Application Guide catalog - Watlow - #22

Continued

General considerations in selecting various lead types are:

• Temperature of lead area

• Contaminants in the lead area

• Flexibility required

• Abrasion resistance required

• Relative cost

Temperatures listed indicate actual physical operating limits of various wire types. Wires are sometimes rated by CSA, UL® and other agencies for operating at much lower tempera­tures. In this case, the rating agency temperature limit is the maximum level at which this wire has been tested. If agency approvals are required, don't exceed their temperature limits.

Teflon® is a registered trademark of E.I. du Pont de Nemours & Company.

UL® is a registered trademark of the Underwriter's Laboratories Inc.

Each heater type has specific installation costs to be considered.

• Machining required— mill, drill, ream

• Materials required— heater, brackets, wiring

• Labor to mount and wire heating elements

The total system operating cost is a composite of two factors. It is usually best to examine cost on an annual basis:

• Total cost of energy (kW Hours) ($/kWH)

The cost of a new heater, lost produc­tion time, removal and installation of the new heater must be considered. Generally, these costs are actually much greater than expected. Heater life must be such that replacement can be scheduled and planned dur­ing off-peak production times to avoid lost production.

• Removal of existing heater

• Equipment downtime cost

• Material cost— heater, brackets, wiring

• Labor to remove and install heating elements

• Additional purchasing costs

• Scrap products after heater failure and during restart of process

• Frequency of burnouts

After calculating wattage required and considering various heater attributes, the scope of possible heater types should be narrowed considerably. Now, several factors not previously examined must be considered before final heater type selection: installation, operation and replacement costs.

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