Aluminum vs Copper Ground/Neutral Bar - Mike Holt's Forum

If they are UL Recognized then I have to used them in a UL listing eligible product? Or, do they simply loose their UL recognition if not incoporated into a UL listing eligible product. UL listed will not loose its listing if used in a non UL listing eligible product?

Can a standard be "recognized" or "listed"? For example, can a breaker be either listed or certified to UL 508?

The bars I am looking at "UL Recognized and CSA Certified for 600 Volts". Am I definitely wrong to think that the neutral ground bar has to be UL 467 listed or recognized?

UL recognizes parts that are intended solely to be incorporated into UL listed products. That is all recognition means. it does not mean you can put it in a UL listed product, or any other product for that matter. UL does not certify components or products. Listed or recognized are the two choices available.

Listed products such as UL508a control panels have a series of requirements that have to be met to meet the listing requirements. That includes what components you are allowed to use within that listed product. The UL requirements for the listed product will tell you very explicitly what component products can be used. Some components will be UL listed, others will be UL recognized. Some are neither. There will be directions in the listing standard that tells you what components can be used and in what way.

I don't know what UL standard your product is being listed to so I cannot tell you with any certainly what components are acceptable.

This is what UL508a says in part about grounding components.

14.2 An industrial control panel shall be provided with a field wiring terminal for the connection of an
equipment grounding conductor. The terminal shall comply with:
a) The component requirements of a field wiring terminal in accordance with Section 28, Field
Wiring; or
b) The requirements in the Standard for Grounding and Bonding Equipment, UL 467.

Table SA 1.1 lays out the parts you can use. I can't cut and paste from it because it is a formatted table and the forum does not allow most formatting.

For paragraph
14.2(a) Recognized Terminal Blocks UL XCFR2
14.2(a) Recognized grounding bar kits UL 67, UL 891 QEUY2 Procedure described only
14.2(b) Listed Grounding and Bonding Equipment UL 467 KDER
14.2(b) Recognized Grounding and Bonding equipment UL 467 KDER2

What does this mean? Well it means you can use these things for ground terminals for field wiring.

"Procedure described only" means UL has to specifically approve it. In practice it usually means if you pay them they will let you use it.

Just because the ground bar is UL467 (listed or recognized) does not mean it is Ok to use it in a UL508a control panel. It still has to be category code KDER or KDER2.

Most of the UL467 listed stuff I have run across is insanely expensive. I don't recall seeing any that are only recognized.

some ground/neutral bars are UL486 recognized. I have the UL file number for the bar I currently use, and when I look it up it comes up KDER.file number, so I'm thinking that I have a listed under UL 467 category KDER. No where on the UL website does it say that the file number is listed under UL 467. Could the KDER mean anything else?

The panels are not UL 508, though I would like them to be someday. Some panels get UL inspected at the request of the customer, but most do not. I am in the process of CE marking, and I am using IEC-. UL uses this same standard for our equipment. It has a basic section on grounding and bonding, and then has a component requirements section.

The component needs to be tested to the relevent IEC standard
or tested to and the relevent safety requirements of the applicable standard
or tested to a non IEC standard that is equal to or greater than the relevent IEC standard.

Most UL listings and recognitions are adequate, as long as the application of the product does not negate the UL listing or recognation.

I have several issues with my equipment.

1) i currently use a copper grounding/neutral bar that has the KDER category listing. This bar accepts the grounded service conducter, and all of the accessible parts that are hazardous live are bonded to the same terminal bar. I would like to switch this bar to aluminum if possible.

2) I'm trying to bond all of my accessible and removable panels back (from the inside of the equipment) to this ground/neutral terminal. I have to install studs on the removable access panels, and also on the frame of the equipment. A conductor is then ran from the access panel to the frame. The frame is bonded to ground through the terminal on the sub panel. The resistance of the connection from the panel to the ground terminal has to be less than 100 milliohms.

The panels are powder coated, and it is complicated to get the studs on the panels and not have them covered with the powder coat. The frame is simply painted, and not as much of a challenge to reach a conductive surface. I can get the studs on the panels, but then have to worry about them rusting because of the exposed stainless steel where the stud is inserted for bonding. UL will come out and inspect stuff on a one up basis but it is crazy expensive.

CE has nothing whatsoever to do with products meant for use in the US.

I don't know how people in Europe feel about it but in the US what you are describing is specifically forbidden by the electrical code and by every UL standard I have ever heard of.

You are only allowed to connect the grounded conductor to earth or ground at a single point and that is at either the service point or where the system starts if it is s SDS.

If you are bringing in a neutral or grounded conductor from outside the equipment and in anyway connecting it to the frame, that is a serious code violation, and potential safety hazard.

Unless your equipment is service rated, you are not allowed to land any service conductors in it at all, grounded service conductor or ungrounded service conductor. It is just not allowed.

There is no requirement in any code I have heard of for a 100 milliOhm bonding connection. It may be an equipment spec. My suggestion is get a stud welder and weld a SS or brass stud to the frame if you are unable to connect to it in some other way. personally, unless there is an equipment spec that requires the bonding wires, I would not put them in. the fasteners that hold it together are probably quite adequate. Yes, I understand. For my equipment, UL uses UL- as our product standard. For CE marking, I use BS-EN as our Harmonized Standard. Both are word for word the same, and are IEC-. For CE, I components (where safety is a consideration):

The component needs to be tested to the relevent IEC standard
or tested to and the relevent safety requirements of the applicable standard
or tested to a non IEC standard that is equal to or greater than the relevent IEC standard.

So I need to have components that are used for grounding and bonding comply with one of the above.


The equipment is permanently connected to a disconnect, 3 phase conductors and a green conductor are fed to the equipment. I call the green conductor a "service ground", so please correct me if I am wrong. I believe this green conductor is grounded back at its source, the secondary of the service transformer. This green conductor is connected to what I call "the protective conductor terminal" on the sub panel of the equipment. This protective conductor terminal is the top terminal of the UL listed ground/neutral bar. The bar has 14 input terminals.

Any panel components that have grounding studs are also connected to one of the open positions on this terminal bar. The frame is not normally directly connected to the terminal bar, unless an inspector requests us to connect the frame and the removable panels to the terminal bar. Everything is already connected to the frame by metal to metal contact, but this connection does not always satisfy the inspectors so they make us run seperate conductors. These seperate conductors from the panel and frame are what I am talking about.

I do not currently ground the removable access panels to the frame, but if I wanted to is 200.2(B) forbidding this type of connection from the access panels to the frame and then to to the main equipment neutral/ground bar?

200.2(B) Continuity. The continuity of a grounded conductor
shall not depend on a connection to a metallic enclosure,
raceway, or cable armor.

I have to go with a direct connection to a terminal on the bar?

You have a major problem with English and technical words and phrases.

A grounded conductor is not the same thing as an equipment grounding conductor (EGC).

Most times the neutral in a circuit is the grounded conductor, although the grounded conductor is not always neutral. In the US it is generally white in color. It has to be a wire or bus bar.

The EGC is the green wire, or sometimes green with yellow, or bare conductor. The EGC does not have to be a wire or bus bar. The frame can sometimes serve as an EGC, as can metallic conduit and various other conductive metal parts.

I suggest that you get out your UL508a spec and the NEC and read carefully the definitions sections. I think that would help both you and us. It is very difficult to help you when you are not using standard terminology.

Another problem is that you mix up concepts from Europe with the US. Anytime you use the term "CE" I cringe. It is completely and totally meaningless in the US.

200.2(B) is from the NEC. As a practical matter, it has no bearing on the equipment you are making. You have to make it to the UL standard for use in the US. The NEC is for electrical installations only. It has almost nothing to do with equipment standards. I am referring to Equipment Grounding Conductors, and will hence refer to them as such. Sorry to make you cringe at CE, but please understand the the standard I am using is IEC . has its own terminology and definitions. This standard is used by UL as UL-, and is also used as a harmonized standard to the Low Voltage Directive as BS-EN-. I am not mixing US and CE Marking, but the standards are word for word the same standard.

Inside of my equipment, I am trying to adhere to IEC-. Neither NFPA 70 and NFPA 79 apply absolutely to the inside of my equipment, but I try to apply their reasonings and statutes where relevent. A lot of the standard is clear, a lot of the standard is vague, and where it is vague I have to be able to explain my applications. Your explanations help a great deal towards this goal. To be honest, I probably gain more "intuition" from this site than anywhere else. I hope to someday be as technically omnipotent as a lot of people on this forum, but not quite there yet.

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General

Copper and copper alloys are widely used because they combine unique properties at an economical price. These include high thermal and electrical conductivity, ease of manufacture, high recyclability and good corrosion resistance. Copper, a noble metal that occurs naturally in its elemental form, is almost totally impervious to corrosion from soils found worldwide. But it would be misleading to infer that copper will not corrode.

Corrosion

Galvanic corrosion is an electrochemical process whereby one metal corrodes preferentially to another whenever both metals are put in electrical contact and immersed in an electrolyte. What is surprising to some is that soil or air can be an electrolyte.

Underground

Copper is the preferred metal for grounding conductors and electrodes. This is not only due to its high degree of connectivity, but also its corrosion resistance. In most soils, copper electrodes outlast alternates such as galvanized steel. However, there are certain conditions where tinning (coating with tin) the copper would be useful.

The designer of a grounding system typically performs a soils analysis before designing the grounding system. Soil aggressiveness and chemical composition will determine the appropriate steps to take.

When the chemical composition of the soil is unknown (in the absence of soil testing), it is the user’s choice to stipulate tinning or bare. In most cases, bare copper is sufficient, although we recommend exceeding the rather minimal gauge requirements of the NEC. 4/0 AWG or larger is commonly found in industrial environments.

If you want to learn more, please visit our website Copper Plated Steel Flat Bar For Grounding System.

When soils are highly acidic, or alkaline, or suspected of being so, backfill material such as bentonite can greatly extend the life of bare copper. Further, bentonite retains water, thus can greatly increase contact area with the soil, thus reducing grounding resistance. Carbon-based backfills often contain other contaminants, such as sulfur and other elements which are harmful to copper and should be avoided.

Above-ground Outdoor Construction

Outdoor air can act as an electrolyte because it contains a variety of components which can cause corrosion of any metal. Varying moisture levels, salt and other contaminants are just a few. In overhead, outdoor construction, copper runoff can cause staining of pavement materials. It’s one reason why older overhead wiring (before plastic coverings) was usually tinned. In addition, copper runoff can be very corrosive to galvanized steel support structures, even when not in direct contact. In such cases, tinning of the conductors is recommended to prevent such conditions.

“Precipitation run-off from copper and copper alloys can attack galvanized parts (BS : and IEC -1-2, section 5.2); therefore, bare copper conductors or copper bus bars shall not be installed above galvanized steel, such as a tower, unless the steel is protected against the precipitation run-off “ (IEC -1-2, section 5.2, quoted in Motorola R56.)

Lastly, for connection to the main grounding bus, or any connection point, consider connectability. In a recent research project conducted by Powertech Labs, copper connections in mechanical connectors passed thermal cycling tests under IEC -1, while the overwhelming majority of aluminum connections largely did not pass, irrespective of preparation. See Building Wire for more information on this study.

Further Reading

The general information in this document is a limited look at the complex subject of corrosion, and further investigation is encouraged. The following sources contain additional information on grounding and corrosion.

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