Boat Dock hazard.

[jim dungar]

An isolation transformer would typically only mitigate issues caused by the load side of the transformer, stray voltage/current caused by the utility could still be a concern

 

[jim dungar]

Could one use 250.6(B) to "Stop Objectionable Current" by removing the primary to secondary bonding?

Removing this 'grounded conductor' bonding creates an isolation transformer. The 'grounding conductors' would still connected.

 

[winnie]

Removing this 'grounded conductor' bonding creates an isolation transformer. The 'grounding conductors' would still connected.

Does NEC require the primary EGC be connected to the secondary GEC? Or is this simply common practice because common transformers have a single chassis and a single grounding lug?

If you had a transformer with a non-metallic enclosure, with grounding of the core somehow isolated to only one or the other side, could you ground the derived secondary to a local grounding electrode that was _isolated_ from the primary EGC?

-Jon

 

[Electromatic]

..., could you ground the derived secondary to a local grounding electrode that was _isolated_ from the primary EGC?

-Jon

That's kind of what I'm thinking. This isolated grounding would be local to the dock area, and the separation from the primary grounded conductor would not be a path for remote, "stray" voltage to return to the utility.

 

[jim dungar]

Does NEC require the primary EGC be connected to the secondary GEC? Or is this simply common practice because common transformers have a single chassis and a single grounding lug?

If you had a transformer with a non-metallic enclosure, with grounding of the core somehow isolated to only one or the other side, could you ground the derived secondary to a local grounding electrode that was _isolated_ from the primary EGC?

-Jon

Typically the utility system is an MGN bonded to the same dirt as the isolated grounding electrode.

I see no way to isolate the dock itself from earth and thus from the utility MGN path.

 

[winnie]

Typically the utility system is an MGN bonded to the same dirt as the isolated grounding electrode.

Yes, but if there is significant distance between the isolated grounding electrodes, then the resistance between the two electrodes will reduce the current flowing between the two. Neutral isolators on the utility side of things work, even though stuff is grounded on both sides of the isolation point.

The question is there is a way to perform the equivalent on the NEC side of things.

-Jon

 

[ramsy]

You would need a transformer that somehow isolates primary and secondary terminals, and provides a separate 'ground fault current path' for each.

Golddigger's Neutral Isolator automatically closes during a fault.

 

[drcampbell]

High-isolation transformers exist. The primary and secondary windings are physically separated so that an insulation failure will not result in a primary-to-secondary short. (this design also minimizes capacitive coupling) But I'm not aware of any that would be big enough for a boat dock.

1.1VA to 36VA High Isolation Split Bobbin Transformer

Wabash offers Printed Circuit Boards for High Isolation Transformers 24VAC to 24VAC. 1.1VA, 2.4VA, 6VA, 12VA, 20VA, 36VA. Single Primary 24V. Frequency 50/60Hz. Low capacitive coupling, no Electrostatic Shield needed. UL/cUL recognized.

www.wabashtransformer.com

 

[synchro]

Does NEC require the primary EGC be connected to the secondary GEC? Or is this simply common practice because common transformers have a single chassis and a single grounding lug?

If you had a transformer with a non-metallic enclosure, with grounding of the core somehow isolated to only one or the other side, could you ground the derived secondary to a local grounding electrode that was _isolated_ from the primary EGC?

-Jon

Could an outdoor rated 120V/120V transformer to be put on a wooden pole without a connection between primary and secondary side EGG's, and be allowed by 250.110 Exception No. 2 ?

250.110 Equipment Fastened in Place (Fixed) or Connected by
Permanent Wiring Methods.
Exposed, normally non-current-carrying metal parts of fixed equipment
supplied by or enclosing conductors or components that are likely to
become energized shall be connected to an equipment grounding
conductor under any of the following conditions: ........

Exception No. 2: Distribution apparatus, such as transformer and capacitor
cases, mounted on wooden poles at a height exceeding 2.5 m (8 ft) above
ground or grade level shall not be required to be grounded.

If such a transformer setup was done, perhaps a 30 mA GFPE could feed the transformer to protect against any primary to secondary leakage current that could flow into the secondary's grounding electrode and elevate its voltage.

 

[hillbilly1]

Let’s go about this from a different angle, remove all 120 volt wiring, and change to 12 vdc, change lighting to dc, the receptacles were probably for a radio or tv, change those to 12 vdc. No bonding of the dock required.