Sizing Conductors

Status
Not open for further replies.
I'll buy that!

I'll buy that!

iwire said:
IMO you can roll that up to a 300 amp Secondary OCPD as long as the secondary conductors are sized for that.
Click to expand...

After further review........I think I'll side with you on this.
New language in 2005 (NECPLUS comment as reference)

240.21(C): Revised to clarify that transformer secondary conductors must have an ampacity not less than the rating of the overcurrent protective device in which they terminate and that the use of the ``next higher standard rating'' is not permitted.
Click to expand...

so....... note 1 in 450.3(B) is applicable in respect to possibly exceeding 125% max OCPD......but the conductors do have to be full size......
 
ibew441dc said:
After further review........I think I'll side with you on this.


so....... note 1 in 450.3(B) is applicable in respect to possibly exceeding 125% max OCPD......but the conductors do have to be full size......
Click to expand...

If the transformer has a 4 to 1 ratio for example the delta primary phase current is 90.2A then the Wye secondary phase current would be 4 x 90.2 = 360A. What size would the feeders from the secondary be ? Is 208v just the line voltage on Wye side or is it a phase voltage. Is the 120v (neutral to 208 line volts) a phase voltage..... es1451
 
es1451 said:
If the transformer has a 4 to 1 ratio for example the delta primary phase current is 90.2A then the Wye secondary phase current would be 4 x 90.2 = 360A.
Click to expand...
Incorrect.

The 4 to 1 ratio that you are referring to is primary phase(winding) to secondary phase(winding).

The ratio of primary line(voltage) to secondary line(voltage) is 2.3 to 1.
480/208 = 2.3
480 is 2.3 to 1 times greater than 208 (line Voltage primary to secondary)

With out getting off track to the solution you are looking for.......You are not looking for the phase voltage of the wye secondary.

es1451 said:
Is 208v just the line voltage on Wye side or is it a phase voltage. Is the 120v (neutral to 208 line volts) a phase voltage..... es1451
Click to expand...

208 is just the line voltage on the secondary side.
120 is the phase(winding) voltage on the secondary side

Delta - E(line) = E(phase)
I (line) is not = I(phase) [phase current x 1.732 = line]
Wye - I(line) = I(phase)
E(line) is not = E(phase) [phase voltage x 1.732 = line]

Try the numbers again considering this:smile:
 
ibew441dc said:
Incorrect.

The 4 to 1 ratio that you are referring to is primary phase(winding) to secondary phase(winding).

The ratio of primary line(voltage) to secondary line(voltage) is 2.3 to 1.
480/208 = 2.3
480 is 2.3 to 1 times greater than 208 (line Voltage primary to secondary)

With out getting off track to the solution you are looking for.......You are not looking for the phase voltage of the wye secondary.



208 is just the line voltage on the secondary side.
120 is the phase(winding) voltage on the secondary side

Delta - E(line) = E(phase)
I (line) is not = I(phase) [phase current x 1.732 = line]
Wye - I(line) = I(phase)
E(line) is not = E(phase) [phase voltage x 1.732 = line]

Try the numbers again considering this:smile:
Click to expand...
Fantastic !!!! I have found my way home thanks to everyone on this thread......es1451
 
If the pri ocpd is set not to exceed 125% why do we need secondary overcurrent protection. (450.3B note 2)???
 
cpal said:
If the pri ocpd is set not to exceed 125% why do we need secondary overcurrent protection. (450.3B note 2)???
Click to expand...

see 240.4(F)..............the answer is it may or may not be required.........depending on the transformer(s)
 
W of O reference .......if you didn't get it

W of O reference .......if you didn't get it

es1451 said:
Fantastic !!!! I have found my way home thanks to everyone on this thread......es1451
Click to expand...

........Theres no place like home.........theres no place like home...............:D
 
Status
Not open for further replies.
Top