Gems Sensors & Controls LS-1800, LS-77700, LS-1750, LS-3, LS-74780 Operating Manual

Electrical Data

Standard reed switches in GEMS level switch units are hermeti­cally-sealed, magnetically actuated, make-and-break type.
Switches are SPST or SPDT and are rated in Volt-Amps (VA).

See the chart below for maximum load characteristics of GEMS
level switches. CAUTION: Contact protection is required for tran­sient or high in-rush current. Refer to GEMS Bulletin #133702 or
call your GEMS representative.

VA

10

General Use

20

Pilot Duty

50

General Use

100*

* Not U.L. Recognized ** Limited to 50,000 operations

The product is designed and manufactured in accordance with Sound Engineering Practice as defined by the Pressure
Equipment Directive 97/23/EC. This product must not be used as a “safety accessory” as defined by the Pressure Equip­ment Directive, Article 1, Paragraph 2.1.3. The presence of a CE Mark on the unit does not relate to the Pressure Equipment
Directive.

This product is suitable for Class I and Class II applications only, per the requirements of standard EN60730 and any

additional specific requirements for a particular application or medium being sensed. Class I compliance of metal

bodied units requires a ground connection between the metal body and the earthing system of the installation. Class

I compliance of plastic bodied units in contact with a conductive medium requires that the medium be effectively

earthed so as to provide an earthed barrier between the unit and accessible areas. For Class III compliance, a supply

at safety extra-low voltage (SELV) must be provided. Please consult the Factory for compliance information on

specific part numbers.

Volts

0-50

120

100

0-30

120

240

0-50

120

240

120

240

Amps AC

.2

.08

N.A.

.4

.17

.08

0.5

.4

.2

.8**

.4

European Pressure Directive Addendum

Amps DC

.13

N.A.

.10

.3

.13

.06

0.5

.4

.2

N.A.

N.A.

Typical Wiring Diagrams

(Circuit Condition Dry)

SPST, Normally Open or Closed

Red

Red

SPST, With Thermostat Option

SPDT

COM

=

N.O.

N.C.

Thermostat switches open or close
when ambient temperature reaches
specified setpoint. Thermostat units
not CE approved.

Orange,

Yellow

White

Black

Red

Green

or

Red

Black

Important Points!

Product must be maintained and installed in strict accordance
with the National Electrical Code and GEMS product catalog and
instruction bulletin. Failure to observe this warning could result
in serious injuries or damages.
An appropriate explosion-proof enclosure or intrinsically safe
interface device must be used for hazardous area applications
involving such things as (but not limited to) ignitable mixtures,
combustible dust and flammable materials.
*** Warning: To prevent ignition of flammable or combus­tible atmospheres, disconnect power before servicing.
Pressure and temperature limitations shown on indi­vidual catalog pages and drawings for the specified level
switches must not be exceeded. These pressures and tem­peratures take into consideration possible system surge
pressures/temperatures and their frequencies.
Selection of materials for compatibility with the media
is critical to the life and operation of GEMS level switches. Take

care in the proper selection of materials of construction; particu­larly wetted materials.
Life expectancy of switch contacts varies with applica­tions. Contact GEMS if life cycle testing is required.
Ambient temperature changes do affect switch set points,
since the specific gravity of a liquid can vary with tempera­ture.
Level switches have been designed to resist shock and
vibration; however, shock and vibration should be minimized.
Liquid media containing particulate and/or debris should
be filtered to ensure proper operation of GEMS products.
Electrical entries and mounting points may require liq­uid/vapor sealing if located in an enclosed tank.
Level switches must not be field repaired.
Physical damaged sustained by the product may render it un­serviceable.

Single-Station Level Switches

Instruction Bulletin No. 72947

=

Series Mounting HEX Size

LS-1700**

LS-1700TFE*

LS-1750**

LS-1755**

LS-1800**

LS-1850**

LS-1900**

LS-1900TFE*

LS-1950**

LS-19735*

LS-3*

LS-30*

LS-38760**

LS-74780*

LS-77700**

TH 800-A***

Level Temp

1/8" NPT

1/8” NPT

1/8" NPT

1/8" NPT

1/8" NPT

1/2" NPT

1/4" NPT

1/4" NPT

1/4" NPT

1/4" NPT

1/8" NPT

3/8" - 16 Str. Thd.

1/8" NPT

1/8" NPT

1/8” NPT

1/4" NPT

1/4" NPT

1/4” NPT

1/8" NPT

3/8" - 24 Str. Thd.

1/4" NPT

3/4" Wrench Flat

9/16" Wrench Flat

* Plastics ** Alloys

1/2"

1/2”

1/2"

1/2"

1/2"

5/8"

21/32"

5/8"

5/8"

1/2"

1/2"

1/2"

1/2"

1/2”

5/8"

5/8”

1/2"

3/4"

5/8"

(Slosh Shield Version

(Slosh Shield Version

(Slosh Shield Version)

Float

Diameter

1"

1-13/32”)

1-1/8”

1-1/2"

1-13/16”)

1-1/32"

1-1/4"

3-1/2"

1-7/8"

2-1/8"

2-1/16"

1-1/2"

1"

1"

1-1/4"

1-7/8" (P/N 76707)

3/4” (P/N 201540)

1-7/8"

1-7/8"

1-1/2”

1"

1-1/2"

1-1/4"

P/N 72947
Rev. Y

Specialty Switches: Please use caution when handling these units,

***
as shock may damage the thermostat temperature setting.
Thermostat units not CE approved.

Installation

A standard NPT female boss in tank top, bot­tom or side is all that is required. Units oper­ate in any attitude - from the vertical to a 30°
inclination - with lead wires up or down. Stan­dard IPS pipe extends units to any intermedi­ate level in the tank. (Figure 1)
Moisture Protection: When moisture exists
in conduit and extension pipes, the potential for
this moisture to "wick" down the wire leads and
into the switch assembly exists. Should this
happen, the switch will appear to be closed due
to a high resistance path through the moisture.
The following suggestions may help to prevent
this from happening:

1. Pitch conduit away from the level switch
when possible, so that condensation will drip
away from the level switch assembly.

(Figure 2)

2. When a vertical run of extension pipe is used
to extend a level switch down from the top of
the tank, a non-conductive silicone oil should
be used to fill the vertical run. Alternatively, an
appropriate potting may be used to fill the ver­tical run to occupy the space in which conden­sation will normally form. (Figure 3)

CAUTION

Most of GEMS level products incorporate a pot­ting cap or are fully potted. Due to the bonding
characteristics of the potting to the wire leads,
there is no way of assuring a water-tight seal
at the potting joint. Our potting cap will resist
moisture to some degree, but the precautions
mentioned above should be used to assure
moisture doesn't enter the switch and cause a
short.

Consult your GEMS representative for more

suggestions on how to lessen the effects of moisture.

Thread Treatment

1.

Sealing: When threading metal threads into a metal coupling, pipe sealant or

®

Teflon
sealing plastic threaded units, a compatible pipe sealant such as No More

LeaksTM from Permatex

2.
installer should use a suitable wrench and tighten the threads one to one and one­half additional turns past hand-tight. Over-torquing of the threads will result in
damage to the plastic mounting plug.

tape is recommended. Due to potential compatibility problems, when

®

is recommended.

Tightening: When threading a plastic level switch into a metal coupling, the

No More Leaks is a trademark of Permatex® Industrial Corp., a subsidiary
of Loctite Corporation. Teflon is a registered trademark of DuPont Corporation

- Figure 1 -

Conduit

- Figure 2 -

- Figure 3 -

30°

Max.

Silicone

Oil

3. The Effect of Thread Engagement on Actuation Points
The length of mounting threads engaged at installation is important in calculating
switch actuation points and the actual length of stem extending into the tank. Use
the chart below to find the thread engagement length (T) for a given NPT size.
Factor the dimension into any calculation of switch actuation levels (L) and overall

length (L

).

0

NPT

T Dim.

1/8"

.27"

1/4"

.39"

1/2"

.53"

3/4"

.55"

1"

.68"

1-1/4"

.71"

2"

.76"3"1.20"

- See Examples Below -

Definition of Variables Used in Examples Below

A = Mounting Length
T = Thread Engagement
P = Distance from coupling (bung) top to inside surface of tank or bracket

= Overall length from bottom of mounting

L

0

L = Switch actuation level as measured from inside surface of tank or

bracket to fluid surface

L1 = Switch actuation level, nominal, as measured from bottom of
mounting (based on a liquid specific gravity of 1.0)

Internally Mounted LS-1900

(Standard Length)

LS-1900 Series internally mounted
through a 1/4" NPT hole. To
calculate "L" dimension:

L = L
L = 1-3/16" + (21/32" - .39")

L = 1.46"

Internally Mounted LS-1700/1750

LS-1700/1750 internally mounted
through a 1/8" NPT hole. To
calculate "L" dimension:

L = L
L = .63" + (.56" - .27")

L = .92"

+ (A-T)

1

(Standard Length)

+ (A-T)

1

L

0

Fluid
Level

21/32”

1-3/16”

Fluid
Level

L

0

↓

A

↑
↓

9/16”

L

1

↓

A

↑

=5/8”

↓

1/4” NPT

↑

L

↓

1/8” NPT

L

↓

T

↑

Actual

Tank

Intrusion

↓

↓

T

↑

Actual

Ta nk

Intrusion

↓