how to read this 480V single phase transformer wiring diagram

Status
Not open for further replies.
Besoeker

Besoeker

Senior Member
Location
UK
Smart $ said:
True, but it does infer you no longer 'live' there, and I am assuming your presence here originates from the island. :p
Click to expand...
It originates from wherever I happen to be at the time of posting. It is mostly west of the Greenwich meridian. But not invariably so.:p
 
ritelec

ritelec

Senior Member
Location
Jersey
I see how it might be wired but any problems with "ratings" that it doesn't show 120/240 operating at the same time?(480v side of 2nd pic)
 
ActionDave

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
ritelec said:
I see how it might be wired but any problems with "ratings" that it doesn't show 120/240 operating at the same time?(480v side of 2nd pic)
Click to expand...
Nothing to worry about a'tall. A Watt is a Watt, and a VA is a VA. A kva just means adding or taking away zeros.

Rock on. And be sure to make a cut around 3 khz. I don't like my ears shredded.
 
kwired

kwired

Electron manager
Location
NE Nebraska
malachi constant said:
That was my next question. Had my head in the code book before I looked up to see these responses. (FYI I'm working with the 2011 NEC.)

This transformer will be relocated to the side of an existing woodframe garage. We will provide a new 60A MCB panel within the garage. This panel will in turn feed a couple existing circuits in the garage and two new outbuildings - each of which is small enough to be fed with a single 120V 20A/1P breaker.

Article 250 has changed significantly since I last took a class on service grounding, so let me take my best guess as to what needs to happen.

Start with the outbuildings, they are easy. 250.32 Buildings Supplied by a Branch Circuit. (A) Grounding Electrode. "Exception: A grounding electrode shall not be required where only a single branch circuit supplies the building and the branch circuit includes an equipment grounding conductor." (That's not verbatim but close enough.) So no grounding electrodes required, correct? Just run an equipment grounding conductor to each device and we're good.

Back to the garage: I assume 250.30 is where to start. Looks like I must follow (A)(1) through (A)(8):
(1) System bonding jumper. Required, we will put it at the source.
(2) Supply-side bonding jumper. Required.
(3) Grounded Conductor: Not required as we have a system bonding jumper at the source [see (A)(1)].
(4) Grounding Electrode. Required. (1) and (2) are not available, so exception allows connection to any electrode listed in 250.52(A). I assume a single ground rod (as described in 250.52(A)(5)(b)) at the 480V:240V transformer is acceptable.
(5) Grounding Electrode Conductor. Required. Connect (1) to (4).
(6) Grounding Electrode Conductor, Multiple Separately Derived Systems. Not required.
(7) OK.
(8) No metal, not required.

I am foregoing the disconnect on the primary side of this transformer, as there is a main disconnect on the new panel on the secondary side. The two outbuildings each will have one single-pole main disconnect switch as the service enters the building.

Man, this part of the code is confusing. Getting closer to understanding it. I think I have it right on this project. Please let me know if I am off on something. Thanks!
Click to expand...
225.31 still requires a disconnect on the supply side of the transformer. Not necessarily because of the transformer but because it is the supply at a separate building or structure.

The secondary needs a disconnect because we now have a separately derived system, and the arrangement of that system would require a disconnect on the secondary regardless of where it is located.

If we had a two wire secondary (connected for 120 only and not 120/240) and the primary protection was sized to protect the secondary we could get by without secondary protection. See 240.21(C)(1) for this application.
 
Status
Not open for further replies.
Top