TRANSFORMER WORRY

[bure961]

I have come across transformer installations that has been in stalled in the mid 80's where there is not a connection to building steel ,they use bonding bushings on sealtight connectors that attach to a bonding lug on the transformer case. I do not see any egc on either primery or secondary to the transformer.

How can one determine if this is safe design or was legal in the 80's ? This design is for a 480 volt to a 208y 120 volt 75 kva . I have limit contact to transformer wiring and this is whyI ask these questions.

 

[infinity]

Here's the 2011 NEC requirement for LFMC used as an EGC:

250.118(6) Listed liquidtight flexible metal conduit meeting all
the following conditions:
a. The conduit is terminated in listed fittings.
b. For metric designators 12 through 16 (trade sizes
3/8 through 1/2 ), the circuit conductors contained in
the conduit are protected by overcurrent devices
rated at 20 amperes or less.
c. For metric designators 21 through 35 (trade sizes
3/4 through 1 1/4 ), the circuit conductors contained in
the conduit are protected by overcurrent devices
rated not more than 60 amperes and there is no
flexible metal conduit, flexible metallic tubing, or
liquidtight flexible metal conduit in trade sizes
metric designators 12 through 16 (trade sizes
3/8 through 1/2 ) in the ground-fault current path.
d. The combined length of flexible metal conduit and
flexible metallic tubing and liquidtight flexible
metal conduit in the same ground-fault current
path does not exceed 1.8 m (6 ft).
e. If used to connect equipment where flexibility is
necessary to minimize the transmission of vibra-
tion from equipment or to provide flexibility for
equipment that requires movement after installa-
tion, an equipment grounding conductor shall be
installed.

The 1981 NEC stated that:

351-9 Grounding. Liquidtight flexible metal conduit shall be permitted as a grounding conductor where the conduit and the fittings are approved for grounding. Where an equipment bonding jumper is required around liquidtight flexible metal conduit, it shall be installed in accordance with Section 250-79.
Exception: Liquidtight flexible metal conduit shall be permitted as a grounding means in the 1 1/4" and smaller trade sizes if the total length in any ground return path is 6 feet (1.83 m) or less and the conduit is terminated in fittings approved for grounding.

So you can see that if you were under the 1981 NEC the requirements were different than the 2011 NEC. Either code cycle would require something other than the metallic raceway as an EGC if it were larger than 1.25" trade size. Also the 2011 would require a wire type EGC if flexibility were required for vibration regardless of the size of the LFMC.

 

[Smart $]

Here's the 2011 NEC requirement for LFMC used as an EGC:



The 1981 NEC stated that:


So you can see that if you were under the 1981 NEC the requirements were different than the 2011 NEC. Either code cycle would require something other than the metallic raceway as an EGC if it were larger than 1.25" trade size. Also the 2011 would require a wire type EGC if flexibility were required for vibration regardless of the size of the LFMC.

Even with a compliant EGC on both line and load sides, what about a GEC requirement for separately derived system?

 

[infinity]

Even with a compliant EGC on both line and load sides, what about a GEC requirement for separately derived system?

I figured that I would leave that one for someone else.

 

[Haji]

Even with a compliant EGC on both line and load sides, what about a GEC requirement for separately derived system?

What if it were an ungrounded system?

 

[augie47]

What if it were an ungrounded system?

Since the secondary 208/120, 250.20(B) would require the system to be grounded.
From other posts, it's seems clear a proper primary grounding means is needed.
I don't have a '81 Code but I would bet a grounding electrode was required.;

 

[don_resqcapt19]

What if it were an ungrounded system?

The only difference between a grounded and an ungrounded system as far as grounding is the fact that the ungrounded system will not have a main or system bonding jumper.

 

[don_resqcapt19]

Even with a compliant EGC on both line and load sides, what about a GEC requirement for separately derived system?

The code certainly requires a grounding electrode and grounding electrode conductor for this application, but assuming that the transformer is in the same building as the primary feeder OCPD, I don't see a technical or safety reason for one...just a code rule.

I can see a need for bonding of the secondary grounded conductor to building steel and or metal water piping in the area of the transformer.

 

[Sahib]

As regards safety, I think the

grounding electrode and grounding electrode conductor

is equivalent to

bonding of the secondary grounded conductor to building steel and or metal water piping in the area of the transformer

when building steel and or metal water piping is not available.