4. Replace switch housing cover and place control into service.

If control has been furnished with NEMA 7/9 explosion

proof (cast) or NEMA 4 moisture proof (gasketed) switch

housing, check the following:

1. After wiring connections have been completed, housings

must be sealed at the conduit outlet with a suitable com-

pound to prevent entrance of air.

2. Check cover to base fit to be certain gasketed joint is tight.

A positive seal is necessary to prevent infiltration of mois-

ture laden air or corrosive gases into switch housings.

3.0

Preventive Maintenance

Periodic inspections are a necessary means to keep your

Magnetrol level control in good working order. This control

is a safety device to protect the valuable equipment it serves.

A systematic program of preventive maintenance must be

implemented when the control is placed into service. If

the following is observed, your control will provide reliable

protection of your capital equipment for many years.

3.1

What to do

3.1.1 Keep control clean

Be sure the switch housing cover is always in place on the

control. This cover is designed to keep dust and dirt from

interfering with switch mechanism operation. In addition,

it protects against damaging moisture, and acts as a safety

feature by keeping bare wires and terminals from being

exposed. Should the housing cover or any seals become

damaged or misplaced, obtain a replacement immediately.

3.1.2 Inspect switch mechanisms, terminals, and

connections monthly

a. Mercury switches may be visually inspected for short circuit

damage. Check for small cracks in the glass tube containing

the mercury. Such cracks can allow entrance of air into the

tube causing the mercury to oxidize. This is noticeable as

the mercury will appear dirty or dull, and will not break

into clean, round pools. If these conditions exist, replace the

mercury switch immediately.

b. Dry contact switches should be inspected for excessive wear

on actuating lever or misalignment of adjustment screw at

point of contact between screw and lever. Such wear can

cause false switch actuating levels. Replace switch mecha-

nism if wear or misalignment are apparent.

7

46-602 B40 Liquid Level Switches