Transformer disconnect

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Djelite

Member
Location
Ny
Occupation
Electrician
Since the code now requires a transformer disconnect for all transformer. On the primary side why do you need a main disconnect after the secondary? Wont the new rule accomplish the same job?
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
You don't need a disconnect on the secondary.

You usually need overcurrent protection on the secondary, either for transformer secondary protection, secondary conductor protection, or both.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
The primary disconnect is the only "disconenct" required by Art 450 as "disconnecting" the primary obviously disconnects the secondary. As david points out, it's the rules associated with Art 240 and 408 that address secondary disconnecting which is most often related to the device served and overcurrent.
 

Djelite

Member
Location
Ny
Occupation
Electrician
The primary disconnect is the only "disconenct" required by Art 450 as "disconnecting" the primary obviously disconnects the secondary. As david points out, it's the rules associated with Art 240 and 408 that address secondary disconnecting which is most often related to the device served and overcurrent.
So if you disconnect the transformer primary everything is disconnected. Why do you need a main connection with this rule?
 

Djelite

Member
Location
Ny
Occupation
Electrician
You now need a main disconnect for any transformer. This disconnect is located before the primary side of a transformer. If you disconnect the primary of a transformer everything is disconnected. If everything gets disconnected why do you need a main disconnect after the seperately derived system?
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
You now need a main disconnect for any transformer. This disconnect is located before the primary side of a transformer. If you disconnect the primary of a transformer everything is disconnected. If everything gets disconnected why do you need a main disconnect after the seperately derived system?
See post #2
 

Djelite

Member
Location
Ny
Occupation
Electrician
Sorry i never said you a disconnect on the secondary side of a transformer. I said you need a disnnect after the secondary side which is the seperately derived system
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
You now need a main disconnect for any transformer. This disconnect is located before the primary side of a transformer. If you disconnect the primary of a transformer everything is disconnected. If everything gets disconnected why do you need a main disconnect after the seperately derived system?
Go back and read post 2 again. No main disconnect is required on the secondary side of the transformer. In almost all cases you need overcurrent protection for the secondary conductors and in some cases you need overcurrent protection for the transformer. The installation of the required overcurrent protection almost always results in some type of disconnecting means.
 

xformer

Senior Member
Location
Dallas, Tx
Occupation
Master Electrician
Since the code now requires a transformer disconnect for all transformer. On the primary side why do you need a main disconnect after the secondary? Wont the new rule accomplish the same job?
IMHO if the transformer is providing power to a panelboard, the panelboard is required to have an OCPD but the secondary of the transformer is not.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
IMHO if the transformer is providing power to a panelboard, the panelboard is required to have an OCPD but the secondary of the transformer is not.
There's not enough information given to determine if the secondary of the transformer is required to have an OCPD.

It may/it may not, depending on how it meets the requirements of 450.3.
 
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