230.71 and Table 450.3(A)

Status
Not open for further replies.
I am currently performing an assesment of a university campus building that was built in approximately 1958. The building has 2 MV (12kV) feeders to a selector switch. The selector switch feeds 2 service transformers and main switchboards. According to the original drawings, each transformer is fuse protected via an HVL switch, at just under 250% of the transformer FLA rating. The selector switch, transformers and main switchboards are located in the locked building basement, which can be considered a a supervised location, as only university facilities shop technicians have access. According to Table 450.3(A) and the above conditions, no transformer secondary 480V protection is required. The 480V switchboards do not have main breakers and each have more than 6 feeder breakers (10 and 20 respectively). Can the HVL switches be considered as the service disconnecting means required by 230.71? I am not sure if the selector switch is load rated, but if it is can it be considered as the service disconnecting means?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I agree that you don't need secondary protection for the transformer. But you do need protection for the secondary conductors (from the transformer to the switchboard), per 240.21(C). Your situation does not meet any tap rule or exception thereto, so I think you have one violation there. Also, I believe that the switchboard has to have overcurrent protection, though I cannot find an article that explicitly says so. I am certain, however, that the transformer's primary side protection cannot be used as the means for protecting the switchboard. So I think you have a second violation there.

Regarding your questions, I think you cannot take credit for a breaker, fuse, fused disconnect, or simple disconnect, as being a building's service disconnecting means, if there is another upstream component, such as your primary selector switch. So I think you have a third violation there.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
For the panel protection on the load side of the transformer...what about 408.36?
I saw that. But it applies to Part III, "Lighting and Appliance Panelboards," not to switchboards. I looked for a similar statement in Part II, but could not find it there.
 
Thanks you hit the the spots I was hoping. If the selector switch is load rated I belive it can serve as the service disconnecting means. I agree that the transformer secondary conductors and switchboard need to be protected. Generally speaking, if you protect one you protect the other. The switchboard I'm focused on is a unit sub-type with short 3000A bus connections for the transformer secondaries to the switchboard. The switchboard consist of a 1600A bus distribution section and a 2400A bus distribution section. The 1600A dist section has 1075A of overcurrent protective devices and the 2400A section has 1225A (each has provisions for additional devices). The total of existing overcurrent protective devices is 2300A which is less than the 3000A rating of the secondary conductors and the total of each section is less than the section rating. 240.21(C)(2) seems to apply with the exception of 240.21(C)(2)(1)b. Since there is more than a single overcurrent-protective device I would assume that I need to add all the device ratings similar to what is stated by 240.21(C)(3)(1). If my assumption is correct, it appears that the transformer secondary conductors are protected according to the requirements 240.21(C)(2). Would you agree?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
If the selector switch is load rated I belive it can serve as the service disconnecting means.
Even if the selector switch is rated for being manually opened under full load (I think this is what you mean by "load rated"), that is not enough for it to serve as the building's required service disconnection means. For starters, does it have an "OFF" position, and not just the "Source #1" and "Source #2" positions? Also, is it "service rated?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Since there is more than a single overcurrent-protective device I would assume that I need to add all the device ratings similar to what is stated by 240.21(C)(3)(1). . . . Would you agree?
I would not. 240.21(C)(2)(1)(b) talks about a single device. It doesn't give you the option of taking credit for a set of devices that add up to a low enough value.
 
Good questions. I'm not sure that the selector switch has an "off" position and I doubt that a 12kV selector switch is rated as "service entrance equipment".

What about the transformer secondaries? Do you think I can I hang my hat on 240.21(C)(2), with a qualification that protective devices and calculated loads are limited less than the individual distribution bus ratings and together total less than 3000A?

I know it may be mute, if the selector switches are not properly rated, but if they are it may matter....
 
Thanks for being a sounding board. I should probably learn to go with my gut instead of trying to find a loophole......... In the end I will most likely recommend that equipment be replaced or upgraded, but in reality the university is their own "authority having jurisdiction" and may say that they are okay with the way it is.....
 

iwire

Moderator
Staff member
Location
Massachusetts
The building has 2 MV (12kV) feeders to a selector switch. The selector switch feeds 2 service transformers and main switchboards. According to the original drawings, each transformer is fuse protected via an HVL switch, at just under 250% of the transformer FLA rating. The selector switch, transformers and main switchboards are located in the locked building basement, which can be considered a a supervised location, as only university facilities shop technicians have access. According to Table 450.3(A) and the above conditions, no transformer secondary 480V protection is required. The 480V switchboards do not have main breakers and each have more than 6 feeder breakers (10 and 20 respectively). Can the HVL switches be considered as the service disconnecting means required by 230.71? I am not sure if the selector switch is load rated, but if it is can it be considered as the service disconnecting means?


It sounds to me like this building has no "service" so nothing in Article 230 applies.

It sounds like the utility service ends somewhere else on campus meaning this building has only a feeder (or two) and the rules in Part II of Article 225 will apply. (Very similar rules but worth looking at the right section)
 
It sounds like the utility service ends somewhere else on campus meaning this building has only a feeder (or two) and the rules in Part II of Article 225 will apply. (Very similar rules but worth looking at the right section)




I agree this may not be a service...the OP states "feeder" in his first sentence.


When instructing, I say the exact same thing...
 
After reading through 225 part II I see that there are definately some nuances, but it still requires a disconnecting means (with some exceptions) that is rated as "service equipment". It also requires 6 or fewer disconnects same as 230.... I'm not sure this helps....
 
Just an FYI follow up. 230.200 covers services exceeding 600V which allows a selector switch or HVL to serve as the service disconnecting means as long as they meet the requirements of 230.204 and 230.205.
 
Status
Not open for further replies.
Top