Another electrical question

I forgot to mention. The subpanel that is wired this way and bonded has been wired such that all of the grounds are on one bar and all of the neutrals are on another. So, it was wired internally as the other subpanel was except for the feed line and the bonding bar connecting the two. Should it have been wired with a neutral and a ground and not bonded as the other panel was. If so, I will have an electrician correct this.

Thanks

Barry

It may be "OK" since presumably it was inspected, but it is not to code, assuming you are in the US in an area where the NEC is the requirement.

On the other hand, it is not a clear and present danger either.

jk

I'd be interested in chapter and verse. Not because I'm trying to be a smartass, but because I spent a good hour at the library going through the NEC and I couldn't find a clear answer.

Ultimately, I asked the oldest city inspector what he wanted and it was to keep ground and neutral separate in the subpanel. BTW, in my case the subpanel is about 40 cable feet away from the entrance panel.

Google Groups is acting weird this morning and I can't comment to Jim's first post.

Just want to add a bit to what he said. One of the things that happens is called " Fretting Corrosion ." You have two conductors clamped together, they are making metal to metal contact but the surfaces are not so smooth that air is excluded. Where there is metal to metal contact, there is no oxidation and of course where there is no contact, a little oxidation does not matter.

But the shop cools off and there is some thermal contraction. The joint moves ever so slightly and now you have shifted things so the high points on one piece are touching the places that have some oxide. And the resistance is higher. With things as small connectors that are not gold plated, you can get an open circuit from an oxide film you can not see. With power connections you get higher resistance that leads to more heat and more oxidation.

For " dry circuit " contacts ( low voltage not sufficient to punch thru the oxide film ) the cure is something that coats the surface and wets the surfaceair enough to keep the air excluded. The original stuff used was mineral oil and microcrystaline wax. Now you buy something as Gold Wipe or Kramlin oil.

I have not tried coating power connections, but since the kilns at the high school keep burning up connectors, I may give it a try. I was thinking of using the compound that is used on aluminum wire connections. Any comments?

Dan

On Tue, 11 May 2004 03:26:23 GMT, Jim Stewart brought forth from the murky depths:

The NEC is fun to read, isn't it? (Go see your optometrist.)

That's what I understand. The bonding is done only at the main panel and all subs are separate to eliminate any ground loops or current on the neutral.

Yes, the inspectors are the people to ask. If there's a fire, they will determine if the insurance is payable.

LJ Wannabe Sparky and shop self-wirer.

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I'm going with Article 250.24 "Grounding Service Supplied Systems. Specifically 250.24 (A)(1) and 250.24(A)(5)

250.24 (A) "System Grounding Connections" A premises wiring system supplied through a grounding AC service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5)

250.24(A)(1) "General" The connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.

250.25(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.

This is from the 2002 NEC Handbook.

Nate

Don't know if you could do this with a kiln connector but:

Application of stellite #6: One day there was a box of #6 stellite TIG rods in the blowout sale bin at my local welding supply shop. I grabbed them.

I have an older but perfectly serviceable (except for one problem) electric stove. The contacts on the plug-in elements are a bullet shaped copper cylinder molded onto the end of the wire that sticks out of the connector end of the elements. The copper corodes slightly, contact resistance increases, more heat is generated, corrosion rate increases, even more heat is generated, ..., connector mounted on stove top fails. I managed to score one of the last stove top connectors for this model in captivity - mfr wants you to replace element AND connector with "new" expensive style.

My fix: melt off copper "bullet", build up Stellite #6 bullet, grind to final shape. Clean contacts on stove top connectors and re-install all. Fix was done in '96 - all contacts are still bright and clean.

I have a TIG outfit so why did I use O/A for this? Answer: What would you do for a ground? There is no room where the wire exits the element and the other end is a lot of resistance away. ...

Ted

Google does not work well for regular posting.

Replace with solid gold contacts? :^)

I would think that if both contacts were made of the same material, there would be no relative motion, and hence no fretting wear.

Maybe some other material, we have some nickel crimp lugs used for high temperature service.

Jim

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This is absolutely incorrect. The bonding between neutral and earth should only occur at the distribution transformer. Period! Anything else creates a ground loop. If the earth reference at the transformer is either non-existent or poor call the electric company and have them fix it. Ground loops can create serious problems for electronics for both you and your neighbors, not to mention a safety issue and for heaven's sake never bond your lightning protection to your transformer safety earth plane. Steve

SOme else has already answered this, but the NEC is fun. If you know where something is it is easy to find, if you don't you can't.

Code requires you to bond the neutral to the ground at the service entrance, and allows it no place else "downstream", except for separately derived systems, which again have only a single ground to neutral bond.

A service entrance neutral may (and probably will) have more than one bond. THe one in your service entrance, the one at the transformer, and the ones at everyone else's service entrance served from that transformer. jk

Thanks for taking the time to look it up.

Ok, first question. Is the "grounded service conductor" neutral or ground? I presume it's neutral because it's "service"

This seems to clarify that it's neutral as it has a service disconnecting means.

Now we've switched gears and instead of calling neutral a "grounded service conductor" we're calling it a "grounded circuit conductor" I guess it must be the same thing. Or maybe it changes names after it goes through the disconnect...

In any case, thanks for the effort.

to look it up.

It is your incoming neutral conductor. Your ground is still called ground (or some times grounding) conductor.

Once your are past the service disconnecting means, it is just a grounded circuit conductor. Just like you phase conductors are now circuit conductors rather than service conductors.

jk

Sorry, that's wrong. Period. :-)

Code requires that the grounding conductor (safety ground) and the grounded conductor (neutral) must be bonded together and tied to an approved Earth ground at *the service entrance panel*. The Earth ground can be a made electrode (a ground rod), a Ufer ground, buried cold water piping, etc. The utility's distribution transformer secondary may or may not have its own ground, depending on the wiring practices of the particular utility.

That's wrong too. The only sure way to achieve lightning protection for electronic equipment is to use ground window technique, which requires a single point bond of *all* grounding conductors at the service entrance, and appropriate supression of all nominally "hot" conductors to the same point. This prevents excessive potential differences from appearing

*across* the protected equipment. No potential difference, no damaging current flow through the protected equipment.

Gary

I do have some Stellite. Some I purchased years ago and some more I found at Boeing Surplus. But these are not my kilns and sometimes the school has Seattle Pottery do major rebuilds. So I don't want to change configuration. Well I really want to, but am not going to do that.

One of the problems is that the kilns are designed so that the height can be changed. They have a bottom, then a ring with an element, then another ring with its heating element, etc, until the top. The rings are designed with a male elecrical connector on one side and a female on the other. So you can have say three rings stacked or four rings stacked. So although the connectors are made with brass contacts, the expansion of the rings affects the insertion depth of the contacts.

For home use, the failure rate is low enough to be tolerated. Otherwise Seattle pottery would do something like nickle plate the contacts. For the use the kilns get at the high school, the failure rate is one or two connector pairs per semester. About $30 or so per connector pair. Maybe a bit more as the school thinks they need to buy the connectors from Seattle Pottery so as to get industrial strength connectors.

Dan

Perhaps you should put "US" in front of the "Code requires". Note that he is posting from a ".de" domain (Germany -- Deutchland), and he may well be *right* as far as the codes in Germany apply. And your work to US codes may fail miserably in Germany.

But -- *he* is wrong for work in the US. I think that the original question was posted by someone in the US, so for that, you win.

Enjoy, DoN.

The bonding is done only at the main

That's what the inspector told me as he removed the bonding screw from the sub panel in our pump shed.

Harold

Yes. Short version:

GroundED conductor = white wire, neutral wire, return, white screw, carries load current.

GroundING conductor = green wire, ground wire, personal protective ground, green screw, does not carry current to speak of except during faults.

Jim

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The grounding conductor is indeed the wire that connects to ground (earth) and does not normally carry any current. It's for personal protection. About 50 years ago the color was changed in N.A. from green to yellow/green. At the same time the color was changed in Europe from yellow to yellow/green. The reason was a GI with his young wife in Berlin had brought over from the States his household goods including a washing machine. A local electrician was called in to change the cord and plug and he connected the green (power) wire from the new cord to the frame were he had removed the US cord green wire. When the young wife plugged in the washer and dipped her hands in the sop, she got electrocuted. That's why the ground wire must show at least 30% yellow color and at least 30% green color. HTH