level switch contact rating

[Charbel]

Dear,

I am trying to size level switch contact rating for a specific application.

we will be using multilin 469 as below:

http://www.electricalmanuals.net/files/RELAYS/GE/469/GEK-106289D.pdf

and we will be using level switch interlocked with the functioning of the pumps (as dry run level protection) as below

http://www.exman.com/fsms.html

I appreciate any help in sizing the contact of the level switch.

thanks a lot!

charbel

 

[danw]

It isn't clear to me what logic interlocks which other logic (MultiLin and pump-down level switch logic), but the level switch animation shows the level switches FST and FSB driving MS1 a motor starter contactor.

That pump-down circuit depends on a latching output from MS1, so if you don't drive a contactor directly with the FSB/FST contacts, you'll need an equivalent latching contact from a relay or from the MultiLin device to achieve the pump down action shown in the animated graphic.

For sizing, it depends on what the level switches 'drive'. A digital input to the MultiLin, or a motor starter, or a relay used for latching.

 

[Charbel]

It isn't clear to me what logic interlocks which other logic (MultiLin and pump-down level switch logic), but the level switch animation shows the level switches FST and FSB driving MS1 a motor starter contactor.

That pump-down circuit depends on a latching output from MS1, so if you don't drive a contactor directly with the FSB/FST contacts, you'll need an equivalent latching contact from a relay or from the MultiLin device to achieve the pump down action shown in the animated graphic.

For sizing, it depends on what the level switches 'drive'. A digital input to the MultiLin, or a motor starter, or a relay used for latching.

dear, thank you for your quick reply,

actually if it will be driven by the digital inputs, it will not be more than 20mA as indicated in the datasheets (please refer to attachment)

but I would expect more if it will be driven from the contactor of a 20KW motor, what do you think, it will be in order of 1A or more?

thanks a lot!!

 

[cjd1965]

Hi I would take it into a relay and use the relay contacts to do the work. A 4 pole 10A relay is cheap and easily replacable

 

[Tom Jenkins]

In general a dry contact to the Multilin input will be fine, and there is no concern about amp ratings. If the level switch is in a raw sewage wet well you would be well advised to use an intrinsic safety relay between the switch and the Multilin. This assumes you are using the Multilin to stop the pump, which is implied by your question.

You need to clarify your design concept. The circuit in your example is a common way to control a pump with a wet well. A typical design has the Multilin as a motor protection relay, with one of its output contacts in series with the motor starter coil, just as you would put an E-Stop switch contact. You would not normally run the level switch to the Multilin, although you certainly could make that work.