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Clearances for Exposed GTO Cables and Terminations

Posted By Les Beros, Monday, July 01, 2002
Updated: Thursday, February 14, 2013

There have been numerous inquiries to my office about the requirement of increased clearances for combustible sleeving and electrode boots from conductive and combustible materials, (which equates to everything) when used with high voltage GTO cables and terminations. The growing necessity to increase the clearance requirements has brought changes to Section 34 (high voltage sign section) of the 2002 Canadian Electrical Code (CEC). The changes in the code have been mostly implemented due to arcing and tracking problems that have been a problem in the field with the non-secondary ground fault protected power supply circuits.

The high voltage tracking problem was usually caused by poor installation practices, the occasional use of unapproved material that has been available in the sign industry, or the improper use of approved equipment. These poor installation practices have resulted in numerous fires and equipment failures, which have sometimes given neon lighting an unfair dangerous image. Neon lighting when installed to manufacturer’s specifications and the proper electrical codes can and does have a long life that is free of problems and maintenance callbacks.

The clearances have also been increased, because of the requirement in rule 34-300(1) under the Section 34 heading of Neon Supplies, in the 2002 CEC, which introduced the use of secondary-circuit ground-fault protection for most neon supplies in this code.

Photo 1. Glass sleeve

34-300(1) Secondary-Circuit Ground-Fault Protection

"(1) Neon supplies other than the following shall have secondary-circuit ground-fault protection:

(a) Transformer with isolated secondaries and with a maximum open circuit voltage of 6000 V or less between any combination of leads or terminals; and

(b) Transformers with integral porcelain or glass housing for neon tubing and requiring no field wiring of the secondary circuit.”

At a recent 2002 CEC Section 34 seminar in Calgary, Alberta, sponsored in part by Allanson International, the presenter determined that the correct clearances need to be followed for the neon installations using the secondary-circuit ground-fault protected power supplies. The housing type of power supply will not require it as there is no GTO cable involved in the installation. With a reduced clearance the circuit would experience nuisance tripping, which causes problems to the sign contractor and their customers in lost time, exposure and revenue.

These new rules covering neon supplies and the entire rewrite of Section 34 have also been an attempt to bring the Canadian Electrical Code and National Electrical Code (NEC) closer together so that eventually there may be a possibility of a bi-national electrical code covering both countries together. As the sign industry grows and evolves, the distances and business barriers across North America are getting shorter and shorter. We are now seeing signs and neon products crossing the 49th parallel in both directions.

In the past the clearances required for nonmetallic sleeving and boots were covered by rule 34-216(8) in the 1998 CEC and were a minimum of 19 millimeters. The new clearance requirements can be found under the heading of Wiring Methods in the 2002 CEC.

34-400(6) High Voltage Wiring Methods

"(6) Where cable is used for high voltage wiring of signs and outline lighting is exposed, the cable shall be ran inside GTO sleeving to a point at least 50 mm inside the raceway, and spaced at least 38 mm from conducting or combustible material.”


Photo 2. Polymeric sleeve

For all neon systems, the required clearance for exposed sleeved GTO cable and electrode termination boots will be 38 millimeters. This clearance is required under all circumstances, between the polymer products and all other materials, located indoors, outdoors, and to all supporting material or backing for the neon tubing. These clearances should be given great consideration at the design stage of the neon installation and the neon glass tubing bent to accommodate the required clearances. When a back-to-back connection is used to join the neon tubing together with combustible material, there might be a requirement for long supports, to keep the 38-millimeter clearance between the termination boots and GTO sleeving covering the cable from the surrounding structural material. Because long supports will be used, an additional number of supports may be required for keeping the tubing steady under wind and snow loading that will affect the glass tubing and the appearance of the installation.

To restate this, the clearances as noted above are mandatory requirements of the 2002 CEC and of the 2002 NEC 600.32(E). This 38-millimeter clearance is now in effect in Canada, or will be shortly, and will remain in effect unless there is a change during a future code cycle. Inspectors should be spreading the word that these clearances will be increased to assure most contractors will hear about the change and are starting to prepare for them. Sign contractors will have to comply with the increased clearances as of the adoption date of the 2002 CEC in their areas or jurisdictions. In the past, some code adoptions may have taken up to one year. Most have been working towards shortening this time frame. Generally the inspections department or the authority having jurisdiction (AHJ) will inform the contractors of the effective adoption date of the code by sending out a bulletin or notice. All field-wired neon sign installations submitted for inspection after this adoption date must be in compliance with the rules of the 2002 CEC.

Sign installers may decide to look at an alternate method to cover the GTO cable and the neon terminations. One method to prevent exposure of the GTO cable and the connections is the use of porcelain or glass cups and glass tubing. I have contacted several manufacturers of these products to inquire about the clearance requirements for their product to conductive and combustible material, as the NEC has called for the 38-millimeter clearance for some time now. These types of cup terminations are to be held in position by a metallic clip or support supplied with each cup, and this holder will provide the proper clearance of the termination. When one compares the 38-millimeter requirement for combustible type products to about 6-millimeter or less for glass or porcelain, this may influence one’s decision as to which type of termination and covering to use.

The proper installation instructions supplied with each component will have to be followed. If one is not familiar with a specific component of the installation, ask the contractor to supply the literature on it. Most manufacturers also have and support web sites covering their products. Indoors, the termination cups usually can be installed and supported in almost any position. Outdoors, where exposed to the weather, the glass type "G” and "GG” cups should be held at a 45-degree angle from the horizontal so moisture will not collect in the cup. The porcelain types are not approved for direct exposure to weather and must be installed indoors or under a protected ledge or roofline. The exposed GTO cable on a back-to-back connection between the two tubing electrode terminations shall be covered with glass tubing or sleeving. The "GG” cup type termination covers may also be used where no GTO cable is used between the tubing electrodes; for example, when the neon tube electrodes are positioned side by side so the neon tube’s termination conductors can be just twisted together.

The other location to watch for is when the GTO cable is run from either neon supply terminal and is sleeved upon leaving the raceway to any electrode connection. There may be a need to support the sleeved GTO cable between the raceway and the termination to maintain the required clearance.

GTO sleeving is a defined term in the CEC and is not approved, nor should it be used, as a general raceway. If the GTO cable is exposed anywhere, then the installation is not code compliant.

34-002 Special Terminology

"GTO sleeving means a flexible polymeric sleeve intended to enclose luminous tube sign GTO cable operating at not more than 7500 volts-to-ground and intended to be installed within an approved raceway.”

Neon suppliers and manufacturers are constantly looking to improve their product and develop new products to help the sign contractor design and install a code-complaint sign which is not only economical, but safe and reliable. At least one manufacturer has available a product approved for wet locations called a conduit plug assembly (CPA unit) which provides covering for the GTO cable leaving the raceway to the point of termination in an "G” cup at the neon tubing electrode. It shall be used as a complete system, which includes the raceway seal when used outdoors. The GTO cable is covered with glass tubing, which is supplied with the CPA unit, and it may be extended to allow for a longer distance. The use of these types of noncombustible terminations and GTO cable coverings are the only alternatives I have investigated for the replacement of combustible type products; there may be others. In decisions about alternatives to the increased required clearances, some of the sign personnel here in Saskatchewan indicated that the glass terminations have worked quite well, but they had to be allowed for at the design stage.

Along the same line where high voltage GTO cables are used with hanging signs and are not enclosed in an approved raceway, similar clearances will need to be followed. This is stated in 34-402 of the 2002 CEC and also in Wiring Methods.

34-402 High Voltage Cables in Show Windows and Similar Locations

"Where high voltage cables used with signs hang freely in the air and are not enclosed in raceways, as in show windows or similar locations, they shall:

(a) Be enclosed in approved GTO sleeving; and

(b) Have a separation of at least 38-mm from combustible and conducting material; and

(c) Be located so as to be free from mechanical damage; and

(d) Not be used to support any part of the sign.”

The intent of this rule is also to assure that the proper clearances of the sleeved GTO cable is maintained to the sign supports and surrounding material.

On the subject of clearances, you may have already read in the 2002 CEC that approved nonmetallic raceways may be used once again for GTO cables. This change was made in rule 34-400(5) to allow harmonization with the 2002 NEC. It states that when a nonmetallic raceway is used, then that raceway shall have a clearance of 38 millimeters from all conductive and combustible material for installations operating up to 100 Hz. If the installation were over 100 Hz, then the clearance would need to be increased to 44 millimeters. This clearance will be hard to achieve throughout the run of raceway and even harder to maintain over time. The supports for the raceway will have to be substantial and of a proper type material to meet the intent of the rule. When a bonding conductor is required to be run in conjunction with the nonmetallic raceway to bond any metallic sign parts, the bonding conductor will also have to be kept 38 millimeters from the raceway, as it is considered a conductive material.

The last point of clearances to be made is in 34-106 under General Requirements. The first part of this rule (1)(a to c) deals with the sign location. But the last part of 34-106(1) talks about the actual height of sign and states: "(d) No part of the sign or outline lighting, other than its support, is less than 2.2 meters from grade.” In other words, the high voltage sign components and glass should not be lower than this height, so that they not be subject to damage or easy contact by unauthorized persons. The second reference to heights of components is in the last part of the same rule:

"(2) Notwithstanding Subrule (1)(d), freestanding signs, indoor signs, and outline lighting including installations in show windows and similar locations shall be permitted to be mounted with electrical components less than 2.2 meters above grade where approved for the location or where mechanical protection is provided to prevent persons or vehicles from coming in contact with the electrical components of the sign.”

I seem to observe this violation mostly in restaurants and bars were the sign is in a window or is hung from the building structure inside. A second location is where outline lighting or border tubing is too low inside the building. These neon components would have to be enclosed or kept over the 2.2-meter height.

The inspection of neon installations is an unusual occurrence for most electrical inspectors. Most jurisdictions have little enforcement control over the sign contractor, as few are required to be licensed, unlike electrical contractors. The licensing of all electrical sign installers that are doing field wiring would be a big step forward as it holds responsible the installer instead of the electrician who connected it, or the business owner who owns the sign. With sign contractors being required to be licensed an electrical permit would be required and the installation would then have to meet the code in effect. In Saskatchewan all field-wired neon installations shall be done under the authority of a permit submitted by a licensed sign contractor and be inspected, with all corrections completed before it is energized.


Read more by Les Beros

Tags:  Featured  July-August 2002 

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