TRANSFORMER SECONDARY 1

[tulum]

Hey Folks,

I am laying out a small distribution transformer that will have 2 feeders... here are the specifics;

Primary phase Protection: 50A Din fuses 4160v
Transformer: 225kVA, delta grounded wye (15a) 600v secondary
Secondary phase Protection: none
Feeder 1: CH series C JD MCCB (100A trip)
Feeder 2: Sames as feeder 1

The NGR has a se-325 for GF protection and will be used to shed both feeders upon a GF occuring.

The name of the game is to keep the cost low... so we did not go with a main on the secondary.

Question:

I am running separate feeds to each feeder (only 15' max). What size do I have to make the cables to insure the primary fuses protect the cables?

In this case I will probably just size them to the secondary FLC + 125% which exceeds the breaker frame ratings anyways; but what if the feeder cables were only sized for 100A?

 

[waross]

Hi tulum; Are you in Canada?
Check section 26, Installation of electrical equipment, Transformers. My old edition has an exception refering back to section 14, Protection and Control. At 15 feet your feeders would qualify for the 7.5 meter rule. The minimum size is 1/3 as long as the cable capacity equals or exceeds the rating or setting of the overcurrent device. You may have to include the length of the primary conductors in the 7.5 meters but probably not.
Check with the UHJ anyway.
respectfully

 

[tulum]

Waross,

Thanks waross, from memory I believe you are right... once again (and yes I am in CANADA).

I will check my code book when I get into work tomorrow.

Regards,
TULUM

 

[tulum]

Waross,

I checked the code, and as far as I can tell my situation almost cuts the mustard for the tap rule.

I believe the exception is section: 14-100 (f) (v)

... and The secondary conductor terminates in a single overcurrent device rated or set at a value not exceeding its ampacity...(which is not my case)

So am I correct in assuming the cables need to be sized for 125% of FLC?

Regards,
TULUM