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The Benefits of Fault Protection, Part One

Whose fault is it? Secondary-circuit ground-fault protection arms installers against ungrounded problems.

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Fault protection. Its very mention makes some sign installers shiver. Since the 1999 mandate for use of ground-fault protection in neon signs and outline lighting, everyone has heard a related horror story, and some have lived them — phantom nuisance tripping, multiple service calls under warranty, performance unpredictability and unexpected costs. Are these the new reality for neon applications?

No longer a novelty for the U.S. sign industry, fault protection is clearly here to stay. As a result, perhaps it’s helpful to examine initial experiences, assess their impact and make changes accordingly. Now that the first burst of frustration is behind most of us, let’s look at where we are and what we’ve learned with fault protection.

As you read further, you may find that fault protection benefits a general client base and provides opportunities for sign companies. This article offers recommendations based on real-world experience.

SCGFP fundamentals

For more than two years, many jurisdictions across America have required fault protection, or more correctly, secondary-circuit ground-fault protection (SCGFP). Some municipalities mandated its use even earlier as a consequence of implementing the 1996 National Electric Code (NEC). Widespread use of SCGFP effectively began in September 1999, when Underwriters Laboratories (UL) called for UL 2161 transformers and power supplies in all UL 48 signs.

The fault-protection initiative has greatly impacted the U.S. sign industry, as code- and standards-writing bodies intended. They wrote the new regulations to change how signs and outline lighting were manufactured and installed with the ultimate goal of making electric signs safer, thereby reducing the risks of fire and damage to property.

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Published by the National Fire Protection Assn., the NEC guides local jurisdictions that write and enforce safety codes. The "authority having jurisdiction" (AHJ) adopts and implements the local code, which is enforced by inspectors who survey individual applications. UL devises and publishes "standards" that apply to the nuts and bolts of code installations. For the sign industry, UL has become the main listing agency for code-compliant equipment and procedures.

The NEC clearly requires SCGFP. The text of the 1996 and 1999 NEC Article 600 for Electric Signs and Outline Lighting states that all neon transformers must have fault protection, the two main exceptions being neon transformers that feature integral housing receptacles and those of "isolated" design.

Consequently, UL assembled and published UL 2161, the Standard for Safety for Neon Transformers and Power Supplies, in September 1996. This standard further defines what’s available in code-compliant transformers. Under UL 2161, transformers of 3000V to ground and below, which are also 30mA or less, don’t require add-on, fault-protection circuitry. That’s why you can purchase a 6kV, 30mA standard transformer that bears a UL logo and label indicating code compliance.

UL has determined that SCGFP devices should provide two major functions: protection from loss of ground and from significant current leakage to ground. These two functions must be kept in mind when using transformers in the field. If an SCGFP transformer trips, one, or both, of these conditions exist.

Our challenge in the field is to quickly identify and locate a fault. More importantly, we must design sign installations that minimize these conditions. Then, everyone benefits.

What we’ve learned

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SCGFP isn’t the death knell of neon. Granted, a few local hassles and disruptions have caused some customers to seek alternatives to neon. On the brighter side, the incidence of neon-related fires appears to have decreased. Which does more damage to our industry, the high-profile bad press of a fire or grassroots grumbling? Given more experience, signshops will accept the use of SCGFP as commonplace and simple.

As precedent, Europe has used SCGFP since the early 1990s, and it’s been widespread for five years. The European Electric Code (EEC) integrated fault protection into Cenelec pan-European standards before the United States implemented its code. And North American code harmonization is not yet complete. Whether correlated or not, European use of neon for signs, architectural lighting and displays has noticeably increased.

Realistically, neon serves as an integral medium for the sign industry. No alternative lighting source offers comparable flexibility, diversity, reliability, light output and lifetime economics. The medium’s 70-year success record boasts millions of long-lasting examples. While LED and fiberoptic technology have been vetted highly, luminous-tube innovation warrants notice as well. Developments in phosphor coatings and electronic power supplies offer great promise for energy efficiency and economic effectiveness.

Anti-neon publicity hinges on "nuisance." And, early SCGFP experience played along. It’s called "nuisance tripping," isn’t it? The very nature of its name implies negativity. Fault protection — whose fault? Does it protect? What’s at risk? Does all the discourse about safety and regulations mean that neon is unsafe? If you didn’t know better, what would you conclude?

Neon installations aren’t inherently unsafe. Misapplication, misunderstanding and misuse cause the problem. The SCGFP transformer serves as only the traffic cop providing silent enforcement.

During SCGFP’s first years, transformers have functioned appropriately. They’ve shut down in conditions of high current leakage and ground loss. Frustration has stemmed from the high incidence of field conditions leading to transformer tripping, the main source of unpleasant surprises. Conditions are worse than we expected. Here’s an illustration.

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Voltage in neutral

Prior to last year, very few industry people had more than a passing awareness of the field incidence of neutral voltage. Now, almost everyone involved in the manufacture and use of SCGFP transformers knows the significance: Its presence on a sign installation can mean unexpected trips.

In principle, neutral voltage shouldn’t be present. If more than 5V exist, a potential problem probably exists. Voltages of 20, 30, 40V (or higher) between neutral and ground may cause damage to electrical equipment or even a fire. This situation doesn’t bode well for neon-transformer longevity.

Unfortunately for us, job-site conditions may introduce current into the neutral. For example, unbalanced loads on different legs of a three-phase system can generate a great deal on the neutral. Line harmonics caused by large quantities of electronic devices may also cause neutral voltage.

Frustratingly, we’ve all learned more about this phenomenon because first-version SCGFP circuits may have been designed to shut off in those circumstances. The faults have alerted us to serious conditions. In troubleshooting, we’ve measured as high as 80V. Whether the transformer trips or not, these conditions need to be remedied.

If you’d like more information regarding this phenomenon, Mike Masi of Allanson International Inc. (East Providence, RI) wrote an excellent technical paper on the subject that you can request by calling him at (401) 831-6366 or e-mailing him at mmasi@allanson.com.

SCGFP’s good news

Where’s the good news? How do we get comfy with neon again and get past nuisances, neutrals and horror stories? How do we accept fault protection as a benefit?

It takes practice. We must also accept that current practice may differ slightly from past practice. SCGFP’s use requires most of us to do something different, depending on previous technique and habitual procedures.

Satisfactory use of SCGFP devices begins with knowing their purpose. We must better understand how we use electrical system ground and control leakage to ground.

Of the two, leakage to ground is perhaps more controllable by sign personnel. For example, the required clearance and spacing between high-voltage components and ground plane can usually be managed. Spacing, which can be written into specs and job prints, doesn’t usually require major changes during a field remedy.

Minimizing a neon installation’s operating voltage lessens leakage to ground via careful sizing and transformer selection. Break up your loads. Use less powerful (less than 15kV) transformers, if possible. The key is to keep loads below the "ideal" listed rating, for example, on a footage chart.

Leave yourself some room. While 10% is good, 20% is usually better. Use a multimeter and high-volt probe to verify your selection at the job site. Not only will SCGFP circuitry trip less, transformers will last longer.

Additionally, when designing your neon job, explore code-compliant SCGFP alternatives such as housing-type and lower-voltage transformers. For channel letters measuring 3 ft. or more, use internal-housing transformers — a "no-brainer." They’re safe, reliable and the least-expensive option.

Code compliance of lower-voltage transformers isn’t as clear cut. Your AHJ makes or breaks this option. As presently written, UL 48 and 2161 assume that voltages below 3001V to ground and currents limited to 30mA are "inherently" protected. However, inspectors who conservatively interpret NEC require fault protection on all transformers (with the noted exceptions).

Obtain written verification that the 3000V interpretation will be accepted at the job site. If that fails, take the conservative route and plan for fault protection.

Conservative practice invariably proves best. For example, when selecting electrode housings and other insulators, glass and ceramics always perform better than plastic. Also, use better grades of GTO insulation. Measures taken to inhibit the path of energy from neon and HV cables to ground lessen the incidence of tripping. The cost increases of using premium components will easily outweigh the cost of nuisance service calls.

Use as little GTO as possible; less is always best. If you use longer runs, keep the ones attached to the transformer terminals — the ones that carry the highest operating voltage — shorter. Keep leads under 10 ft.; 5 ft. is ideal. Compensate by using transformers rated for lower output voltage.

Good judgment should dictate a reasonable compromise. Your challenge is to minimize the chances of tripping. Ironically, the benefits from SCGFP occur when everyone forgets it’s there. No fault — no service call.

Border tubing using 15kV transformers run at maximum footage with 20-ft. GTO leads can cause faults.

Solid-state transformers offer another alternative. Virtually all of these neon-power supplies have SCGFP features built into their circuitry, making them code-compliant. For applications with minimal need for added GTO, such as channel letters, these may be your best economic option.

The Zen of being grounded

The fundamentals of harmonious ground-fault practices center on grounding. If functional service ground is present, everyone’s happy. Prior to the SCGFP requirement, transformers would hum right along without a service ground, albeit under unsafe conditions. Now, they will trip. Next month, we’ll examine grounding and troubleshooting SCGFP applications.

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