Sub Feed Panel

[howelloregon]

I have a consumer who has built on to both sides of his house. We wants to add a new panel on one of the additions and sub-feed the existing panel from the new one. The on-site electrician said that the code stated a need for four wires between the panels. We are the authority having jurisdiction, but I thought you only needed three wires. Which is right?

 

[iwire]

Re: Sub Feed Panel

How would you do it with only 3 wires?

 

[petersonra]

Re: Sub Feed Panel

Originally posted by iwire:
How would you do it with only 3 wires?

L-N-G?

Legal but not all that great of an idea in my mind.

 

[iwire]

Re: Sub Feed Panel

Originally posted by petersonra:
L-N-G?

Legal but not all that great of an idea in my mind.

 

[ryan_618]

Re: Sub Feed Panel

Do you really think your qualified to assume the rule of the authority having jurisdiction?

 

[charlie]

Re: Sub Feed Panel

I assume from your comment and the way you have signed into this forum that you are indeed an electric utility engineer and follow the NESC most of the time and are not familiar with the NEC in general. If this is true then you are inspecting the service and meter fitting to make sure there are no glaring mistakes that would cause anything to blow up, then energize the service. Since there are not inspectors where you are located, you end up being the AHJ by default.

I highly recommend that you find someone that knows the Code to do the inspections for you before someone loses there home or worse, a life. It is obvious that you do not know the rules in the NEC and that is why the members of this forum are coming down on you a bit.

 

[kpepin]

Re: Sub Feed Panel

I don't know... the 2005 NEC does have a nice FPN in Chapter 1 about AHJ!

The answer the question, YOU NEED 4 Wires.

Sub-panels need a ground wire connected back to the main ground. Phase, Phase, Grounded, and Grounding conductor (1,2,3...4)

 

[charlie]

Re: Sub Feed Panel

I don't know... the 2005 NEC does have a nice FPN in Chapter 1 about AHJ!

If the area that the electric utility serves has no AHJ, by default, the electric utility becomes one or anything could get hooked up. On the last page in this section of the IPL Goldbook, I am listed as the AHJ for one area that we serve. I have no real authority other than the ability to tell the customer that he will not get power until he fixes his service. The only thing that I inspect is the meter fitting, service and grounding. The rest is up to him, we make sure that the part we energize is safe.

 

[howelloregon]

Re: Sub Feed Panel

Based on the response to our post, I feel the overwhelming need to apologize to all the experts that replied. After all we are just a lowly electrical utility, and do not possess the knowledge necessary to recieve a straight forward reply. We were under the misconception that this site was intended for people who "NEEDED" guidance and direction when pertaining to the NEC, our mistake.

We live in the world of the NESC, I cringe every time one of our 23,000 members calls on us for guidance beyond our "point of service", but we try to help where we can. This would be a new concept to you people.

We work with 'real' voltage everyday. Not the kind that "tingles", the kind that blows off your feet and all your fingers,"cooks" your internal organs,and stops your heart. So when you people fall off your high horses and need a question answered about the NESC, give us a shout, we will be glad to answer all your stupid questions, without hesitation and smart remarks.

Our linemen that have been hooking up homes for 36 years are still under the impression that it is acceptable to use three conductors to sub-feed the panel. There is a driven ground at both panels, and the neutral is bonded to the grounding bar in the panels. That's three wires 1..2...3..., not four wires, just three, 1....2......3...... That's how we do it with three wires. Phase, Phase, Nuetral, Done. There's three wires in the meter loop, three wires in the service wire, and three wires in the top of the load center at each home on our system. With the exception of some mobile homes that have a four wire system. It must be a MIRACLE that these homes are still standing, because surely thousands of catastrophes would have happened by now.

To my knowledge no one cited where in the code it states that the circuit between panels has to be four conductors. That is all we were asking for in the first place.


Troy Hogsett, PE

 

[tom baker]

Re: Sub Feed Panel

If you are referring to a panel in the same building or structure, then the grounded neutral can not be used as an equipment ground.
The NEC does not use the term "sub-panel", but the rule is in 250.142(B).
If a seperate building or structure, then the NEC allows it, but it is not recommended. This rule is in 250.32.

 

[petersonra]

Re: Sub Feed Panel

The code is very clear about how many wires have to be run. Only services get away with 2 hots and a neutral.

Anything downstream of the service needs an EGC except in a very few limited cases.

 

[don_resqcapt19]

Re: Sub Feed Panel

Troy,
Look at 250.24(A)(5). A three wire connection to a sub panel with a grounding electrode would be a grounding connection to the grounded conductor on the load side of the service disconnect.

250.24(A) ... (5) Load-Side Grounding Connections. A grounding connection shall not be made to any grounded circuit conductor on the load side of the service disconnecting means except as otherwise permitted in this article.

Don

 

[charlie b]

Re: Sub Feed Panel

Originally posted by howelloregon:That's how we do it with three wires. . . . Phase, Phase, Neutral, Done. . . . It must be a MIRACLE that these homes are still standing, because surely thousands of catastrophes would have happened by now. Troy Hogsett, PE

The fact that a dangerous situation has not yet led to an injury does not render the dangerous situation safe. Draw a circuit diagram, and look at the possible current paths. Draw circuits that represent metal connections between the buildings and that represent the absence of such connections (as discussed in the code sections cited by Tom). I think you will quickly see where and how a dangerous situation might arise. The basic danger is having current flowing, as a routine event and not just as the result of a fault condition, through exposed metal surfaces.

Charles E. Beck, P.E.

SIDE NOTE TO ALL FORUM MEMBERS:
This thread has the beginnings of an ?insult contest.? Do not pursue that path. Let there be no more personal comments or sarcasm, or I will delete the entire thread.

[ December 22, 2004, 11:19 AM: Message edited by: charlie b ]

 

[iwire]

Re: Sub Feed Panel

howelloregon

How about we start again with a clean slate?

I should have done what Charlie E did and looked at your profile and I might have understood where you where coming from.

You got grief because the question you asked is common knowledge for electricians and most of us are used to the AHJ being an electrician versed in the NEC.

So are we OK now?

The problem with using a 3 wire feeder (H, H, N) to subpanel in a house is this.

There is a good chance you will end up carrying some of the current from the neutral through the copper plumbing inside of the house.

That is a safety issue that may start a fire or give someone a shock if they seperate the pipe while working on it.

Say from this subpanel you feed an electric hot water heater, once we tie the equipment grounding conductor from the subpanel to the hot water heater we have put the plumbing pipes inside the house in parallel with the neutral conductor.

Yes this happens all the time outside the house in areas with underground metal water piping systems that are bonded at each house.

Being buried that does not pose much of a problem.

Bob

 

[hurk27]

Re: Sub Feed Panel

One of the other things that could happen is lets say you have the water pipes bonded to the main service as required in article 250. then you have a washer that was fed from this sub panel. now someone reach's to turn off the water while leaning on the washer and a ground fault happened at this very instance. the voltage drop of the neutral feeding this sub panel will now be on the washer grounding and frame, thus there will be a voltage difference between the washer and the water valve this person was touching and could receive a lethal shock. The only time the NEC allows a neutral to be used as a grounding conductor after the main service disconnect is for an out building that has no electrically conductive pathways like water pipes, gas pipes, phone/cable wires. between these two buildings. The reason for this is the problems that Bob and I described. After the main service disconnect the neutral and grounding conductors have to be kept separate. If this was not true then why do we have to have a third grounding terminal on a receptacle. why not just bond the frame of a drill or washer to the neutral in the cord?
Because it is a shock hazard is why. Because any short in a appliance that is wired like that would produce a voltage drop and cause a voltage differential to be between the tool and earth.

Hope this helps.

 

[howelloregon]

Re: Sub Feed Panel

I have been out on vacation, but would like to thank the people that gave us cordial responses.

I understand what you guys are saying, but one point you have not addressed is that the "old" panel that is now being sub fed used to be the main panel. All the grounding conductor wires and grounds are inter-twined. There is a jumper between the grounding bars. To my knowledge the electrican was not going to splice all the wires necessary to separate the grounding wires from the neutrals. This is what make this situation unique.

Wouldn't the neutrals and the grounding conductors have to be separated before the "case shock" hazard would exist? I know this is a little off of a "textbook" case, but that's usually when we get asked.

I also realize that if it were new construction we probably wouldn't be having this discussion.

Troy Hogsett, PE

 

[gregoryelectricinc]

Re: Sub Feed Panel

You make a good point there Troy. To meet NEC the onsite electrician will definitley need to seperate all the grounded and grounding conductors from the branch circuits in the original panel.

 

[karl riley]

Re: Sub Feed Panel

Just to try to summarize, when you add a new panel as the service panel and the original service panel becomes a sub panel, you have to both run a 4 wire to the old panel but also you must disconnect the neutral/ground bond in the old panel. That bond is necessary in the new service panel.

I also would urge veteran forum members to hold off on their sarcasm, etc. and just give a simple answer to a simple question. We are quick to start wars, and we are learning it is much harder to end them. Applies to verbal stuff too.

Merry New Year to all.

Karl

 

[crossman]

Re: Sub Feed Panel

I am new to the forum... and I actually am enjoying the "subpanel" battle here and on another old thread I dug up.

My first post and my first two cents:

I believe everyone is overlooking another safety issue of using the grounded conductor also as an equipment grounding conductor on the load side of the service.

Consider: Residence, all wood construction, NM cable. 120/240 single phase Service Panel feeds a small 120/240 subpanel that is mounted to wood studs. A three-wire cable feeds the subpanel and the neutral is also used as an equipment ground to the subpanel enclosure. There are two 120v branch circuits from the subpanel. One feeds a 100 watt light bulb which is on. The other BC feeds a 3-wire receptacle. An electric drill motor with its metal case grounded through the receptacle is plugged in. The drill motor is off.

So far so good?

Now, the neutral in the feeder cable is disconnected at either the service panel or the subpanel (or the connections become high resistance because of corrosion or whatever, or the neutral gets cut, whatever, somehow we lose the neutral between the service panel and subpanel.)

Anyone see any hazards here? Hint: doesn't involve the water pipes or any other parallel paths...

[ January 03, 2005, 06:04 PM: Message edited by: crossman ]

 

[iwire]

Re: Sub Feed Panel

Welcome to the forum crossman.

Originally posted by crossman:
Anyone see any hazards here? Hint: doesn't involve the water pipes or any other parallel paths...

Well yes but that is the same hazard posed by an open neutral on the supply side of the service.