3 wire feed to a cottage and grounding requirements

[allenwayne]

This is the senario,300 ft from mdp is a undrground feed to a guest cottage.For some reason unknown to me they only ran 3 # 2 al conductors.
The panel is in the kitchen of all places and the clearance is is encroached by counter space,the request was to hook up a package unit a/c.
I was considering bringing the 4 lighting circuits into a 6x6x4 pvc j box out side the building and nippling into a wp breaker box using the 6x6 as a way to extend the circuits into the new panel There is no ground per say and I will sink 2 ground rods ( the area is all sugar sand)The wp panel will have a main breaker so that there is a means of disconnect.
The reason for this is thst a package unit will be replacing one that I wish I had a pic of how it was installed. The panel is within sight of the unit so there goes the disconnect the water heater is inside and I told the customer that I will have to add a disconnect for it.There are only four circuits in the cottage,who ever wired it did install 2 appliance circuits but no gfci devices also told h/o they will be required the 2 remaiing circuits feed bath room l/r and bed room and dining area.Luckily ther dining is on the kistchen circuit so that is a no brainer .I asume I will have to add an afci to the remaining circuit to cover the bed room.I can eliminate the bath from the l/r quite easily and re feed off thel/r from the bedroom afci.
So there wil be 2 SA circuits one feeding the dining area the bath will be seperate and the l/r and bed room will cover the afci issue.
My only problem is that there is wil be a main disconnect at the cottage and since there is only a 3 wire feed from the mdp that the ground rods at the cottage will be okay to satisfy 250

 

[iwire]

Re: 3 wire feed to a cottage and grounding requirements

Allen treat the 3 wire feeder exactly like you would treat a typical service.

Bond the neutral to the disconnect enclosure, connect some grounding electrodes to the neutral and from that point on you will have to run separate neutrals and grounds.

This is specifically allowed for detached buildings by 250.32(B)(2) and take a look at 250.32(A) as well.

250.32(B)(2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of

(1) That required by 220.22

(2) That required by 250.122

 

[allenwayne]

Re: 3 wire feed to a cottage and grounding requirements

Bob I just wanted ti be sure that my plan was ok thsnks

 

[hurk27]

Re: 3 wire feed to a cottage and grounding requirements

Just keep in mind that the AC unit is going to dim lights with that size wire @ 300' for #2al you only have 40 amps for a 3.2%drop

 

[allenwayne]

Re: 3 wire feed to a cottage and grounding requirements

that has already been dscussed with H/O`r he is ok with that.range is gas and so is water heater
It`s just that 2 rooms were added and the old unit couldn`t handle the load.
To me it was easier to move existing h/r`s to an wp enclosure and go from there.basically I wanted to be sure that addng the ground rods was the way to go.I don`t do much service,new construction mostly and wanted your valued o opinios

 

[pierre]

Re: 3 wire feed to a cottage and grounding requirements

Allen
Are there any metallic paths from the main house to the cottage?

 

[roger]

Re: 3 wire feed to a cottage and grounding requirements

These metallic paths mentioned by Pierre could be a phone cable, water pipe, or even a coax.

Roger

 

[pierre]

Re: 3 wire feed to a cottage and grounding requirements

Thanks Roger. I woke up very early this morning and I am ready to go back to bed

 

[al hildenbrand]

Re: 3 wire feed to a cottage and grounding requirements

Posted by Roger:

These metallic paths mentioned by Pierre could be a phone cable, water pipe, or even a coax.

And since the range and water heater are gas fired, don't overlook the possibility of a metallic gas line that is privately owned and installed without continuity isolators ("continuity isolators". . .whatever those little nonconductive coupling thingys are called )

 

[roger]

Re: 3 wire feed to a cottage and grounding requirements

Good morning Al, good point.

Roger

 

[roger]

Re: 3 wire feed to a cottage and grounding requirements

Pierre,

Originally posted by pierre:
Thanks Roger. I woke up very early this morning and I am ready to go back to bed

being that it is Saturday, and my biggest "Have to do item" today is mow, I did go lay back down for about a 1/2 hour after I posted that.

Roger

 

[al hildenbrand]

Re: 3 wire feed to a cottage and grounding requirements

A good mow is something not to be approached lightly.

 

[allenwayne]

Re: 3 wire feed to a cottage and grounding requirements

Just wanted to make sure i was correct in the way is intend to do it.Phone company has installed there own ground rod and the direct tv sat. company has installed their own ,I was considering using one of these but decided to install one myself since thiers is so tar away.I don`t do much retro fits but This is for a really good friend and wanted to do an A - 1 job for him.Thanks again for the advice

 

[allenwayne]

Re: 3 wire feed to a cottage and grounding requirements

Almost forgot the house usespropane and the 100 lb tank is around 10 ft away and i am going to bond the nipple seperatley from the isolated ground bar in the wp panel

 

[roger]

Re: 3 wire feed to a cottage and grounding requirements

Allen, the way these items are grounded is not the point at hand. You must be sure that there are no cables, metallic water pipes, cast iron waste piping, conduits, etc... going from one building to the other.

It is common for the phone company to individually ground at multiple buildings even though the infrastructure is copper conductors joining all the buildings together.


Roger

[ July 16, 2005, 01:15 PM: Message edited by: roger ]

 

[awg]

Re: 3 wire feed to a cottage and grounding requirements

I have been reading this thread with some interest because this question was put to me lately and now I feel like I may have misled him.
I am assuming that this cottage is fed from the panel of another dwelling. I thought that the equipment grounding conductor and neutral were bonded at the service entrance
only and would need a 4 wire feed to an outbuilding. My understanding was that driving another ground rod and bonding the neutral and equipment ground after this point could create some problems. If this is ok why would anyone go to the expense of another conductor (300')? Does the fact of having the new main make the difference.I have looked in the archives and researched the areas of the code that have been suggested till my head hurts. I am just looking for some clarification as most of my experience is in industrial construction (mostly controls) and I don't get into this very often.

I would appreciate further clarification,thanks.

 

[iwire]

Re: 3 wire feed to a cottage and grounding requirements

If a building is detached from the building the feeder originates from and there are no bonded metallic paths (water, gas, CATV etc) between the two buildings it is up to the installer if they want to run a equipment grounding conductor or not.

As long as the above rules are followed there are no problems.

If someone comes later and runs a metal water pipe between these two buildings it would be required to be bonded at each building, at this point the water pipe would become parallel to the neutral between the buildings and would have part of the neutral current flowing on it.

If you run a separate equipment grounding conductor or not you are required to provide grounding electrodes at every separate structure served by a feeder or two or more branch circuits.

 

[physis]

Re: 3 wire feed to a cottage and grounding requirements

There's 230.40 Ex. No. 3.

 

[iwire]

Re: 3 wire feed to a cottage and grounding requirements

The code sections to look at are

250.32(A)

250.32(B)(1)

250.32(B)(2)

Sam's 230.40 Ex 3 is a different way of handling it.

The 250.32 sections are dealing with feeders.

230.40 Ex 3 is dealing with service entrance conductors which do not have a separate equipment grounding conductor.

[ July 16, 2005, 03:33 PM: Message edited by: iwire ]

 

[physis]

Re: 3 wire feed to a cottage and grounding requirements

I don't know why I'm thinking 230.

Edit: That's probably why I wasn't finding what I was looking for.

[ July 16, 2005, 03:38 PM: Message edited by: physis ]