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Neutral-Ground connection, main panel


Mr Z
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250.24. Grounding Services

(A) Grounding Neutral. Alternating-current services that are supplied from a grounded electrical system from the utility must have the grounded (neutral) conductor connected to a grounding electrode of the specified in 250.52 in accordance with Part III or Article 250 in accordance with (1) though (5). See 250.24©.

This clearly states that the neutral of the service must be connected to earth ground.

Does it state anywhere that this connection MUST be made in the panel, or can you have separate grounding rods for each buss, neutral and ground?

Due to the electronics in the house, I would rather the neutral and grounding conductors were as separate as possible.

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That is, must you connect the busses in the panel...

Short answer...YES!

Longer answer...the ground rods are there mostly for powerful surges, such as lightning. They don't provide a reliable path for lower voltages. The main safety reason that the grounding gets connected to the grounded conductor back to the utility is to provide a good path to clear ground faults. Without that bonding at the service a ground fault/short might not trip the breaker.

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That is, must you connect the busses in the panel, if you run ground rods to both the neutral bus, and the grounding buss independent of each other?

It's not just about the ground rods. It's about the grounding electrode system.

Why don't you tell us what your concern is? Installing proper grounding shouldn't cause any problem with your electronic equipment.

- Jim Katen, Oregon

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You can have an "isolated ground receptacle". But this just means the ground wire could be insulated and would *only* connect to ground at the panel (not anything along the way like junction boxes).

Many circuits in a house are already like this. You would find this type of outlet in a hospital or office. The following link has more on this.

http://ecmweb.com/mag/electric_basics_i ... grounding/

The outlets are typically orange like this...

35623_300.jpg

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Basically what I was going to do with the new panel is have all my bare conductors on the proper bus, and bonded to ground rods outside.

And, I was going to put all the neutrals (white) on their respective buss, and drive ground rods for them as well.

Maybe a little overkill, but I have a shop with a tablesaw, compressor, and other motor loads, and I'd rather not have any wired connection of the ground and neutral if possible.

They would both be grounded to earth, just not bonded to the other in the panel.

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That is QUITE dangerous!

The grounds at the shop MUST be connected to the neutral at the main panel. Otherwise you are risking fire or electrocution.

Note that you can get electrical "noise" on the power wires as well and THIS would be the most common source of electrical noise. This can come from other people connected to the electric lines in your area.

You can fix this by plugging your electronics into an "On-Line - Pure Sine Wave UPS". On-line means 100% of the power which comes from the UPS is made by the UPS and not passed through from the utility connection. And pure sine wave means it is the best electricity you could possibly get as opposed to "square wave".

Other cheaper UPS only "make" electricity when the power goes out. And other cheaper UPS will make a square wave or modified sine wave.

Here is what electricity from "cheap" sources looks like...

http://www.jkovach.net/projects/powerquality/

So far as grounding and reducing noise...

A good ground system, with multiple ground rods and EVERYTHING grounded, is your friend! Sink two or more ground rods placed 6 ft. apart and bond them together with large diameter copper wire.

Then "distance" with isolated ground wires is your friend. Wire has resistance with length. So run your shop equipment grounds directly to the main panel (per code, including subpanel requirements, etc.) But basically separate subpanel from electronic stuff.

Then run isolated grounds or dedicated circuits for your electronic stuff to the main panel. If using isolated insulated wire grounds, you would need to run a second ground wire to the electrical box to ground a metal box and an isolated ground receptacle mounting yoke (metal part on outlet you screw to electrical box). Or if a plastic electrical box and a dedicated circuit/wire, use a regular receptacle and then no need for the second ground as the mounting yoke would be grounded as well.

Then install "whole house surge protection" at the main panel and use good quality surge protection power strips at each electronic device.

Do all this and your electronics will have the cleanest power in the state!

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That is, must you connect the busses in the panel...

Short answer...YES!

Longer answer...the ground rods are there mostly for powerful surges, such as lightning. They don't provide a reliable path for lower voltages. The main safety reason that the grounding gets connected to the grounded conductor back to the utility is to provide a good path to clear ground faults. Without that bonding at the service a ground fault/short might not trip the breaker.

OK, but the neutral would be connected to the ground rods, it would have it's own, and quite separately so would the bare conductors from the house. But, that would not be sufficient in the case of a ground fault?

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You want ALL grounds connected to neutral. If a hot touches a ground wire, then there would be a path back to the neutral and this would trip the breaker.

If you had separate grounds rods and the ground in question was not electrically connected to the neutral - just grounded, this would not cause the circuit breaker to trip in the case of a ground fault. The ground is not that good a conductor of electricity.

So say a stray wire touches the metal housing on your drill press and you have a separate ground for this. This ground fault would not trip the breaker. Then you would walk up and touch it, then you would be electrocuted! Then we could not discuss grounding anymore with you and this would make me sad! [:-weepn]

Or if you connected the ground from your shop panel to the same ground rods as your main panel (and not in the panel), this would be dangerous as well. It is quite common for lawnmowers and the like to brush by ground wires going down a wall and break them. So best to connect the ground to the neutral in the panel.

Basically electrical codes/rules are there because of what has happened in the past. People have been electrocuted and died, then new rules put in place to keep it from happening again. Follow the electrical code rules and you will have a safe electrical system - for YOU! (And your family, and others who may purchase your house in the future.)

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Just wanted to throw it out there and double check.

Thanks Billy Bob, and I'll have to see about cost, but I like your ideas on isolating the electronics.

The lawnmower breakage didn't cross my mind, and that would put a major hole in the plan I had.

Thank you much for your input.

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Just wanted to throw it out there and double check.

Thanks Billy Bob, and I'll have to see about cost, but I like your ideas on isolating the electronics.

The lawnmower breakage didn't cross my mind, and that would put a major hole in the plan I had.

Thank you much for your input.

Billy Bob has given you good advice, read it carefully. Your plan has a much bigger problem than the lawnmower.

You need to understand that, in the world of household electrical wiring, the word "ground" has several different meanings.

Grounding as in the "grounding electrode system" or the connection of the electrical system to the earth has nothing at all to do with "equipment grounding," which is what you have at the metal shell of your drill press. They are two completely different systems that have nothing to do with one another. Say it three times.

Your plan would rely on the earth as a fault path -- a very dangerous arrangement.

What is it that you're afraid will happen if you connect the grounding conductors to the neutral?

What kind of electronics are you concerned with?

- Jim Katen, Oregon

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