Transformer Monitoring Installation

110.14(D)

Member
Location
IL USA
A customer requires power monitoring at the secondary of the following transformer:
KVA: 1000
Primary Volts: 13200 VAC
Primary Current: 43.7
Secondary Volts: 480Y/277
Secondary Amps: 1203

Proposed installation has the monitoring device mounted on a wall @ 8' away, total lead length @ 12', CT leads and voltage leads in separate conduits. Monitoring equipment voltage leads terminate at a disconnect/fuse holder with FNQ-R-5 fuses. SCCR rating is "Exempt Per UL-508A Paragraph 49.5".

I've read 240.21(C) and don't see how this could be compliant. Most of the monitoring equipment I'm familiar with is entirely enclosed in switchgear as mentioned in the article.

If I'm referencing the wrong article, please direct me where to find the correct reference to determine placement of OC/Short Circuit protection and conductor size, if it's even possible.
 

ron

Senior Member
Is your concern that the voltage sensing leads are not protected? We typically mandate that the fuse protection you mention occurs within the 10' lead length of the transformer secondary terminations per 240.21(C)(2)(1) exception.
Or is your concern the lack of short circuit ratings?
 

110.14(D)

Member
Location
IL USA
My concern is the #10 leads attached to the secondary bus leaving the transformer enclosure unprotected. Code based size and placement of fuses is what I'm looking for.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
IMO this is a class 1 circuit.

725.3 Other Articles. Circuits and equipment shall comply
with the articles or sections listed in 725.3(A) through (N).
Only those sections of Article 300 referenced in this article
shall apply to Class 1, Class 2, and Class 3 circuits.
Article 240 is not mentioned in 725.3 (A) thru (N).

Take a look at 725.45.
 

110.14(D)

Member
Location
IL USA
240.21(C)(2)(1) exception gets you 10' lead length
Exception: Where listed equipment, such as a surge protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors
supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions.



Looks like the exception is dependent upon the manufacturer's instructions which unfortunately don't specify protection size, placement, or conductor ampacity, so it may not help us here.

240.21(C)(2) requires compliance with (1), (2), (3), and (4). Seems like (1), (2), (3) are in place and I'll find the size of the primary OCPD rating tommorow to do the calculation described in (4).
 

110.14(D)

Member
Location
IL USA
IMO this is a class 1 circuit.



Article 240 is not mentioned in 725.3 (A) thru (N).

Take a look at 725.45.
725.2 Definition of Class 1 Circuit:

Class 1 Circuit. The portion of the wiring system between the
load side of the overcurrent device or power-limited supply and
the connected equipment.

At this time I don't have an overcurrent device at the point of supply.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
725.2 Definition of Class 1 Circuit:

Class 1 Circuit. The portion of the wiring system between the
load side of the overcurrent device or power-limited supply and
the connected equipment.

At this time I don't have an overcurrent device at the point of supply.
Where does it say anything about point of supply. It says load side of oc device.
 

zog

Senior Member
Location
Charlotte, NC
A customer requires power monitoring at the secondary of the following transformer:
KVA: 1000
Primary Volts: 13200 VAC
Primary Current: 43.7
Secondary Volts: 480Y/277
Secondary Amps: 1203

Proposed installation has the monitoring device mounted on a wall @ 8' away, total lead length @ 12', CT leads and voltage leads in separate conduits. Monitoring equipment voltage leads terminate at a disconnect/fuse holder with FNQ-R-5 fuses. SCCR rating is "Exempt Per UL-508A Paragraph 49.5".

I've read 240.21(C) and don't see how this could be compliant. Most of the monitoring equipment I'm familiar with is entirely enclosed in switchgear as mentioned in the article.

If I'm referencing the wrong article, please direct me where to find the correct reference to determine placement of OC/Short Circuit protection and conductor size, if it's even possible.
Is there are reason they want to mount it on the wall? There should be a panel on the transformer designed to hold the optional monitoring equipment. We install a lot of Powerlogic monitors, the CM2350 should do everything you need to do and has protection built into the unit.
 

110.14(D)

Member
Location
IL USA
Yes Zog that would have been ideal, didn't happen that way. I don't know why it has to be where it is, I have no influence over how any of this gets done.

Anyway, back to 240.21(C)(2)(4).

As long as we've come this far, just to satisfy my personal curiosity, according to the described formula this would this be the required ampacity of an unprotected secondary?

OCPD setting based on ABB current relay with tap pins in position 6 x INST.(X TAP) dial set at 14.

(OCPD Setting x (Primary Voltage/Secondary))/10
(84 x (13200/480)) / 10 =
(84 x 27.5) / 10 =
2310 / 10 = 231 Amps
 
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ron

Senior Member
Anyway, back to 240.21(C)(2)(4).

As long as we've come this far, just to satisfy my personal curiosity, according to the described formula this would this be the required ampacity of an unprotected secondary?

OCPD setting based on ABB current relay with tap pins in position 6 x INST.(X TAP) dial set at 14.
The the rating of the overcurrent device protecting the primary of the transformer would be the 51 relay. The value you were calculating with above; was it the 50 relay or 51 relay setting?
Was the 51 setting at 84A or the 50 setting at 84A? Since the FLA of the primary was 43.7A, I'm not sure if the 51 setting would be as high as 84A.
 

110.14(D)

Member
Location
IL USA
That would be a model 51I. Not being familiar with the device I downloaded the manual. Works out to @192% which table 450.3(a) seems to allow. Impedance is 5.79 in supervised location.
 
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