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# Control for latching relay

## Control for latching relay

(OP)
Hi all,

Please I need help for a little issue.

I have a latching relay in a lighting panel board that should control a lighting circuit. This lighting circuit should be controlled from a push button installed in the site and from BMS. The control circuit should take into consideration an override (priority) for the signal coming from the BMS.

Example: If the circuit lighting was turned on from the BMS command, a person on the site doesn't have the right to turn off the circuit, that means if he pushes the push button, the lighting will not turn off. It remains on.

Please can I anyone help me in the control diagram ?

I have made this little proposal, but I think it needs some modifications.

Kind Regards,

Rami

### RE: Control for latching relay

the push button and the pulse from the RMS are in parallel so they have the same control capability.

### RE: Control for latching relay

(OP)
Hi Jacksopher,

Thank you for your kind feedback.

I know my proposal is missing something.

Can you help me to modify it ?

Thank you,

Regards,

Rami

### RE: Control for latching relay

Connect the push button to the BMS system and handle it in the software.
It may take a second latching relay to solve the problem with hardware and there will be more failure modes and the reliability will be poor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

### RE: Control for latching relay

(OP)
Hi Bill,

Connect the push button to the BMS system and handle it in the software.
It may take a second latching relay to solve the problem with hardware and there will be more failure modes and the reliability will be poor.

Kindly can you show me your idea by sketching a control diagram ?

Thank you,

Ragards,

### RE: Control for latching relay

Rami2015,

This is eng-tips, not eng-we-do-the-work-for-you. We have no idea what hardware you have. You need to design the circuit, and if you want feedback on it, you can post your control diagram sketch.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
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### RE: Control for latching relay

Your diagram does not allow for ever turning off the lights except by turning-off the breaker.

Try this: http://escventura.com/manuals/ab_typicalWiringDiag...

Learn to draw ladder diagrams like those in the above link. It is an essential tool for designing control wiring circuits.

### RE: Control for latching relay

I guess you have a mechanically latching relay rather than electrically latching. In that case, you could connect the local push button to the hot side of the lighting load instead of the neutral bar.

### RE: Control for latching relay

I'm not sure what a BMS is but I assume PLC to relay controlled with software energizing the relay on or off. Your diagram as you know is poor. May I suggest you use a key lock style light switch for power to the lights this might accomplish what you need with safer results.

Chuck

### RE: Control for latching relay

BMS Building Management System ? (I had to look it up.)

Use two parallel switches (or these latching relays if you wish) to provide the override. If either switch (relay) is on, then the light is on.

LOOK -^

Does this meet the partially defined description of "override"?

### RE: Control for latching relay

(OP)
BMS stands to Building Management System. The control is performed from distance from a microcontroller that sends a pulse to the latching relay, that when receiving the pulse on its coil gets energized and the its switch close and the lighting circuit becomes on. All this configuration is made by software (Programming the microcontroller), but the latching relay is hardware and it exists inside the panel board.

Now, suppose a person is in the corridor , and he pushes the push button, that should not turn off the light because the BMS signal has the priority over the pushbutton.

### RE: Control for latching relay

This is probably a pulsed type of relay. One pulse turns the relay on and a second pulse turns the relay off. Imagine a solenoid turning a toothed wheel one tooth each time it is energized. In one position the switch is open, at the next position or tooth the switch is closed.
Repeat.

Bill
--------------------
"Why not the best?"
Jimmy Carter

### RE: Control for latching relay

Replace your latching relay with a PLC.

### RE: Control for latching relay

(OP)
Replacing a latching relay (10$-15$) to a PLC costs too much.

### RE: Control for latching relay

The pushbutton has to go through the BMS, no other real choice. The BMS is programmable so you can program the operation you want.

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