Drop the neutral?

Status
Not open for further replies.
H

hardworkingstiff

Senior Member
Location
Wilmington, NC
It is my understanding that if I don't need a neutral at a sub panel then I don't need to take the neutral to it.

Here is the scenario. There is a service disconnect at the shore line. We want to install a 480-volt 3-phase panel at the end of a 400' long fixed pier leading to floating docks. Transformers will be used on the floating docks. We won't need a neutral for anything, so I'm of the understanding that the neutral can stop at the service disconnect and doesn't need to be carried to the sub panel.

Right/wrong?

Thanks,
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Lou,
How are you going to handle the grounding electrode and grounding electrode conductor that is requied for the secondary side of the transformer?
 
H

hardworkingstiff

Senior Member
Location
Wilmington, NC
don_resqcapt19 said:
Lou,
How are you going to handle the grounding electrode and grounding electrode conductor that is requied for the secondary side of the transformer?
Click to expand...

Pull a 3/0 (cu.) from shore (ground rods) and cadweld a tee off to the transformers. Spoke with the AHJ and they agreed to that. It's close to 1,000' from shore to the fartherest transformer. Seems like it's not so great an install.

I'm open to suggestions!
 
Last edited:
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
hardworkingstiff said:
I was thinking, since there is really nothing to connect the GEC to except the ground rods, then it really doesn't have to be larger than a #6, right?
Click to expand...

That is correct. 3/0 is not necessary. Also throwing a #6 into the water will not do much good either. Water is a bad conductor of electricity. Now go under water and drive a rod you may be on to something good. :D
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
At my dad's marina, we drove threaded brass rods right at the transformer through the water into the bottom, we had to thread two 20' sections together to reach the bottom of the dock at low tide, and left extra wire for high tide. Since it was salt water, the impedance was super low.
 
ericsherman37

ericsherman37

Senior Member
Location
Oregon Coast
Or you could get your scuba gear on, grab a sledge and some cable staples (stainless of course) and swim down to the bottom to drive your ground rod and install your GEC. Or maybe you could just staple the bare wire down the dock piling for a ways.

How about a code proposal allowing for "water-encased electrodes" for 2011?
 
ericsherman37

ericsherman37

Senior Member
Location
Oregon Coast
hurk27 said:
At my dad's marina, we drove threaded brass rods right at the transformer through the water into the bottom, we had to thread two 20' sections together to reach the bottom of the dock at low tide, and left extra wire for high tide. Since it was salt water, the impedance was super low.
Click to expand...

How stiff are those kind of rods? I imagine 40' would be pretty wiggly and hard to drive?
 
electricmanscott

electricmanscott

Senior Member
Location
Boston, MA
hurk27 said:
At my dad's marina, we drove threaded brass rods right at the transformer through the water into the bottom, we had to thread two 20' sections together to reach the bottom of the dock at low tide, and left extra wire for high tide. Since it was salt water, the impedance was super low.
Click to expand...

How did you comply with 250.53 (A) (G) and 250.62 (B) ;)
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
How did you comply with 250.53 (A) (G) and 250.62 (B)
Click to expand...

Was there code in 1976 lol,

I think they were driven about 15' into the silt bottom, I know the water was about 20' deep at low tide, so we had to cut some off, I remember sitting in a john boat with a hacksaw for ever, at least it seemed lol, can't remember what the wire was we use but it was flexible and special for marine applications, I remember when you stripped it it had a greassy like coating, kind of like DB phone cable. the transformers were also fed with this type cable.
 
mikeames

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Master Electrician - 2017 NEC
Dennis Alwon said:
That is correct. 3/0 is not necessary. Also throwing a #6 into the water will not do much good either. Water is a bad conductor of electricity. Now go under water and drive a rod you may be on to something good. :D
Click to expand...

No but salt water is good.
 
Status
Not open for further replies.
Top