Why must ground & neutral be seperate in subpanel?

I installed a subpanel when I switched from an electric stove to gas. I used the 40A 220V breaker that formerly served the stove to power the sub panel. The cable is #4 with two conductors and a ground. I have 6-

15 amp breakers in the panel providing branch circuits for my kitchen and other areas of my house. The grounds and neutrals all share the common bus bar in the sub panel. Everything has worked fine for years now. Can someone explain why I read that ground and neutral are to be isolated in the sub panel? Please don't answer because of the NEC since that does not explain why. What is the risk of my current situation?

Thanks, Joe

Reply to
joseph.hollyday
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While I agree that what's there is correct and functional "circuit wise" I think the reason the code requires a separate ground conductor is this:

That common ground/neutral might develop an open between the sub panel and the main panel because of a "loose connection" at one end or the other. If that happened currents returning on the neutrals of those "new" branch circuits would lift the whole "ground" of the sub panel off true ground and would create a dangerous situation by making things like the grouning slots in recepticals rise above ground to dangerous voltage levels.

Jeff

Reply to
Jeff Wisnia

Essentially, because the ground wire is connected to things that people are expected to touch.

When you connect the nuetral and ground together, you create the possibility of the ground becoming hot, and energizing things like the outside of your refridgerator. This is bad. The probability of this happening goes up astronomically if there is a nuetral/ground interconnection anywhere but in the main service entry.

Aside from the chance of something coming loose and putting some random voltage between 105 and 240 volts on the outside of your bathtub, there's also the problem that your ground wire is not zero resistance, which means that if you touch both it and another path to ground, at least some of whatever current is on it will choose to go through you. (This is why, for example, you can get a shock from the casing of a malfunctioning appliance, even if it's grounded.)

Reply to
Goedjn

For one thing, it puts current into the ground conductor between the subpanel and main panel.

Reply to
Richard J Kinch

The Reason is that there is current goes through a nuteral and no current goes through a ground and if the ground and nutural are tied together they both have current passing through them and the only time that current should go through a ground is when there is a short or something similar...

but to make thing even moree confusing is then why is the nurural and ground tied together at the main pannel and that is to bond the nuural to the earth ground...

Reply to
Phillip Devoll

The neutral (white) is a return ... it carries the same current as the hot wire (black). The ground wire is a non current-carrying safety wire (often bare copper). The purpose of the ground wire is to reduce voltages in the case of lightning or an accident (wires falling across other wires outside of your home and raising the voltage with respect to ground to a dangerous level). The ground wire only conducts current in the case of a fault. Ground fault circuit interrupters need the ground wire to detect such faults and open the circuit when they occur.

People are often shocked and even electrocuted with voltages with respect to ground ... one is standing on a wet basement floor ... one is touching a faucet ... one is in the tub or shower. The voltage with respect to ground is the big issue here (for safety reasons).

An ungrounded electrical system in your home would allow voltages to rise to thousands of volts above ground and fry you if you happened to be grounded (in a tub or standing on a wet concrete floor).

Reply to
Charles Schuler

OK, so the ground is bonded to the neutral at the service panel.

What about the transfromer at the pole? Is the neutral center-tap in the North American System bonded to the transformer enclosure? Is this point often connected to a ground wire running down the pole and into the earth?

Also, why in the US systems is the top wire on the pole the hot wire (for the transformer primary) and the neutral is usually several feet below this? Is this arrangement not more prone to lightning damage?

Beachcomber

Reply to
Beachcomber

I believe that GFIs are often recommended in cases where there is no ground for safety. They do not need a ground AFAIN.

Bob

Reply to
Bob F

It's not that they're to be isolated at the pony panel (we call it up here), it's that there is to be a single connection to "ground", and it's to be at the main panel ... kind of like it's just not right to connect the bare copper and white in a receptacle :-) Or, that receptacle box if wired that way could float above ground if there's sufficient current through that bare copper ... a "potential" for ... geez, that smarts.

Reply to
bowgus

They need the ground wire.

Reply to
Charles Schuler

When a ground is available at an outlet with a GFCI it is preferred (and required) that it be installed,

However, where there is no ground the NEC still recognized that a GFCI can still provide protection by detecting an imbalance in currents between the neutral and hot wire. In this case, the user must be informed (with a small sticker on the outlet) that the GFCI is ungrounded.

Beachcomber

Reply to
Beachcomber

Actually, they don't.

See section 210-7(d) in the NEC, and section 26-700(9) in the CEC.

GFCIs are a legal substitute for a grounded outlet in an existing installation where there is no ground available in the outlet box.

Chris

Reply to
Chris Friesen

All household grounds must meet only at a common point for reasons similar to why ground loops create hum in a stereo system. Neutral, equipment ground, and earth ground that connect at a common point (main breaker box safety ground) avoids 'ground loops' and other adverse or surprise currents.

To explain same using a different perspective, first, all wires are electrically different at both ends. That difference increases as more current flows. To better explain this, we express that difference as a separation or electrical distance.

A three prong appliance is powered from wires that are distant from the breaker box (because they carry current). A separate safety (equipment) ground wire connects directly (shorter) to breaker box safety ground because it carries no current. Appliance connected electrically shorter to breaker box means greater human safety.

Again, if safety ground and neutral wire were connected anywhere (other than in breaker box), then that safety ground wire would be electrically farther from breaker box (because it carries current). Another perspective that explains why NEC demands separate neutral and ground wires.

Another situation: suppose neutral and safety ground wire were both carrying current. Suddenly that common wire breaks. What happens to appliance connected to third prong safety ground? It suddenly becomes electrically hot - directly connected to black hot wire. AND no safety ground exists to protect human and trip circuit breaker. We want neutral wire separated from safety ground so that any neutral wire break always leaves appliance still connected directly to breaker box safety ground and not connected to a neutral wire that is no longer connected to breaker box. Just another reason why those two wires always remain separate.

Home has its own single point safety ground inside breaker box. Power wires connect that system to another system that has its own single point ground - pole transformer. Pole transformer connects primary (high voltage) ground, secondary neutral, and earth ground to a common point. Lightning strike to primary (high voltage) wire simply gets conducted safely to earth at transformer which is but one reason why that primary wire can be highest on pole.

Meanwhile, household s> I installed a subpanel when I switched from an electric stove to gas. I

Reply to
w_tom

So, what is the proper way to connect a 220v sub-panel that has a single bus bar for neutral and ground to a main panel with the neutral bar bonded to the ground bar?

Reply to
The Streets

A GFCI does not need a ground. Then some people get the strange idea that it PROVIDES one. It does not.

Reply to
Mark Lloyd

There isn't one.

To make a Code-compliant connection, you must install a second bar so that you can separate the neutral and ground conductors for the various circuits to separate busses. The neutral bus must be electrically insulated from the ground bus and from the panel chassis, and the ground bus must *not* be insulated from the chassis.

*Also* you must connect the subpanel to the main panel using *four* conductors, e.g. black, red, white, and bare (or green). White goes from the neutral bus bar in the main panel to the neutral bus bar in the subpanel. Bare (or green) goes from the ground bus bar in the main panel to the ground bus bar in the subpanel. Black and red go from the two lugs on the circuit breaker in the main panel which feeds the sub, to the lugs on the main breaker in the subpanel.
Reply to
Doug Miller

That was the old way - keeping the hot wire as far from people/animals as possible. The vast majority of new installations will put the ground wire on top.

But what about the rural Canadian systems where there is only a hot wire with no ground at all? Are they any more susceptable to lightning than a US hot top wire system?

Reply to
Bob

No one said GFCIs did. BobF said they are "recommended in cases where there is no ground". They are. What's your beef?

Reply to
krw

I said that because people have. Just not in THIS thread, but in this group.

I was saying that only because some people think they provide ground.

Reply to
Mark Lloyd

Thanks everyone, especially Doug for this post which spells it out clearly. Please comment on this proposed "fix": I run another wire back to the main panel (I'll probably use some 12/2 with ground) and attach all three conductors to the ground bar in the main panel. Then, at the sub panel, I will connect all grounds to the new cable but not to the neutral bus bar. Now all grounds will be grounded back at the main panel, and the neutral in the sub will be isolated from the grounds and from the sub panel chassis. (as long as I remove the grounding screw from the neutral bus bar) Thanks again for your responses. Joe

Reply to
joseph.hollyday

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