3 wire feeder to subpanel free –
Well, I think I know the answer, so let me rephrase – Why is it safe to run a 3 wire to feed a service panel, but not to feed a sub panel? George Stolz Moderator Staff member. Location Litchfield, CT. One major reason the grounded circuit conductor is NOT permitted to be grounded on the load side of the service is, should the grounded service conductor become disconnected at any point on the line side of the ground, the equipment grounding conductor and all conductive parts connected to it will carry the neutral current, raising the potential to ground of exposed metal parts not normally intended to carry current.
This could result in arcing in concealed spaces and could pose a severe shock hazard, particularly if the path is inadvertently opened by a person servicing or repairing piping or ductwork. Even without an open neutral the equipment grounding conductor path will become a parallel path with the grounded conductor, This could involve current flowing through metal building structures, piping, and ducts. Stick, One major reason the grounded circuit conductor is NOT permitted to be grounded on the load side of the service is, should the grounded service conductor become disconnected at any point on the line side of the ground, the equipment grounding conductor and all conductive parts connected to it will carry the neutral current, raising the potential to ground of exposed metal parts not normally intended to carry current.
Click to expand Thats why we BOND the neutral to the ground Last edited: Feb 15, Location Massachusetts. Well we run a 3 wire to a service because the power company does not provide a forth wire and the NEC has no authority to make them do so.
I am willing to bet that is at least part of the answer. I’d tend to agree with Bob, which probably comes as no surprise. Ethan, my comment was more along the lines of, that is another one of your seemingly innocent questions that could result in a post thread. Keep ’em coming. Maybe the theory is that service conductors are less lkely to be compromised due to their stricter installation requirements length, wire methods, etc?
Another thought: the neutral is generally larger than a required EGC would be, and would have a lower impedance during a fault. Current seeks a path back to the source. Once it has made it back to the main service panel, it has essentially achieved that goal. What happens after that, whether the current travels along a neutral or a ground or a phase conductor, is an SEP issue.
Often used as a technique for rendering electrical hazards invisible. Location Leander Texas. Ok, thats fair BUT, can’t the same thing be said of a service panel? Not fair, Jon, beating me to my own punchline.
Someone Else? Credit Douglas Adams, author of the five volume trilogy that began with? The Hitchhiker? Dirk Gently? As an example of an? SEP Field,? All around that area a field is created. The closer you are to the spot, the less comfortable you are, perhaps fearing that someone will think you are at least partially to blame.
But the further you get from the spot, the more readily you can relax, knowing that the incident is? I would have considered the xfm as the source. Let’s see, what change happens at the service panel? Why is it safe to run a 3 wire to feed a service panel, but not to feed a sub panel? When you have multiple ground-neutral bonds, you create a situation where some amount of current will flow on your ‘ground’ conductors.
However as long as your ground conductors are well bonded and have sufficient ampacity, this does not create much of a hazard. In the past and in millions of grandfathered installations, the neutral was used to bond the frame of electric ranges and dryers. Multiple grounding of the neutral appears to have benefits in terms of protection from lightning, at least on the scale of utility distribution of power.
Usually this isn’t a problem In urban areas with shared underground metallic pipes and shared utility transformers, each ‘ground to neutral’ bond in each service is in parallel with other bonds in adjacent houses. Significant current flows on the shared water pipes, and this isn’t a problem until the plumber goes to work on the pipes. Multiple grounding of the neutral appears to cause problems when the bonding of the ground system is not sufficient.
We don’t care about a 0. We care quite a bit about a 10V difference between two metal surfaces that a person could touch simultaneously. The shell of an individual structure is probably a good dividing line between permitting and prohibiting multiple grounding of the neutral.
Outside of the structure the scale of distances is such that problems will be uncommon, and the benefit of multiple grounding more important. Inside of a structure you have utilization equipment in close proximity and greater chance of touch potential, and we prohibit the such multiple bonding.
But at the boundary of the structure plumbers working on the water main and in situations sensitive over longer distances farms where metal structures can ‘focus’ potential differences , problems with multiple earth bonding can still be noticed. But that time spent outside the house is not relevant to the safety of the person standing inside the house. It cannot shock the person, if for example the person touched a section of conduit, because it is heading towards the?
Charlie, There are a few places where I’m not understanding the physics you are using. But that time the current spent outside the house is not relevant to the safety of the person standing inside the house. What changes is that the direction of current flow is away from the house.
3 wire feeder to subpanel free. Subpanel fed by 3 wire without EGC
There needs to be a means to ground them at the sub panel without using the neutral. This can be done by adding a bus bar that is bonded to the metallic assuming conduit supplying the sub panel. If the sub panel in a separate building is fed by a 4 wire circuit, no additional GES would be required other than via the ground conductor feeding the panel? If the conduit does not serve as a means to bond the equipment, a four-wire feed would be necessary.
Regardless of the feed 3-wire or 4-wire , a separate building requires its own grounding electrode system GES via ground-rod, water pipe, ufer, etc.
Thanks for the feed back. In most cases around here, the distribution panel is quite a distance from the service panel and is fed only with the wire no conduit. It looks like you’re using an ad blocker. We get it, but 1 terrylove. If you’d like to support the site, please allow ads. Forums New posts Search forums. What’s new New posts New resources New profile posts Latest activity.
I understand that my current setup is grandfathered in and code is now 4 wire but I won’t be able to add this very easily to the main panel.
I also understand the risk of a 3 wire subpanel and that an open neutral will put V to grounded metal surfaces. I’ve read through this site and other sites and believe my diagram shows how this would have been wired prior to the wiring codes. Still, I’d still like the experts to add their inputs.
So my questions are, is this the safest way to approach this without adding a 4th wire, and do I need a separate grounding rod at the new subpanel when I already have a grounding rod at the garage subpanel which is about 30 feet away?
PS, Part of this diagram was taken from this site, but I wanted to add my own setup to make sure there weren’t any additional issues. Thanks and your inputs are greatly appreciated. You will need to run 4-wire from the grandfathered subpanel to the new sub-sub-panel. You will need land the neutral and ground feeders on neutral and ground buses in the existing subpanel. You will need to separate ground and neutral buses on the new panel.
Tell you a story. A company did a remodel on an old 2-story building. They needed wheelchair accommodations in upstairs hallways and bathrooms. Three years later, they built another building right next to it, with a 2nd floor walk-between.
The other shoe will eventually drop, you will want to upsize the existing feeder. At that point you will go 4-wire, and since the new extension is 4-wire, you are Code complete. The current subpanel has the same breaker size as the intended feed to the sub-subpanel. Get rid of it. This would be at main panels only. The cable running from your main panel to the subpanel depends on the amperage rating.
For instance, for a 30A panel, use a 10 AWG, three-wire conductor. Answer: No. Whether you need two or not is determined by the soil and local regulations. So, check your local code requirements.
The subpanel may be equipped with a main breaker to allow for power interruption without having to go back to the main panel, but it is not required to have a main shutoff circuit breaker , since the feeder breaker back in the main panel serves this function.
According to the National Electrical Code, or NEC, a ground system should have a grounding resistance of 25 ohms or less.
A detached building with a subpanel needs its own ground rod , regardless of if there are three wires or four wires feeding it. The earth is a very poor conductor. There is a neutral in a three phase four wire system.