MV Distribution Substation Primary Disconnect

[EEJaime]

I am being asked this question and instinctively I thought I new the answer, but in trying to back it up with a code reference, I am having difficulty locating a specifically applicable code section.

I am using the 2001 California Electrical Code, (1999 NEC with California amendments). This is being used because it was the code in effect when the project went through plan check.

I have an existing customer owned 4.16kV/3ph distribution system in an airport terminal. The system uses a fusible switch lineup to feed various substations throuhout the space. When the designer replaced some existing substations with larger ones he basically duplicated the existing layout.

I have two substations, one each with a 1500kVA, and 2000kVA Transformer, Delta-Wye with a 480Y/277V/3ph/4w secondary distribution board. When I design this type of system, I always specify a switch on the incoming primary feed. An air switch or SF6 depending on the facility. In this case however we indicate these substations without a primary disconnect switch. The feed to it is protected at the Main Distribution Switchboard by a Fused Switch, sized per CEC.

My question is, am I required to have a local disconnect switch on the incoming primary feeder before the transformer?

And if I am required to have this, where in the CEC is this called out. Can the feeder OCP device suffice? Or is a local disconnecting means necessary. The substation is remote from the distribution switchboard.

I am drawing a blank.

Any assistance in pointing me in the right direction will be appreciated. Thank you in advance for your input.

 

[smithge]

I believe that you are stating that each substation has individual and properly sized overcurrent protection, however the fused disconnect is some distance away from the subsation.

Unfortunatly I am not familiar with the CEC. However looking at the NEC Article 100 defines "In Sight From" as 50 ft. and combined with 110.58 that states "a switch or circuit breaker" ... "shall be within sight of each transformer or motor location"...

Unless you can find some other exceptions you have 50 ft with which to place the new equipment from the existing fused disconnect.

 

[dpc]

Article 110.58 applies only to tunnels, I believe.

There is no general requirement in NEC for a local disconnecting means at a transformer.

It is fairly common to see unit substations in industrial facilities protected by a remote circuit breaker with no local disconnecting means.

dpc

 

[EEJaime]

Thank you smithge, that is the reference I was looking for. I knew this was somewhere. However, the version of the code I am looking at, (this is not a California revision), states:

"110-58. Disconnecting Means. A switching device, meeting the requirements of Article 430 or 450, shall be installed at each transformer or motor location for disconnecting the transformer or motor. The switching device shall open all ungrounded conductors of a circuit simultaneously."

It does not specifically state within sight, but knowing my AHJ, this will be interpreted literally, "...AT EACH TRANSFORMER OR MOTOR LOCATION...".

Many thanks.

 

[EEJaime]

DPC,

You are right, I did not catch that. That saves me considerable trouble. I appreciate the input. I know that motors require local disconnection, but was not sure of transformers.

Thank you,

EEJaime