant>>>.875vdc>>>BDFB/BDCBB>>>.875vdc>>>equipment load
AT&T
Battery >>> .25vdc>>>Power plant>>>.75vdc>>>BDFB/BDCBB>>>.75vdc>>>equipment load
Another good point to make is that as that most all dc power plants use switch mode power supplies.
while there is a utility outtage and the generator has failed, the batteries begin to discharge.
as the voltage goes down, the amperage Goes UP. A lot of customers require you to design your power cables around 42vdc tables and thats a different topic with respect to "volts per cell" in batteries,, see CD or Deka battery tables,, also GNB (all valve regulated lead acid)
now lets determine the wire size required for a 60A circuit using two very different distances.
You have to meet the greater of two considerations.
The typical dc power wire is usually :
RHH/RHW/Low Smoke Class I Flex cabling No Cloth Braid, Flex - Low smoke, No Halogen = List# 24194 L2
~to play it safe and as typical in commuinications facilities, the NEC table 310.16 in raceway 75*c column is observed.
--you will rarely ever get to set up your power cables in cable tray as shown in the "triangle" pattern / spacing the NEC illustrates so that benefit is typically not ever going to be your $ saving on your project.
in the below example, you are cabling from the BDFB/BDCBB using .875vd
A 60A circuit is 42 feet one way
~nec table 310.16 75* column says to use #6 awg.
GR1275 + other telcordia standards require a voltage drop CM cable determination.
we are going to use 11.1 k factor and 80% ocp for the below
11.1 x 84' x 48amps / .875 = 51148cmills of copper required
#6awg meets both the NEC and the GR1275
A 60A circuit is 84 feet one way:
~nec table 310.16 75* column says to use #6 awg.
GR1275 + other telcordia standards require a voltage drop CM cable determination.
we are going to use 11.1 k factor and 80% ocp for the below
11.1 x 168' x 48amps / .875 = 102298cmils of copper required
#6awg meets
#1/0 meets GR1275
In this case this 60A circuit must be wired with 1/0
If 1/0 lugs do not connect properly from the source end and to the load end, 1/0 to #6awg Htaps must be used.
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