Using same contact for two different alarms

[Designer69]

we need to use the same fan failure alarm contact to provide two different alarms to two different annunciator circuits. (see attached)

originally I was going to just connect both different annunciator sources to the same contact then I realized that this could be a big mistake as 2 voltage sources are now connected in parallel.

is there a better way to do this? a common workaround?

There are no other available contacts for this fan failure alarm that we know of, so if new additional components is what we need, so be it.

Thank You

 

[Designer69]

using interposing relay might not be very feasible because it's hard for us to find out if there's even enough juice in the circuit to support driving it.

 

[gar]

170928-1420 EDT

Your drawing makes no sense.

Never would you ever take a voltage source (in your case 24 V) and short across that voltage source with a low ohm resistance (your relay contact).

What you probably have, that you show as a 24 V voltage source, is a voltage source with a fairly high internal impedance, likely resistive, or resistive for your purposes. This could be a 500 ohm coil on a relay.

There are major problems to what you suggest. Find out more about your components, and study why you could have a problem.

Since you are probably concerned with safety rules that is where you start.

From a simple logic perspective you need the equivalent of a double pole relay controlled from your single contact.

.

 

[Designer69]

thanks Gar. Yeah that 24V is the internal power supply voltage to the annunciator. I don't know exactly how the annunciator is internally wired.

It does sound like the interposing relay is the best way to do this.

Thank You

 

[drktmplr12]

thanks Gar. Yeah that 24V is the internal power supply voltage to the annunciator. I don't know exactly how the annunciator is internally wired.

It does sound like the interposing relay is the best way to do this.

Thank You

Interposing relay is the only way to do it.

I suspect a DPDT relay is not going to give you any problems with the power supply whether it is 120 VAC or 24 VDC. The power consumption in either case is about 1 Watt for Single-pole and Double-pole Models. See the data sheet, third page, first table.

Check the power source and make an educated decision. If you have a 100 W source you are probably okay without checking. If you have a 10 W source its best to check the power budget and see if the relay will fit.

 

[Ingenieur]

What are the loads?
if you use the same dc +/- for both loads and the contact and pwr supply is rated to handle both loads, I see no issue
need more info
an isolation/interposing relay is a simple solution also

 

[gar]

170928-1517 EDT

If the relay contact is just a contact (what some call a dry contact), then that contact has to be used with a power source and some load (a relay coil). You need to know whether or not this is an isolated contact (neither terminal is connected to any other circuit).

If the said contact is a switched power source, then you just need a relay coil to be controlled.

In my opinion a switched power source should never be called a contact.

If you have a switched power source, then you need to know if it can supply adequate current to whatever load you place on it.

.

 

[gar]

170928-2216 EDT

Designer68:

The drawing in your first post showed 2 separate 24 V DC supplies. That implies a low source impedance (power supply internal resistance). These should have been defined as something other than a DC voltage supply. These are the destination to be controlled. By what name should these be called? I would probably call them the controller input.

Your single controlling contact I would call an output.

Use of the words output and input alone are not sufficient to define their circuits. You really need to study and tell us what is the internal circuit of the output and the input.

Even without diagrams of the circuits there are some simple tests you can perform that probably will identify the circuitry behind the two terminals.

.