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Among its other uses, this equipment keeps process plants running and gas flowing through pipelines in cold weather. But installation errors can defeat the purpose of installing this equipment. It's not just that a pipeline or vessel can freeze and the material inside it be unavailable for use. It can freeze and rupture, causing extensive environmental damage or worse.
Freeze protection (Photo 1) is what most people think of first, but many heat-tracing systems are not for freeze protection. The applications are numerous. For example, the system's job may be to maintain fluid temperature to lower the viscosity for better flow (Photo 2).
To prevent failure:
Use only equipment that's identified as being suitable for the chemical, thermal, and physical environment [427.10].
Install the equipment per the manufacturer's drawings and instructions, and follow applicable industry standards [427.10].
Carefully determine what physical hazards might result in physical damage to the equipment, and provide the necessary protection [427.11].
Also:
For external surfaces of heating equipment operating above 140 degreesF, protect personnel from contact by installing physical guards, isolating the equipment, or thermally insulating the equipment [427.12].
Every 20 ft or less along any electrically heated pipeline or vessel, post the appropriate caution signs or markings to indicate the presence of this equipment [427.13]. The NEC requires this if the equipment needs periodic servicing, but something similar is wise even when there's no periodic servicing.
Disconnects
You must provide a disconnect that can be locked open and that simultaneously opens all of the ungrounded conductors [427.55(A)]. At this voltage level, the neutral is the grounded conductor. So you can typically wire these with a switch that "opens the hot" (the other conductor) to break the circuit. But you may not need that switch. If the branch circuit switch or breaker is readily accessible to the equipment user, it can serve as the disconnect.
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Carefully review the drawings to verify the disconnect will remove all power in the circuit and thus provide certain (no chance of backfeed) isolation of the equipment. Using the supply breaker as...