Introduction: Avoiding Expensive Mistakes in Glass Insulator Selection

Throughout my years working in power transmission and substation projects, I’ve encountered numerous cases where improper selection or misunderstanding of glass insulators led to costly failures and downtime. I’m Thor, an electrical engineer at Wei Shoe Electric, specializing in high-voltage insulation and protection systems. A IEEE study found that 30% of insulator-related failures stem from incorrect selection (IEEE Transactions on Power Delivery, Vol. 38, No. 4, , DOI: 10./TPWRD..). This comprehensive guide covers everything you need to know about glass insulators—from definitions, types, and working principles to applications, selection criteria, industry standards, procurement, maintenance, and challenges—to help you make informed decisions and avoid expensive mistakes.

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What Is a Glass Insulator and How Does It Work?

Definition of Glass Insulator

A glass insulator is a specialized component used to isolate electrical conductors in high-voltage power transmission and distribution systems. Its primary role is to prevent electric current from leaking to the ground while withstanding mechanical loads, environmental stress, and electrical surges.

Working Principle

Glass insulators leverage the high dielectric strength of tempered glass (20–25 kV/cm) to block current flow between energized conductors and grounded structures. The suspension or pin-type design ensures mechanical tension from overhead lines is transferred safely while maintaining electrical isolation.

Types of Glass Insulators

• Pin-Type: Used in low-voltage distribution (e.g., 11kV), such as CD 154 (Hemingray-42).

• Suspension: Applied in high-voltage transmission (110–800kV), with ball-and-socket connections per IEC .

• Post: Supports substation busbars, with mechanical strengths up to 300kN.

Glossary of Terms

• Creepage Distance: The shortest path along the insulator surface, preventing flashover.

• Specified Mechanical Load (SML): Maximum tensile load (e.g., 120–300kN).

• Radio Interference Voltage (RIV): Measures corona discharge, typically <100μV.

Where Are Glass Insulators Used?

Common Applications

• High-voltage overhead transmission lines (69kV to 800kV)

• Substation busbars and disconnect switches

• High-altitude or high-pollution areas

• Coastal and offshore power systems

• Railway electrification networks

Why Glass Is Still Widely Used

Glass insulators remain popular due to their transparency (enabling visual inspection of internal damage), superior aging performance (functional beyond 40 years), and high mechanical strength (120–300kN).

Properties and Characteristics of Glass Insulators

Key Performance Indicators

• Electrical Strength: 20–25 kV/cm, ideal for high-voltage systems.

• Mechanical Strength: 120–300kN, per IEC .

• Pollution Flashover Resistance: Smooth surface aids self-cleaning, suitable for moderate pollution (IEC , Level II–III).

• Aging Resistance: Minimal degradation over decades.

Disadvantages of Glass Insulators

• Fragility during transport and handling.

• Higher risk of mechanical breakage from impact.

• Susceptibility to pollutant adhesion in high-humidity or coastal areas.

Comparison with Alternatives

• Porcelain Insulators: Proven durability, but heavier; less transparent for inspection.

• Composite Insulators: Lightweight, hydrophobic, but limited long-term reliability data.

Why Some Regions Prefer Alternatives

In high-pollution (IEC Level IV) or vandalism-prone areas, composite insulators offer better resilience, leading some utilities to shift away from glass.

How to Select the Right Glass Insulator

Selection Criteria

• Voltage Rating: Match system voltage (e.g., 11kV for distribution, 500kV for transmission).

• Mechanical Load (SML): Support conductor tension (e.g., 120kN for 69kV, 300kN for 500kV).

• Creepage Distance: Per IEC , e.g., 31mm/kV for Level III pollution (500kV requires 15,500mm).

• Altitude & Environment: Apply correction factors for high altitude (>m); use anti-salt fog designs for coastal zones.

• UV & Salt Spray Resistance: Essential for offshore or desert environments.

Selection Example

For a 500kV transmission line in a Level III pollution area:

• Creepage distance = 31mm/kV × 500kV = 15,500mm.

• Choose suspension insulators with 300kN SML, IEC -compliant ball-and-socket connections.

Selection Process

   1. Determine system voltage and pollution level (IEC ).

   2. Calculate the required creepage distance.

   3. Select SML based on conductor tension.

   4. Verify environmental compatibility (e.g., UV, salt spray).

   5. Confirm compliance with IEC or ANSI C29.2.

International Standards and Compliance

Glass insulators must meet rigorous standards to ensure safety and performance:

• IEC : Defines creepage distance (e.g., 31mm/kV for Level III pollution) and mechanical/electrical performance.

• IEC : Specifies ball-and-socket connections for suspension insulators.

• ANSI C29.2: North American standard for pin-type and suspension insulators.

• UL : Certification for ground fault-related equipment in substations.

• OSHA .304: Ensures electrical safety to prevent worker hazards.

• IEC : Guides selection based on pollution levels (I–IV).

Compliance Tip: Verify UL or CE certification and match insulators to project-specific standards (e.g., NEC 230.95 for U.S. distribution systems).

Procurement and Supplier Guide

Price Range

• Pin-Type (11kV): $50–$150 / €40–€120.

• Suspension (110–500kV): $200–$500 / €150–€400.

Recommended Suppliers

• Wei Shoe Electric: As a leading direct-from-factory manufacturer in China, we provide high-quality glass insulators compliant with UL, CE, and IEC standards. Our customizable solutions (e.g., tailored creepage distances, anti-pollution coatings) meet specific project needs, offering cost efficiency and fast delivery (4–6 weeks). Contact us at [ protected] or visit www.weishoelec.com for tailored support.

• ABB, Siemens, Lapp Insulators: Renowned for UL- and CE-certified insulators.

• Newell, Sediver: Compliant with IEC and ANSI C29.2.

Procurement Tips

• Request UL or CE certification documents.

• Confirm delivery timelines (typically 4–8 weeks).

• Evaluate the total cost of ownership, including maintenance.

Maintenance and Testing Methods

Maintenance Guidelines

• Cleaning: Every 6–12 months (every 3 months in high-pollution areas, IEC Level IV); use high-pressure water or RTV silicone coating.

• Inspection: Visually check for cracks, glaze loss, or microcracks; use infrared thermography for internal defects.

• Lifespan: Typically 40+ years; monitor for surface wear.

Testing Procedures

• Residual Strength Test (IEC ): Apply 70% of rated load to detect cracks.

• RIV Test (IEC ): Measure corona discharge, ensure <100μV at rated voltage.

• Thermal Shock Test: Simulate extreme temperature changes to verify durability.

Tip: Document test results to ensure compliance with OSHA .304 safety standards.

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Real-World Application Cases

Case 1: 500kV Transmission Line in Canada

• Application: Toughened glass suspension insulators (160kN SML, IEC ).

• Compliance: Meets ANSI C29.2.

• Outcome: Over 10 years of reliable performance, zero flashovers.

Case 2: Coastal Substation in Australia

• Application: Anti-salt fog glass insulators (200kN SML).

• Compliance: IEC Level IV (high pollution).

• Outcome: Zero flashover incidents after 5 years.

Case 3: U.S. Low-Voltage Distribution System

• Application: 69kV pin-type insulators (CD 154, 80kN SML).

• Compliance: NEC 230.95, UL-certified.

• Outcome: 8 years without faults, easy visual inspection.

Case 4: European Railway Electrification

• Application: 25kV suspension insulators (120kN, anti-pollution design).

• Compliance: EN railway standard.

• Outcome: Zero flashovers in high-pollution areas, saving €15,000/year in maintenance.

Figure 1: Causes of Insulator-Related Failures – 30% due to incorrect selection (IEEE, ).

Is Glass a Good Insulator? Clarifying Material Properties

Electrical Insulation

Glass is an excellent electrical insulator due to its high resistivity and dielectric strength (20–25 kV/cm), making it ideal for high-voltage applications.

Thermal Insulation

Glass is a poor thermal insulator compared to materials like foam. Only electrical properties are relevant in power systems.

Addressing Common Confusions

• Is glass an insulator or conductor of electricity? It’s a strong electrical insulator.

• Is glass a good insulator of heat? No, glass conducts heat relatively easily.

• Why are glass and rubber good insulators? Both have few free electrons, preventing current flow.

Market Demand and Lifecycle Considerations

Current Market for Glass Insulators

Despite competition from composite insulators, glass insulators remain in demand for:

• High-voltage bulk transmission systems.

• Regions with strict inspection requirements.

• Areas favoring visual detection of damage.

Assessing Insulator Age and Lifespan

• Monitor surface wear, glaze loss, or microcracks.

• Glass insulators often remain functional beyond 40 years.

Recycling and Disposal

• Recycling: Into glass production, it is highly environmentally friendly.

• Disposal: Follow local environmental standards to avoid landfill waste.

Frequently Asked Questions (FAQ)

Q1: Why are glass insulators still used today?
A: Their durability, self-cleaning surface, and stable long-term performance make them ideal for high-voltage systems.

Q2: What is the most common failure mode?
A: Breakage from mechanical impact during shipping or installation.

Q3: How do I choose between glass, porcelain, and composite insulators?
A: Consider voltage, pollution level (IEC ), maintenance needs, and transparency for inspection.

Q4: Can broken glass insulators still function?
A: No, even small cracks compromise insulation integrity.

Q5: What certifications should I look for?
A: IEC , ANSI C29.2, UL , ISO , CE.

Q6: How do I select the creepage distance?
A: Use IEC (e.g., 31mm/kV for Level III pollution) and multiply by system voltage.

Q7: How do I perform an RIV test?
A: Apply rated voltage, measure corona discharge with an RIV meter, ensure <100μV (IEC ).

Conclusion & Technical Recommendations

Glass insulators are vital for reliable high-voltage systems, balancing electrical performance, mechanical strength, and longevity. Proper selection based on voltage, mechanical load, environmental conditions, and certified standards (IEC, ANSI, UL) is critical to avoid failures. Consult experienced engineers to verify specifications before procurement.

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Ted's Top Ten Tips
For New Insulator Collectors

Written by W. H. (Ted) Ingram

The "Ten Tips" listed below are suggestions for new insulator collectors, based upon my own experiences. Some of them could have a whole page devoted to them, but rather than do that, I have attempted to be brief and give you just enough to convey the idea. The Case Study is factual, and serves to illustrate the importance of some of my advice.

Case Study:

Several years ago I noticed a classified advertisement in my local newspaper about an insulator collection for sale. I contacted the seller on the , and made arrangements to see him and his collection. My goal was to buy the collection if it was a decent one, as I was a relatively new collector at the time, anxious to expand my own collection. The below are the salient details of my visit and observations:

• the collection consisted of about 75 cheap and common glass insulators, in clear and aqua colors;
• many of the insulators were so damaged that I would have thrown them away;
• most of the insulators had been purchased from antique shops;
• the seller knew no other insulator collectors, and was not aware that insulator collecting was an organized hobby with clubs, a Web page, reference books, terminology, identification systems, etc.;
• the seller was not aware that insulators came in colors other than what he had in his collection – the honey amber Dominion CD 154 that I brought with me was a marvel to him;
• his asking price for the collection was $500 which is what he said they had cost him, but the Price Guide value would have been about $50-100 if they had all been in good physical condition;
• there was nothing in his collection that I wanted – those that I didn’t already own were too damaged to be collectible.

My impression was that the seller needed to sell his collection because he and his wife had recently purchased a new house, and needed the money to finish the yard – landscaping, fences, etc. Although he was personable, I tactfully declined to buy the collection. About six weeks later I was again reading the classified ads, looking for insulators to buy. I saw an interesting ad and called the number in it. It turned out to be the same seller – I hadn’t recognized his number, and he still hadn’t sold his collection.

1) Get A Mentor

New collectors should try to find a more experienced collector, and then use that collector as a mentor. Most of us are flattered by someone asking questions about a subject that we know something about. Don’t be bashful about telephoning a collector and inviting yourself over after you’ve explained that you’re a new collector -- insulator collectors are some of the most friendly and generous people that you’ll ever meet. Preferably, your mentor should be a local collector so that the two of you can occasionally visit each other. The experienced collector can offer advice in the form of education, and advice about what pitfalls to avoid. When I was a new collector, I was fortunate to have several established collectors to buy insulators from at attractive prices, to volunteer general information and advice, and to answer questions.

Secondly, insulator collectors are almost always pleased to have someone take an interest in their hobby – few people do, including their ‘significant others’. Therefore do not be surprised if your potential mentor wants to show his/her collection to you – use the opportunity to ask questions and acquire knowledge about insulator collecting. Pick the brains of the collector, with the goal of learning as much about insulator collecting as he/she does. And remember that ‘no question is a stupid question’, and ‘if you ain’t asking, you ain’t learning’.

2) Buy the Reference Books

Insulator collecting is a highly organized and detailed hobby, with its own terminology, identification systems, price guides, history and practices. Therefore you must possess a certain amount of knowledge for you to know what it is that you’re collecting, to assist you in collecting, and to communicate knowledgeably with other collectors. To be able to do that, you have to acquire the reference books applicable to that portion of insulator collecting (glass or porcelain) that you’re interested in. You’ll find that after a short period they’ve become invaluable tools that have paid for themselves. Some common examples illustrate why you need the reference books:

• Another collector phones or emails you and says that he/she has a CD 102 for trade – the reference books will tell you that a CD number applies only to glass insulators, and what shape/design/style and size a CD 102 insulator is;
  
  
• You’re in an antique store and see an attractive insulator for $20 – the price guide will tell you if that price is reasonable or not;
  
  
• You see an attractive red colored insulator for sale on eBay – the reference books will tell you that there is no such thing as an authentic red insulator, so the eBay insulator is probably an altered one.

3) Buy Wisely

Regard your collection as an asset that will appreciate in value over time. Whether insulators will appreciate in value and be investments is debatable, and I’m not suggesting that will happen – I honestly don’t know. But you should acquire insulators with the view that you may want to sell or trade them in the future, and hopefully recover most of your acquisition costs if you do. Therefore buy the best insulators that your budget can afford, particularly with respect to their physical condition. Most insulator are not ‘mint’ and we all have to have some damaged insulators in our collections (e.g. I have yet to see a CD 196 insulator for sale/trade that was in good physical condition). But establish a standard of acceptable physical condition for your collection and budget, and then stick with it. Many collectors will buy damaged insulators and then ‘upgrade’ them in the future when the opportunity arises. If you do the same, pay a price for that first insulator that is commensurate with the damages.

With the recent parcel rate increases by the American and Canadian post offices, shipping costs are becoming a significant portion of insulator acquisition costs. Because insulator collectors reside all over North America, with a few overseas, insulator acquisition frequently requires that they be sent by mail or commercial courier. When you’re buying or trading for insulators that have to be shipped to you, keep in mind that the first one in a parcel is the most expensive to ship, and the last one is the cheapest. This is because of the way that the parcel rates are structured – the last weight increment is the cheapest. While this may sound like common knowledge, I still come across collectors who buy one or two cheap insulators at a time, and then have the postage to send them equal or surpass their value. This is important, because the convention is that the buyer pays for the shipping costs. I recently quoted a collector $4.48 for postage costs to send the one small insulator that he was interested in. But to send him a parcel of four insulators, the postage costs were only $7.82 – obviously ‘more is better’ to lower average shipping costs.

Therefore if you’re acquiring insulators where you have to pay the shipping costs, buy a sufficient quantity to minimize your average shipping costs. To do that, try to patronize those sellers that are selling at least a couple of insulators that you want to acquire – try to get the biggest bang for your shipping dollar. Avoid buying from sellers that only have one insulator of interest to you. Of course, there will be times when that is not always possible because other considerations will over-ride the economics. An example might be that you’ve finally found a scarce insulator that has been difficult to acquire in the past, and it could be a long time before it becomes available again.

4) Specialize

The current price guide for North American glass insulators cites over 9,000 different insulators – different because of the different combinations of CD numbers, colors, primary embossings, and specific embossings. Granted, the differences between some are subtle (e.g. the difference between two specific embossings might only be one having periods after abbreviations, and the other one doesn’t). But if we include the differences that the price guide doesn’t address, such as the different variations in the color ‘aqua’, then the number becomes larger. And then if we include foreign glass insulators, porcelain insulators, and insulator related items (radio strains, guy wire strains, dead-end spools, knobs, etc.) we’ve got a huge number that is not yet known.

My point here is that no collector has the time and money to acquire all insulators, and the space to display or store them. Therefore I suggest that after you’ve acquired enough information about insulators to know roughly what there is out there to collect, start to consider specializing. There are many ways to specialize, so I won’t get into them in this brief article – just establish some collecting criteria once you know what appeals to you the most. Not all collectors specialize – many just acquire insulators that appeal to them, and there’s nothing wrong with that – instead of a collection that has a theme, their collections are eclectic. But the advantage of specializing is that it functions as a screening process for insulators that are outside of your collecting criteria. There is no shortage of insulators to acquire, and it’s tempting to acquire many of them -- but if they are not within your specialty, resist temptation and use your money or traders to acquire those that are.

5) Stay in Touch

It is important that you communicate with other insulator collectors. I have met a few insulator collectors who have been collecting in isolation, and it’s been a frustrating experience for both of us. From my perspective, they have no knowledge about the hobby -- supply sources, contacts, new developments, current prices, and terminology. The above Case Study is about such a collector. The advantages of communicating with other collectors are the following:

• Contacts for selling, buying and/or trading to enhance your collection;
• Keeping abreast of current market prices;
• Expanding your knowledge of the hobby and learning of new developments;
• Moral support in your hobby/interest;
• Once you’ve become an established and knowledgeable collector, the hobby can benefit from your contributions.

You can be part of the insulator collecting community by any one of the following:

• if you live in an area where there is an organized insulator collecting club, join it;
• join the National Insulator Association (NIA) and receive its periodical;
• subscribe to the Crown Jewels of the Wire magazine;
• if the distances and expenses aren’t too great, attend the conventions and swap meets;
• if you have Internet access, subscribe to Insulator Collectors on the Net (ICON) – it’s free, convenient and informative.

6) Catalog Your Collection

When I was a new collector there were several occasions when I purchased insulators from antique shops and flea markets, only to find out later that they were duplicates of what I already owned – I couldn’t remember what I already had in my collection. I then made a computerized inventory of my collection, and took a hard copy of it whenever I knew that I would be insulator shopping. I won’t go into a lot of details, because there is an excellent article written by Bill Meier about cataloging your insulator collection. If you don’t have a personal computer, you can still catalog your collection the old fashioned way – I recommend using a columnar pad purchased from a stationary store.

I strongly recommend an inventory if your collection is 100 or more insulators. My own inventory consists of one spreadsheet for each of my 14 ‘sub-collections’, the total of all of them being about insulators. At a glance, I can determine if I already own a certain insulator when I see a similar one for sale, and if I do, whether I need an upgrade for it or not. I also compare the total acquisition costs of my collection to the total Price Guide values to determine if my total acquisition costs are reasonable or not.

Besides allowing you to know what your collection consists of, an inventory is also advisable for insurance purposes. As an example, if your collection eventually grew to be worth $5,000 (very easy to do) and you then had a house fire or vandalism, the inventory would be invaluable in helping you file an insurance claim. For that reason, you should keep a recent copy of your inventory with your other valuable papers in your safety deposit box.

7) Stay Within Your Budget

Like so many other items and activities, the sky’s the limit with respect to the amount of money that can be spent on insulators – prices range from free to thousands of dollars. Therefore it is important that you establish financial limits that are reasonable for your disposable income, and then stay within those guidelines. Ask yourself if your insulator collecting costs are in addition to, or in place of your other recreational expenses. If the costs are in addition to your current hobby and recreational expenses, can you afford insulators?

I am aware of a few collectors that became so enthusiastic about insulator collecting that they forgot about financial common sense, and eventually suffered the consequences. You don’t have to be rich to be an insulator collector – most insulators are priced below $20, and it is possible to build a very respectable collection on a limited budget over time. Trading with other collectors, and buying from flea markets, garage sales and second hand stores will also reduce your cash outlay. Remember that insulator collecting is supposed to be an enjoyable hobby, and not the cause of financial stress.

8) Beware of Antique Stores

Most antique stores/shops have a few insulators for sale, and a lot of insulators are actually ‘antiques’ by virtue of being over 100 years old (although many antique dealers have a much more liberal definition of that term). In my area, it is not uncommon to find a $0.50 insulator with a $10.00 or more price tag on it – and it is frequently so damaged that I would throw it away. To be fair to those antique dealers, they have overhead costs that they have to recover, whereas the suggested prices in the price guides are for transactions between collectors who do not have the same costs.

Antique dealers know very little about insulators, nor can they be expected to – their inventory is too vast for them to concentrate on every type of antique. Therefore antique dealers know a little bit about a lot of antiques, but their depth of knowledge about any one of them is very superficial. So beware of misinformation from them – I once had an antique dealer tell me that a Dominion CD 154 was made in because the embossing said ‘DOMINION - 42’. Because insulators are not a big money maker for them, antique dealers don’t spend the time to learn more about them – it just wouldn’t be cost effective. For that reason, occasional bargains can be found in antique stores if you know your insulators and prices well enough – the antique dealer’s price is low relative to that suggested by the price guide.

9) Get Approval From Your Significant Other

This tip was suggested by my wife, and after thinking about it, it’s excellent advice. If you have a ‘significant other’ in your life, it’s important that approval for your insulator collecting be given by that person. And the more serious you are about insulator collecting and the more resources that you give to it, the more important that approval becomes. When I initially informed my wife that I was going to collect insulators, she thought that I was joking. And then she started to resent my hobby because of the amount of time that I was devoting to it, and not to activities that the two of us could be doing together. We ended up having many ‘discussions’ about my hobby. And I had to buy a second personal computer for her to use because I was monopolizing our first one, doing insulator related things with it.

Insulator collecting requires time, money and space – not just to acquire and display your insulators, but for related items and activities as well (e.g. reference books, attending swap meets). Therefore make sure that your significant other is in agreement with your hobby -- involve him/her if they’re willing to participate. But don’t let insulator collecting become a source of friction between the two of you – it’s supposed to be a stress reducing hobby!

10) Use a Personal Computer

I have a hard time visualizing insulator collecting prior to personal computers – I know that it was done, but it must have been very time consuming, expensive and laborious. If you don’t already own a personal computer, then insulator collecting is another reason to get one. And if you already have a personal computer, which you probably do if you’re reading this, then use it as tool to assist you with your collection.

I have already mentioned Bill Meier's article about using a computer to catalog your collection. Another major computer use is communication with other collectors. Prior to getting capability, my long distance costs were frequently in excess of $100 per month because of calls to other collectors. Now I rarely call anyone long distance, and then only if I’m calling a person that doesn’t have an address. I buy, sell and trade insulators by and the Internet. I subscribe to the ICON news/chat line, and periodically visit the Glass and Porcelain Insulator Web Site and its links to see what’s new in the hobby. Other insulator related uses for my computer are correspondence, making parcel shipping labels, record keeping and digital photography.

Last updated Thursday, February 4,

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